M.M. Ferguson* - J.C. Stevenson Memorial Lecturer
Department of Zoology, University of Guelph, Guelph, Ontario, Canada.
Genetic markers provide valuable genetic information needed for the effective management and conservation of economically important species. Research being conducted at the University of Guelph will illustrate that no one marker type is appropriate for all applications given cost, sampling need, and required level of polymorphism. Despite recommendations that common sense should prevail in marker choice, early methodologies are perceived by many as dated with low funding potential. In fact, the newest generations of genetic markers are often touted as panaceas for all fisheries applications. I will present a decision tree on the choice of an appropriate genetic marker system for fisheries applications based on characteristics of a particular species (eg. effective population size) and the experience of myself and others. I will then perform a reality check on the limitations of several relatively new genetic markers and emphasize the power of using multiple marker types simultaneously. Finally, I will discuss an exciting new role of genetic markers by illustrating how such markers can be used to identify and locate genes that control an organism's appearance, physiology and life history and determining how they work. Hopefully, the collection of such data should convince the most hardened skeptic that genetic analysis is not just stamp collecting.
This presentation will describe research activities being conducted in a European Union project called "Mechanisms influencing long term trends in reproductive success and recruitment of Baltic cod: implications for management". The primary goals of the programme are to (1) identify and describe the dominant biotic and abiotic processes affecting the maturation of cod and the developmental success of cod early life stages in the Central Baltic; (2) incorporate these processes into recruitment models to enhance prediction of future stock fluctuations due to the state of the spawning stock, environmental perturbations, and species interactions; and (3) assess the biological basis and evaluate the feasibility of cod stock enhancement programs for the Central Baltic. The project includes a long-term data analysis component, an extensive field sampling program for eggs, larvae and 0-groups, laboratory rearing studies and a physical oceanographic modelling component. Results to be presented during the talk will include investigations of how environmental processes affect habitat quality for successful cod reproduction, the horizontal and vertical distribution of cod eggs and larvae and species interactions (e. g., predation).
The effects of large-scale hydroelectric dams are well known and include such variables as changing water levels, sediment loading, and the impediment of fish migration. Fewer studies have been conducted on the effects of low-head barriers. Kelso and Noltie (1990) observed that low-head barriers caused a behavioural response in adult pink salmon preventing upstream migrations while movements of adult coho and chinook salmon were observed to be relatively unaffected. No studies to date have reported the effects that low-head barriers have on non-salmonid fish communities. Using a batch-marking technique (Panjet), I have attempted to study seasonal movements of fish communities on streams with low-head barriers as compared to matched controls. Four streams around Lake Ontario (2 with low-head barriers, 2 controls) were sampled using one-pass backpack electrofishing techniques (Simpson and Lyons 1995). Fish were identified, measured, given a condition score and all fish were marked according to their sampling location (above barrier, below etc.). Sites were resampled twice throughout the summer season (June - Aug 1996) in order to mark a larger sample of fish. Recaptured fish were scored based on their original segments. Fall, winter and spring resampling will also take place. Blockage of movements upstream for entire fish communities has implications on food-web interactions as well as fish reproduction and overall community health. This research is funded by the Great Lakes Fishery Commission, and is carried out in collaboration with the Ontario Ministry of Natural Resources, Department of Fisheries and Oceans Canada, Michigan State University and the University of Wisconsin - Madison.
Recent studies have identified large scale changes in the trends of productivity of Pacific salmon and other species in the Pacific Oceans. These shifts in productivity are coincident with large scale changes in the climate and the ocean. The combined biological and physical changes are commonly referred to as regime shifts. We show that indices of global energy redistribution also change at the same time as Pacific salmon productivity shifts. Two indices, the length of day (LOD) and the atmospheric circulation index (ACI) are closely related to each other and to major shifts in the abundance of Pacific salmon, sardines, walleye pollock and other species. Fisheries for these species in the late 1980s accounted for approximately 30% of the catches of all fish from all oceans, thus the productivity shifts have profound impacts on world catches. Because the shifts occur quickly and can be quite large, the time that a change occurs is an important and new reference point in fisheries management. It is necessary to detect the changes and make the appropriate management decisions quickly so that overfishing does not collapse the stock. In low productivity regimes, it is important to recognize that management actions may not be able to rebuild stocks to levels observed in higher productivity regimes.
Young-of-the-year (YOY) brook trout, Salvelinus fontinalis, spawned in a lake were observed migrating into, and inhabiting small (< 2m wide) inlet streams. Up to 81% of the entire YOY population in a lake system were estimated to inhabit its streams by midsummer. Some YOY overwintered and remained in the streams during their second summer. Such behaviour suggested fitness advantages were gained by stream residence. The advantage may be related to the streams'’ characteristic stable temperatures and flows that existed because the streams occurred in forested catchments where groundwater dominated their baseflow. In addition, the (size) of the small streams and the significance of catchment hydrology for sustaining these habitats are important findings for the future management of watersheds with lake-dwelling populations.
The construction of southern Alberta's Oldman River Reservoir in 1991 created concerns about possible accumulations of mercury in reservoir fish and impacts on pre-existing fish populations, notably bull trout (Salvelinus confluentus) a species currently threatened, or of special concern, in North America. To address these issues, the Alberta Environmental Centre has monitored mercury concentrations and inventoried fish populations in the reservoir and its tributaries since 1991. This initiative formed part of a larger monitoring and fisheries mitigation program for the reservoir implemented by the Alberta Government. Reservoir fish populations were sampled in the fall of each year (1991 to 1995) using standardized gill netting procedures. Electrofishing was used to sample fish from upstream and downstream tributaries. In addition to bull trout, the dominant fish species inhabiting the reservoir are mountain whitefish (Prosopium williamsoni), rainbow trout (Oncorhynchus mykiss), longnose sucker (Catostomus catostomus), and white sucker (Catostomus commersoni). Throughout the period of study, overall fish abundance in the reservoir was high compared to similar reservoirs in Alberta. Catch rates for bull trout ranged from 0.26 to 0.94 fish/hour/100 metres of net, suggesting that relatively stable populations of this species continue to exist upstream of the dam. Dietary analysis indicates that bull trout are using the abundant prey base available to them in the reservoir and may be adjusting to impoundment by acquiring an adfluvial life history pattern. Bull trout exhibited higher mercury concentrations than any other fish species examined and showed significant increases in mercury concentrations following impoundment. However, muscle mercury concentrations in bull trout, and all other species examined, have remained well below the 0.5 mg/Kg guideline for safe consumption recommended by Health and Welfare Canada.
Biochemical growth indices are often used in field and lab studies to assess the impacts of various factors on recent growth rates of fish. However, for these data to be properly interpreted, it is crucial to know the time period which they reflect. This study measured RNA concentrations and ornithine decarboxylase (ODC) activity in juvenile Atlantic salmon (4.2 g initial weight) to compare their rates of response to temporary feeding reductions. Three levels of food reduction (50% of control, 20%, fasting) lasting 2,4, or 8 days were compared to a control group (constant feeding at 2.7% of body weight per day). ODC activity responded very rapidly (within 2 days) to changes in feeding level, but did not show a difference between fasting fish and fish on a sub-maintenance ration. RNA concentrations of fish on reduced rations were less than controls after 2 days, but were not statistically different until the fourth day. After 8 days, all 4 rations were reflected in RNA concentrations. Biochemical responses to re-feeding at the control level occurred at about the same rate as responses to decreases in feeding.
Information collected from research surveys (1971 to 1994) was consistent with the existence of strong asymmetrical competition for food, with Atlantic cod dominant over American plaice. There was almost complete overlap in spatial distribution between the two species. Diets of cod < 40 cm long and plaice < 35 cm long overlapped broadly, with mysids and gammarid amphipods being the principal shared prey. Increased cod abundance corresponded with decreased abundance and growth (size-at-age for ages 6 to 12) of plaice. Increased cod abundance corresponded with decreased growth of cod -- evidence for intraspecific competition in the presumed competitively dominant species. Plaice size-at-age was negatively correlated with plaice abundance for age 4 and 5, not correlated with plaice abundance for ages 6 and 7, and positively correlated with plaice abundance for ages 8 to 12. Environmental conditions (or some other factor such as size-selective fishing mortality) appeared to affect the strength of the competitive interaction from 1991 to 1994, when growth of both species was reduced compared to other years.
Prior to 1995, 195 coded wire tagged steelhead trout (Oncorhynchus mykiss) were recovered in high seas commercial and research fishing operations. Between 1984 and 1989, 8 matching tags were recovered. Matching tags are defined as fish from the same release group caught in the same fishing operation on the high seas. A test of hypothesis was developed to determine whether these recoveries were significantly different from what would be expected if steelhead populations moved in an uncoordinated manner. The overall test indicated that some tagged steelhead trout populations travelled in a significantly (P<0.05) coordinated manner on the high seas. The temporal and spatial pattern of recoveries indicated that steelhead released in Idaho were not found in the Gulf of Alaska to the same extent as steelhead released from B.C., Washington. Recoveries of Idaho steelhead appeared south of the Aleutian archipelago at a younger age than did steelhead from B.C.
The Fraser River in British Columbia is among the world’s greatest salmon-producing rivers, and substantial mixed-stock commercial fisheries have traditionally harvested returning Fraser River sockeye salmon (Oncorhynchus nerka). In order to prevent overexploitation of the component stocks, effective management of the fisheries requires accurate and precise estimates of stock composition. Scale characters have traditionally been used to estimate stock compositions, but they are limited in their ability to discriminate among stocks, and are subject to significant annual variability. In order to provide greater differentation among stocks, variation at four microsatellite DNA loci was surveyed in approximately 25 sockeye salmon stocks, with samples from some stocks spanning a range of about 15 years. No significant annual variability in allele frequencies was observed at the microsatellite loci. The utility of microsatellite DNA variation for estimation of stock composition of mixed-stock fishery samples was examined through computer simulations, whereby a mixture of known composition was constructed, and the stock composition estimated with reference to the baseline stocks. The use of variation at four microsatellite loci resulted in the ability to discriminate among a wider array of stocks than possible with scales, with estimated stock-specific mean compositions of 100-fish samples within 4% of the true stock mean, and with a standard deviation of generally less than 5%. This analysis indicated that variation at microsatellite DNA loci can provide an effective method of discriminating among stocks and for determining stock composition in mixed-stock samples.
The plasticity of fish relative to diets and growth rates is well-known. Rarely has this been quantified for markedly different lake types and relative to monitored diet, the prey resource base, and background of potential competitor species. This will be done here for yellow perch and golden shiner in 8 water-bodies. Perch grew best in Atkins Lake, a small warm lake where, in the absence of competitors, they assumed some piscivory by year 1. However, growth was also good in sunfish lake where they were pure planktivors. Growth was poorest in small cold deep lakes with oligotrophic tendancies. Golden shiner grew best (as did pumpkinseed) in the estuary of the main Cataraqui River, possibly because in this spacious system access to optimum food types was maximized.
Data from groundfish scientific surveys on the continental shelf of northeast Newfoundland were used to examine the relationship between abundance of species at individual stations, bottom temperature, and depth in the period 1978 to 1993. For 25 common species the individual niches on temperature and depth (-2 to +5 oC, 50 to 1,000 m) were characterised in terms of fish abundance, and these are presented in graphic form. Niche axes described in this way appear to be a useful way to visualise and compare habitat differences among continental shelf fishes. Even though each species on the Newfoundland Shelf had its own particular temperature-depth pattern, these could still be categorised into classes of broad to narrow niches. Changing environments are expected to affect the niche space and thus the abundance patterns of species in these classes differently.
Atlantic salmon of the Kola peninsula return to their native rivers to spawn in the spring and fall, forming two distinct runs. Spring salmon spawn in the autumn of the year that they enter fresh water. However, fish from the autumn run spend approximately 12 months in the river system before spawning and may overwinter a second time, before returning to the sea as kelts. The autumn run, which comprise seventy-five percent of the river's population, may therefore spend up to 1.5 years in fresh water, without feeding. This project will compare the energy stores and selected life history characteristics of these two runs, to identify any specialised adaptations which would allow for this long period of fasting. Preliminary results show that, when compared to the spring run, autumn fish smolt at an earlier age (3yrs vs. 3.4yrs), are larger in size as returning adults (average weight 4.4kg vs. 1.7kg for spring fish), and have higher energy reserves. The autumn run also consisted primarily of multi-sea winter individuals, whereas the spring run was mainly grilse.
A longterm Russian database on liver weights indicates that there has been substantial interannual variation in the physiological condition of Northeast Arctic cod. The dominant signal in the liver condition time series is the dramatic decrease in liver condition which occurred in the late 80's as a result of the collapse of the Barents Sea capelin stock. This event had major repercussions for the reproductive potential of the stock. At the individual level, fecundity-at length was reduced by as much as 50% in poor condition years. At the stock level, the proportion of females-at-length was well below expected values for intermediate length classes suggesting that mature females in poor condition years experienced higher mortality rates. Maturity ogives for the poor condition years were also anomalous: a higher than expected proportion of female cod in intermediate length classes were classified as immature. This suggests that mature females may skip spawning when conditions for growth are poor. These biological responses suggest that spawner biomass is unlikely to be a sensitive measure of the reproductive potential of the stock when physiological condition varies over time. Describing the relationship between spawner biomass and egg production is therefore critical to interpreting the nature of the relationship between spawner biomass and recruitment.
Trace elements incorporated into the growing surface of the fish otolith (ear stone) reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic manner. Since otoliths grow continuously without resorption throughout the life of the fish, individuals which spend at least part of their lives in different water masses produce otoliths of different elemental composition. Thus the otolith elemental composition ("elemental fingerprint") serves as a stable environmentally-induced marker of natural aggregations of fish, independent of genetic identity. Using ID-ICPMS to maximize the accuracy of the otolith assay procedure, we tracked the annual migrations of 7 Atlantic cod (Gadus morhua) stocks in and around the approaches to the Gulf of St. Lawrence. Our primary objective was to identify the stock composition of the dense mixed-stock aggregations which form at the approach to the Gulf each winter. Based on the spatial distribution of the elemental fingerprints both prior to the fall migration and during spring spawning, it appears that the winter aggregations can be identified as to stock origin with considerable accuracy. This information will be of value to fisheries managers wishing to minimize the risk of overexploitation on individual cod stocks.
We describe geographic and size-related trends in tagged Atlantic cod (Gadus morhua) infected with the gill parasite Lernaeocera branchialis in coastal Newfoundland and Labrador, and assess the effect of infection on cod survival in the wild. We test three null hypotheses using cod-tagging studies conducted between 1962 and 1992: 1) infection rates in the northwest Atlantic are latitudinally invariant; 2) infected cod have the same survival probability as uninfected cod; and 3) infection rates among cod size/age classes are length invariant. Infection rates varied among studies from 0% along the Labrador coast to 20% along the south coast of Newfoundland. The first hypothesis was rejected given a significantly negative relationship between infection rate and latitude. The second hypothesis was rejected in two geographic regions when it was determined that ~8% fewer infected and tagged cod from southern and northeast Newfoundland were reported recaptured relative to uninfected cod similarly tagged and released. This implies that infected cod suffer an 8% differentially higher mortality relative to non-parasitised cod. The second hypothesis was not rejected for cod from southern Labrador and the southeast coast of Newfoundland. The final hypothesis was rejected when it was determined that the proportion of cod infected was generally greatest in the 43-49 cm length class and then decreased significantly with increasing length. However, differential survival between infected and uninfected cod within length classes was not observed. As infected cod appear subject to parasite-induced mortality, the magnitude of which varies geographically, the parasite's use as a population marker warrants caution. L. branchialis also has the potential to affect the recovery of depleted northwest Atlantic cod stocks in a geographically differential manner.
Growth increment widths in pectoral fin rays from five geographically distinct populations of lake sturgeon across Canada were analysed as an analog for total yearly growth. Increment widths were adjusted for fish age using a methodology similar to that used by dendrochronologists. Yearly growth among individuals within populations was inversely correlated with river discharge. The relations between water discharge and environmental identities limiting sturgeon growth will be discussed.
