bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of relations among fish life history parameters with a bioenergetics-based population model
Authors: Jensen A L
Published: April 2011

Relations among life history parameters were sought in simulations using a simple bioenergetic population model. The relations among parameters generated in simulations were close to those reported in field studies and obtained in theoretical derivations. The simulations also indicated that there is an optimum number and mass of eggs, for as egg mass increased, total adult biomass increased to a maximum and then decreased. The observed mass is nearly equal to the optimum mass in the simulations. In the simulations the optimal relations among life history parameters resulted from simple relations among food abundance, population abundance, growth, and mortality. Natural selection has resulted in bioenergetic and population relations that maximize adult biomass, and these processes result in the observed relations among life history parameters.
Parameter estimation in modelling the dynamics of fish stock biomass: are currently used observation-error estimators reliable?
Authors: Chen Y , Andrew N
Published: April 2011

Production models are used in fisheries when only a time series of catch and abundance indices are available. Observation-error estimators are commonly used to fit the models to the data with a least squares type of objective function. An assumption associated with observation-error estimators is that errors occur only in the observed abundance index but not in the dynamics of stock and observed catch. This assumption is usually unrealistic. Because the least squares methods tend to be sensitive to error assumptions, results derived from these methods may be unreliable. In this study, we propose a robust observation-error estimator. We evaluate the performance of this method, together with the commonly used maximum likelihood method, under different error assumptions. When there was only observation error in the abundance index, maximum likelihood tended to perform better. However, with both observation and process errors, maximum likelihood yielded much larger estimation errors compared with the proposed method. This study suggests that the proposed method is robust to error assumptions. Because the magnitude and types of error cannot often be specified with confidence, the proposed method offers a potentially useful addition to methods used to fit production models to abundance index and catch data.
Temperature as a key factor determining the regional variability of the xenobiotic-inducible ethoxyresorufin-O-deethylase activity in the liver of dab (Limanda limanda)
Authors: Lange U , Saborowski R , Siebers D , Buchholz F , Karbe L
Published: April 2011

Water temperature exhibits a strong influence on the regional variability in activity of the 7-ethoxyresorufin-O-deethylase (EROD) in the liver of dab (Limanda limanda) from the German Bight during the spawning and postspawning seasons. The relationship between EROD activity and water temperature found in situ was, surprisingly, not masked by migrations of dab. Correlations between EROD activity and temperature could not be explained by a direct temperature effect in terms of temperature compensation. Instead, we suppose that temperature influences EROD activity indirectly via its influence on the duration of the gonadal cycle and thus on the time of spawning, which we assume to be coupled with the seasonal variation in EROD activity. Significant negative correlations between EROD activity and the condition factor, gonadosomatic index, and liver-length index could be attributed to the parallel or opposite temporal changes of these parameters. In the liver of spawning females, no linear relationship was detected between the EROD activity and the concentration of the polychlorinated biphenyls (PCB), which have been previously determined.
Effects of oil-laden sediments on growth and health of juvenile flatfishes
Authors: Moles Adam , Norcross Brenda L
Published: April 2011

Juvenile yellowfin sole (Pleuronectes asper), rock sole (Pleuronectes bilineatus), and Pacific halibut (Hippoglossus stenolepis) had reduced growth following 30-90 days of exposure to sediments laden with Alaska North Slope crude oil. Changes in fish health bioindicators after 90 days, i.e., increases in fin erosion, liver lipidosis, gill hyperplasia, and gill parasites, coupled with decreases in macrophage aggregates, occurred at hydrocarbon concentrations (1600 µg/g) that reduced growth 34-56% among the flatfishes. Chronic hydrocarbon pollution of nearshore nursery sediments could alter growth and health of juvenile flatfishes. Recruitment of juveniles to the fishery may decline because of increased susceptibility to predation and slower growth.
Impacts of density-dependent growth and maturation on assessment advice to rebuild depleted U.S. silver hake (Merluccius bilinearis) stocks
Authors: Helser Thomas E , Brodziak Jon KT
Published: April 2011

We examined how density-dependent growth and maturation rates would affect scientific advice to rebuild U.S. silver hake (Merluccius bilinearis) stocks to a minimum biomass threshold (SSB50) using an age-structured stochastic projection model. Uncertainty in recruitment and initial stock sizes at age was incorporated to more realistically capture the stochastic nature of the stock's dynamics through time. Performance measures including spawning stock biomass (SSBt), risk (prob(SSBt< SSB50)), and fishery yields were examined under model assumptions of static life history parameters in contrast with density-dependent parameters for various constant fishing mortality rate (F) harvest policies. Model results indicated that unless compensatory mechanisms are accounted for, scientific advice may be too optimistic and lead to unrealistic expectations of F targets to achieve stock rebuilding, requiring longer rebuilding times and entailing more risk and unrealized sustainable yield. For instance, projected median southern stock SSBt exceeded the SSB50 of 104 000 metric tons (t) with 40% risk to the stock by year 20 from harvesting at F = 0.50. However, under the density-dependent assumption, median SSBt did not rebuild as expected, and after 20 years reached only 75 000 t with 85% risk to the stock. Also under this assumption, median yields increased from 9000 to 27 000 t by year 20 but were 30-40% lower than what would have been expected under density independence.
Phytoplankton responses to nutrient and grazer manipulations among northeastern lakes of varying pH
Authors: Bukaveckas Paul , Shaw William
Published: April 2011

