bluuebunny/crossref_metadata_2025 huggingface dataset:
Condition and performance of juvenile Atlantic salmon (Salmo salar): effects of rearing practices on hatchery fish and comparison with wild fish
Authors: McDonald D G , Milligan C L , McFarlane W J , Croke S , Currie S , Hooke B , Angus R B , Tufts B L , Davidson K
Published: April 2011

This study examined the effects of various modifications of rearing practices on hatchery-reared Atlantic salmon (Salmo salar) fingerlings and compared condition and performance of hatchery fingerlings (age 0+) and yearlings (age 1+) with those of wild-reared Atlantic salmon. Reduced fish density (and increased ration) in rearing tanks promoted increased growth and condition factor and significant changes in muscle composition, including increased muscle lipid content and glycolytic enzyme activity, specfically phosphofructokinase and lactate dehydrogenase. However, these changes had no effect on anaerobic capacity. Moreover, swimming performance was poorer in fingerlings reared at low compared with normal density. Raising the water velocity from 0 to 4 cm ·s-1(~0.7 body length ·s-1) had overall beneficial effects, most notably increased endurance in fixed velocity sprint tests and a reduction of ion loss in an epinephrine challenge test. Increasing velocity to 9 cm ·s-1had no further effects. Wild fingerlings were larger with better fin quality and superior anaerobic capacity and swim performance. Even larger differences were seen between hatchery-reared and wild yearlings. It is concluded that significant changes in morphology, physiology, and muscle biochemistry of juvenile Atlantic salmon can be brought about by changing hatchery rearing conditions, but these changes are of limited effectiveness in reducing the difference between hatchery-reared and wild fish.
Consequences of prey fish community dynamics on lake trout (Salvelinus namaycush) foraging efficiency in Lake Superior
Authors: Mason Doran M , Johnson Timothy B , Kitchell James F
Published: April 2011

We used a size-structured model, indexed by age, that combines bioenergetics and foraging theory to evaluate the effects of prey fish community structure (species dominance, size structure, and density) on the diet and net foraging efficiency of lake trout (Salvelinus namaycush) in Lake Superior. Prey size structure was important for young lake trout but decreased in importance for older lake trout, especially with increasing prey density. The model predicted that rainbow smelt (Osmerus mordax) should dominate the diet of young lake trout due to the size-dependent capture limitations of larger prey. In contrast, lake herring (Coregonus artedi) should dominate the diet of oldest lake trout owing to a higher net energy return than rainbow smelt. Model results are consistent with age-specific diet and size-at-age of lake trout during the last 40 years. Diets of intermediate-sized lake trout do not reflect the recent resurgence of lake herring populations. Absence of a dietary switch is probably due to higher capture probability for rainbow smelt. Lake trout growth and production will likely be highest with a mixed prey species assemblage of young rainbow smelt and older lake herring.
Modeling foraging in the northern anchovy (Engraulis mordax): individual behavior can predict school dynamics and population biology
Authors: Nonacs Peter , Smith Paul E , Mangel Marc
Published: April 2011

Many economically important oceanic fishes travel in large schools, but the foraging behaviors of these schools and the life history consequences of these behaviors have rarely been addressed. The availability of extensive information on bioenergetics of the northern anchovy (Engraulis mordax) allows us to use this species as a case study. We modeled two types of potential behavior that fish could use to exploit a patchy environment: (i) maximizing growth rate or (ii) maximizing survivorship to adulthood and reproduction, which is a function of both growth and avoiding predation. Patterns from existing data sets on gut contents and growth rates from the field for juvenile E. mordax were consistent only with the prediction of maximizing survivorship. The model makes further testable predictions about (i) expected swimming velocities between zooplankton patches, (ii) patterns of size segregation in the formation of schools, (iii) the proportion of zooplankton patches that schools consume, and (iv) reactions to decreases in environmental quality. Overall, the model predicts that anchovies spend at least 25% of their time in schools that are too large to be energetically economical and suggests further research on several variables that could affect populations of schooling fishes.
Winter mortality of young-of-the-year Hudson River striped bass (Morone saxatilis): size-dependent patterns and effects on recruitment
Authors: Hurst Thomas P , Conover David O
Published: April 2011

Winter mortality plays a significant role in the dynamics of some temperate fish populations and has been shown to be size-dependent for some species, but not for others. Our objective was to determine how winter mortality affects the recruitment dynamics of Hudson River striped bass (Morone saxatilis). We used catch-per-unit-effort data from three separate surveys targeting young-of-the-year (YOY), overwintering, and age 1 striped bass. Age 1 abundance was negatively correlated with the severity of winter. In contrast, the abundance of age 0 fish was not correlated with age 1 abundance, suggesting that winter mortality greatly modifies year-class strength. A progressive increase in the mean length of YOY fish, coupled with a decrease in the coefficient of variation in length, occurred during some winters. Laboratory experiments showed that growth in length requires temperatures in excess of 10°C; hence, these changes likely result from selective mortality of smaller fish. Direct evidence of size-dependent mortality was obtained from a laboratory experiment that exposed fish to ambient conditions throughout the winter. Accounting for interannual differences in the severity and size dependency of winter mortality may improve our ability to evaluate striped bass year-class strength in the Hudson River.
An experimental analysis of crayfish (Orconectes rusticus) effects on a Dreissena-dominated benthic macroinvertebrate community in western Lake Erie
Authors: Stewart Timothy W , Miner Jeffrey G , Lowe Rex L
Published: April 2011