Within still-water pools along the sides of streams, we examined the social behaviour and growth rate potential of recently-emerged brook charr differing conspicuously in their level of activity and diet. Rates of encounters and interactions between fish were density dependent. Aggressive fish were either inactive or very active, while nonaggressive fish exhibited intermediate levels of activity. Encounters and interactions were closely timed with prey capture attempts and aggressive fish made more foraging attempts per min than nonaggressive fish. Growth rate potential, assessed using tissue concentrations of RNA, was highest for sedentary fish and for active fish making frequent foraging attempts, and lowest for fish exhibiting intermediate levels of activity. Our findings support the conclusion that the behavioural variation represents short-term adaptive specialization arising from intraspecific competition and that it takes the form of alternative sit-and-wait and active search tactics with roughly equal growth rate potential, a component of fitness. Our findings also support contentions that adaptive, individual behaviour plays an important role during initial steps in the evolution of resource polymorphisms.
Achieving a maximum size is often regarded as the key to successful winter survival for young-of-the-year (YOY) smallmouth bass (Micropterus dolomieu). Ongoing studies indicate poor survival of larger YOY predicted to survive in New Brunswick at the species' northern range. Summer, fall, and early winter habitats (substrate type, depth distribution, activity) of YOY were examined using direct underwater measurements. Seasonal influences on available and selected habitats were apparent. We tested predictions that such seasonal changes influenced size-predicted, winter survival rates at the species northern range.
Two of the largest trubutaries in Saint John (Saint John River and Little River) are the sites of waste disposal including waste from untreated sewage, an oil refinery, paper mills, a brewery and a power-generating station. No study has yet investigated the possible physiological consequences to aquatic vertebrates living in these heavily polluted sites. Mummichogs (Fundulus heteroclitus) were placed in water from Little River estuary for a 12-day laboratory exposure at dilutions of 100%, 10% and 0% dilutions. Mummichogs were also placed in chambers anchored within the subtidal zone throughout SJH for a 4-week exposure. Blood and gonad samples have been taken for the analysis of plasma steroid levels and in vitro gonadal steroid production. Results will indicate if changes in reproductive endocrine function occur at sub-lethal exposure levels.
We used historical data from lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis) and walleye (Stizostedion vitreum) fisheries in Ontario to test whether angling CPUE (catch per angler-hr) is proportional to fish density (number of fish per hectare). A non-linear relationship indicated that catchability (proportion of stock removed per unit of effort) increases as density decreases. We speculate that this is due to the clumped distributions of fish and anglers' abilities to locate high-density patches even when overall abundance is low. Consequently, CPUE is not a good index of abundance: substantial changes in abundance can occur that would not be detected by changes in CPUE. Simulations of a fishery characterized by density-dependent catchability indicate that overexploitation is not only difficult to detect, but also difficult to escape from once it occurs. Once fishing has depleted the stock below a critical level, a massive cutback in effort is needed to allow for recovery. These results stress the need for indicators, other than CPUE, to evaluate stock status.
There is evidence for a recent cooling in the Gulf of St. Lawrence and for its possible adverse effects on cod production in terms of weights-at-age and condition. Based on research trawl surveys, we examined distribution changes in juvenile and adult cod from the northern Gulf of St. Lawrence in relation to the cooling event, using comparisons of selected and available temperatures and depths, in an effort to understand how the environment exerted its impacts. Juvenile and adult cod were not exposed to colder temperatures in winter during the cold event. Adults now occur 200 m deeper in winter than before the onset of the cold event. In summer median temperatures occupied by both juveniles and adults have dropped slightly (0.5°C) while there is no change in depth distribution. These results suggest that if there were direct adverse effects of cooling, they were felt primarily in summer but that indirect effects such as on prey abundance and distribution may have been more important.
Overfishing of the traditional cod and flounder off Newfoundland has lead to the development of new fisheries based on "underutilized" species. But basic background information is often lacking, and data necessary for assessing abundance are not available. Furthermore, the "new" species tend to be either forage fish, and hence probably important in food webs, or relatively rare. Thus substantial risks of overfishing and even significant ecosystem change are associated with these fisheries. Novel approaches to data collection and management are required if risks are to be minimized. One such is to tap directly the considerable fine-scale ecological knowledge possessed by those engaged in the fishery itself. These data, particularly when augmented by inferences from scientific surveys, can improve an understanding of the dynamics of the species involved. The lumpfish (Cyclopterus lumpus) roe fishery on the Bonavista Peninsula, northeast Newfoundland, illustrates our argument. We used semi-structured taped interviews with local fishers and follow-up phone interviews to develop a picture of local lumpfish biology and to derive estimates of overall and individual changes in effort and catch, both on the short-term (recent years) and throughout a full fishing career. The lumpfish fishery appears headed for a collapse. Reduced landings in the 1990s result from declining lumpfish abundance (which is reflected directly in catch rates) and not from reduced effort.
Information about the genetic diversity of fish stocks is now a necessary part of any management program. Information about genetic variation of broodstocks can be used to as a guide to choose an appropriate broodstock for rehabilitation plans. Genetic data can then be used to monitor the success of rehabilitative efforts. Genetic profiles of lake trout (Salvelinus namaycush) in Ontario are difficult to develop because traditional techniques for genetic stock assessment do not detect sufficient variation. Therefore different molecular techniques, using polymerase chain reaction technology are being explored. The results of a study of lake trout microsatellite DNA are discussed. Genetic profiles of a variety of hatchery and wild lake trout stocks were produced. The stocks included lake trout from Ontario including the Haliburton region, Killala L., L. Manitou, Iroquois Bay, L. Michipicoten, Parry Sound, and Slate Island. Fish from Clearwater L. in Manitoba were also analyzed. The amount of variation detected is compared to that seen when other techniques such as allozyme electrophoresis and PCR-RAPD are used.
This papers explores the ecosystem impacts of fishing on a multispecies
fishery. A new dynamic multispecies ecosystem model, Ecosim(1) is used to
examine both the ecosystem effects of fishing and the impacts of different
gear types in a multigear fishery. The tropical multispecies, multigear
fishery of San Miguel Bay, the Philippines is used as a case study for
this work. Different hypotheses are made about the trophic dynamics of the
ecosystem and their implications are outlined. A comparison is made
between a traditional single species (yield-per-recruit) analysis of this
fishery and the holistic multispecies, multigear analysis presented here.
The utility of a multispecies, ecosystem approach to fisheries assessment
and management is discussed and management recommendations made.
[1.Walters, C., V. Christensen and D. Pauly. Structuring dynamic models of exploited ecosystems from trophic mass-balance assessments. In Press: Reviews in Fish Biology and Fisheries.]
Two morphological forms of mountain whitefish (Prosopium williamsoni) occur in the Fraser River system.One form, the "normal", has the head and body morphology typical of this species. The other form, the "pinnochio", has an elongate, pointed snout and a slim body. The two forms are distinguishable by their second summer (@ 100 mm FL) and diverge thereafter. Their length-weight relationships are significantly different: the "pinocchios" are lighter for size than "normals". Field observations indicate that in the summer the two forms forage on the same riffles; however, the "normals" swim horizontally and forage above the substrate, while the "pinocchios" forage in a heads-down position and use their snout to probe interstices in the gravel and to turn over rocks. It is not clear if this foraging dichotomy has a genetic basis or if the elongate snout is a phenotypic response in fish that chance to start foraging on the substrate. Restriction fragment analysis of juveniles and adults reveals significant differences in haplotype frequencies between sympatric samples of the two forms. This suggests either positive assortative mating or differential mortality.
We measured upwelling and downwelling irradiance for the spectrum 300- 850 nm in 15 lakes with diffuse attenuation coefficients (kd) ranging from 0.086 (ultraoligotrophic) to 5.38 (hypereutrophic). Ultraoligo- trophic lakes were characterized by maximum transmission in the UV-blue wavelengths (430 nm) and high absorption in the red part of the spectrum. Eutrophic-hypereutrophic lakes absorbed mostly in the UV-blue and transmitted mainly in the green and red parts of the spectrum (>560 nm). Mesotrophic lakes showed broad band transmission with maximum in the green (530 nm). We incorporated 27 additional lakes to our data set (Vant and Davies-Colley, 1984) to establish the following relationships linking various apparent optical properties: log (kd)=0.23-0.84log(SD) (R2=0.87); log(kd*SD)=-0.2-0.33log(Re) (R2=0.69); EZD=1.85+1.69*SD (R2=0.86), where SD: Secchi Depth, Re: average reflectance and EZD: Euphotic Zone Depth (depth where 1% of the incident irradiance remains). Although perhaps restricted to summer stratification, SD values can be used to obatin Re and Kd ones, and to approximate the beam attenuation coefficient by the direct ocle formula (Preisendorfer, 1986).
Embryos from a 3 male X 3 female sockeye salmon fertilization event were reared under each of three lighting regimes: full spectrum minus UV (UV-), full spectrum with UV (UV, corrected for intensity differences with UV-), and a dark (control, C) treatment that did not transmit any light until full yolk absorption. The light treatments were on a 8h:16h L:D cycle. At the start of the experiment, each cross consisted of a monolayer of 300 egss held in a porous container with circulating water at 11 degrees C. Mortality counts were taken every day thereafter. The UV treatment suffered the highest mortality at all stages of fish development followed by the UV-, and C, which suffered very few casualties. The total number of fish that survived to hatching was significantly different between treatments (UV: 181+/-76, UV-: 238.9+/- 56.4, C: 289+/-6.3), and it was significantly lower for all crosses involving female 2 (F2). By the fry stage, the numbers of fish remaining were 5+/-5.4 (UV), 166.11+/-12.24 (UV-) and 288+/-5.68 (C), with all the F2 crosses dead in the UV and an average of 5.67+/-2.3 left in the UV-. These results show that light, and especially UV, is damaging at the embryo stage and that sensitivity to UV may be a maternally-inherited trait.
Debate on the control of population dynamics of stream-dwelling salmonids has often focused on the role of environmental variables or competitive interactions as influences on the behaviour and densities of salmonids in streams over time. Despite these efforts, few studies have experimentally manipulated these variables to examine their independent effects. I conducted an experiment using a series of artificial stream channels to examine the influence of food abundance and competitor density on the mortality and behaviour of juvenile steelhead trout (Oncorhynchus mykiss). Both experimental factors were inversely related to the final densities of trout at the end of the eight week experiment. I also found significant influences on the aggressive behaviour, growth and size distributions of fish in response to increasing levels of food abundance and competitor density.
Reports of inshore spawning of northern Atlantic cod (Gadus morhua) led to questions about the contribution of inshore spawning components to the rate of recovery of this stock. In April, 1995 the largest inshore spawning aggregation ever observed (16,800 tonnes) (G. Rose pers comm) was discovered in Smith Sound, Trinity Bay. We hypothesised that this large spawning aggregation would provide a spawning "signal" that could be detected against the "background" spawning of the bay cod population. We sought to determine if the spawning of this aggregation of cod would lead to a detectable pulse in the abundance/density of eggs, larvae, and settled 0+ group juveniles. Data was collected in conjunction with ongoing ichthyoplankton and juvenile surveys, thus allowing for the comparison of the 1995 data with previous years. Cod egg density was significantly higher in 1995 than the pooled average of the previous sampling years (1991 and 1993). When all survey stations are included, the 1995 mean (0.51 eggs/m3) was 14 times greater than the pooled mean of the previous surveys (0.04 eggs/m3). When just the stations that were sampled during each year are considered, the 1995 mean (0.58 eggs/m3) was 30 times greater than the pooled mean of the previous surveys (0.02 eggs/m3). Increase in numbers of post-settlement, age 0+ fish was tested at three different spatial scales: the entire northeast coast of Newfoundland, individual bays, and areas within bays. There was no detectable increase in density of settled juveniles at any of the three spatial scales, even within Trinity and Conception Bays. This may be due to advection/diffusion of eggs/larvae to low concentrations, or to high mortality in the early life stage.
Reproductive dysfunctions (reduced gonad size, delayed maturation, and decreased plasma sex steroids) in wild fish exposed to bleached kraft pulp mill effluent (BKME) may impact fish populations. In previous studies, sex steroid levels were significantly reduced in goldfish (Carassius auratus) exposed to beta-sitosterol. The structure of beta-sitosterol is similar to cholesterol, which is the precursor to the steroid hormones. Preliminary work with goldfish suggests that plasma lipid levels decrease because of beta-sitosterol exposure. We are administering beta-sitosterol to brook trout (Salvelinus fontinalis) at four dosages [control, 20ug/g, 50ug/g, 100ug/g] via slow-release implants for twenty days. We are measuring sex steroid, lipoprotein, cholesterol, phospholipid, and triglyceride levels in the plasma. Reductions in these plasma parameters would be supported by mammalian studies which show that phytosterols in the diet lower plasma cholesterol levels. However, the significance of lower lipid levels for teleost fitness, including steroid production, is unknown.
Recent attention has focused on sustainability and diversification of the Atlantic Canadian aquaculture industry through the development of methods for the commercialization of non-salmonid fish species. Diminishing fishing quotas and high market values have attracted interest towards haddock (Melanogrammus aeglefinus). Larvae are adapted to a light regime that is influenced by the attenuative and absorptive properties of their aquatic environment. These environmental conditions should be considered when transferring haddock larvae to the aquaculture hatchery. Light conditions that maximize the contrast between prey and the environment facilitate the detection and capture of food by larvae, particularly during the critical switch from endogenous to exogenous feeding. Enhanced feeding should result in improved growth rates and reduced mortality. The objective of this study was to determine the impact of light intensity, tank colour, and photoperiodicity on the growth and survival of larval haddock. The results of this experiment confirm the importance of light in the aquaculture mesocosm. Determination of the best photic environment in which to raise haddock larvae is an important step towards the eventual commercialization of this species.
The determination of the stomach content and measurement of gastric evacuation rates have been useful tools in determining the in situ feeding rates of fish. A reexamination of literature data, however, revealed that the commonly used exponential gastric evacuation model cannot be automatically extended from stomachs to the entire gastrointestinal tracts or from adult to juvenile fish and fish larvae without prior testing of the underlying assumptions. Prolonged retention of some residual food in the gut after linear evacuation can 'mimic' curvilinear evacuation rates and may lead to biased conclusions about the actual evacuation and ingestion rates. Using simple linear regressions on untransformed data over the linear portion of the evacuation time course, the estimated ingestion rates are frequently in good agreement with the ingestion rates obtained from the initial increase of gut content at the beginning of a feeding period. For the exponential model to be applied, the assumptions of a proportional release must be rigorously met, but the best least square fit is little indication for the physiological validity of the model.
I investigated thermal habitat selection by young-of-the-year (YOY) brook trout (Salvelinus fontinalis) in a lake in Algonquin Provincial Park, Ontario. Throughout May, trout selected areas within 2 m of shore that were near their preferred temperature of ~15 oC. In early June,trout selected areas within 4 m of shore with bottom temperatures near, or at, their upper thermal tolerance of 20 oC. In July, when ambient lake temperatures ranged from 23 to 26 oC, trout selected the coldest available bottom temperatures located in discrete areas 3 to 8 m from shore. In such areas, trout lay on bottom, rarely foraged and defended small areas from a central-place. Groundwater flow rate accounted for 87% of the variance in trout density in the littoral zone in July whereas bottom water temperatures did not account for significant additional variance. One particular location, where a spring flows into the lake, contained as many as 123 trout/m2. I conclude that YOY brook trout seek out areas with cool groundwater seepage at the expense of feeding when ambient lake temperatures approach their lethal limit (25 oC) and the defence of those sites suggests cold groundwater is a limiting resource in summer.
We describe the space-use and foraging movements of YOY brook charr in two lakes in Algonquin Park, Ontario. In contrast to territorial salmonines in streams, fish in both lakes did not forage from a central-place, space used did not increase with body l ength, aggression was rare, and displacement distances (net and max.) increased with activity (proportion of time spent moving). Fish were highly active and had large total displacement distances, but max. and net displacement distances were much smaller ; thus, fish moved back and forth over the same areas. Fish that moved a greater total distance captured more potential prey items than sedentary fish, but rejected most of them. Fish movements were sufficient to disperse the cohort along the entire sho reline but fish remained concentrated near the spawning area in each lake. We conclude that YOY brook charr in lakes are not space-limited due to territoriality as they are in streams.