Short-term nutrient enrichment and zooplankton exclosure experiments were conducted at 14 lakes representing various stages of acidification (pH 4.6-6.8). We measured changes in chlorophyll as an indicator of the severity of nutrient limitation and grazing intensity and compared these with independent measures of P limitation (cell P quotas and phosphatase activity) and grazing (zooplankton densities and inferred community grazing rates). Results from nutrient enrichment experiments showed good correspondence to measured phosphatase activity but not cell P quotas. Phytoplankton in acidic lakes (pH < 5.0) responded more strongly to nutrient enrichment and exhibited fourfold higher biomass-specific phosphatase activity compared with nonacidic lakes. Phytoplankton responses to the removal of macrozooplankton did not exhibit any consistent pattern among lakes of varying acidity. Although the largest herbivores (Daphnia) were more abundant in nonacidic lakes, their absence in acidic lakes was compensated for by increased abundance of smaller species (principally Diaptomus minutus and Bosmina longirostris). The magnitude of the response to grazer removal was positively correlated with lake zooplankton densities at the time of the experiment, and the use of a nonlinear model enabled us to explain 84% of the variation in this response among the 14 sites.
Nucleic acids and enzymes in Atlantic cod (Gadus morhua) differing in condition and growth rate trajectories
Authors: Dutil Jean-Denis , Lambert Yvan , Guderley Helga , Blier Pierre U , Pelletier Dany , Desroches Martine
Published: April 2011

Atlantic cod (Gadus morhua) were exposed to one of four feeding regimes, 16 weeks of food deprivation (U) or satiation feeding (F) or two 8-week periods of food deprivation followed by satiation feeding (UF) or vice versa (FU), to determine whether relationships between nucleic acids or enzymes and growth rates result from a general enhancement of individual condition or are a direct result of enhanced growth rates. Final condition factor (K) differed between treatments, but did not differ between the mixed treatments after either 8 weeks of negative growth (FU) or 8 weeks of positive growth (UF). Intestinal cytochrome c oxidase activity matched the expected short-term growth rates, not only in fed and unfed fish but also in cod exposed to the mixed treatments (FU and UF). White muscle lactate dehydrogenase activity reflected growth rates, but initial levels were not reached within 8 weeks in FU cod. The liver glutamate pyruvate transaminase : DNA ratio reflected differences in K, but not differences in recent growth rates. Myofibrillar proteins decreased in unfed cod, while sarcoplasmic proteins followed changes in K more closely. The RNA:DNA ratio in white muscle did not reflect changes in K or changes in growth rates.
Fine-scale mapping of fish distribution from commercial catch and effort data using maximum entropy tomography
Authors: Vignaux M , Vignaux G A , Lizamore S , Gresham D
Published: April 2011

We present a technique for mapping the spatial distribution of fish using commercial catch and effort data. The relative fish density can be estimated at scales smaller than the length of the unit of effort, such as a tow, by using a Bayesian maximum entropy method. This can take advantage of the fact that the tows cross to give information about the density in those areas. This is a novel application of a well-tested technique that has been used in other fields such as astronomical imaging. Its utility and robustness is demonstrated both on simulated data and on real data from the trawl fishery on spawning hoki off the west coast of the South Island of New Zealand.
Genetic heterogeneity, detected by PCR-SSCP, among samples of larval Pacific oysters (Crassostrea gigas) supports the hypothesis of large variance in reproductive success
Authors: Li Gang , Hedgecock Dennis
Published: April 2011

Differences in genetic composition among samples of larvae produced during a single spawning season by a semi-isolated population of Pacific oysters (Crassostrea gigas) in Dabob Bay, Washington, confirm a specific prediction of the hypothesis that this and other marine animals have large variances in reproductive success. To study the genetics of single larvae, we cloned and sequenced part of the mitochondrial genome and developed polymerase chain reaction (PCR) primers to amplify four segments totaling nearly 2300 base pairs, or 13% of the genome. PCR products were digested with restriction enzymes into smaller fragments, which were then screened for single-strand conformational polymorphisms (SSCP). Seven plankton samples (total N = 877), taken between 10 and 21 August 1993, showed a common composite PCR-SSCP haplotype that comprised from 53 to 85% of samples. Nevertheless, exact probability and permutation tests reveal that early and late samples from north Dabob Bay differed significantly from the rest. These differences cannot be ascribed to spatial variation and are consistent with the hypothesis that larvae are produced by relatively few adults, in accord with previous observations of substantial genetic drift in this large population.
Dispersal of male and female Antarctic fur seals (Arctocephalus gazella)
Authors: Boyd I L , McCafferty D J , Reid K , Taylor R , Walker T R
Published: April 2011