Quantitative descriptions of trophic interactions between Dreissena (zebra and quagga mussels) and other organisms are needed for an understanding of Dreissena's effects on energy flow and community dynamics in the Great Lakes. We used a field experiment to quantify effects of crayfish (Orconectes rusticus) predation on a Dreissena-dominated benthic macroinvertebrate community in western Lake Erie. Rocks colonized by Dreissena and associated macroinvertebrates were placed in cages and cageless reference plots located at a depth of 4 m. Crayfish (0, 8.3, and 20.8 individuals ·m-2) placed in cages were allowed to graze for 28 days. Dreissena had a greater effect than crayfish on the macroinvertebrate community, with positive relationships observed between Dreissena densities and both total macroinvertebrate biomass and densities of the amphipod Gammarus fasciatus. However, crayfish at densities of 20.8 individuals ·m-2 still reduced non-Dreissena macroinvertebrate biomass and Gammarus densities by 33 and 37%, respectively, relative to crayfish exclosures. Crayfish had negligible effects on Dreissena densities or shell length frequency distribution. Because crayfish and amphipods are prey for several fish species, trophic interactions among Dreissena, amphipods, and crayfish may be important in channeling energy from Dreissena to higher trophic levels in the Great Lakes.
Thermal limits and ocean migrations of sockeye salmon (Oncorhynchus nerka): long-term consequences of global warming
Authors: Welch D W , Ishida Y , Nagasawa K
Published: April 2011

Ocean surveys show that extremely sharp thermal boundaries have limited the distribution of sockeye salmon (Oncorhynchus nerka) in the Pacific Ocean and adjacent seas over the past 40 years. These limits are expressed as a step function, with the temperature defining the position of the thermal limit varying between months in an annual cycle. The sharpness of the edge, the different temperatures that define the position of the edge in different months of the year, and the subtle variations in temperature with area or decade for a given month probably all occur because temperature-dependent metabolic rates exceed energy intake from feeding over large regions of otherwise acceptable habitat in the North Pacific. At current rates of greenhouse gas emissions, predicted temperature increases under a doubled CO2 climate are large enough to shift the position of the thermal limits into the Bering Sea by the middle of the next century. Such an increase would potentially exclude sockeye salmon from the entire Pacific Ocean and severely restrict the overall area of the marine environment that would support growth.
Estimating the value of in-season estimates of abundance of sockeye salmon (Oncorhynchus nerka)
Authors: Link Michael R , Peterman Randall M
Published: April 2011

Fishwheels have recently replaced a gillnet test fishery for in-season estimation of escapement of sockeye salmon (Oncorhynchus nerka) to the Nass River, British Columbia. We used an empirically based Monte Carlo simulation model to estimate the potential benefits (in terms of future harvests) of using this new method. We found that using the information from the fishwheels in place of the gillnet test fishery may increase the average annual catch from current ocean fisheries by 2.7% ($229 000) due to the greater accuracy of in-season estimates. When the additional costs of operating the fishwheels instead of the gillnet test fishery were taken into account, the fishwheel program still resulted in an annual net benefit of about $180 000. Eliminating the deviations from the target escapement for Nass River sockeye salmon by having perfect monitoring of escapement and perfect control over harvesting has a potential annual value of more than $1 million (CAN). However, much greater benefits from fishwheels are unlikely to be realized because of the highly variable response of the commercial fishing fleet to additional fishing opportunities and the 5-day lag of the escapement estimates provided by fishwheels.
Biochemical correlates of growth and condition in juvenile Atlantic cod (Gadus morhua) from Newfoundland
Authors: Couture Patrice , Dutil Jean-Denis , Guderley Helga
Published: April 2011

The aim of this study was to examine how the biochemical composition of tissues varied with growth rate and condition in juvenile Atlantic cod (Gadus morhua) caught in the wild and kept in captivity. The hepatosomatic index, brain water content, and muscle sarcoplasmic protein content as well as the activities of phosphofructokinase, lactate dehydrogenase, nucleoside diphosphate kinase, and citrate synthase in the muscle, nucleoside diphosphate kinase and citrate synthase in the intestine, and cytochrome c oxidase and citrate synthase in the brain increased with growth rate or condition factor. Conversely, liver and muscle water contents were lower in fish with a higher growth rate. A multiple regression model that included the hepatosomatic index, water content of muscle and brain, and citrate synthase activity in the intestine explained 79.7% of the variability of growth in mass under our conditions. A similar model, using liver water content instead of muscle water content, explained 82.5% of the variability of growth in length. These easy to measure variables may be used in fisheries management to estimate the growth rate of fish in the wild.
Method for estimating variability due to sampling of catches on a trawl survey
Authors: Cotter A JR
Published: April 2011