Historic data from high seas fishing and tagging of sockeye salmon have been interpreted to show that sockeye from British Columbia typically make one loop of the Gulf of Alaska for each year spent in the ocean. We have constructed an individual based model of sockeye migration that combines realistic fish behaviour with dynamic properties of circulation and temperature in the Northeast Pacific. Results of simulations with this model show that over a range of plausible behaviours for the fish, interannual variations in oceanic water properties and circulation generate widely different patterns of fish movement in the ocean, few of which look anything like the presumed annual looping pattern. Yet, the simulated fish distributions fit the observed distributions reasonably well. The results have implications for all three of the most significant problems in Pacific salmon management: 1) timing and 2) routes of return migration and 3) recruitment to coastal fisheries.
The effects of large scale exploitation of walleye on the boreal fish communities of Henderson Lake were studied. The pulse fishery removed approximately 90 percent (3375) of the adult walleye (1980-4) from Henderson lake during a period of negligible recruitment. Following the exploitation, the ninespine stickleback, a major forage item, declined and disappeared by 1984. We expected that such an extensive harvest would have collapsed the walleye population allowing northern pike and yellow perch to increase in size and number with northern pike becoming the sole top predator. By 1986 northern pike and yellow perch populations had increased dramatically and two large year classes of young of the year walleye were produced. Unsuccessful attempts to determine adult walleye abundance in 1986, 1988 and 1991 seemed to support the hypothesis that the population would not recover. However, in 1994 and 1995 population estimates indicated that the walleye population was starting to recover to about 30 percent (871 fish) of preharvest numbers. The ninespine stickleback was once again caught in seine hauls. Northern pike numbers and yellow perch catch per unit effort (CUE) were considerably less than 1986. Good indices of the harvest and recovery were average length at age for younger walleye and northern pike and length distributions for both species. Condition factor and length weight data were poor indices and was not correlated to fish abundance. Schumacher-Eschmeyer estimates were not a good indicators of population abundance during the harvest phase of the study while CUE was considerably closer to actual adult walleye numbers throughout the study period.
The goal of this research is to identify the mechanisms and strengths of density-dependent interactions within size-structured populations of rainbow trout, Oncorhynchus mykiss. The approach is to experimentally create populations that vary substantially , within normal natural ranges, in size-structure and density and to quantify the feeding and spatial behaviour, growth and survival of individuals that vary in size. Growth and mortality rates of rainbow trout differed among size- and age-classes. Not s urprisingly, smaller size-classes had higher mass-specific growth rates and higher mortality rates than did larger size-classes. There was no evidence of density-dependent growth or mortality in the smallest size class but strong density-dependent growth and survival in the larger size-classes. Overlap in diet composition and use of space indicated the potential for strong exploitative competition among size classes. The competitive interaction between the age-0 and age-1 cohorts was asymmetrical with a significant effect of the larger class on growth of the smaller class but no reciprocal effect. Evidence indicates that interference rather than exploitation creates the observed asymmetrical interaction which favours gro wth and survival of larger-bodied individuals.
Electrofishing is a commonly used technique for capturing fish in streams. The aim of the present study was to determine if the capture of juvenile Atlantic salmon by different electrofishing techniques and equipment causes physical injury in parr. Differ ent aged parr, as well as all sampling mortalities were collected by 3 different teams in 7 New Brunswick rivers in 1995. Specimens were X-rayed and examined by autopsy. Contrary to studies on trout, our results indicated negligible spinal injuries (< 1% ) and haemorrhages (< 3%). Analysis of mortalities indicated 3.0 % of parr suffered spinal injuries, and 7.5 % had haemorrhages. To determine the effects of water conductivity (Cond) and water temperature, age-2+ parr were collected in 1995 from the Lit tle Southwest Miramichi R. (low Cond), Catamaran Bk. (intermediate Cond), and Tomogonops R. (high Cond.), during the month of July (high Temp) and September (intermediate Temp). July samples collected from Catamaran Bk. and Tomogonops R. showed an inciden ce of 11.8 % and 4.8 % of spinal injuries, respectively ; 5% haemorrhages were found in the sample from the Little Southwest Miramichi R. No injuries or haemorrhages were found in parr collected at the intermediate Temp (September).
Previous video studies of 2 small, undeveloped Ontario lakes showed that small fish activity in littoral fringe habitats (Z less than 0.2 m) was more than four times higher than that in spatially-complex midlittoral habitats. In contrast, 1995 studies of a much larger and heavily cottaged lake found no evidence that fringe habitats were particularly attractive. In 1996 we evaluated two possible explanations for this difference between the larger and the smaller lakes: 1) that high densities of docks and boathouses in the larger lake might allow predatory fish to reduce small fish densities in adjacent fringe habitats; and 2) that more vigorous wave action in the larger lake might reduce the attractiveness to small fish of exposed fringe habitats, in comparison with protected ones. Sixty shoreline sites in Lake Joseph, Ontario were selected to represent high and low densities of shoreline structures and high and low exposure to waves and boat wakes. In July and August snorkelers repeatedly recorded fish densities in along-shore transects and measured wave heights and other environmental variables. These measurements were supplemented by video recordings in a subset of sites. We will present a progress report evaluating the two explanations of the differences in habitat usage that were recorded in our earlier studies.
We evaluated the patterns of benthic macroinvertebrate colonization of artificial substrates in lentic systems. Taxa generally follow a saturating curve (Michalis-Menton curve) with an initially rapid increase in densities, up to a plateau within a short period of time (less than 8 days). We propose that this initial colonization is due strictly to random encounters with the substrate, and that the plateau represents a balance between immigration and emigration. Both taxonomic richness and abundance of benthi c invertebrates fit the saturating function, and asymptotes were reached rapidly. Accordance with the saturating colonization curve improved with increasing densities of individuals and improved for taxa which were spatially aggregated. As a whole individuals in various genera became more spatially aggregated with time. We propose both an artificial substrate design and a proposal for sampling protocol, including an estimate of the optimal time for colonization. Furthermore, we include a comparison of species composition and abundance of benthic macroinvertebrates on artificial samplers and in the diets of rainbow trout (Oncorhynchus mykiss), a facultative benthivore. Sampler contents after four days of colonization do a good job of explaining diet of the fish.
Sperm competition should be a determining process of the reproductive success of individual males in communal spawners like cod, where females release eggs synchronously in an open environment. Both, sperm quantity and quality are important factors. If the volume of milt produced by a male is proportional to its body size, large males should profit a competitive advantage over smaller males, which will be modulated by the association of body size to sperm quality (i.e. fertilization success). Two sets of sperm competition experiments were performed, using genetic markers to determine the proportion of larvae sired by different males. The first experiment tested whether sperm quality is affected by sire size, when sperm volumes are equalized among males. The results indicated that spermatocrit was more important than body size in determining fertilization success and suggested that sire condition factor could affect sperm quality. In the second experiment spermatozoa numbers were equalized among males (spermatocrit accurately prdicted sperm density) to assess the effect of sire size and condition on fertilization success. The results are being analyzed.
The Atlantic cod (
The inconnu is a highly migratory whitefish of considerable importance to subsistance and conmmercial fisheries in the western Arctic. Researchers have suspected that inconnu in the Mackenzie River system are represented by both freshwater and anadromous migratory forms, however, little detailed information is available to substantiate these suspicians. Through the use of strontium analysis on otoliths, seasonal gillnetting and radio telemetry, we have confirmed the existance of two forms of inconnu within this river system. Strontium analysis has shown that inconnu in the Great Slave Lake area undergo their entire life cycle within freshwater, whereas inconnu in the lower Mackenzie river annually migrate between brackish and freshwater areas upon reaching maturity. Seasonal gillnetting and radio telemetry indicate substantial differences in the timing and extent of spawning migrations of these two forms of inconnu.
The relative importance of solar radiation, air temperature, and wind as predictors of littoral water temperature were examined in partial-year hourly time series from two small boreal forest lakes 250 km northwest of Thunder Bay, Ontario. At hourly time steps, changes in light energy had a significant positive association with changes in hourly average water temperatures, especially in models for littoral and shallow bay environments. Air temperature had a small positive association, slightly higher at littoral locations than at mid-lake locations; wind velocity had a small negative association in models for mid-lake locations only. At daily time steps, only air temperature was significantly associated with water temperature. Examination of the data from these lakes and from four additional lakes with partially clearcut shorelines suggests that riparian clearcut logging could warm shallow embayments by about 1oC, and warm other littoral environments by about 0.5oC, particularly on southern shores. These effects would be expressed primarily as increased daytime temperature peaks on sunny days. Wind-induced mixing may increase after clearcutting, and would tend to counteract these temperature increases. Daily average surface water temperatures seem to be controlled mainly by regional air temperature, and are not likely to be affected significantly by localized clearcut logging.
Among the many hyptheses advanced to explain the collapse of the northern (NAFO Div. 2J3KL) cod stock is the idea that many cod succumbed to physiological stress occasioned by inadequate feeding, the latter being caused by a decline in prey resources or a reduction in prey availability. An increase in natural mortality due to insufficient energy reserves may be difficult to demonstrate, but it should be possible to determine if fish exhibited certain symptoms of stress at the time when natural mortality is thought to have increased. This paper will document changes in abundance and distribution of prey, kinds and quantities of prey in cod stomachs, and the level of energy reserves in the cod, the last being measured as somatic condition (body weight relative to length) and liver size. Emphasis will be placed on spatial variability in these variables as determined from sampling during autumn bottom-trawl surveys in 1978-1996, but information from surveys in winter and spring will also be considered.
Until recently, the identification of substrate characteristics which constitute habitat for demersal fish, has been costly and subjective. We "sampled" the bottom using echo sounder signals and a QTC VIEW integrated acoustic processor to quantitatively identify potential habitat for juvenile Atlantic cod in 1995 and 1996. Validation of unique echo sounder "signatures" of bottom type and habitat use by juvenile cod were determined using Canadian Navy submersibles (PISCES IV & SDL-1). Habitat use by juvenile cod was age- specific and varied seasonally. In spring, age 1+ juveniles associated with gravel substrates, while age 2-4 juveniles associated with areas of high bathymetric relief or coarse substrate (rock & boulder). In fall, these associations with bathymetric relief and substrate particle size broke down - age 1+ juveniles were observed at shallower depths compared to age 2-4 fish which were observed deeper. We suspect that habitat associations were related to age-specific predator avoidance behaviour.
The principal challenge of managing lake trout populations in Ontario lies in the necessity of establishing sustainable levels of exploitation for all populations, using knowledge derived from a very limited sub-sample. We use both theoretical arguments and empirical observations to establish that: (i) differences in both the life history parameters and yield characteristics of Ontario lake trout populations can be predicted from habitat variables; (ii) angler predation on Ontario lake trout populations exhibits density dependent catchability; this effect can be predicted empirically and is consistent with simple predation models where the prey are patchily distributed and the predators can find the patches. Our results show that information on both the size of a lake, and its annual thermal structure, is minimally sufficient to build a fully specified, age structured population model for the lake trout fishery of that lake. Both equilibrium analysis and dynamic simulation of such models show that: (a) lake trout populations living in small lakes are more sensitive to exploitation than lake trout populations living in large lakes; (b) the level of density dependence exhibited by the catchability coefficient of lake trout anglers is sufficient to make control of fishing effort a complex and unreliable strategy for managing exploitation.
The abundance and survival of juvenile bull trout (Salvelinus confluentus) is necessary when developing models to predict the harvestable surplus of sub-adults or adults from a population. However, 15 years of data from Eunice Creek, a small headwater stream located in the foothills of Alberta, indicates that the abundance of juvenile bull trout can vary by several orders of magnitude among years. Juvenile bull trout abundance ranged from a low in 1983 of < 9 fish/km to a high in 1985 of 640 fish/km. Periods of low bull trout density in Eunice Creek were the result of no recruitment from 1979 to 1982, as indicated from length-frequency data. Co-existing rainbow trout (Oncorhynchus mykiss) were usually less abundant ( 30 fish/km) than bull trout but their populations remained relatively stable and did not show recruitment failures from 1979 to 1982. We developed an age-structured population model for bull trout in Eunice Creek which incorporates density-dependent survival of juveniles and varying rates of mortality in the adult population. High rates of mortality in the adult (or harvestable) population are unlikely to sustain the population.
What has caused the declines in yellow perch (Perca flavescens) stocks in western lake Erie (1987-present)? It has been proposed that the white perch (Morone americana) competes with the yellow perch. However, an examination of abundance, recruitment and growth trends of both species from 1978 to 1995 suggests that competition is not directly responsible for the changes in abundance. The white perch became abundant between 1981 and 1984, during which time the growth and reproduction of the yellow perch was poor. However, perch growth has improved from 1987 to present, in the presence of strong white perch numbers. Throughout this time series, reductions in phosphorous loading and the invasion by the zebra mussel have reduced the energy available to the species. Under these circumstances, the increase in yellow perch growth suggests a shift in the energy allocation strategy of the species. To examine this possibility, we performed energetic analyses on mature fish prior to spawning, and compared the growth patterns of cohorts at the beginning, middle and end of the time series using the scale back calculation technique.
We trace the origins and fates of the 1986 and 1987 year classes of the northern (NAFO Divisions 2J3KL) cod population from research survey, commercial catch and other data. We attempt to determine initial year-class strength relative to other year-classes and examine survival, growth, maturation and spatial distribution at each subsequent age to the present. From this we draw conclusions on whether or not these year-classes were indeed strong, and if so, why they had all but disappeared by 1992 when the moratorium was imposed. The significance of the fate of these year-classes in the collapse of the population is considered.
We examined how the composition of brook charr and Atlantic salmon diets varied in relation to seasonal change (June, July, and August), habitat type (pools and riffles), and population densities (con- and hetero-specific). Fish were collected at daytime in small streams of eastern Quebec. Both species preyed mainly on drifting invertebrates; salmon consumed more benthic organisms, but less terrestrial prey than charr. For charr, dietary diversity declined late in summer; diversity did not vary significantly between habitats. The dietary diversity of salmon showed no significant seasonal change. Salmon had a less diverse diet in riffles than in pools, and had a less diverse diet than charr in riffles but not in pools. Dietary overlap between the two species declined for the two habitats as the summer progressed. For salmon, the major source of variation in dietary composition was seasonal change, with little influence of habitat type or competitor densities. For charr, there was a strong interaction between seasonal change and salmon densities: at low salmon densities, charr diets varied little with season, but at high salmon densities charr diets shifted markedly from aquatic to terrestrial prey over the summer. Interspecific interactions do not appear to influence salmon diets, but such interactions may drive charr to rely on allochthonous food sources late in summer.
Conventional approaches to estimating annual production, such as Ricker's numerical method, require sampling fish populations on two or more occasions. In stream salmonids, a self-thinning equation often adequately describes the temporal trajectory of decline in cohort numbers in relation to increase in mean individual weight. The equation therefore yields a cross-sectional or snapshot view of production in the population. We used Ricker's method and a method based on integrating the area under the self-thinning curve to calculate annual production of brook trout, Salvelinus fontinalis, in streams of eastern Quebec. Production estimates obtained by the two methods were well correlated and were influenced similarly by various sources of variation: inter-site differences, temporal variability, inter-habitat differences, and effects of Atlantic salmon, Salmo salar. In salmonid populations that conform to the self-thinning relation, annual production can be estimated from point samples via the self-thinning relation. Because it reduces sampling effort, this approach may provide a useful alternative to conventional methods that require repeated sampling, particularly for comparative surveys of multiple sites across a large area.
This study was undertaken to determine the female and male contributions to the variability of early life history traits in yellowtail flounder. Nine traits were measured, but only one reported herein. Individual batches of eggs were divided into four and each of these fertilized with sperm from a single male. Eggs were reared in a flow through system, at 6C (std. dev. 1.5C) until hatch (90 degree-days). Larvae were measured for standard length when the body first straightened (4 days post hatch).. Preliminary investigations using a mixed model ANOVA indicated significant differences among females (F=44.2, p<.0001), and among males (F=4.42, p=.0003). However, multiple comparison procedures showed that only one male, producing smaller larvae, was significantly different from the rest of the males (p<.05), whereas all of the females were significantly different from each other (p<.05). This suggests that the male contribution to larval length (and maybe other early life history traits), at least on an individual basis, may be great. This would have profound implications for broodstock management in aquaculture, but may also be important to larval survival in natural stocks.