This study examined the foraging locations of adult male and female Antarctic fur seals (Arctocephalus gazella) in the Scotia Sea during the postbreeding period. Satellite transmitters were used to track adult males and females and to obtain information about dive depths. Male fur seals migrated away from the breeding area during the postbreeding period whereas females remained close to the breeding grounds and foraged in the same area during two consecutive years. The most intensive foraging by females was associated with the edge of the continental shelf of South Georgia. Males dived deeper than females. Counts of males at South Georgia and at the South Orkney Islands support the result from satellite tracking data showing that males move from South Georgia to the South Orkney Islands at the end of the breeding season. Unlike males, females were limited in their foraging range by the necessity to return to feed dependent young, so breeding sites are likely to be located close to foraging areas that are optimal for females. Locations used for feeding by females were avoided by males, either because they were suboptimal for males or because foraging by females at South Georgia causes local depletion of food, and males, which have the option to forage further afield, can forage more successfully in regions where there are no females. Comparison with fisheries data also suggests that these fur seals are targeting the most abundant exploitable prey.
Phosphorus loading reductions needed to control blue-green algal blooms in Lake Mendota
Authors: Lathrop Richard C , Carpenter Stephen R , Stow Craig A , Soranno Patricia A , Panuska John C
Published: April 2011

We evaluated the reductions in P loading needed to control blue-green algal blooms in Lake Mendota, Wisconsin. After developing a 21-year loading data set, we used a P mass balance model expressed as a difference equation with an annual time step indexed from mid-April. We defined and estimated a loss parameter lambda as the proportion of the lake's April P concentration lost through sedimentation and outflow during the following year. Using the distribution of annual lambda 's and input loadings, we predicted the steady-state distribution of April P concentrations that would result from scenarios of altered inputs due to changes in management practices. These results were then linked to the probability of summer blue-green algal blooms. For no load reduction, the probability of a bloom (>2 mg algae ·L-1) on any summer day is about 60%. This probability decreases to 20% with a load reduction of 50%. Our approach illustrates how managers can consider reducing the frequency of extreme events like algal blooms, which may correspond more to the public's perception of lake water quality than average conditions.
Biomagnification and bioaccumulation of mercury in an arctic marine food web: insights from stable nitrogen isotope analysis
Authors: Atwell Lisa , Hobson Keith A , Welch Harold E
Published: April 2011

Several recent studies have shown that the use of delta 15N analysis to characterize trophic relationships can be useful for tracing biocontaminants in food webs. In this study, concentration of total mercury was measured in tissues from 112 individuals representing 27 species from the arctic marine food web of Lancaster Sound, Northwest Territories. Samples ranged from particulate organic matter through polar bears (Ursus maritimus). Using delta 15N values to identify trophic position, we found that total mercury in muscle tissue biomagnified in this food web. Polar bears were a notable exception, having a lower mean mercury concentration than their main prey, ringed seals (Phoca hispida). Most vertebrates showed greater variance in mercury concentration than invertebrates, and there was a trend in seabirds toward increased variability in mercury concentration with trophic position. Within species, we found no evidence of bioaccumulation of mercury with age in the muscle tissue of clams (Mya truncata) or ringed seals. Because stable nitrogen isotopes illustrated the relationship in this biome between trophic position and mercury level on a continuous, quantitative scale, we were able to determine that log10[Hg] ( µg/g dry weight) = 0.2( delta 15N) - 3.3. The measurement of delta 15N values and mercury concentration allowed us to quantitatively assess mercury biomagnification within this extensive arctic marine food web.
Reconstruction of trophic state in Danish lakes using subfossil chydorid (Cladocera) assemblages
Authors: Brodersen Klaus P , Whiteside Melbourne C , Lindegaard Claus
Published: April 2011