Many catches arising on trawl surveys of fish stocks are sampled for the measurement of fish lengths and the collection of otoliths for age determination, thereby increasing the variability of the estimated abundance indices, expressed as catch per hour by species and year-class. This paper demonstrates how catch-sampling variability can be assessed, using the English groundfish survey of the North Sea (EGFS) as an example for analysis. Unbiased estimators are derived for catch-sampling covariance matrices for numbers-at-length of a species by size category, by haul, and by sampling stratum and for numbers-at-age by stratum. The same statistical principles could be applied to derive appropriate estimators for other surveys having different catch-sampling procedures. A method is also put forward for estimating the relative importance of variability due to catch sampling and that due to the design of the survey, i.e., due to the number, location, and timing of fishing stations and the method of fishing. Analysis of a small set of EGFS data for haddock (Melanogrammus aeglefinus) is included for illustrative purposes. Implications for survey design and catch-sampling efficiency are briefly discussed.
Assemblages and biogeography of demersal fishes of the east coast of North America
Authors: Mahon Robin , Brown Stephen K , Zwanenburg Kees CT , Atkinson D Bruce , Buja Kenneth R , Claflin Larry , Howell Geoffrey D , Monaco Mark E , O'Boyle Robert N , Sinclair Michael
Published: April 2011

This study describes and maps demersal fish assemblages for the east coast of North America from Cape Hatteras, North Carolina, to Cape Chidley, Labrador, evaluates evidence for interannual shifts in assemblage distribution, and examines the relationship of the assemblages to accepted biogeographical boundaries. Demersal trawl survey data collected from 1975 to 1994 were analyzed. Visual classification of distribution maps for the 108 most abundant demersal species revealed nine species groups, based on both geography and depth distribution. Eighteen assemblage groups were identified using principal components analysis (PCA) and mapped. Assemblage groups were also identified by cluster analysis. Fish assemblages identified by both methods were spatially coherent. Assemblage distribution patterns were not consistent with accepted biogeographical boundaries. The PCA explained only 56.3% of the variance in distribution of the species, indicating that the assemblages should be interpreted as indeterminate, potentially adaptable entities rather than as rigid ecological constructs. Assemblages were persistent in composition through time but appeared to shift in location. The apparent looseness of the assemblages and their persistence through time in spite of severe impacts from fishing suggest that single-species management approaches may not be entirely inappropriate for the major groundfish species in the study area.
Swim speeds and energy use of upriver-migrating sockeye salmon (Oncorhynchus nerka): simulating metabolic power and assessing risk of energy depletion
Authors: Rand Peter S , Hinch Scott G
Published: April 2011

We simulated metabolic power consumed by Fraser River sockeye salmon (Oncorhynchus nerka) during upriver migration based on direct measures of activity from physiological field telemetry. The most accurate prediction of energy expenditure was obtained by expressing activity as a fine time scale (5 s) stochastic process. By imposing a daily time step, predictions of energy use were considerably lower than observed energy use, suggesting that the practice of modeling field energetics at a daily time scale, particularly for relatively active fish, may render dubious results. Daily mean power consumption through the Fraser River Canyon by the average migrant was about 20 W, about fourfold higher than for less constricted reaches. Power consumption predicted at fine time scales ranged from <1 W (0.1 body length·s-1) during periods of reduced activity to 1700 W (8 body lengths·s-1) during bursts while navigating through turbulent canyon reaches. Through Monte Carlo simulations representing environmental variability observed during 1950-1994, we determined that 8% of the salmon runs during this time resulted in high risk of exhaustion for the average migrant that could lead to elevated in-river mortality. Reducing harvest levels on sockeye salmon that may be exposed to these unfavourable conditions may assist agencies in achieving a risk-averse management strategy.
Methyl mercury in aquatic insects from an experimental reservoir
Authors: Hall B D , Rosenberg D M , Wiens A P
Published: April 2011

Our objective was to study the effects of experimental flooding of a small wetland lake on the methyl mercury (MeHg) concentrations in aquatic insects and to compare MeHg concentrations in insects with those in water and fish from the same system. Insects were collected from the shorelines of the experimental reservoir before and after flooding, an undisturbed wetland lake, and an oligotrophic lake, all in the Experimental Lakes Area in northwestern Ontario. Samples were identified to the lowest possible taxon and categorized into functional feeding groups (FFGs; predators or collector/shredders). The insects were analyzed for MeHg and total Hg using clean techniques. Contamination was not a problem because levels of MeHg in insects were much higher than background concentrations. Odonata, Corixidae, Gerridae, Gyrinidae, and Phryganeidae/Polycentropodidae exhibited increases in MeHg concentrations in response to flooding. When data were grouped into FFGs, increases were observed in predators. There were insufficient numbers of collector/shredders collected to make a definitive conclusion on MeHg increases. Predators exhibited an approximately threefold increase in MeHg concentrations after flooding compared with a 20-fold increase in water concentrations and a four- to five-fold increase in fish concentrations. Trends in MeHg concentrations in aquatic insects from reservoirs and natural lakes in Finland and northern Québec were similar to ours. Evidence of an increase in MeHg concentrations in the lower food web helps explain increases in MeHg concentrations in fish from reservoirs because food is the major pathway of MeHg uptake in fish tissue.
Quantitative genetic variation and genotype by environment interaction of embryo development rate in pink salmon (Oncorhynchus gorbuscha)
Authors: Hebert K P , Goddard P L , Smoker W W , Gharrett A J
Published: April 2011