Lake trout reproduction was characterized in three small lakes 250 km northwest of Thunder Bay, Ontario. Physical characteristics of preferred spawning habitat, quantified as depth, substrate size, interstitial space, organic material, embeddedness and permeability, differed significantly between lakes. Principle Components Analysis differentiated a) deeper sites with smaller substrate and more organic material and embeddedness and b) shallower shoreline sites with larger, cleaner and less embedded substrate. Hydraulic permeability, indexed by the dissolution of gypsum cylinders, was higher in coarser substrates. Lake trout egg deposition density in egg traps averaged 70 eggs / m2 , of which 45% were viable by late Fall. Lake trout embryo survival and emergence in enclosures varied with substrate size, and was highest (75%) in cobble/rubble mixtures. Experimental siltation of incubation enclosures did not affect survival and emergence. Experimental nutrient enrichment (P and N) of a spawning shoal increased epilithic (primarily algal) biomass by 2.6 times over the summer; the effects of this on reproductive habitat are not known at present. This research suggests that physical and bathymetric characteristics of individual spawning shoals may result in site-specific vulnerabilities to terrestrial disturbance associated with timber harvesting.
Oxygen consumption, CO2 excretion and nitrogenous waste excretion (ammonia-N, urea-N) were measured during aerobic swimming (45% and 75% UCrit) in juvenile trout at either 5 or 15oC. There was a positive relationship between swimming speed and whole body O2 consumption and CO2 excretion rates at both temperatures. Although these rates were higher in fish acclimated to 15oC, there was no significant effect of temperature on the respiratory quotient (R.Q.; ratio of CO2 excretion/O2 consumption) at either swimming speed. Fish acclimated to 15oC had higher ammonia excretion rates and a greater nitrogen quotient (N.Q.; ratio of nitrogenous waste excretion/O2 excretion) at both swim speeds compared to cold-acclimated fish. Instantaneous fuel use, as calculated from the R.Q. and N.Q., indicate that acclimation temperature influenced the proportion of carbohydrates, lipids and proteins utilized during aerobic swimming in trout. In particular, protein and lipid use increased at warmer temperatures.
Substantial energy reserves are required for maturation and reproduction in cod. The seasonality in food availability and feeding success can markedly influence the annual cycle in energy storage and expenditure and hence the pattern of energy allocation between growth, maintenance and reproduction. Energy investment in reproduction and energetic condition of mature and immature cod in the northern Gulf of St-Lawrence were examined in order to determine the energetic consequences of reproduction in situat ions of lower available energy reserves. Since 1990, the condition of cod before winter declined significantly indicating that lower energy reserves were available for overwintering and reproduction during the recent years. These lower energy reserves had a negative impact on both reproductive effort and energetic condition of spawning fish. Energy investment in reproduction was low and spent fish ended out with poor condition and significantly lower energy reserves then immature fish suggesting a higher probability of mortality in reproductive fish.
Des réserves substantielles d'énergie sont requises pour la maturation et la reproduction chez la morue. Les changements saisonniers dans la disponibilité de nourriture et le succès d'alimentation peuvent influencer de façon marquée le cycle annuel d'accu mulation et de dépense d'énergie et de là le patron d'allocation d'énergie entre la croissance, le maintien et la reproduction. L'investissement d'énergie dans la reproduction ainsi que la condition énergétique de morues matures et immatures dans le nord du golfe du St-Laurent ont été examinés dans le but d'évaluer les conséquences énergétiques de la reproduction dans des situations où comme observé depuis 1990, de plus faibles réserves d'énergie sont disponibles pour la période d'hivernage et la reproduc tion. Ces plus faibles niveaux d'énergie ont eu un impact négatif sur l'effort reproducteur et la condition énergétique des poissons reproducteurs. L'investissement d'énergie dans la reproduction était faible et les poissons matures suite au frai, étaient en mauvaise condition. De plus, ils montraient des niveaux de réserves énergétiques plus faibles que les poissons immatures suggérant une plus grande probabilité de mortalité chez les morues reproductrices.
Haul roads have been identified as the component of timber harvesting operations imposing the greatest impact on aquatic ecosystems. The construction of road features (including: road surfaces, cutbanks, and ditches) involves mineral soil exposure and compaction, and redistribution of sediment. These impacts can generate water yield and peak flow increases, amplifying the potential for sediment transportation to aquatic habitats. In order to identify the impacts of forest roads on aquatic habitat in Northwestern Ontario, we measured physical and biotic characteristics of reaches immediately above and below crossings. Preliminary analyses reveal only minor differences in the variables observed. To quantify lateral sediment transport from forest roads and cutovers on a catchment scale, we have modified methods originally developed for an agricultural sediment transport study. This method will provide measures of lateral sediment transport from roads and cutovers which will be used to model timber harvest impacts and assess the effectiveness of riparian buffer strips at mitigating aquatic impacts.
The early life history of striped bass (Morone saxatilis) at the northern extreme of its geographic range in the Miramichi River Estuary is described for the first time from ichthyoplankton, beach seining and by-catch surveys undertaken between May and De cember 1992. Spawning occurred immediately upstream of the edge of the salt wedge from late May to early June at daily temperatures ranging from 14.3 to 18.8oC. The onset of feeding by larvae coincided spatially and temporally with blooms in their prey, a nd shifted rapidly from immature to adult copepods. Age-0 striped bass underwent an inshore and downstream migration during their first summer, which was consistent with the distribution of the main prey items of individuals greater than 50 mm long: mysi ds (Neomysis americana) and sand shrimp (Crangon septemspinosa). Growth rates and pre-winter lengths attained during the first year were higher than those reported for more southerly populations in the centre of the species' geographic distribution and may reflect a need for fish at this latitude to reach a certain length before overwintering.
The link between offspring survival and recruitment has often focused on larval size and/or growth-related processes including size-specific mortality and starvation. We consider the magnitude and the pattern of variation in mortality rates of larval and juvenile smallmouth bass with emphasis on the contribution of seasonal variation in prey abundance, offspring size and offspring growth rates to this variability. During a 5-year field study we quantified growth and mortality rates and idenfified biotic and abiotic factors that contributed to these patterns. Variation in growth and mortality were examined at two levels: year-class and brood (family). We predict that, if growth rate is an important component of offspring survival, then the instantaneous mortality rates of broods will be negatively associated with instananeous growth rates during a given developmental period. Both growth and mortality rates differed significantly across developmental periods within years and within developmental periods among years. Instantaneous mortality rates were negatively related to instantaneous growth rates during the larval period in all years suggesting that growth rates may be an important component of larval survival. Results are discussed in the context of the importance of growth-related processes to offspring survival and recruitment.
Predation is believed to be an important factor determining the life history characteristics of fish and other populations of aquatic fauna, but studies on this subject are often based on relative predation rates of juveniles and adults that are assumed, based on the type of predator community in a given system. In this study, we determined relative predation rates on juveniles and adults from five populations of pumpkinseed (Lepomis gibbosus) to test the following predictions: (1) populations with high rates of predation on adults relative to juveniles will exhibit early maturity and high reproductive investment; and (2) individuals in a population will mature, on average, at a body size where predation risk is minimal. To test these predictions, ten fish from each of four size classes (corresponding to ages 1-4) were exposed to the threat of predation for four days (two periods of two consecutive days) in each lake by tethering the fish for 4 h periods. Four foot trap-nets were used concurrently to determine the relative density and composition of potential pumpkinseed predators in each lake. Overall predation on the tethered fish ranged from 13-36%, and yearling fish were the most heavily predated in all cases. Preliminary analysis indicates size-class predation rates are strong predictors of size and age at first maturity, and that size at maturity tends to be larger in communities with more size-selective predators such as largemouth bass and yellow perch.
Detailed fisheries data is often collected by observers in an effort to improve compliance to regulations. However, these data can also provide unique insights into non-regulatory aspects of the fishery. As an example, I have used data collected by the International Observer Program (IOP) on the Silver Hake (Merluccius bilinearis) trawl fishery of the Scotian Shelf to examine two factors that may influence catch rates at sea: 1) predictable variations in fish availability and 2) interactions among fishing vessels. IOP Records of continuous fishing in the same areas indicate a cycle in hake availability of approximately one week in duration. This cycle may reflect an interaction between diurnal migrations and tidal flows. The analysis of positional data indicates that vessel interactions influence fishing activities. At high vessel densities, the deployment of fishing gear changes in a manner that reduces fishing success. These analyses illustrate the applicability of regulatory data to other areas of fisheries science.
Catch compositions recorded by the International Observer Program (IOP) differ both qualitatively and quantitatively from that in the logbook data. Our study examined bottom trawlers over 65 feet fishing in NAFO Division 4X of the Scotian Shelf. We focused on data from trips in 1993 that landed cod, haddock, and/or pollock. IOP hauls were more mixed than those in the logbooks, that is, there were fewer hauls where only one species was caught. This may indicate unreported discarding or more precise targeting during unobserved trips. To distinguish between these two fishing strategies, the distributions of hauls during observed and unobserved trips in the logbook data were contrasted. Observed trips did not differ in location or depth from unobserved trips, suggesting that fishers used a different discarding practice when an observer was aboard. This analysis contributes to the quantification of unreported catches in logbook data, and the more accurate estimation of fishing mortality from fisheries data.
Cnidarians are important predators of fish eggs and larvae in marine waters, but they are generally not considered to influence the survival of fishes in freshwater systems. We have found that Hydra oligactis occurs in high population densities (up to 30,000 / meter sq.) in Lake Opinicon, Ontario, and that it can capture and ingest the larvae of bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfishes. Hydra that were fed fish larvae turned black. Those fed a variety of zooplankton species remained brown. The ingestion rate of Hydra on larvae in 8L laboratory microcosms was higher during the night (0.181 larvae / predator / hr) than during the day (0.091 larvae / predator / hr). Hydra was most abundant on the introduced macrophyte, Myriophyllum spicatum. Bluegill and pumpkinseed nests were surrounded by dense beds of M. spicatum in some areas, and larvae had to swim through the plants (with the attached Hydra) in order to reach open water. We sampled Hydra in the vicinity of bluegill colonies on the morning after larval swim-up. The number of black Hydra (indicating ingestion of larval fishes) decreased with increasing distance from a nest site; from 72% black within colonies to 31% at 2 m outside of colonies. We estimate that up to 22% of the larvae produced by a colony can be consumed within this 2 m zone. Many more larvae are likely killed by Hydra that are abundant throughout the lake.
Smallmouth bass were deliberately introduced into Algonquin Park since the late 1800’s. Although the deliberate stocking of smallmouth bass has ceased, further colonization is possible through dispersal into waterbodies adjacent to the 70 lakes with naturalized populations. The objectives of the current study are to identify lakes in Algonquin Park that have suitable trophic, physical and chemical conditions for smallmouth bass; and, to identify current and potential impacts of smallmouth bass on fish communities. A discriminant function analysis, based on eight trophic, five physical and five chemical parameters measured in over 4,000 Ontario lakes, was used to predict the potential spread of smallmouth bass in Algonquin Park. The current and future impacts of smallmouth bass on Algonquin Park fish communities were identified by examining frequency of co-occurrence between smallmouth bass and other species, and by species-area relationships.
Trawlers have fished for cod (Gadus morhua) and other groundfish since the 1960's and shrimp (Pandalus borealis) since the late 1970's off Labrador in NAFO Divisions 2J, 3K and 3L. The shrimp gear captures other species, including small cod which are of no commercial value and many of the non-cod directed ground fisheries take a bycatch of cod. Cod was discarded from all of these fisheries and amounts were generally under-recorded in the fishing logs. Also, discards were not accounted for in the landing statistics, the basis for catch data as input for the assessment of the stock. Concerns have frequently been expressed about the level of discarding from the offshore fisheries, often as anecdotes related through the media. These fisheries have been observed since 1980 and at a level of 100% since 1987 in the cod (Jan. to Apr.) and shrimp fisheries providing the opportunity to quantify amounts and numbers discarded from these fisheries. This paper reports discard amounts based on fishery observer records from the shrimp, cod and other directed fisheries. It also examines the spatial and temporal variability in discarding and examines the reasons for substantial reductions in discard rates observed during the late 1980's and early 1990's. The largest component was from the cod directed fishery and total estimated discards for cod and shrimp fisheries combined peaked in 1986 at 10,211,389 fish (9,403 t). Given the closure of ground fisheries and the introduction of an excluding device in the shrimp gear in the early 1990's, total discards estimated for 1994 was 57,396 fish, a fraction of the numbers discarded during the mid 1980's.
The declines in sizes of populations and demographic shifts to young fish in Northwest Atlantic cod (Gadus morhua) have prompted much interest in the reproductive potential of small virgin females and their ability to rebuild these populations. Experimen tal evidence indicates that first-time spawners, when compared to repeat spawners, perform poorly. They breed for a shorter period, exhibit lower fecundity, produce smaller eggs with lower fertilization and hatching rates, and their larvae have a smaller window of opportunity available to match environmental conditions favourable for survival. These results have a direct bearing on the development of mathematical models of parent-progeny abundance relationships and fish life history strategies, and sugg est that traditional stock-recruitment models may overestimate the reproductive potential of current age-truncated populations.
We tested the hypothesis that spawning activity affects feeding behaviour and food intake levels of Atlantic cod (Gadus morhua). The individual behaviour of eight mature and six immature cod were monitored over 20 feeding sessions (11 weeks). Appetite a nd food consumption were suppressed during pre spawning (9-22 days) and spawning periods (10-50 days), with an abrupt increase occurring in feeding activity during the last quarter of spawning or shortly after release of the last egg batch. Immature cod fed throughout the experimental feeding period. Mature male cod were more aggressive than females and required a shorter time to consume food, though females consumed greater quantities than males. Females lost, on average, 36% of initial body weight an d males 12% during spawning, whereas immature fish gained 8% over the same period. Fecundity ranged from 1-4 million eggs among females. The volume of eggs produced by four individual females (range=1,285 to 5,995 ml in 4-11 bat ches) ranged from 99-195% (mean=150%) of a female's post spawning body volume. Laboratory results were supported by stomach fullness index values of Georges Bank cod exhibiting different maturity states.
In the Gulf of St. Lawrence, cod frequently spend time in waters with low levels of dissolved oxygen (hypoxia). We tested whether or not various levels of hypoxia reduced the growth rate of cod. Twenty individually-tagged cod were kept at each of six oxygen conditions (44, 54, 64, 74, 84 and 88% of saturation) at 10C. Capelin was fed ad lib for one hour, three times a week. At the beginning of the experiment, there were no differences in length (mean ± SE: 44.2 ± 0.3 cm), mass (715 ± 17.3 g) or condition (Fulton K, 0.81 ± 0.01) between groups. After 84 days significant growth in length and mass, as well as significant improvements in condition, occurred in each treatment. Maximum growth in length (6.6 cm ± 0.44) and in mass (776.8 g ± 54.7) as well as the best condition (1.11 ± 0.02) were obtained at 84% instead of 88% (5.9 cm ± 0.31; 713.0 g ± 55.4; K of 1.10 ± 0.26), but these differences were not significant. At 44% O2 saturation, however, increases in length (4.0 ± 0.2 cm) and in mass (327 ± 23 g) were significantly less than those of any other treatment except 54%. Furthermore, condition was lower (0.91 ± 0.87) and muscle water content higher (79.9% ± 0.1) than in any other treatment. At 54%, growth in length was less than at 84%, whereas growth in mass and condition were lower, and muscle water content higher, than at 84 or 88%. Growth in mass was significantly reduced at 74% relative to 84%, whereas condition was lower at 64% than at 84 and 88% O2 saturation. Cod growth and/or condition can be negatively affected when O2 levels fall below 80% of saturation.