Surficial sediments from 32 Danish lakes were screened for subfossil chydorid (Cladocera) assemblages. Two data sets from 1965 and 1992 were examined by cluster analysis and nonmetric multidimensional scaling (NMDS) for lake classification. The best environmental variable to explain the 1992 species data was total phosphorus (TP) (r = 0.58, Spearman rank correlation), and NMDS defined three lake classes that were significantly different in communities (p < 0.01, ANOSIM) and in TP values. Canonical correspondence analysis found a strong relationship between the species data and log(TP) (axis 1 eigenvalue = 0.30, total inertia = 0.85, log(TP) intraset correlation = 0.92). Environmental variables were tested by forward selection and six variables were found to be statistically significant by 99 unrestricted Monte Carlo permutations. Weighted averaging regression and calibration models were established from the 1992 chydorid data and corresponding contemporary log-transformed TP data. The model's predictive ability was assessed by the bootstrapped coefficient of determination and the bootstrapped root mean squared error of prediction ( r2boot=0.79 , RMSEboot = 0.24). The patterns of changes in chemical and biological variables (diversity, Bray-Curtis dissimilarity) over the 27-year period placed the 32 lakes in six different response groups.
Interdecadal variation in developmental timing of Neocalanus plumchrus populations at Ocean Station P in the subarctic North Pacific
Authors: Mackas David L , Goldblatt Robert , Lewis Alan G
Published: April 2011

A single copepod species, Neocalanus plumchrus (Marukawa), makes up much of the mesozooplankton biomass in the subarctic Pacific. Its vertical distribution and developmental sequence are both strongly seasonal. Together, they produce a strong and narrow (<60 days duration) annual peak of upper ocean zooplankton biomass in spring and early summer. At Ocean Station P (50°N, 145°W), seasonal phasing of this annual maximum has shifted dramatically between 1956 and the present. Both time series observations of N. plumchrus stage composition ratios and measurements of total upper ocean zooplankton biomass produce consistent pictures of this change. Population development was very late in the early 1970s (biomass maximum in mid-July to late July), early in the late 1950s (late May - early June), and very early in the 1990s (early May to mid-May). The changes in timing are strongly correlated with large-scale year-to-year and decade-to-decade ocean climate fluctuations, as reflected by spring season temperature anomalies in the surface mixed layer within which the juvenile copepodites feed and grow (r2 = 0.56, development about 60 days earlier in warm than in cold years). But the change in developmental timing is too large to be explained solely by physiological acceleration of individual development rate. We suggest instead that the cause is interannual differences in survival among early versus late portions of the annual copepodite cohort.
Influence of large woody debris on retention, immigration, and growth of coastal cutthroat trout (Oncorhynchus clarki clarki) in stream pools
Authors: Harvey Bret C
Published: April 2011

Over 4 months and about 1 year, coastal cutthroat trout (Oncorhynchus clarki clarki) age-1 in Little Jones Creek, California, remained at similar rates in pools with and without large woody debris. This result was based on attempts in July and November 1995 to collect and tag all fish in 22 pools and three collections of fish from the same pools in November 1995, May 1996, and August 1996. Retention of fish appeared to be greater in pools with large woody debris in May 1996. The presence of large woody debris in pools did not influence immigration or growth of cutthroat trout. However, both immigration and growth increased downstream over the 3850-m study reach. Low retention and substantial immigration of cutthroat trout into experimental pools indicate that movement is important in the dynamics of this population. First- and second-order channels appear to be important sources of fish for the third-order study reach, while the study reach may export significant numbers of fish to downstream reaches accessible to anadromous fish.
Low-effort regression estimation of daily ration in young walleye, Stizostedion vitreum
Authors: Madon Sharook P
Published: April 2011

I used a low-effort regression approach to estimate daily rations of pond-reared age 0 walleye, Stizostedion vitreum (16.0-37.2 mm total length). The regression model predicted average 24-h food mass () from two or three consecutive point estimates of food mass (Ft) in fish guts taken at a sampling interval of 3 h. Predicted values were multiplied by gastric evacuation rates and by 24 h to yield daily ration estimates. Accuracy tests of the low-effort regression model for age 0 walleye based on resampling revealed that 93-100% of predicted values fell within 2 SEs of observed values determined from nine fish collections over 24 h. The age 0 walleye regression model provided estimates of daily ration that were within the 95% confidence intervals around observed daily ration values for conspecifics in an independent test pond (this study) and in other distinct pond systems. The age 0 walleye regression model also provided estimates of daily ration that were within the 95% confidence intervals around five out of seven observed daily ration values for age 0 lake yellow perch, Perca flavescens, also a diurnal feeder like walleye. The model reliably provided estimates of daily ration for fish that were 1.5-4.5 times the mean wet weight of the largest fish included in the model's domain.
Multiple spawning and the dynamics of fish populations: inferences from an individual-based simulation model
Authors: Lowerre-Barbieri Susan K , Lowerre James M , Barbieri Luiz R
Published: April 2011