Quantitative genetic variation of development rate was evident among 20 half-sib and 40 full-sib families within each of two seasonally separate components of a population of pink salmon (Oncorhynchus gorbuscha) (Ho: no sire effect on temperature units at hatch, P < 0.02). Differences between averages of families spawned 3 weeks apart may have had genetic or environmental sources (e.g., in constant 8°C, early embryos hatched at 606 temperature units, and late embryos, at 625). Statistical interactions between paternal effects and environment (embryos were cultured in four temperature regimes, two simulated natural regimes and two constant temperatures; Ho: no sire by regime interaction effect on temperature units at hatch, P < 0.09) were weak evidence that genotype by environment interactions contributed to variation. Paternal effects in analysis of variance (evidence of additive genetic variation) were detected only at later stages. Evidences of genetic variation and of interactions between genotypes and environments are pertinent to resource conservation because they suggest that harvest management or hatchery practice have the potential to reduce genetic variation in salmon populations.
Management of evolving fish stocks
Authors: Heino Mikko
Published: April 2011

Mortality caused by harvesting can select for life history changes in the harvested stock. Should this possibility be taken into account in the management of renewable resources? I compare the performance of different harvest strategies when evolutionary change is accounted for with the help of an age-structured population dynamics model. Assuming that age of first reproduction is the only evolving trait, harvesting of only mature individuals selects for delayed maturation and results in increased sustainable yields. Unselective harvesting of both mature and immature fish selects for earlier maturation which causes the sustainable yield to decrease. Constant stock size and constant harvest rate strategies perform equally well in terms of maximum sustainable yield, both before and after evolutionary change. The maximum sustainable yield for fixed-quota strategies is lower. All those strategies have similar evolutionary consequences given a similar average harvest rate. Coevolutionary dynamics between fish stock and the stock manager indicate that the evolutionary benefits of selective harvesting are attainable without incurring yield losses in the near future.
Assessing the impacts of acidification on Atlantic salmon (Salmo salar): a simple model of stream chemistry
Authors: Marmorek D R , Lacroix G L , Korman J , Parnell I , Watt W D
Published: April 2011

We developed a model that simulates the effects of changes in sulphate (SO42-) deposition on the chemistry of naturally organic-rich streams, linked this chemical model to a model of Atlantic salmon (Salmo salar) production (Korman et al. 1994. Can. J. Fish. Aquat. Sci. 51: 662-680), and assessed its performance on three acidified streams in southwest Nova Scotia. The chemical model closely tracked current chemistry by estimating the charge density required for charge balance on each sampling date. Calculated charge densities were generally low (1-3 µequiv./mg dissolved organic carbon (DOC)), inversely related to DOC, and positively related to pH. Predictions of minimum pH and salmon smolt output were relatively insensitive to the assumed F-factor (watershed neutralization of deposited acidity) in the parameter range most likely for the three streams. The model permits rapid impact assessment of acid deposition scenarios with a modest amount of input data (acid-neutralizing capacity, pH, SO42-, and DOC, ideally sampled weekly) while retaining natural cycles and processes.
Declines in benthic macroinvertebrate populations in southern Lake Michigan, 1980-1993
Authors: Nalepa Thomas F , Hartson David J , Fanslow David L , Lang Gregory A , Lozano Stephen J
Published: April 2011

Densities of the major benthic macroinvertebrate groups declined dramatically at sites shallower than 50 m in southern Lake Michigan between 1980 and 1993. Declines in Diporeia, Oligochaeta, and Sphaeriidae ranged from 40 to 75% at these depths. Total densities declined from 16 800·m-2 in 1980-1981 to 4800·m-2 in 1992-1993 at sites in the 16-30 m depth interval and from 21 300 to 11 300·m-2 at sites in the 31-50 m depth interval. Changes at sites deeper than 50 m were minimal; only sphaeriids declined to any extent. Declines in oligochaetes and sphaeriids occurred uniformly throughout the nearshore region and over the entire sampling period. Declines in these two groups were most likely related to reductions in phosphorus loads and a general decrease in productivity in the nearshore area over the sampling period. On the other hand, declines in Diporeia occurred mainly in the later portion of the sampling period and were greatest in the southeastern region of the lake. Densities at many sites in the southeastern region were < 100·m-2 in 1993, down from 3000-8000·m-2 in 1980-1987. We hypothesize that the filtering activities of large populations of Dreissena polymorpha in nearshore waters may be having a negative impact on Diporeia in deeper waters by decreasing the amount of food available to this surface-feeding detritivore.
Colonization by lentic macroinvertebrates: evaluating colonization processes using artificial substrates and appraising applicability of the technique
Authors: Benoît Hugues P , Post John R , Parkinson Eric A , Johnston N Tom
Published: April 2011