Dans le Golfe St-Laurent, la morue passe souvent de longues périodes dans des eaux pauvres en oxygène (hypoxiques). Nous avons étudié les effets de divers niveaux d'hypoxie sur le taux de croissance de la morue. Vingt morues marquées furent élevées à 44, 54, 64, 74, 84 et à 88% de saturation en O2, à 10C. Du capelan leur était offert à volonté pour une heure,e trois fois par semaine. Au début de l'expérience, il n'y avait pas de différences de longueur (moyenne ± erreur type de 44.2 ± 0.3 cm), de masse (715 ± 17 g) ou de condition (K de Fulton de 0.81 ± 0.01) entre les traitements. Après 84 jours, des croissances significatives en longueur et en masse ainsi qu'une amélioration de la condition furent observées dans tous les groupes. La croissance maximale en longueur (6.6 cm ± 0.44) et en masse (776.8 g ± 54.7) ainsi que la meilleure condition (1.11 ± 0.02) furent observées à 84% au lieu d'à 88% (5.9 cm ± 0.31; 713.0 g ± 55.4; K de 1.10 ± 0.26), mais ces différences n'étaient pas significatives. Mais à 44%, les gains en longueur (4.0 ± 0.2 cm) et en masse (327 ± 23 g) étaient significativement inférieurs à ceux de tout groupe sauf celui à 54%, alors que la condition était moindre (0.91 ± 0.87) et le contenu en eau du muscle plus élevé (79.9% ± 0.1) que pour tout autre groupe. À 54%, la croissance en longueur était moindre qu'à 84%, alors que la croissance en masse et la condition étaient moindres, et le contenu en eau du muscle plus élevé, qu'à 84 et à 88%. À 74%, la croissance en masse était moindre qu'à 84%, alors qu'à 64% la condition était moindre qu' à 84 et 88%. La croissance et la condition de la morue peuvent être diminuées quand les tensions d'O2 baissent sous 80%.
Atlantic cod is a cold water species, residing in waters with annual mean temperatures of 1 to 11 oC. Cod that inhabit waters at the lower end of their temperature range grow more slowly, reproduce later and therefore have a slower replacement rate. The question arises, in anomalously cold years are cod in a given area adversely affected, and could cold temperatures lead to sudden declines in stock production? If cod stocks are vulnerable in anomalously cold years, why is it? Can cod die from the cold itself, do they stop feeding below a given temperature, do they become more vulnerable to predators, does delayed spawning lead to low larval survival? The effects of cold water have been examined to a limited extent among stocks, extensively within stocks, and at the level of the physiology of the individuals. Our goal is to synthesize the information across these scales and to link the suggested effects of cold years on stock abundance to the research that has been carried out on the individual's ability to feed, grow, swim and survive.
In a bioenergetic model, the energetic costs associated with activity can be calculated using swimming speed, acceleration and angle of turn of an individual fish. If these characteristics are not significantly different between two individuals of the same species or between two species in the natural habitat, the estimation of swimming costs can be greatly simplified. We estimated these characteristics for different fish species found in the littoral zone of two lakes of the Laurentian region (North of Montreal) and two of the Eastern township region (South of Montreal) during summer 94 and 95. Using under-water video cameras, we filmed the littoral zone five times during the day, one hour at a time (at 6h, 11h, 14h, 17h and 19h). We used the stereocinematographic method to estimate the X,Y,Z coordinates of individuals in real space, which allow us to estimate the swimming speed and complexity (acceleration and angle of turn) of these fish. These estimates are compared for individuals of the same species among lakes and for individuals of different species living in the littoral zone of the same lake.
Dans un modèle bioénergétique, les coûts énergétiques associés à l’activité peuvent être calculés en utilisant la vitesse de nage et les taux d’accélération et de virage d’un individus. Si ces différentes caractéristiques ne varient pas de façon significative en milieu naturel entre des individus de la même espèce ou même entre les espèces, l’estimation des dépenses énergétiques des poissons serait simplifiée. Nous avons estimé ces caractéristiques pour différentes espèces de poissons retrouvés dans la zone littorale de 2 lacs de la région des Laurentides et 2 de l’Estrie (Québec) durant l’été 94 et 95. À l’aide d’un système de caméras vidéo sous-marines, nous avons filmé des individus durant 5 tranches d’une heure (6h, 11h, 14h, 17h, 19h). Avec la méthode stéréo- cinématographique, nous avons estimés la position dans l’espace (coordonnés x,y,z) de ces poissons ce qui permet par la suite d’estimer la vitesse et la complexité (taux d’accélération et de virage) de la nage. Ces estimés sont comparés pour des individus de la même espèce retrouvés dans des milieux et des lacs différents et pour des individus d’espèces différentes vivants dans les mêmes conditions environnementales
La croissance en rivière des saumons atlantique juvéniles varie en fonction des conditions abiotiques et biotiques de l'habitat qu'ils occupent. La qualité d'un habitat peut être exprimée comme étant la différence entre les bénéfices et les coûts d'exploitation. En associant les coûts et les bénéfices à des conditions abiotiques et biotiques, il serait possible de déterminer le potentiel de croissance d'un habitat en connaissant les variations spatiale et temporelle de ces conditions abiotiques et biotiques. Une différence dans les facteurs de conditions a été observée entre 4 sites de la rivière Ste-Marguerite (région du Saguenay). Notre objectif a été de déterminer les coûts et les bénéfices d'exploitation de ces habitats et ainsi expliquer les différences observées dans les facteurs de condition. Ä deux reprises durant l'été un suivi journalier de la consommation des tacons nous a permis d'évaluer les bénéfices. En simultané, l'utilisation de caméras sous-marines, nous à permi de calculer l'utilisation du temps, la durée et l'amplitude des mouvements de capture des proies. Ces données sont considérées comme des indices des coûts d'exploitation de l'habitat. La moyenne de la durée des mouvements de capture est similaire pour trois des sites (2.42 à 2.56 sec) mais différente pour le quatrième (3.36sec); le pourcentage du temps utilisé pour les mouvements de capture dans ce quatrième site a aussi été plus élevé (11 à 22%) que pour les trois autres sites (4 à 15%). Ces résultats pourraient expliquer en partie, pourquoi le facteur de condition de ce site est le plus bas des quatres sites d'étude.
Growth in rivers for juvenile Atlantic salmon is a function of the abiotic and biotic conditions of the habitat. Habitat quality can be expressed as the difference between benefit and exploitation cost. It should be possible to determine habitat growth potential by the association of costs and benefits to abiotic and biotic conditions, and their spatiotemporal variations. Differences in condition factors were observed between 4 study sites on the Ste-Marguerite River (Saguenay). Our objective was to determine habitat exploitation cost and benefit to explain condition factor differences among sites. Daily consumption was estimated twice during summer to determine the benefits. At the same time, we used underwater cameras to evaluate indices of costs, such as: time budget and length and amplitude of movements to capture prey. Average movement length was similar for three of the four sites (2.42-2.56 sec for three sites and 3.36 sec for the fourth); the percentage of the time budget used for capture movements was also higher for the fourth site (11-22% relative to 4-15% for the others). These results may explain part of the differences among sites.
Human induced stratospheric ozone depletion causes a continuing increase of harmful UV-B radiation (280-320 nm) incident at the earth’s surface. UV-B penetrates clear ocean waters down to ecologically significant depths (20-30m). Early developmental stages of Atlantic cod dwell in the surface layers of the Gulf of St. Lawrence and the Atlantic Ocean. Increases in incident UV-B may negatively affect recruitment in cod and threatens also early developmental stages of other commercially important species (shrimp, crab, lobster). Cod eggs were exposed to ambient sunlight and to simulated sunlight 280-800 nm (intensity round July solar noon spectrum) using solar simulators with 25% additional UV-B. Radiant fluxes (irradiance per cm-2) were measured with an OL-754 spectroradiometer. Results of the in situ experiments show high sensitivities to ambient UV-B. In the laboratory experiments, exposure to the lower wavelengths in the UV-B gave highest egg mortality. Different egg stages showed different sensitivities. Controls showed high survival rates. Different long-pass cut-off filters were used in order to generate accurate Dose-Response Curves and a Polychromatic Action Spectrum for cod egg mortality. Action spectra serve as a first step in predictive modelling of UV-B effects for various percentages of ozone loss.
From 1993 to 1995, cod egg abundance and distribution, fisheries acoustic surveys, and analysis of trawl catches provided evidence of spawning for the northern Gulf of St. Lawrence cod stock off Newfoundland'’s westcoast. From the relative proportion of spent fish and various developmental stages of cod eggs, spawning could not have started before the end of March or early April. Spawning started while cod were still in dense shoals, and larger cod started to spawn earlier than smaller cod. The water column in the northern Gulf was weakly stratified in early May, with cold water (less than 2°C) extending to the surface. Cod eggs were distributed throughout the water column but with higher concentrations in the cold intermediate layer (CIL). The vertical distribution of cod eggs was determined by egg size and organic (lipids, proteins) composition. Stage I egg density estimates in May 1994 ranged from 1025.0 to 1026.0 kg·m-3, which is higher than that of the upper mixing layer. Between 1980 to 1989, there was a weak positive relationship between the CIL temperature anomalies and cod year-class strength (i.e. abundance of 3-yr-old cod). However, it is unlikely that below-average CIL temperature alone had a major impact on the recent collapse of the northern Gulf stock. Nevertheless, the poor state of the spawning stock (low abundance, poor fish condition, and less buoyant eggs) and harsh late winter and early-spring conditions in the northern Gulf (i.e. below average water temperature) could limit the potential for high recruitment and rapid recovery of the northern Gulf cod stock.
The monitoring of enzyme activity and energy reserves has shown that cod in the northern Gulf of St. Lawrence were characterized by slow growth and poor condition. They experienced a short growing season and exhibited slow to negative growth rates in summer, and negative growth rates from fall into early summer. Slow growth resulted in marked variations in condition within a year. There were also marked differences in growth rate and condition between years. Growth rate and condition covary in growth experiments in the laboratory, but they may follow different time patterns in the wild. Growth rate of cod in the northern Gulf of St. Lawrence for instance declined through the 80's while energetic condition did not vary during that period. Condition started to decline only later in the late 80's when growth rates had become extremely low. This situation may not be unique to the northern Gulf. There is a wide range in growth rates among different cod stocks in the North Atlantic. Stocks exposed to lower temperatures have slower growth rates, but these stocks also tend to vary more widely in mean annual growth rates. This variability in mean annual growth rate is shown to be associated to a decrease in the condition of fish in stocks with the slowest growth rates. Laboratory experiments show that this situation creates a strong selective pressure on the stocks.
Le monitorage de l'activité enzymatique et des réserves énergétiques montre que la morue du nord du Golfe Saint-Laurent se caractérise par une faible croissance et une mauvaise condition. Les morues ont connu une courte saison de croissance, une croissance lente voire négative au cours de l'été, et une croissance négative entre l'automne et le début de l'été. Ceci a entrainé de fortes variations saisonnières de la condition des individus. La croissance et la condition ont aussi varié de façon marquée entre les années. En laboratoire, croissance et condition énergétique covarient, mais en nature elles suivent des patrons différents. Par exemple, chez les morues du nord du Golfe Saint-Laurent, la croissance a ralenti au cours des années '80, alors que la condition énergétique individuelle se maintenait. La condition des morues s'est détériorée vers la fin des années '80 alors que le taux de croissance était devenu très faible. Cette siuation n'est peut-être pas unique à ce stock. Les taux de croissance varient beaucoup entre les stocks de morue dans l'Atlantique. Les morues qui vivent dans les eaux plus froides croissent moins vite, mais leur taux moyen de croissance est aussi plus variable entre les stocks. Cette variabilité semble associée à une baisse de la condition des poissons chez les stocks caractérisés par une croissance plus lente. Des travaux en laboratoire démontrent que cette situation exerce une forte pression sélective au sein des stocks.
Northern and Southern Gulf of St. Lawrence cod stocks have been shown to follow a marked cycle in energetic condition with maximal values being reached in fall and minimal values being reached in spring, during the spawning period. In summer, energy reserves were built up at a much slower rate than expected at prevailing temperatures, suggesting that food resources were limiting cod production. In winter however, energy reserves were used up at a much slower rate than expected under full starvation at ambient temperature. Food resources may have determined survivorship in winter since levels of energy reserves in spring were close to levels resulting in mortalities in laboratory experiments. Levels reached in spring indicated that some feeding had taken place in winter or that cod which were in poor condition at the onset of winter may actually have died from exhaustion. Historical data for other cod stocks in the Northwest Atlantic suggest that poor condition may have been a general feature for many stocks in recent years. The results are discussed in terms of fishery management practices.
Il a été démontré que la condition énergétique des morues du nord et du sud du Golfe Saint-Laurent suivait un patron accentué de variation saisonnière, les poissons étant en meilleure condition à l'automne et en mauvaise condition au printemps, pendant la reproduction. Les réserves énergétiques sont accumulées plus lentement l'été que ne le suggèrent les températures ambiantes ce qui laisse supposer que la nourriture limite la production de morue. En hiver au contraire, les réserves sont utilisées moins vite que pendant un jeûne total sous les mêmes conditions. La disponibilité de nourriture a peut-être limité la survie en hiver puisque les niveaux de condition au printemps étaient près de ceux qui entraînent la mort en conditions contrôlées. Les niveaux de réserve au printemps indiquent que les morues se sont nourries ou que les morues en plus piètre condition ont été éliminées au cours de l'hiver. Les données historiques pour d'autres stocks dans l'Atlantique suggèrent que cette situation n'est pas unique au Golfe Saint-Laurent. Nous discutons des implications quant aux méthodes actuelles de gestion des stocks de poisson.
In 1993, fish communities were sampled at 21 stations (19 on the Châteauguay River and 2 on the Trout River) along 72 river kilometers of the Châteauguay River basin, Quebec. The objective was to assess the effects of urban, industrial and agricultural pollution using various community attributes and the Index of Biotic Integrity (IBI) adapted to Quebec. For the Quebec portion of the river, upstream stations were classed as good to excellent. Downstream from Ormstown's raw sewage effluent and aux Outardes River, where reduced densities of insectivorous cyprinids, increased percentages of pollution tolerant fish species and the appearance of DELT (deformities, erosion, lesions and tumours) anomalies on 7% of community individuals could be observed, the station classed fair. The recovery over the next 16 kilometers was followed, in the Sainte-Martine area where agricultural, industrial and urban activities are concentrated, by the most significant river degradation. There was a decrease in insectivorous cyprinids decrease and an increase in the percentage of tolerant fish species. In addition, 8% of individuals were affected by DELT anomalies and there was a difference between the Index of Well Being (IWB) and the Modified IWB which was indicative of degraded sites. All these factors contributed to a poor IBI. The small recovery upstream from Mercier was immediately followed by a relapse downstream from Mercier's raw sewage effluent where a decrease in the number of species, an increase in the percentage of tolerant fish species and a reduction in insectivorous cyprinids could be observed. Overall, over the 69 kilometers studied along the Châteauguay River, the biotic integrity was excellent over 9 kilometers (13%), good over 36 kilometers (52%), fair over 13 kilometers (19%) and poor over 11 kilometers (16%). The Trout River's biotic integrity was excellent over the 3 kilometers surveyed (100%).
The concepts underlying fisheries management are introduced by linking the Gordon-Schaefer bio-economic model to recruitment overfishing. Activities which lower the cost curve are high risk to the degree that the open access equilibrium point coincides with higher effort levels and lower spawning stock biomass. Collapse is defined to occur when fishing effort is not restricted and spawning stock biomass is reduced to levels below that required for moderate to good recruitment. Changes in the ecosystem can alter the spawning stock biomass which is required for moderate recruitment, and thus the effort levels which will generate collapse. This activities of fisheries management are introduced in a second model. Within the framework of these models, two cod stocks on the Scotian Shelf off Nova Scotia, Canada, are described with the aim of illustrating the principles underlying survival and collapse. The shelf is characterized by strong gradients in bottom temperature, generally less than 4°C on the western Shelf. Grey seal abundance is considerably higher within the eastern stock area. Recruitment dropped sharply in the mid-1980s for the eastern Scotian Shelf stock and biomass has declined to very low levels. The fishery was closed in 1993. Recruitment to the western Scotian Shelf stock has not declined, and the spawning stock biomass is at moderate levels. One stock has collapsed and the other has survived. The fisheries management activities, changing environmental conditions, and seal predation changes on juvenile cod are described. For both management units fishing effort was not restricted to target levels since the introduction of quota management in 1977. As a result, there has been growth overfishing. It is concluded, however, that differences in management and fishing activities between the two areas cannot account for the differential stock responses. Colder environmental conditions and increases in juvenile natural mortality due to seal predation are concluded to the contributing factors to the decline in stock production and recruitment for the eastern stock.