We used an individual-based Monte Carlo simulation model to assess how aspects associated with multiple spawning (within a spawning season) affected survivorship, lifetime fecundity, cohort egg production, and yield-per-recruit of a highly exploited species. To make our model more realistic, we included and tested the effects of individual variability in growth and a seasonal growth pattern. Birth months influenced when fish first matured and became vulnerable to the fishery. There was a sixfold increase in mature fish at the beginning of their first spawning season associated with having been born early versus late the previous season. Early born fish had a lower average life-span than later born fish. Although early born fish had lower survivorship they produced the most eggs because of an early size at first maturity, low fishing mortality in the first year, and their larger size at age. These results suggest multiple spawning can have important implications for recruitment and adult population dynamics.
Relationships between Alaskan salmon catch and North Pacific climate on interannual and interdecadal time scales
Authors: Downton Mary W , Miller Kathleen A
Published: April 2011

Using multivariate time series models, Alaska's statewide commercial catch of three salmon species during 1925-1994 is shown to be related to surface temperatures in particular large regions of the eastern North Pacific. Previous research has indicated that interdecadal changes in Alaskan catch levels are related to large-scale changes in the climate regime of the North Pacific. The present work focuses on interannual variability by controlling for climatic shifts in the mid-1940s and mid-1970s. For sockeye (Oncorhynchus nerka) and chum (O. keta), relationships with temperature occur within a few months after ocean entry with warmer regional temperatures enhancing survival. For sockeye and pink salmon (O. gorbuscha), relationships with temperature occur at the time and location of the return migration, suggesting that colder ocean temperatures may enhance spawning success or egg survival. In addition, the models show a significant positive relationship of chum catch to pink catch 2 years earlier, suggesting a common influence on smolts of the two species. The results support the contention that climatic factors affecting the marine environment play a significant role in salmon production on interannual, as well as interdecadal, time scales.
Morphometric and meristic differences between shallow- and deep-water populations of white hake (Urophycis tenuis) in the southern Gulf of St. Lawrence
Authors: Hurlbut Thomas , Clay Douglas
Published: April 2011

Linear discriminant function analysis of morphometric and meristic characters was used to assess the extent of differentiation between shallow- (<100 m) and deep- (>200 m) water populations of white hake (Urophycis tenuis) from the southern Gulf of St. Lawrence (NAFO Division 4T). Although meristic characters provided some evidence for stock separation, the best statistical separation was obtained with morphometric characters. Morphometric discriminant functions derived from "learning" samples were able to correctly classify 82 and 84% of the "test" samples for both females and males, respectively. A greater relative snout length in fish sampled from along the Laurentian Channel compared with those from the Northumberland Strait area was the primary discriminating character for both sexes. Our morphological evidence and previous tagging and distributional studies suggest that the populations from these two areas represent separate stocks; therefore, the traditional management unit for white hake in NAFO Division 4T may no longer be appropriate.
Expression of viral hemorrhagic septicemia virus in prespawning Pacific herring (Clupea pallasi) exposed to weathered crude oil
Authors: Carls M G , Marty G D , Meyers T R , Thomas R E , Rice S D
Published: April 2011

Expression of subclinical viral infection in response to toxicant exposure has not previously been reported, but evidence presented herein indicates that activation of viral hemorrhagic septicemia virus (VHSV) may occur in Pacific herring (Clupea pallasi) exposed to crude oil encountered after an oil spill. Decreased incidence of hepatic inflammatory cells as a function of total polynuclear aromatic hydrocarbon (TPAH) concentration was evidence for immunosuppression in exposed fish, and decreased immune surveillance is a possible mechanism by which subclinical VHSV could be reactivated. Adult Pacific herring of unknown status regarding infection by VHSV were captured from the wild and exposed to weathered crude oil for 16-18 days. TPAH concentration in tissue, VHSV prevalence, and mortality were correlated with dose. Histopathologic lesions were significantly correlated with TPAH concentration and prevalence of VHSV, but not gender or length. Significant lesions included increased hepatocellular necrosis, splenic thrombosis, and decreased inflammation in the liver.
Using Bayesian decision analysis to help achieve a precautionary approach for managing developing fisheries
Authors: McAllister M K , Kirkwood G P
Published: April 2011

Bayesian decision analysis offers a useful framework for helping to achieve a precautionary approach to managing developing fisheries. With few data on the resource, data and experience from ecologically similar fish populations (or prior information) can also be used to quantitatively evaluate alternative procedures for managing the resource and to provide management advice. We applied Bayesian decision analysis to a hypothetical developing fishery in which a logistic model was fitted to catch per unit effort data. We evaluated the trade-offs in yield and the risk of depletion of catch and effort control rules. Effort control rules yielded average catches nearly 40% larger for levels of risk similar to those given by catch control rules. Management procedures designed to reduce the risks of implementing high harvest rates and to promote resource recovery at low stock sizes reduced the risks of overexploitation and caused only very small reductions in average catch. However, -50 and +100% biases in prior probability distributions for some parameters and the use of overly precise priors (CV < 0.5) in stock assessments caused large increases in the risk of overexploitation.
Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence
Authors: Swain D P , Chouinard G A , Morin R , Drinkwater K F
Published: April 2011