Our objectives were to describe the patterns of colonization of lentic macroinvertebrates on artificial substrates and to evaluate how this information can then be used to effectively and efficiently sample macroinvertebrates in vegetated littoral zones of lakes. Colonization of taxa in terms of both richness and density generally followed a Michaelis-Menton saturating curve with an initially rapid increase in densities up to a plateau within a short period of time (< 8 days). We propose that this initial colonization is due to random encounters with the substrate and that the plateau represents a balance between immigration and emigration. Accordance with the saturating colonization curve improved with increasing densities of individuals. As a whole, the spatial pattern of colonization by orders of macroinvertebrates became more aggregated with time, indicating that true random encounter colonization occurs mainly in the early stages, and consequently, this is the time when sampling should best represent relative abundance. In addition, we found that invertebrate colonists of the substrata were concordant with prey items in the guts of rainbow trout (Oncorhynchus mykiss), a facultative benthivore.
Influences of natural acidity and introduced fish on faunal assemblages in California alpine lakes
Authors: Bradford David F , Cooper Scott D , Jenkins, Jr. Thomas M , Kratz Kim , Sarnelle Orlando , Brown Aaron D
Published: April 2011

In an alpine area of the Sierra Nevada of California, naturally acidic waters and introduced fishes both strongly affect the distributions of native amphibians, zooplankton, and macroinvertebrates. The study area in Kings Canyon National Park contains 104 lakes with pH values between 5.0 and 9.3, including 10 lakes with pH < 6.0 (defined here as acidic lakes) and 18 lakes with introduced trout. We surveyed 33 of these lakes (8 acidic, 7 non-acidic with trout, 18 non-acidic without trout) for water chemistry and faunal assemblages. Yellow-legged frog tadpoles (Rana muscosa), common microcrustaceans (Daphnia, Hesperodiaptomus, Diaptomus), and larvae of a caddisfly (Hesperophylax) were rare or absent in acidic lakes but common in non-acidic lakes, and microcrustacean and macroinvertebrate species richness decreased with decreasing pH. Large and (or) mobile, conspicuous taxa, including tadpoles, large-bodied microcrustaceans (Hesperodiaptomus, Daphnia middendorffiana), and many epibenthic or limnetic macroinvertebrates (baetid and siphlonurid mayfly nymphs, notonectids, corixids, limnephilid caddis larvae, and dytiscid beetles), were rare or absent in trout lakes but were relatively common in lakes lacking trout, and the taxon richness of macroinvertebrates was reduced by trout.
From two dimensions to three: the use of multibeam sonar for a new approach in fisheries acoustics
Authors: Gerlotto François , Soria Marc , Fréon Pierre
Published: April 2011

We present a methodology applying multibeam sonar for three-dimensional (3D) observation of fish schools that enhances the conventional use of vertical scientific echo sounders. The sonar we employ has 60 beams of 1.5° each. Its working frequency is 455 kHz. It is applied on a vertical plan normal to the vessel route, observing from the surface line to the bottom with a range set to 100 m. The sampled volume is 14 times larger than the volume observed with vertical echo sounding. The contribution of this new methodology to fisheries acoustics is detailed for school classification, internal school structure, spatial distribution of schools, fish behaviour, and biomass estimates. For each of these points, we present some preliminary results with the aim of defining the real progress in fisheries acoustics research as a result of 3D acoustics. Finally, we present a list of technical and methodological improvements that we are developing in order to make multibeam sonar fully adapted to fisheries acoustics.
Stable carbon and nitrogen isotope patterns in baleen from eastern Arctic bowhead whales (Balaena mysticetus)
Authors: Hobson Keith A , Schell Don M
Published: April 2011

Previous measurements of naturally occurring stable isotopes of carbon (delta13C) and nitrogen (delta15N) along the baleen plates of western Arctic bowhead whales (Balaena mysticetus) have provided a continuous lifetime record of the feeding or nutritional ecology of these animals that migrate annually between isotopically different foodwebs. However, virtually nothing was known about isotopic patterns of eastern Arctic bowheads. We measured delta13C and delta15N values along the baleen plates of three eastern and one western Arctic bowhead whales taken from Canadian waters in 1988 and 1996. In contrast to western Arctic animals, we found strong evidence for periodic fluctuations in delta15N but not delta13C values in the eastern Arctic specimens. We interpret these results as evidence that eastern Arctic animals do not move between foodwebs that differ in delta13C signature and suggest that these whales either (i) move annually between areas isotopically enriched in 15N but not 13C, (ii) shift diet annually by about one third of a trophic level, or (iii) undergo seasonal fasting that results in enrichment of baleen delta15N resulting from protein catabolism.
Spatiotemporal modelling for the annual egg production method of stock assessment using generalized additive models
Authors: Augustin N H , Borchers D L , Clarke E D , Buckland S T , Walsh M
Published: April 2011