Recent studies have examined the development of anti-predator behavior in larval marine fish. These laboratory studies have staged predation encounters within arenas containing upwards of 50 larvae. An inherent problem of this design is the inability to identify an individual larva and then assign measured response parameters to it. This study is one of the first to pair morphometric data of individual larvae with measurements collected on their escape behaviour and swimming ability. For this study, two groups of American plaice yolk-sac larvae were reared at 5oC and 10o C. Individual larvae were sampled from each group over a starvation period lasting 14 days for the 5oC and 7 days for the 10o C groups. Once escape responses and swimming ability were video-recorded, larvae were anaesthetized and recorded a second time under higher magnification. These results will be used to determine the influence of temperature-related development on escape responses and swimming behaviour as expressions of anti-predator behaviour in yolk-sac larvae of American plaice.
A conceptual model (Barber and Yuen 1994, 1995) which associates a variety of trends both supposed and real, ie in coastal salinity, coho feeding success, coho weight, coho interactive competence, coho survival, and both Fraser River sockeye (FRS) prespawning mortality and diversion, is extended to include the downtrend in Fraser River pink salmon (FRPS) weight. It is the premise that FRPS feeding success is less in coastal water: for returning FRPS a change from density-independent feeding-success and growth (Barber 1996) to density- dependent feeding-success and growth begins at entry into coastal water; here periods of less persistent wind (particularly in late spring and early summer) with less-developed Langmuir circulations, together with increased abundance (density) of other returning salmon, especially FRS, and with increasing recognition of coastal processes, eg aspects of tidal motions experienced previously as oceangoing juvenile, lead to schooling and eventually to cessation of feeding. Cross-spectral work in time series (B.C. catch statistics) indicates coherence at trend between FRPS weight and both FRS diversion and coho weight: with coho weight a determinant of diversion and with diversion a measure of FRS density in coastal water we show the decline in FRPS weight is inversely associated with FRS density.
For the past few years, solar ultraviolet radiation has increased due to the decrease in the thickness of the ozone layer. The UVB radiation is expected to cause an important damage to marine organisms near the surface. The goal of this study was to determine the effect of UVA and UVB radiation on the mortality and on the hatching success of Atlantic cod eggs exposed to ambient solar radiation. This study was carried out during July, August and September 1996 (a total of 5 experiments). In each experiment, cod eggs were maintained outside in an open basin with continuous flow of sea water at two depths, surface and 50 cm. The eggs were placed in three groups of open quartz vessels (7 replicates). One group received the full spectrum, the second group was protected by mylar sheet (blocking UVB), the third group was covered by OP-2 (blocking total UV). Each day dead eggs were counted. At the end of the exposure (ten days), hatching success was noted. The difference among the three treatments is marked by highest mortalities and virtually no hatching in the fully exposed quartz vessels for both depths. Generally, the eggs in the surface vessels, covered with mylar, showed lowest mortalities, the OP-2 covered slightly higher. At 50 cm depth mortalities were similar in both the mylar and OP-2 covered vessels. Hatching success was usually higher in the OP-2 covered vessels for both the surface and 50 cm depth.
Rates of growth and development in fish are most variable during the larval and juvenile stages because the principle sources of mortality for young fish, predation and starvation, are size- dependent. Therefore factors that affect growth rate, such as variation in food supplies, should affect juvenile survival and thus year-class strength. We conducted a field experiment to examine how pond productivity affects growth rate and survival of young-of-the-year fish. Adult fathead minnows (Pimephales promelas) were stocked in a set of experimental ponds, nutrient concentrations were manipulated and characteristics of young fatheads living under the different nutrient regimes were quantified. Pond sides treated with nutrients responded with an increase in primary production. The young fish produced in the enriched pond sides exhibited increased body size and decreased mortality throughout the season compared with the untreated pond sides. Egg production was also observed to increase in the enriched pond sides. These results suggest that pond production can strongly influence growth and survival of young-of-the-year fathead minnows.
With the increasing concern about the impact of coastal development on aquatic habitat comes the need for extensive studies regarding mitigation and compensation measures. Such measures have become standard in coastal design and construction. However, the study of the effects of these breakwaters and artificial shoaling structures has lagged behind this implementation. Government guidelines are necessarily general and remediation is quite site-specific. Past studies have concentrated on hydroelectric sites and inland waters not subjected to coastal conditions. Further, the structural stability of artificially created habitat and its effect on the bio-diversity of an area of engineered mitigation along an open coast need to be determined. Research being conducted at Queen's University concentrates on fish habitat as well as examining artificial fish spawning beds, through various methods. An initial search of regulations pertaining to aquatic habitat, mitigation and compensation is currently underway, in order to compare and to evaluate them critically. This search is carried out with the help of various environmental engineering firms. All relevant biological information is being collected, with the help of the Queen's Department of Biology and the Ontario Ministry of Natural Resources. A fish survey has been implemented to study the behaviour of fish in both natural and `artificial' environments. This involves a snorkel and mask study in various types of habitat, including natural bays, open shoreline, within and around marinas/breakwaters and also over artificially created spawning grounds. Statistical and qualitative evaluations of the data will be performed and analysed. This will include biomass estimations, water quality analysis, etc. The structural stability of artificial habitat such as artificial gravel spawning beds against harsh coastal conditions will be tested through hydraulic modeling. This interdisciplinary study will provide concrete data to improve the design of mitigation and compensation measures. With careful biological, environmental and coastal engineering planning and design, the mitigation of fish habitat may be of greater benefit to not only the fish, but to all who use these coastal areas.
Fish, as in most poikilotherms, exhibit annual physiological cycles normally in phase with environmental cycles, frequently represented as temperature. In agricultural and entomological domains the measure of heat available for growth through the year is the growing-degree-day (GDD). We applied this approach to cod as their physiological cycles are, in part, determined by thermal cycles in their environment. As the phase and amplitude of the GDD cycle can exhibit significant interannual variability, it is expected that physiological cycles will vary likewise. We hypothesised that observed variations in annual indices of cod condition on the Grand Bank may be artifact, resulting from classical aliasing (spurious trends caused by inappropriate sampling of a varying cycle). We use four sets of data to address the hypothesis: 1) a water column temperature time series to estimate the "normal" GDD cycle as well as interannual variations in phase and amplitude; 2) a compilation of monthly estimates of cod condition (liver weight, body weight and body length ratios etc.) to estimate the "normal" cycle in cod condition and interannual variations; 3) a similar compilation of reproductive indices for female cod (maturing, spawning, spent) to estimate the "normal" reproductive cycle and interannual variations; and finally, 4) the date of the field surveys used to collect the samples for determining various biological estimates. We show that the normal maturation cycle in cod is predetermined by the normal condition cycle, which is in turn, correlated with the GDD cycle. We then employ these relationships, in concert with sampling date information, to examine interannual trends and variations in condition and spawning state. Finally, we explore the possibility that observed variations in cod migration (timing and distribution) and observed variations in population abundance may be influenced by interaction between variation in the time of sampling and variation in the GDD cycle.
We analyze groundfish trawl survey observations (n=19,868) collected by Canada and the United States during the years 1975-1994 to determine the dynamics of spatial distribution of cod (Gadus morhua) relative to ambient bottom temperatures. Our observations encompass the full geographic (Cape Hatteras, North Carolina to Cape Chidley, Labrador) and depth range (50 to 1000+ m) of the species in the Northwest Atlantic. Cod distribution relative to ambient temperature within stock areas was analyzed using overlays and area analysis of potential maps of cod density and bottom temperature, and cumulative distribution functions (CDF=s). Observations for each stock were selected to represent the most consistently sampled season for the 25 year period and observations were pooled within 5 year blocks to ensure adequate sampling coverage. Cumulative distribution functions showed that median ambient bottom temperature ranged from a low of 0.1 oC to a high of 11.8 oC, while median cod-weighted temperatures, or those temperatures where most cod occur, ranged from a low of 0.7 oC to a high of 9.6 oC. The extremes (25th and 75th percentiles) of these distributions show that cod can occur at both lower and higher temperatures but that the bulk of catches occur in this temperature range. Differences between ambient and cod-weighted bottom temperatures were generally greatest below 1 oC and above 10 oC, and show no obvious pattern at intermediate temperatures, indicating that, as a species, cod preferentially inhabit a temperature range of 1 -10 oC, and that within this temperature range factors other than temperature influence spatial distribution. We consider that this represents the global range of temperatures that the species selects in the Northwest Atlantic. Individual cod stocks differ both by virtue of living in different temperature environments and by the portion of that environment which they selectively inhabit. Georges Bank cod inhabit an area where temperatures range from 4-18 oC and select waters from 5 to 10 oC, while Northern Grand Banks / Labrador Shelf cod select bottom temperatures between 0 and 3 oC from a range of -1.5 - 5 oC. Within stocks, the relationship between bottom temperature and cod distribution relative to temperature is not constant over time. Significant changes in cod distribution relative to bottom temperature were observed for Georges Bank cod, St. Pierre Bank cod, Northern Gulf of St. Lawrence cod, Southern Grand Banks cod, and Northern Grand Banks / Labrador Shelf cod, over the twenty year period of observations. The potential implications of these observations to stock dynamics are discussed.
The harp seal (Phoca groenlandica), which is numerous and widespread in the northwest Atlantic, may have significant influences on the structure of this ecosystem. To quantify these influences, we must understand the functional relationship between harp seals and their prey. If seals are discriminating in their choice of prey, then their consumption of a particular species will not necessarily vary in relation to its availability. By applying Chesson's index of selectivity to stomach contents and research trawl data collected in several near and offshore locations, we found that harp seals preferentially selected capelin relative to other prey species, when given the choice. Arctic cod were also preferred. In general, these predators were neutrally selective towards Atlantic cod, American plaice and Greenland halibut. These patterns rationalize the dietary patterns reported for harp seals generally. They also explain harp seals' switch from a reliance on capelin to Arctic cod seen in the mid 1980's when evidence suggests these cod became very abundant relative to capelin in nearshore waters.
A study of the relationship between microscale turbulence and feeding success of larval radiated shanny (Ulvaria subbifurcata) was conducted on Conception Bay, Newfoundland, during three weeks in July/August 1995. Although previous studies had suggested that the relationship between turbulent velocity and larval feeding should be dome-shaped we found no evidence of such a functional relationship. Rather, differences in feeding success were evident only when days were grouped as either "high turbulence" or "low turbulence" on the basis of Richardson number. Larvae contained significantly fewer items in their guts on high turbulence days. However, these prey items were significantly larger than those found in guts on low turbulence days, resulting in a significantly greater volume of food in larval guts on high turbulence days. Turbulent velocity did not affect between-day variation in RNA:DNA ratios of the Ulvaria larvae. We suggest that the apparent shift in size-selectivity under increased turbulence may result from larvae having higher probability of capturing large prey under increasingly turbulent conditions.
Diphyllobothrium ditremum and D. dendriticum are pseudophyllidean cestodes found as plerocercoid larvae in the visceral organs of their second intermediate hosts, typically salmonids. The obligate life cycle of these parasites involves copepods as first intermediate hosts and fish eating birds (Gavia and Larus species respectively) as final hosts harboring the adult tapeworms. However, an alternate transmission pathway occurs as D. ditremum and D. dendriticum are acquired by piscivorous or cannabalistic salmonids feeding on infected prey. Opportunistic feeders such as brook trout (Salvelinus fontinalis) and Arctic charr (S. alpinus) are more susceptible to infection than are obligate piscivores such as lake trout (S. namaycush). In laboratory experiments, using either copepod- or fish-vectored Diphyllobothrium, we are seeking to develop predictive models on parasite loads for both species in relation to host mortality. Heavy infections of either parasite species result in host morbidity and mortality, which can be ecologically significant in regulating salmonid populations and food web interactions in affected lakes.
The relative weight of fishing (including non-catch) mortality and environmental and ecosystem induced mortality in the collapse of northwest Atlantic cod stocks is still debated. Three forces contributed to the collapse of cod stocks: 1) high exploitation), 2) reduced productivity and 3) abusive fishing practices. An attempt is made to identify the components of each of the three forces leading to stock collapses. The magnitude and interannual variability of each component must be evaluated in order to rank the respective roles of the three main forces in the collapse of cod stocks. Under 1) high exploitation, the collapse of cod stocks is considered in relation to the reliability of data from research surveys and other data sources on abundance or trends (acoustic estimates, tagging data, CPUE), changes in the catchability of fish as a result of geographic displacement, increase in fishing effort and technology improvements, offshore/inshore exchange of cod. Under 2) reduced productivity, the collapse of cod stocks is considered in relation to slow growth, poor condition, low recruitment, increased predation, in the context of general cooling of the ocean and associated changes in fish assemblages. Under 3) abusive fishing practices, the collapse of cod stocks is considered in relation to dumping and highgrading.
We describe results from analyses of physical and biological oceanographic data sets and describe the development of a spatially-explicit individual-based model to simulate migration, feeding and growth processes of salmon in the Northeast Pacific Ocean. Our research objective was to describe how salmon migration, feeding and growth are influenced by patterns of offshore current fields, sea surface temperature (SST) and prey resources. We compiled and analyzed data collected before and after the 1977 regime-shift. We computed spatially-explicit growth rate potential for a representative 500 g sockeye salmon to provide insights into growth conditions extant in the Northeast Pacific Ocean across seasons and before and after the regime shift. Spatial and temporal patterns of high growth rate potential in the ocean appeared to track closely with the patterns of salmon migrations inferred from tagging studies. We also discovered that growth rate potential declines sharply within the southern zone of their distribution, at approximately the latitude where salmon abundance has been observed to decline by one to two orders of magnitude. We describe potential future applications of the model to address issues related to migration theory and management of Pacific salmon stocks.
The objective of the study was to examine the effect of lake herring, Coregonus artedii, and lake whitefish C. clupeaformis on the population structure of three benthic fish species with pelagic larvae. Data on burbot, Lota lota, longnose sucker, Catostomus catostomus, and white sucker, C. commersoni, were examined in relation to the presence/absence of these coregonines. Subyearling burbot were absent or rare at electrofishing sites on the lakes in which lake herring were present, and common in the lakes in which lake herring were absent. The population catch per unit effort of burbot was greater in lakes where herring were absent compared to where they were present. The longnose sucker, with a larvae 50 % smaller than the white sucker, predominated in gill net catches in the lakes without lake herring or lake whitefish, was scarce in the lakes with lake whitefish and absent in lakes with lake herring. In one of the study lakes, analysis of data collected before and after lake herring were introduced indicate that the longnose sucker population declined in abundance following the lake herring introduction. In the same lake, analysis of lake herring diet data from areas where larval fishes were abundant indicated larval fish were common in the lake herring diet. These results suggest that the burbot and longnose sucker go through a larval bottleneck in inland lakes caused by lake herring predation.
Egg loss through superimposition of nest sites occurs in many salmonine mating systems. However, unlike semolparous salmonines which cease feeding during their reproductive lifetimes, satellite males of iteroparous salmonines can be substantial egg predators. We tagged and followed a population of lake-spawning brook trout (Salvelinus fontinalis) throughout two breeding seasons to assess egg mortality through redd superimposition and cannibalism. In 1994 and 1995, 78 % and 72 % of redd sites were used by more than one female, respectively. Brood loss was considerably less as only 25 % and 29 % of egg pockets within redds (i.e., spawnings) were superimposed by larger females. The proportion of spawnings dug up decreased throughout both breeding seasons. Video-tape analysis of spawning events showed cannibalism by satellite males to occur in 24 % of spawnings. Cannibalized dominant males were smaller (375 mm FL) than uncannibilized males (424 mm), although there was no similar difference in female size. As a result, cannibalized dominant males were 20 mm smaller while uncannibalized males were 40 mm larger than their respective mates. These results suggest timing of spawning and mate choice are important determinants of brood success for female brook trout.