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.
Protective effects of water Cl- on physiological responses to waterborne silver in rainbow trout
Authors: McGeer James C , Wood Chris M
Published: April 2011

The importance of water Cl- concentration in mitigating the effects of sublethal waterborne AgNO3 exposure on rainbow trout was studied to test the relationship between physiological response and concentration of ionic silver (Ag+). Trout were exposed to a total silver concentration of 30 nmol·L-1 (as AgNO3) at a range of different water Cl- concentrations from 20 to 1500 µmol·L-1. These levels were chosen by speciation modelling with MINEQL+ to progressively reduce the concentration of Ag+ largely by replacement with dissolved AgClaq. Fish exposed to AgNO3 experienced a loss of Na+; increasing the water Cl- concentration reduced these losses. In vitro measurements after 50 h of exposure showed that Na+ losses were related to Ag+-induced inhibition of gill Na+/K+ ATPase activity; increasing the concentration of Cl- in the water protected against the inhibition of Na+/K+ ATPase activity. The disruption of Na+ regulation in AgNO3-exposed fish was accompanied by increased plasma cortisol and total ammonia concentrations, but blood pH, plasma PCO2 and HCO3-, and hematocrit were, in general, unaltered. Gill silver content increased in all AgNO3-exposed trout and was not correlated with the disruption of Na+ balance. We conclude that physiological measurements in combination with aquatic geochemical equilibrium modelling are useful in developing models to predict the acute toxicity of waterborne silver.
Regimes and stock-recruitment relationships in Japanese sardine (Sardinops melanostictus), 1951-1995
Authors: Wada Tokio , Jacobson Larry D
Published: April 2011

We used reproductive success, rather than abundance or catch, to identify regimes because reproductive success responds faster to environmental changes. Peak abundance of Japanese sardine during 1951-1995 was about 1000 times higher than minimum abundance. A regime shift occurred in the early 1970s when carrying capacity (measured using spawner-recruit models) increased by about 75 times. We hypothesize that this was due to large-scale changes in the Kuroshio and Oyashio Current systems. Long-term environmental variation (regimes), interannual variability in recruitment success, and density-dependent recruitment and growth rates affected dynamics of Japanese sardine. We hypothesize that density-dependent effects on recruitment of Sardinops spp. are common but usually obscured in short data sets by environmental variability and measurement error. Virtual population analysis and forward-simulation modeling approaches gave similar biomass and recruitment estimates. The relationship between sardine biomass and catch per unit search time was nonlinear. Mass-at-age and biomass were correlated, and it may be possible to use mass-at-age as an abundance index. Current abundance is low, and we believe that the environment has shifted to a regime that is unfavorable for Japanese sardine.
An empirical model of fleet dynamics in New England trawl fisheries
Authors: Holland Daniel S , Sutinen Jon G
Published: April 2011

Regulations and changes in market and environmental conditions that change the profitability of one fishery or area will result in a redistribution of fishing effort among alternative fisheries or areas. The magnitude of this effort displacement will depend on the relative profitability of the alternatives for the individual fishers affected. When fishing areas and fishers are heterogeneous, simple aggregate effort models such as those based on ideal free distribution theory may provide inaccurate predictions. We present an empirical model of individual vessel fishery and location choice based on trip data for a group of over 400 large trawlers fishing in New England. The model uses lagged average revenue rates for different alternatives and the individual vessel's past behavior to predict choice of species group and fishing location on a trip-by-trip basis. This model is used to predict aggregate effort levels in different fisheries and areas over time.
Impact of age-0 bluefish (Pomatomus saltatrix) predation on age-0 fishes in the Hudson River estuary: evidence for density-dependent loss of juvenile striped bass (Morone saxatilis)
Authors: Buckel Jeffrey A , Conover David O , Steinberg Nancy D , McKown Kim A
Published: April 2011

We measured bluefish (Pomatomus saltatrix) weights, densities, and prey sizes during the summers of 1992 and 1993 and diets over a 4-year period (1990-1993) in the Hudson River estuary. This information was used to estimate the loss of young-of-the-year (YOY) striped bass (Morone saxatilis) resulting from YOY bluefish predation. We then compared this predation mortality with the total loss of striped bass in the system. Data from sampling surveys conducted since the mid-1970's were used to examine relationships between bluefish abundance and striped bass recruitment levels. YOY striped bass, bay anchovy (Anchoa mitchilli), Atlantic silverside (Menidia menidia), and Alosa spp. dominated YOY bluefish diets. There were ontogenetic and interannual differences in YOY bluefish diets. Bluefish avoided striped bass at low densities but selected for them at high densities, suggesting a density-dependent feeding response. In the early summer of 1993, bluefish predation accounted for 50-100% of the total estimated loss of YOY striped bass. A significant negative correlation exists between the relative magnitude of striped bass recruitment and bluefish abundance. We conclude that YOY bluefish are important predators of estuarine fish and can have a substantial impact on their recruitment.
Channel type and salmonid spawning distribution and abundance
Authors: Montgomery David R , Beamer Eric M , Pess George R , Quinn Thomas P
Published: April 2011