Generalized additive models (GAMs) are used to model the spatiotemporal distribution of egg density as a function of locational and environmental variables. The main aim of using GAMs is to improve precision of egg abundance estimates needed for the annual egg production method. The application of GAMs requires a survey design with good coverage in space and time. If the only results available are from less optimal survey designs, they can be improved by using historical data for spawning boundaries. The method is applied to plankton egg survey data of Atlantic mackerel (Scomber scombrus) in 1995. The GAM-based method improves the precision of estimates substantially and is also useful in explaining complex space-time trends using environmental variables.
Natural and commercial dissolved organic matter protects against the physiological effects of a combined cadmium and copper exposure on rainbow trout (Oncorhynchus mykiss)
Authors: Richards Jeff G , Burnison B Kent , Playle Richard C
Published: April 2011

Environmentally realistic concentrations of a natural dissolved organic matter (DOM) (8 mg C/L as dissolved organic carbon (DOC)) protected against the acute respiratory and ionoregulatory effects of 0.2 µM Cd and 0.8 µM Cu on rainbow trout (Oncorhynchus mykiss). The protection afforded by low natural DOC was the same as that afforded by similar or higher concentrations of commercial DOC. Trout exposed to the metals alone experienced large decreases in arterial PO2, increases in arterial PCO2, increases in blood lactate, decreases in plasma concentrations of Cl, and developed pronounced haemoconcentration. There were no deleterious effects of 31 mg C/L commercial DOC on any measured aspect of trout physiology except for an increase in plasma Cl, which was probably due to elevated aqueous Cl concentrations associated with the DOM addition. No concentration of DOC used in the present study prevented Cd from being bound by trout gills, and some of these fish showed hypocalcemia; however, Cu was kept off the gills of trout exposed to metals plus DOM. Computer modelling using metal-gill binding constants simulated well the accumulation of Cd and the lack of Cu accumulation by trout gills in the presence of DOM.
Analysis of straying variation in Alaskan hatchery chinook salmon (Oncorhynchus tshawytscha) following transplantation
Authors: Hard Jeffrey J , Heard William R
Published: April 2011

In 1976 chinook salmon (Oncorhynchus tshawytscha) gametes from the Chickamin and Unuk rivers in southeastern Alaska were transplanted 250 km to establish hatchery runs at Little Port Walter (LPW), Baranof Island. From 1977 to 1989, 1 862 058 marked smolts from 12 broods were released from LPW. Homing and straying were estimated from adult recoveries at 25 locations in Alaska and British Columbia between 1981 and 1989. Of 22 198 LPW fish recovered over this period, 21 934 (98.8%) were collected at LPW. Of 264 fish recovered elsewhere, 38.3% were within 7 km of LPW; 64.4% were within 25 km of LPW. No LPW fish were recovered from the ancestral rivers, but nine fish were recovered from rivers supporting wild chinook salmon. Straying declined with distance from the release site but varied between hatcheries and streams. Straying declined with increasing age and run size. Straying was similar between the populations but varied among broods, and analysis of straying in experimental groups provided evidence for a heritable component. Males strayed more often than females. Population, gender, run size, and recovery age interacted to produce substantial variation in straying, indicating that run composition can produce complex straying responses.
Why did the Prince William Sound, Alaska, Pacific herring (Clupea pallasi) fisheries collapse in 1993 and 1994? Review of hypotheses
Authors: Pearson W H , Elston R A , Bienert R W , Drum A S , Antrim L D
Published: April 2011

Following record harvests of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, in the 3 years after the Exxon Valdez oil spill, the fishery failed in 1993. The hypotheses advanced to explain this dramatic 1993 decline occur in three categories: (i) effects associated with the 1989 oil spill, (ii) harvesting effects, and (iii) natural phenomena. Based on our review, we are convinced that a combination of increasing Prince William Sound herring biomass and decreasing food supply led to poor condition of Prince William Sound herring, which resulted in the 1993 decline. Other natural causes could have contributed to the decline, including disease, cold water temperatures, increased predation, and other natural stochastic processes. No evidence supports hypotheses that the decline resulted solely from overharvesting or underharvesting. The record high population levels and harvests of Prince William Sound herring in the years after the 1989 oil spill, the lack of change from the expected age-class distribution, and the low level of oil exposure documented for herring in 1989 and the following years all indicate that the 1989 oil spill did not contribute to the 1993 decline. Poor nutritional status, either alone or in combination with disease or other natural factors, was most likely responsible for the 1993 collapse.
Interactions among sediments, organic matter, and microbial activity in the hyporheic zone of an intermittent stream
Authors: Chafiq Mohamed , Gibert Janine , Claret Cécile
Published: April 2011