In coastal waters of Newfoundland, O-group Atlantic cod (Gadus morhua) settle in shallow, nearshore regions occupied by older conspecifics. Intercohort cannibalism is common in cod, however very little is known of the behavioural responses that may limit interactions between juvenile cod cohorts in the wild. We examined the diel variation in stomach content weight and diet composition of O- and I-group cod at a shallow water site to delineate peak feeding activity and resource use of the different cohorts. O- and I-group cod were sampled from standardized collections made with a small siene at regular intervals (3 or 4-hr) throughout 24-hr periods from September-December, 1993. O-group cod exhibited a distinct diurnal feeding pattern. I-group cod fed throughout the diel period but exhibited nocturnal peaks in stomach content weight. O- to I-group cod exhibited a size related shift from feeding predominantly on zooplankton to large benthos and fish (cannibalism) that coincided with a shift from diurnal to predominantly nocturnal feeding. O-group cod were always more abundant in the diurnal catches, exhibiting a 12 to 24 fold decrease in abundance at night, while the catch of I-group cod showed little diel variation. The nocturnal dispersal and lack of feeding by O-group cod coincided with the occurrence of larger conspecifics (II- and III-group), suggesting that prey availability was secondary to predator avoidance in explaining the diel feeding pattern of O-group cod.
Assessing impacts on cod stock productivity, such as seal predation on juveniles, depends on accurate estimates of pre-recruit abundances at key life history stages of cod. When juvenile cod settle to the bottom they can be difficult to sample. Their distribution and survival is dependent on the availability of preferred habitats, and these preferences change with development. Historic distributions of juvenile northern cod (NAFO 2J3KL) did not change over several decades. Offshore, however, their range varied with abundance. High residual errors associated with survey estimates of juvenile cod abundance are associated with preferred habitats. These results suggest that preferred habitats will always be occupied by juvenile cod, whereas non-preferred habitats will not be occupied and marginal habitats will be variably occupied. We discuss the application of digital acoustic techniques to improve our ability to sample juvenile cod by identifying and measuring juvenile cod habitats and abundances.
The quantity of food consumed by fish is an essential parameter for quantifying energy flows in fish communities. Methods used to quantify fish feeding rates in the field are generally labor intensive and tedious, undermining the need for a general predic tive model of fish feeding rates. The purpose of this study was to develop a simple model of fish consumption rates based on field measurements. The model was developed using field estimates of fish daily consumption rates obtained from the literature. Pr eliminary analyses indicated that feeding rates of both marine and freshwater fishes were isometrically scaled to body size, and that the value of the exponent was significantly different from 3/4. Our analyses showed as well that fish feeding rates were not significantly correlated to water temperature, probably due to the small range of temperature values. Furthermore, daily consumption rates of marine and freshwater fishes were not significantly different. Predictive models based on laboratory estimate s tended to underestimate daily ration of fish calling into question their applicability and relevance to the field. This model will provide a simple and useful tool for examining species interactions in lake and marine ecosystems and determining manageme nt policies.
La quantité de nourriture consommée par les poissons est un paramètre essentiel pour quantifier les flux énergétiques dans les communautés de poissons. Les méthodes pour estimer les taux de consommations des poissons en milieu naturel requièrent généralem ent un grand effort d'échantillonage et sont fastidieuses, indiquant la nécéssité de développer un modèle général d'ingestion pour les poissons. L'objectif de cette étude était de développer un modèle simple de taux d'ingestions des poissons. Le modèle a été construit à partir d'estimations effectuées sur le terrain publiées dans la littérature. Les analyses préliminaires indiquaient que les taux d'ingestion des poissons marins et d'eau douce étaient proportionels à la masse (isométrie), et que l'exposant était significativement de 3/4. Ces analyses indiquaient également que les taux de consommation n'étaient pas significativement corrélés à la température, probablement à cause du faible étendu de température. De plus, les taux d'ingestion des poissons ma rins n'étaient pas significativement différents de ceux d'eau douce. Les modèles basés sur expériences réalisés en laboratoire sous-estimaient les taux d'ingestion des poissons sur le terrain, remettant en question leur applicabilité en milieu naturel. Ce modèle fournira un outil simple pour examiner les interactions entre les poissons et pour examiner différentes stratégies d'aménagement de poissons.
Previous tests of resource defence theory have manipulated only one aspect of resource distribution at a time. We tested whether there was an interaction between the effects of the spatial and temporal clumping of food by allowing groups of ten Japanese medaka (Oryzias latipes) to compete, over a 4 week period, for food in a 2 x 2 factorial design. As expected, the intensity of aggression increased as the spatial clumping of food increased and as the temporal clumping of food decreased. However, there was also a significant interaction between the effects of the spatial and temporal clumping of food on intensity of aggression. In addition, monopolization increased as the spatial clumping of food increased, but was not affected by temporal clumping. Our results suggest that care must be taken when extrapolating the results of single factor experiments to multi-factor or field situations. Growth depensation within groups increased over time but was not influenced by the treatments. The significance of these results for aquaculture will be discussed.
We described the spatial and short term temporal heterogeneity of fish abundance in the perimeter of four lakes characterized by different levels of abundance in pelagic predators. Fish relative abundance was estimated by acoustically sampling 25 to 100 % of the complete contour of the lakes at 4 h intervals during 24 h. During hydroacoustics, the transducer was installed on the side of a boat and directed towards the littoral such that the axis of the acoustic beam was set parallel to the surface of the lake. Maximum values of average fish relative abundance in the pelagic zone ranged from 6 to 209 targets/ 1003. Fish relative abundance varied among segments by factors ranging from 3 to 84. Coefficient of variation of fish relative abundance ranged from 64 to 523 % and supported the hypothesis that fish are more heterogeously distributed in lakes containing pelagic piscivores. Our work suggests that the presence of pelagic piscivorous fish may affect the sampling design required to estimate fish abundance and distribution patterns in lakes.
We analyze demersal trawl survey data for the east coast of North America from Cape Hatteras, North Carolina, in the south, to Cape Chidley, Labrador, in the north, collected between 1975 and 1994. We map and describe demersal fish assemblages, and evaluate evidence for ecological regime and assemblage distribution shifts over decadal time scales. Maps for the 108 most abundant demersal species revealed 9 species groups, based on both geographic and depth distributions. PCA of the top 66 species, and major survey months (39,694 trawls sets), extracted 18 principal components (PC’s) with eigenvaluesgreater than 1. The species with high loadings (0.5+) were defined as an assemblage and site scores on the PCs were used to map its spatial distribution. Cluster analyses of these data, at the level of 18 groups, were also mapped. Assemblages identified by all methods were spatially coherent. These assemblages are consistent with those reported in previous studies, which covered only a portion of the current study area. The methods employed identified a number of species groups in common (e.g. the Atlantic cod (Gadus morhua) thorny skate (Raja radiata) and American plaice (Hippoglossoides platessoides) assemblage). The multi-variate analyses indicated that these assemblages did not account for a high proportion of the variance in distribution. They should be viewed as loose assemblages. Assemblages were persistent through time as evidenced by analysis of 5 year subsets of the data set which showed that generally the same assemblages were identified for temporal subsets as were identified by the overall analysis. Changes in the distribution of individual species were analyzed by presence-absence maps, bivariate ellipses of latitude and longitude containing 50% of the individuals of any species caught, and band analysis. Some species such as arctic cod (Boreogadus saida) have extended their range southward since the 1980s, while the northern limit of Atlantic cod has moved southward since 1990. Since geographic limits of species distributions can vary over time and since present stock boundaries are static, population models which account for potentially variable stock boundaries should be developed. Preliminary results on the effects of fishing on the distribution and abundance of assemblages and selected species are also presented. Given the temporal persistence of these assemblages, management strategies could be adapted to optimize harvest of assemblages rather than single species, especially if the assemblages are persistent over smaller geographic areas (i.e. stocks). Species composition of assemblages could be used as background for spatial allocation of fishing effort aimed at reducing by-catch in the harvesting of single species quotas.
Purse seiners fishing commercially for herring comprise a small (approximately 35 vessels) and dedicated fleet. Seasonal fleet dynamics handicap the well-defined spatial and temporal behaviour of several discrete populations of Atlantic herring in NAFO divisions 4WX from the Bay of Fundy, Southwestern Nova Scotia and along the eastern shore out to Cape Breton. We present a population-based spatial-temporal model of seasonal stock dynamics based on fishing locations by purse seiners over the last decade. The proposed model contrasts the adopted aggregate VPA stock assessment approaches that we argue are inappropriate for providing useful management of populations in this fishery. Recent developments in the 4WX herring fishery directly incorporate fleet information in an ongoing, updated estimation of population sizes.
An important objective in aquatic ecology is to determine the degree of coupling between physical forcing and biological response. The task is complicated when the response is fisheries recruitment, a process that integrates many influences over a relatively long time. Advances in remote sensing and optical observation technology should help: the means now exist to characterize physical and biological variability synoptically with remote sensing, and new in situ sensors can make continuous observations of near-surface conditions from moorings and drifters. Optical sensors are particularly well suited for describing variability in primary producers: they provide the means to monitor temporal dynamics, spatial variability, and perhaps the productivity of phytoplankton. Also, measurements of ocean color can be used to estimate water transparency in visible and ultraviolet wavelengths. This information could be useful for inferring the photic environment of fish and the exposure of sensitive stages to potentially damaging ultraviolet radiation. Here, principles of optical observation technologies are discussed and some potential applications in fisheries research are presented.
The literature suggests that buoyancy differences (measured as density = g cm-3) are an indication of whether larvae are feeding or starved. It has been argued that starved larvae are less dense than fed larvae. However, previous studies have failed to co ntrol for the effects of osmoregulatory failure on buoyancy. We ran a replicated split-plot ANOVA design to test the hypothesis that fed larvae are more dense than starved larvae. We measured the density of larval cod in isotonic Percoll density gradients and found that osmoregulation failure had a larger effect on buoyancy than nutritional differences. Our data also suggests that larval density, on its own, is not a good index of nutritional effects, but it was found to be strongly and negatively correla ted with larval survival (R2= 0.79). This study represents the first non-destructive larval condition index that can directly predict larval survivorship. In addition, this bioassay may be used in the field.
Acoustic estimates of distribution and abundance from 1990 to 1994 are used to describe the timing and rate of decline of the northern cod. These estimates are based on adaptive sampling of the hyper-concentrations of cod that formed the bulk of the stock during those years. The results are compared with estimates of the decline based solely on bottom trawl surveys. A theory is introduced on the spatial and behavioral changes that occurred within this stock beginning in the late 1980 s and their impact on the fisheries of the early 1990 s, the decline of the stock, and stock assessments.
Controversies still arise in explaining the mechanisms involved in salmon migration. The influence of the physical environment on Sockeye salmon return timing and distributionis still poorly known. Numerical modelling is a useful tool to study such problems where data are sparse. We therefore combine a fine resolution (5 km, 1 hr) circulation model of the Northern Coast of British Columbia with an individually-based model of salmon migration. The circulation model is three-dimensional and based on the non-linear primitive equations governing ocean dynamics. The individually-based model of salmon migration allow each salmon to be subjected to the surrounding ocean currents and to have its own behaviour such as orientation and swimming speed. Preliminary experiments done using tidal currents alone show a good correlation between the number of returning salmon and tidal currents. This indicates that tidal currents influence grouping of returning salmons, which in turn can affect sampling strategies.
Six hypotheses to explain variations in sockeye salmon (Oncorhynchus nerka) return times to the Fraser River were used to develop new environmental and biological indices for linear regression forecast models of stock-specific run time. Sockeye salmon return to their spawning streams in the Fraser River basin after completing migrations over thousands of kilometres from their foraging grounds in the northeast Pacific Ocean. The principal stock groups return at different times, and for each group the timing may vary by as much as three weeks between years: the early Stuart River stock arrive at the mouth of the Fraser in early summer, the Horsefly River and Chilko Lake stocks in mid-summer, and the Adams River stocks in late summer. Forecasts of these return times are critical for estimating the return abundances required to manage the coastal and in-river interception fisheries of these fish. The indices examined (all of which are available in near real-time for pre-season or in-season forecasts) were: 1) for the temperature displacement hypothesis, sea surface temperatures and thermal limits (i.e. the positions of surface isotherms); 2) for the surface advection hypothesis, surface currents imputed by an empirical model; 3) for the fish length hypothesis, female lengths; 4) for the fish abundance hypothesis, return abundances and catch of British Columbia and Alaska sockeye; 5) for the return time hypothesis, stock-specific return times; and 6) for the full moon hypothesis, the dates of the full moons in June and July. Correlation coefficients and Bonferroni probabilities were used to identify candidate predictor variables for each hypothesis, and alternative multiple linear regression models for return time forecasts were developed for each stock group. The models considered most robust in light of the observed (and anticipated) decadal- scale changes of the marine climate in the northeast Pacific Ocean account for up to 65% of the observed run time variances, with root mean square forecast errors of less than 4 days (for the period from 1950 to 1995). Most of the variability seems to be forced by variations in oceanic environment. Other poorly defined and understood processes, both on the high seas and along the coast, require more data before their effects may be evaluated and these forecasts could be improved upon.
Atlantic cod are distributed in the western Atlantic from Labrador to Cape Hatteras. Spawning areas for cod in many parts of its North Atlantic range are relatively discrete and stable over time. However, it remains uncertain whether such spawning aggregations constitute reproductively and/or genetically distinct populations. Proper resolution of these uncertainties is necessary for a sufficient understanding of the abundance and distribution of the species that is essential for successful management. Analyses using a variety of allozyme and mitochondrial DNA loci are not consistent in their description of the population structure of cod in the northwest Atlantic. We are studying the genetic structure of Atlantic cod using nuclear DNA microsatellite markers. At a variety of scales the allelic variation in six highly polymorphic loci indicates that cod in the northwest Atlantic stock complexes belong to several genetically distinguishable populations. At a meso scale, genetic differences exist between inshore and offshore cod aggregations within the northern cod stock complex off Newfoundland despite the fact that individuals from both populations intermingle inshore during the summer feeding migrations. The magnitude of these genetic differences has remained virtually unchanged during the period 1992-1995. Studies of population structure using other (non-genetic) techniques are consistent with these results. At a small scale, analyses of the genetic composition of a larval aggregation repeatedly sampled on the Scotian Shelf revealed the presence of more than one genetically distinct larval cohort and provided evidence that the aggregation was formed from different spawning events involving different groups of spawners. At relatively large scales, comparison of cod aggregations ranging across the Labrador Shelf, the Grand Bank, Scotian Shelf, Bay of Fundy and Georges Bank show genetic differences among neighbouring spawning aggregations. At ocean-basin scales genetic differences also exist among populations from the western Atlantic, the Flemish Cap, and the Barents and Baltic Seas.
The exploitation dynamics of local patches of flatfish by individual beam trawlers were studied from logbook information of the catch per haul and precise information on fishing positions of a sample of 25 individual beam trawlers. The fishing positions were recorded every 6 minutes with an accuracy of 0.1 nm with an Automated Position Recording. The data show that fishing effort and catch rate (CPUE) are patchily distributed in space. Fishing effort is concentrated in areas of highest CPUE. This pattern is generated by a fishing strategy comprising a searching phase, during which the vessels fishes along a more or less straight line, and an exploitation phase, during which the vessel stays put in a local area by altering course after each haul. The CPUE in areas fished during exploitation were above average. During the exploitation phase, the catch rate declined on average by 30% over a period of 48 hours. Once the catch rate declined below the average of the trip, vessels resumed the searching phase. The decline in catch rate is analysed quantitatively in order to test whether the decline is due to the local depletion of fish. The potential of vessel interactions is analysed by integrating the results of the above analysis with the analysis of the catch rate and effort distribution by trip of the total Dutch fleet taking account of the effect of engine power on the fishing power.
Mercury contamination of fish in the field can be predicted using mass balance models. However, factors influencing mercury elimination, an essential parameter of the mass balance model, are poorly understood. We developed a general model of mercury elimi nation from fish using literature data. Our analysis showed that short-term experiments (less than 70 days) overestimated the elimination rate of mercury and that inorganic mercury was excreted 3-fold faster than methylmercury. Because virtually all the mercury in fish is methylmercury (over 95%), mercury mass balance in fish should rely only on the clearance rate of methylmercury. We therefore developed a methylmercury excretion model using water temperature, body mass, and exposure time (chronic vs acute) as indepen dent variables (r2=0.77). Empirical models that were published prior to this study overestimated the elimination of methylmercury from fish by a factor of 2-6, because they incorporated data obtained in short-term experiments and on inorganic mercury excr etion. This new model of methylmercury excretion should improve the predictions of mercury mass balance models.