Consideration of fundamental channel processes, together with map-based and field investigations, indicates that stream channel type influences salmonid spawning distributions across entire channel networks and salmonid abundance within channel reaches. Our analysis suggests that salmonid spawning patterns in mountain drainage basins of the Pacific Northwest are adapted to, among other things, the timing and depth of channel bed mobility. We hypothesize that because the bed of pool-riffle and plane-bed reaches scours to a variable fraction of the thickness of alluvium, survival to emergence is favored by either burying eggs below the annual scour depth or avoiding egg burial during times of likely bed mobility. Conversely, annual mobility of all available spawning gravel in steeper step-pool and cascade channels favors either adaptations that avoid egg burial during times of likely bed mobility or selection of protected microhabitats. Consistent with these expectations, we find that salmonid spawning distributions track channel slope distributions in several west-slope Pacific Northwest watersheds, implying that spatial differences in channel processes influence community structure in these rainfall-dominated drainage basins. More detailed field surveys confirm that different channel types host differential use by spawning salmonids and reveal finer-scale influences of pool spacing on salmonid abundance.
Assessing the strength of top-down influences on plankton abundance in unmanipulated lakes
Authors: Currie David J , Dilworth-Christie Pam , Chapleau François
Published: April 2011

The trophic structure of aquatic ecosystems can potentially be controlled by two sets of factors: resource availability and predation. The importance of nutrients was demonstrated by two observations: first, that plankton abundance among lakes is strongly correlated with resource levels, and second, that experimental manipulations of resources lead to changes in plankton abundance. In contrast, while experimental manipulations have shown that predators can affect prey abundance, it is less clear whether variation in plankton abundance among lakes is related to variation in predators. To test this, we sampled 29 lakes in Quebec and Ontario. We found strong relationships between plankton biomass and resource levels. Effects of predation were evident between zooplankton and phytoplankton. However, neither chlorophyll nor zooplankton biomass was related to piscivorous fish presence, after controlling for phosphorus. Other published studies that have reported correlations between plankton abundance and characteristics of the fish community failed to control for trophic status. Thus, there appears to be no published correlative evidence that variance in plankton abundance among lakes is related to variation in fish assemblages, even though the link is mechanistically plausible.
Estimation and effects of tag-misread rates in capture-recapture studies
Authors: Schwarz Carl James , Stobo Wayne T
Published: April 2011

Virtually all capture-recapture studies assume that tags are read properly when an animal is captured. However, the animals in resighting studies are often not handled, tags are read at a distance, and misreads can occur. In this paper, we develop a simple model to account for misreads, assess the impact of misreads upon estimates of survival and catchability, and analyze a set of data from resightings of previously branded seals. In general, unless survival, capture, and misread rates are relatively high, most studies have poor power to detect misreads and estimates of survival are not severely biased. Estimates of capture rates will be biased downwards and will tend to estimate the product of the original capture rate and the complement of the misread rate.
Mechanisms underlying amphipod responses to zebra mussel (Dreissena polymorpha) invasion and implications for fish-amphipod interactions
Authors: González María J , Downing Amy
Published: April 2011

We examined mechanisms underlying increased amphipod abundance after zebra mussels (Dreissena polymorpha) invaded Lake Erie. We conducted field substrate preference experiments to test the hypotheses that amphipods prefer (i) high-complexity substrates over low-complexity substrates and (or) (ii) substrates with high mussel feces and pseudofeces deposition over substrates with low deposition. We measured amphipod preference for bare rock, live mussels, and dead mussels in spring (May 1996) and summer (July and August 1995, June and August 1996). Habitat complexity affected amphipod habitat preference, and preference varied seasonally. In spring, amphipod density was highest on dead mussels, but the response was highly variable. In midsummer (June and July), amphipods showed no substrate preference. In late summer (August), amphipods consistently preferred high-complexity mussel substrates. Amphipods never preferred low-complexity substrates. We also evaluated effects of zebra mussel presence on fish-amphipod interactions in laboratory feeding trials. We tested the hypothesis that mussel presence decreases bluegill (Lepomis macrochirus) and yellow perch (Perca flavescens) predation on amphipods. Predation by bluegill but not yellow perch was significantly lowered by mussel presence. Our results support the hypothesis that the increase in amphipods upon zebra mussel invasion is due to increased habitat complexity, possibly by reducing predation risk. However, the effects of zebra mussel on fish-amphipod interactions depended on predator species.
Contrasting patterns of productivity and survival rates for stream-type chinook salmon (Oncorhynchus tshawytscha) populations of the Snake and Columbia rivers
Authors: Schaller Howard A , Petrosky Charles E , Langness Olaf P
Published: April 2011