Interactions between surface and subsurface water in intermittent streams are poorly understood. We predicted that surface discharge patterns would influence retention and transport of fine sediments and particulate organic matter in a first-order intermittent stream, which in turn would affect microbial activity at different depths in the sediment. We measured sediments, dissolved and particulate organic carbon, and microbial and bacterial biomass and activity at three depths (surface and 20 and 40 cm) over a period spanning low and high flows at five stations on an intermittent stream. Discharge influenced physicochemical and sediment characteristics at the upstream stations with coarse substratum. In the finer sediments of the lower reaches, an active hyporheic microbial assemblage primarily governed sediment and organic dynamics. With decreasing discharge and increasing retention of fine sediments and particulate organic carbon, greater microbial hydrolytic activity in bed-sediments occurred downstream. Dissolved oxygen, organic carbon, fine sediments, microbial biomass, hydrolytic activity, and bacterial biomass declined with depth, and changed over time, apparently in response to varying discharge. We conclude that discharge and substratum particle size may interact to control organic dynamics and hyporheic microbial activity in a 1st order stream.
Article
Authors: Dagorn Laurent , Fréon Pierre
Published: April 2011

Among the different assumptions proposed to explain why tropical tuna aggregate around floating objects ("logs"), one of the most recent is that floating objects may represent meeting points for tuna. This "meeting point hypothesis" proposes that tuna can use these floating objects to form larger schools after school fission or dispersion. The influence of meeting points on tuna school sizes is explored through different individual-based models that consider a single fusion rule and a variety of fission rules based on energetic considerations, the role of school size on school cohesion, predator attacks, and dispersion during the night. Results are first analyzed using an averaging approach to study the overall mean school size in habitats having different floating object densities. Second, a dynamic approach is used to compare the temporal dynamics of associated and free-swimming school sizes. The averaging approach indicates that in all the models (except those based on energetics), floating objects increase school size, at least up to a certain object density. The dynamic approach clearly illustrates different dynamics in the school size of associated and free-swimming schools. Most of our models show that tuna associated with logs resume schooling in larger schools after fission events.
Interaction of rearing temperature and maternal influence on egg development rates and larval size at hatch in yellowtail flounder (Pleuronectes ferrugineus)
Authors: Benoît Hugues P , Pepin Pierre
Published: April 2011

We assessed the extent to which temperature interacts with maternal contributions to egg size to affect development time and size of yellowtail flounder (Pleuronectes ferrugineus) larvae at hatch. Maternal effects contributed significantly to differences in egg sizes produced by four females. Eggs from each female were incubated at five temperatures. Development time was most significantly affected by temperature, and female effects were minimal. However, the variance in development time within a population was significantly affected by an interaction between female and temperature effects. Average length at hatch varied significantly among temperatures and females, as did the variance in hatching length within a population. Variance in hatching length explained by maternal effects peaked at intermediate temperatures (~38% explained variance at 7°C), while variance explained by covariation with development time increased linearly with temperature, explaining ~40% variance at 13°C. Overall, the nonadditive interaction between maternal contributions and the environment suggests that female effects must be considered over the entire range of environmental conditions experienced by their progeny. In addition, our results support the idea that it is inappropriate to quantify female effects among eggs and extrapolate these differences to larvae.
Life history characteristics and strategies of the American eel, Anguilla rostrata
Authors: Oliveira Kenneth
Published: April 2011

Several life history hypotheses for the American eel, Anguilla rostrata, were examined using seaward-migrating silver-phase eels collected in the Annaquatucket River, Rhode Island, U.S.A. Female eels were significantly larger and older than males. Female eels also had a significantly higher mean growth rate. The addition of life history data from Annaquatucket River eels to published silver eel data from locations throughout the eels' range shows that female size at migration is positively correlated with latitude (r = 0.56, p = 0.05) but male size is not (r = 0.54, p = 0.17). Female age was not related to latitude (r = 0.57, p = 0.27) but male age showed a positive relationship (r = 0.87, p = 0.05). Growth rates for females and males were inversely related to latitude (r = -0.98, p = 0.02 and r = -0.95, p = 0.05, respectively). Differences between the latitudinal relationships and life history traits of the sexes may be due to differences in life history strategies.
Behavioural and metabolic effects of chronic exposure to sublethal aluminum in acidic soft water in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Allin C J , Wilson R W
Published: April 2011