La teneur en mercure des poissons en milieu naturel peut être prédite à partir d'un bilan massique. Cependant, les facteurs qui influencent le taux d'excrétion du mercure, un paramètre essentiel du bilan massique, sont encore méconnus. Nous avons développ é un modèle général d'excrétion du mercure des poissons en utilisant des données de la literature. Nos analyses indiquent que les expériences à court termes (moins de 70 jours) surestimaient le taux d'excrétion du mercure et que le mercure inorganique était excré té 3 fois plus rapidement que le méthylmercure. Puisque la majorité du mercure est sous forme méthylé chez les poisson (95% +), les bilans massiques du mercure devraient utilisés uniquement les taux d'excrétion du méthylmercure. Un modèle d'excrétion du mé thylmercure a été développé en utilisant la température de l'eau, la masse des poissons et la durée d'exposition (chronique vs aigüe) comme variable indépendantes (r2=0.77). Les modèles empiriques publiés avant cette étude surestimaient l'excrétion du mét hylmercure des poissons par un facteur de 2-6, car ils incorporaient des estimations obtenues dans des expériences à court termes, ainsi que des taux d'excrétion du mercure inorganique. Ce nouveau modèle d'excrétion du méthylmercure devrait amélioré les p rédictions des bilans massiques du mercure.
In species with external fertilization, some males are able to 'opt out' of the physical competition for access to females by adopting an alternative, kleptogamic tactic (Taborsky 1994). Kleptogamic males have evolved a number of behaviours to maximise their reproductive potential (Gross 1982, 1985). They also invest relatively more than parental males in the production of gonadal tissue, which is assumed to increase production of sperm. Similar tactics could also evolve at the level of sperm competition, with kleptogamic males producing faster or more long-lived sperm (Gage et al. 1995). We tested sperm production and motility in a population of bluegill sunfish (Lepomis macrochirus), a colonially nesting sunfish with male parental care and a high incidence of cuckoldry by kleptogamic males. There were no differences in length or swimming speed of sperm, duration of activity or percent of sperm active between samples from kleptogamic and parental males. Milt from kleptogamic males had a higher concentration of sperm. Our results suggest that sneaking male bluegills have not evolved alternate tactics at the level of sperm competition.
Selon la théorie de la quête optimale de nourriture, les individus sélectionneront les habitats qui seront les plus profitables, en termes de coûts et bénéfices. Jusqu'à présent, très peu d'études ont procédé à des évaluations directes (in situ) des bénéfices et des coûts liés à l'alimentation dans un habitat donné. L'omble de fontaine (Salvelinus fontinalis) vivant dans les lacs du bouclier laurentien s'est avéré un bon modèle pour tester cette hypothèse; les individus déplacent leur alimentation du zoobenthos de la zone littorale au zooplancton de la zone pélagique en présence du meunier noir (Catostomus commersoni), qui s'avère pl us efficace à s'alimenter sur les proies du fond. Nous posons donc l'hypothèse que ce déplacement de niche est basé sur une évaluation des coûts et des bénéfices dans les deux habitats. L'évaluation des bénéfices (J/d) reliés à une alimentation en zone li ttorale et en zone pélagique a déjà été effectuée dans le cadre d'un autre projet. L'objectif spécifique du présent projet est d'estimer les coûts énergétiques (J/d) associés à une alimentation benthique en zone littorale, et à une alimentation planctoniq ue en zone pélagique, chez l'omble de fontaine. Ces estimations sont obtenues à l'aide d'une combinaison de mesures directes à partir d'un système de caméras sous-marines et de modèles empiriques développés pour des caractéristiques de nage similaires à c elles observées in situ. Une analyse préliminaire des résultats obtenus sera discutée.
Recently, Walters and Maguire (1996) have identified three main lessons from the collapse of the northern cod stock: (1) assessment errors can contribute to overfishing through optimistic long-term forecasts leading to a build-up of overcapacity or through optimistic assessments which lead to TACs being set higher than they should; (2) stock size overestimation is a major risk when commercial catch per unit of effort is used as an index of stock size trends, (3) the risk of recruitment overfishing exists and may be high even for very fecund species like cod. The basis for those lessons is explained and put in the context of the need for information to make fishery management decisions. Modifications to the role scientific advice currently plays in the fishery management process are suggested.
Recent evidence suggests that rainbow trout (O. mykiss) possess a chemical alarm signal which is localized in the skin. In order to determine if predator-naive hatchery-reared rainbow trout can be conditioned to recognize a predator, we exposed trout to the chemical stimuli from northern pike (E. lucius) and trout skin extract or a distilled water control. Trout exposed to conspecific skin extract and pike odour significantly increased anti-predator behaviour, while those exposed to distilled water and pike odour did not. When conditioned trout were exposed to pike odour alone (vs distilled water control) either four days or 21 days later, they significantly increased anti-predator behaviour. These data are the first to demonstrate that hatchery-reared trout can be conditioned to recognize the chemical cues of a predator and suggest that this may serve as a strategy to train hatchery-reared fish to recognize predators prior to stocking into natural waterways.
A detailed survey of near-shore fish habitat in Lake Simcoe, Ontario has now been completed. The shoreline was divided into eleven sections; the first of these was surveyed in 1982 and the last in 1996. Biological, physical and human development features of the shoreline and near-shore zone (to a depth of 2 m) were documented. Fixed sites were sampled at weekly intervals from May through August and randomly located sites were visited on one occasion during the same period. Fish were collected with a beach seine and separated according to life stage. Several species not previously known for Lake Simcoe were identified: central mudminnow (Umbra limi), brassy minnow (Hybognathus hankinsoni), spotfin shiner (Cyprinella spiloptera), sand shiner (Notropis stramineus) and brook silverside (Labidesthes sicculus). Development features mapped included docks, breakwalls, boathouses, cottages and other shoreline alterations. Substrate type, aquatic macrophyte species present and extent of growth, terrestrial vegetation, location of permanent and intermittent inlets, water depth and water temperature were among the natural features described. In this poster we present sampling methodology, fish abundance and diversity data, as well as a summary of other data on biological and developmental features. Information collected in this program has been and will continue to be valuable to biologists and managers in identifying areas of the lake vulnerable to further development.
I have attempted to lay the foundation for the analysis of environmental influences on the initial sizes of marine fishes. By virtue of their position in the life cycle, fish eggs provide a unique window on the past and future. Looking to the past, the size and other attributes of eggs are likely to vary with the environment, maternal identity, and occasionally with easily measured maternal attributes, which may themselves be influenced by the environment experienced by the female prior to spawning. In terms of forecast, initial sizes of fish may directly influence survival or be predictive of subsequent life history traits that are correlated with the likelihood of surviving through later ages. Three points emerged from this analysis. First, temperature appears to have a dominant affect on egg and propagule sizes resulting in larger sizes generally being evident in cooler waters. This is manifested in nature along axes of season of spawning, water depth, and occasionally latitude of the source population. Second, egg and propagule sizes vary consistently among females within populations although the initial sizes of offspring are not clearly predictable, as a generality, from the ages and sizes of females. Third, many questions remain unanswered regarding initial sizes of fish and the influence of initial size on the likelihood of recruitment. Answers to these questions will require of the researcher a creative use of a combination of field, laboratory, and theoretical tools.
Harp and hooded seals are the two most abundant pinnipeds in the Northwest Atlantic, estimated to total in the order of 5 million and 0.5 million individuals respectively. Before models can be developed to quantify their impact on commercial fish, it is necessary to estimate the amount of prey consumed. To estimate consumption of Atlantic cod by harp and hooded seals off Newfoundland and in the Gulf of St. Lawrence, we constructed a model incorporating age-specific estimates of energy requirements, population size, seasonal distribution and diets. A preliminary model estimated that harp seals consumed 88,000 tonnes (95% C.I. 46,000 - 140,000) off Newfoundland and 54,000 tonnes (95% C.I. 14,000 - 102,000) in the Gulf during 1994. Varying the basic assumptions of the model to assess its sensitivity indicated that changes in the energetic costs of activity and growth, abundance, residency period, or the proportion of energy obtained from offshore areas can affect estimates of total consumption significantly. A similar model using data on the diet of hooded seals in the Newfoundland area is being constructed to provide comparable estimates.
The involvement of the First Nations in fisheries management within their traditional harvest areas has, in the past, been overlooked, but, more recently, governments across Canada are recognizing the importance of establishing partnerships with the aboriginal people. In 1993, the Government of Ontario and the Anishinabek Nation as represented by the Union of Ontario Indians, signed a Conservation and Fishing Agreement. As part of this agreement, the Anishinabek/Ontario Fisheries Resource Centre (AOFRC), a non-profit corporation, was established to collect independent data within the traditional harvest areas of the member First Nations. In 1996, ten fisheries related projects were completed by the AOFRC and various First Nations. These projects include walleye tagging, littoral zone mapping, and nearshore index netting projects which conformed to the Ministry of Natural Resources standards and contributed new data which will assist in management and conservation of fisheries within these waters. As governments continue to downsize, partnerships and agreements will play an increasing role in fisheries management.
Naturally acidic "brownwater" lakes with elevated levels of DOC are common in eastern Canada. Evidence suggests that DOC can buffer H+ ion toxicity at low pH, and may offer protection to aquatic species. However, assessments of acidification effects in eastern Canada have not differentiated between naturally acidic and anthropogenically acidic systems. We compiled data from 1,253 lakes in eastern Canada to test what effect DOC had on fish communities. Clear regional differences were evident; Atlantic lakes supported fewer species on average. However, species common to both regions were found at an average 0.24 pH units lower in Atlantic Canada. Fish were able to tolerate a pH of 0.3 to 0.4 units lower in coloured than in clear lakes. This significant effect (p< 0.001) was only observed below pH 5.0. This corresponds to the maximum range of buffering intensity of organic acids at pH 4 - 5. Maximum potential species curves indicated that clear lakes would lose more species than moderately coloured lakes if pH dropped from 5.5 to 5.0. Our analyses indicate that moderately coloured lakes (DOC > 5 mg/L) support richer communities below pH 5.0 due to the buffering effects of organic acids.
The precocial maturation of male Atlantic salmon (Salmo salar) parr is a life history feature important to the demographics of salmon populations. We initiated a study to determine the effect of precocial maturation on parr growth and smolting of Atlantic salmon stocked as fry in Vermont tributaries of the Connecticut River. The relative abundance and physical characteristics of immature and mature parr were determined through electrofishing surveys completed in October and November and the effect of parr maturity on smolt recruitment was determined through fall marking (acrylic paint fin injections and PIT tags) and April-May recapture of marked out-migrants in counting fences. Mature parr were found in abundance both among and within tributaries, ranging between 43 and 51% of the 1+ parr collected and between 63 and 76% of the 2+ parr collected. Mature and immature parr differed significantly in mean total length (immature greater than mature) and condition factor (mature greater than immature). Data from parr PIT tagged in June and recaptured in October showed that differences in mean length resulted from nearly two-fold differences in individual growth rates of mature (14 mm) and immature (29 mm) parr. The mature to immature ratio of parr in the fall was greater than the ratio for smolts, indicating that mature parr were not recruited to smolt at the same frequency as immature parr. The precocial maturation of parr had a significant effect on parr growth, and in-turn, smolt recruitment. Thus, parr maturation is likely to be an important factor in the demographics of salmon restoration.
We are carrying out stable isotopic analyses (d18O and d13C) on cod otoliths which were collected from the 4Vs Subdivision. Otoliths are deposited in, or very close to temperature-dependent oxygen isotopic equilibrium with ambient seawaterin which the fish lived. Changes in carbon isotopes, however, mainly depict metabolic effects as the fish grows. Thus stable isotopic analyses on cod otoliths can provide unique information on temperature, growth and chemical variations of the ocean. The 13C/12C ratio of all cod otoliths showed a life-long increase from -4 per mil to a maximum near 0 per mil. The early rise is due to a decrease in the fraction of metabolic dissolved inorganic carbon, while the maximum in d13C marks the period of maturity of the cod, and their movement to deeper, 13C-depleted waters.Both temperature and age of maturity decrease steadily from 1984 to 1993, corresponding to a period during which cod stocks in the Canadian Atlantic declined.
Pairs of temperature loggers recording at 5-10 min intervals were placed during July and August at depths of 0.1 m and 1 m in 4 sites in each of two small Ontario lakes . Assuming (with support from the literature) that rates of growth in fish length would be proportional to temperature during each 5-10 min interval, indices of cumulative size change over 50 days were calculated for midlittoral and fringe habitats at each site. In both lakes the four sites varied substantially in the degree of predicted growth enhancement in the fringe habitat, ranging from -8 to +50% in one lake and from -6 to +13% in the other. Negative values occurred in sites that frequently experienced nighttime temperature inversions. Averaged over the 4 sites, growth enhancements predicted for the 2 lakes were +4% and +16% over 50 days. Fish could achieve much greater enhancements by moving out of temperature inversion zones or seeking out the warmest sites. Thus, warm temperatures may be one of the reasons that small fish concentrate in fringe habitats in these lakes. In addition, weather-induced shifts in the locations of the warmest water could be one of the processes generating the day-to-day fluctuations in the levels of fish traffic observed at any site.
Stable nitrogen isotopes are increasingly used as a measure of trophic position of consumers within food webs, although comparative studies require interpretation of consumer d15N relative to a representative baseline d15N signature. Primary consumer d15N from 14 lakes in Ontario ranged from -2ppmil to +9ppmil, exhibiting highly significant differences among primary consumers from littoral, pelagic, and profundal habitats. Primary consumer d13C signature (used to trace the source of production) decreased from littoral to pelagic to profundal habitats. d13C explains 40% of the variation in d15N signatures of primary consumers. Addition of a lake variable explains 72% of the variation in primary consumer d15N. This primary consumer d15N - d13C relationship and the d13C signature of a higher consumer determines the appropriate baseline d15N value from which to measure the trophic position of the consumer. This estimate of trophic position takes into account among-lake and within-lake variation in baseline stable nitrogen isotope signature, and can be used to build trophic position-based models of food web structure.
A study was undertaken to interview approximately 450 fishers to examine the basic premise of population definition within statistical management units spanning from northern Nova Scotia to southwestern New Brunswick. It was found that multiple spawning grounds exist within each management unit for the species examined. Potential implications of having more than one population per management unit include (i) inadvertantly depressing one population to commercial extinction, and (ii) the development of fishing quotas based on single population models which may under or overestimate yield for any one specific population within the management unit. The great majority of these critical habitats remain unprotected to exploitation throughout the year. Re-evaluation of marine protected areas may be warrented. The protection of spawning grounds may be the key to greater sustainability of groundfish populations within traditional management units.
Spring research vessel surveys from 1952-1995 were used to reconstruct the population history of the Southern Grand Bank (NAFO Division 3NO). This time series predates the arrival of factory freezer trawlers in the 1960's and 1970's, and may be influential in examining changes in biomass of an exploited system. The estimate of total biomass for the Southern Grand Bank declined by an order of magnitude from the late 1950's to the early 1960's, and is largely representative of the haddock and Atlantic cod populations at that time. Following this decrease, flatfish biomass increased but was not able to fully compensate for the decrease in haddock and Atlantic cod biomass. Total biomass of forage fish, namely Capelin and Northern sand lance, was found to be inversely related to the gadid biomass. It is hypothesized that changes in species composition have resulted from species interactions precipitated by intense fishing.
Threespine stickleback (Gasterosteus aculeatus) inhabit coastal marine and freshwater systems in northern regions of North America, Europe and Asia. There exists remarkable variation in behavior, morphology and life history among freshwater populations. Males in freshwater populations of the Chehalis River drainage basin in Washington assume a jet-black nuptial coloration during the breeding season, rather than the typical red underside and blue-green dorsum. These black populations are co-distributed with the freshwater Olympic mudminnow (Novumbra hubbsi) which is endemic to the drainage and also assumes black nuptial color. Anadromous threespine stickleback, which are typical in color, overlap with black populations in narrow zones of hybridization. One of my overall research objectives is to test an existing hypothesis regarding the maintenance of the G. aculeatus polymorphism - the 'Character Convergence Hypothesis'. In situ competition experiments involving red and black types of sticklebacks and N. hubbsi (an hypothesized competitor for nesting territories) and direct observations of nesting sticklebacks in the wild suggest that the 'Character Convergence Hypothesis' is not correct.