The effects of increasing hydropower development and operation appear extremely important in the decline and near extripation of stream-type chinook salmon (Oncorhynchus tshawytscha) stocks of the upper Columbia and Snake rivers. We evaluated temporal and spatial patterns of productivity and survival rates (for index stocks from the Snake, upper Columbia, and lower Columbia regions) to determine the cause of dramatic declines of the upriver stocks. This evaluation tested hypotheses about nonstationarity (changes over time in average productivity) in the Ricker recruitment function caused by changes in the physical environment. Individual stocks showed recent declines in indicators of productivity and survival rate; however, the comparisons indicate that upriver stocks showed greater declines coincident with the development and operation of the hydropower system. Evidence from the aggregate run indicates that declines over the last 50 years were quite abrupt and corresponded to construction and completion of the hydropower system.
Effects of migration distance on whole-body and tissue-specific energy use in American shad (Alosa sapidissima)
Authors: Leonard Jill BK , McCormick Stephen D
Published: April 2011

We examined total and tissue-specific energy content of upstream-migrating American shad (Alosa sapidissima) in the Connecticut River. Total energy depletion over the course of the 228-km migration ranged from 35 to 60%. The approximate contributions of different tissues to energy use during migration were white muscle 57%, subdermal fat 27%, red muscle 8%, viscera 6%, and liver 2%. American shad preferentially use energy stores in the skin and its subdermal fat layer (depleted by 63%) while sparing red muscle protein. Both lipid and protein were used as energy sources throughout migration, although lipids were depleted to a greater extent (e.g., white muscle lipid decreased 48% and protein 30%). Large fish expended 2-21% more energy during migration than small fish. Migrating to upriver sites (198-228 km) is 50-100% more energetically expensive than to lower river sections for females. This suggests that upriver range expansion may be limited by females in that they may have reached a threshold level of energy expenditure in this upriver area. American shad may possess physiological mechanisms for tissue-specific energy use allowing maintenance of critical tissues necessary for postspawning survival.
Effect of life history strategy, environmental variability, and overexploitation on the genetic diversity of pelagic fish populations
Authors: Gaggiotti Oscar E , Vetter Russel D
Published: April 2011

We study the effect of recruitment failures and variance in reproductive success on effective population size (Ne) in populations with type III survivorship curves. Special emphasis is put on determining the causes for the large differences in the genetic variability between populations of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). The results indicate that moderate differences in life history between ecologically related species can lead to substantial differences in Ne. The effect of fluctuations in vital rate parameters induced by environmental changes on Nedepends on the life history of each species. The ratio of Neto census size is directly proportional to the total reproductive value of a population, but the sensitivity of this ratio to environmental fluctuations is inversely proportional to the generation overlap. The larger the generation overlap, the smaller the impact of environmental fluctuations on the level of genetic variability maintained by a population. The large difference in heterozygosity between Pacific sardine and northern anchovy populations is likely due to both life history differences between the two species and a recent arrival (founder event) of the Pacific sardine population to the California Current System.
Effects of oil sands related aquatic reclamation on yellow perch (Perca flavescens). I. Water quality characteristics and yellow perch physiological and population responses
Authors: van den Heuvel M R , Power M , MacKinnon M D , Meer T Van , Dobson E P , Dixon D G
Published: April 2011

In order to test the viability of oil sands aquatic reclamation techniques, yellow perch (Perca flavescens) were stocked into three experimental ponds. Pond substrates consisted of either oil sands fine tailings or clay and lean oil sands deposited by the mining operations. Yellow perch were stocked immediately postspawning and subsamples were sacrificed at 5 and 11 months to measure indicators of energy storage and utilization. These indicators included survival, age, spawning periodicity, condition factor, gonad size, fecundity, and liver size. Indicators generally showed patterns consistent with improved energy storage and utilization in the experimental pond yellow perch as compared with yellow perch in the lake from which the stocked fish originated. This was evidenced by increased gonad size, condition factor, and liver size and the disappearance of spawning periodicity. The patterns observed in experimental ponds suggest improved resource availability and (or) reduced intra- and interspecific competition. Yellow perch physiological indicators were also compared with those measured at several remote natural lakes in the area. Fisheries parameters measured in yellow perch from the experimental ponds generally fell within the range of those found in natural lakes.