Triplicate groups of 15 softwater-acclimated juvenile rainbow trout (Oncorhynchus mykiss) were randomly allocated to one of three treatments: pH 6.5 with no aluminum, pH 5.2 with no aluminum, and pH 5.2 with 30 µg labile aluminum·L-1. The aluminum dose was sublethal and continued for 34 days. Treatment effects on swimming behaviour, metabolism, feeding, food conversion efficiency, and blood parameters were determined. Fish exposed to aluminum displayed hypoactivity that was statistically distinct from both control groups from day 1 onwards. Exposure to acid alone elicited no behavioural effects. There were no significant differences in metabolic rates between the treatment groups. Feeding rates of the fish exposed to aluminum became depressed, reaching a minimum on day 15, and gradually recovered thereafter, but never to the preexposure levels. Swimming behaviour was a more sensitive index of exposure to aluminum than feeding. Fish exposed to aluminum had significantly fewer red blood cells and lower haematocrit than the controls, indicating haemodilution. Aluminum is known to act as a respiratory toxicant, restricting aerobic scope. In addition, these data suggest that fish respond to aluminum exposure by reducing metabolically costly activities such as routine swimming behaviour to allow for the increased maintenance costs associated with acclimation and damage repair.
Large woody debris in bull trout (Salvelinus confluentus) spawning streams of logged and wilderness watersheds in northwest Montana
Authors: Hauer F Richard , Poole Geoffrey C , Gangemi John T , Baxter Colden V
Published: April 2011

We measured large woody debris (LWD) in 20 known bull trout (Salvelinus confluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m ranging from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggregates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attached to the stream bank were the most likely to be positioned perpendicular to stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg. Observations indicated that the majority of pools were formed as scour pools by either very large LWD pieces that were perpendicular to the stream or multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without rootwads were relatively consistent. However, among reaches with logging in the watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substantive change in stream habitats.
Effects of stock-specific and environmental factors on the feeding migration of Atlantic salmon (Salmo salar) in the Baltic Sea
Authors: Kallio-Nyberg Irma , Peltonen Heikki , Rita Hannu
Published: April 2011

Atlantic salmon (Salmo salar L.) stocks in the Baltic Sea are mainly exploited during their sea migration. The offshore fishery in the feeding grounds of these salmon permitted us to analyse the migrations of certain stocks on the basis of tag recovery data. Four salmon stocks from rivers draining into Bothnian Bay (25°E, 65.5°N) were selected for study. During 1984-1991, about 135 000 2-year-old hatchery-reared smolts were tagged and released. We applied logit models, with the site of recovery as a multicategory response variable, to analyse the distribution of tag recoveries in the Baltic Sea feeding grounds. The results showed the combined influence of stock, prey abundance, and smolt size on the spatial marine distribution of the salmon. Although stock-specific sea migration patterns were apparent, annual environmental factors had a stronger influence on the sea migration route of salmon than did the stock factor. The salmon released as small smolts (total length [Formula: see text] 17.0 cm) were more frequently caught farther from the release site than were those released as larger smolts (>17 cm). The abundance of suitable prey (age 0+ herring) in the year of smolt release was found to be a key factor influencing the migration distance. The salmon released in the years of strong herring recruitment in the Gulf of Bothnia had a higher probability to stay in the Bothnian Sea for feeding and not to migrate farther south.
Acute effects of suspended sediment angularity on juvenile coho salmon (Oncorhynchus kisutch)
Authors: Lake Randal G , Hinch Scott G
Published: April 2011

To determine the roles of suspended sediment angularity and concentration as contributors to stress and mortality in salmonids, we exposed juvenile coho salmon (Oncorhynchus kisutch) to anthropogenically derived "extremely angular" and "round" silicate sediments over a range of concentrations in 96-h experiments. Stress responses (e.g., decreased leukocrit) were elicited by exposure to both sediment shapes when concentrations were >40 g·L-1, corresponding to the minimum concentration at which physical gill damage was observed. Extremely angular sediments also caused stress responses (e.g., elevated hematocrit, decreased leukocrit) at concentrations <41 g·L-1. However, we found no difference between sediment shapes in causing mortality at any sediment concentration. Further, mortalities were not observed until concentrations were about 100 g·L-1, a value that is about an order of magnitude greater than high natural concentrations in salmonid rivers. Natural fluvial suspended sediments cause fish stress and mortality at much lower concentrations than we found with our anthropogenically derived suspended sediments.
Interindividual variation in the prolonged locomotor performance of ectothermic vertebrates: a comparison of fish and herpetofaunal methodologies and a brief review of the recent fish literature
Authors: Kolok A S
Published: April 2011

Physiological research of locomotor performance in fishes has traditionally adopted an approach in which the mean performance of a number of fish was considered "real" and variation around the mean was considered statistical noise. Drawing on advances made in herpetofaunal studies, an alternative approach has recently appeared in the fish literature in which variation among individual fish has been shown to be repeatable and statistically valid. The incorporation, rather than suppression, of individual variation in experimental design has revealed interesting and biologically relevant relationships between morphological and physiological traits and swimming performance that can be masked by the traditional use of group means. Considering the promising nature of these initial studies incorporating individual variability in fish performance, this paper has two primary objectives. The first is to compare methodologies that have been used in studies involving intraspecific variability in the locomotor performance of fish and herpetofauna. The second is to review the fish literature regarding interindividual variation in prolonged swimming performance.