bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and mortality rates of the zebra mussel,Dreissena polymorpha, in the Lower Mississippi River
Authors: Allen Yvonne C , Thompson Bruce A , Ramcharan Charles W
Published: April 2011

We investigated seasonal growth and mortality of a population of zebra mussels, Dreissena polymorpha, near the extreme southern limit of their current North American distribution. Dreissena in the Lower Mississippi River experience seasonal regimes of temperature and suspended sediment that are distinctly different from those found in northern lentic environments. Shell growth and mortality were determined biweekly using marked animals in caged environments. Tissue condition was also estimated biweekly using mussels from caged and wild environments. Our results demonstrate that, although annual growth is comparable with that reported for more temperate environments, the seasonal pattern of increase is different. Shell growth and tissue condition were highest during the early spring. Tissue condition declined and shell growth ceased during the summer, when temperatures remained at 29-30°C for 3 months. This midsummer depression was accompanied by increased mortality, particularly for mussels greater than 15 mm. Condition improved for all sizes in fall and winter. These patterns of growth and mortality appear to be primarily driven by fluctuations in seasonal temperature and spawning condition with some influence of suspended sediment. Our observations indicate that periodic summer mortality events will occur, and the extent of this mortality will depend primarily on temperature, population size structure, and spring tissue condition.
A new approach to the analysis of stock-recruitment relationships: "model-free estimation" using fuzzy logic
Authors: Mackinson Steven , Vasconcellos Marcelo , Newlands Nathaniel
Published: April 2011

In response to the need for overt recognition of uncertainty in management of natural resources, we present a new, innovative, causal approach for analysis of stock-recruitment relationships and prediction of recruitment. Applying principles and techniques developed from the theory of fuzzy sets, we demonstrate how heuristic reasoning can be used to define stock-recruitment relationships, explicitly characterise vagueness and uncertainty, and provide a functional relationship that combines stock size and past recruitment to predict future recruitment. The approach is termed model-free estimation or approximation. Tested on eight stock-recruitment data sets, there was no significant difference between recruitment predicted by the fuzzy approximation method and the Ricker or Beverton-Holt recruitment functions. We account for effects of nonstationarity by incorporating rules that relate past recruitment to future recruitment in the fuzzy stock-recruitment system. A weighting factor, w, represents the degree of belief in the importance of past recruitment and stock size in predicting future recruitment. The approach is robust with respect to the number of fuzzy sets used to define data clusters, can be tailored to individual circumstances, and thrives in data-poor situations where analytical methods may be inappropriate. It is a simple and broadly applicable solution with important implications for fish stock assessment and fisheries management in general.
Effects of oceanographic circulation on the gene flow, genetic structure, and phylogeography of the rosethorn rockfish (Sebastes helvomaculatus)
Authors: Rocha-Olivares Axayácatl , Vetter Russell D
Published: April 2011

The genetic structure and phylogeography of 88 rosethorn rockfish (Sebastes helvomaculatus) from five localities (California, Oregon, British Columbia, and two in the Gulf of Alaska) were analyzed using DNA sequences from the mitochondrial control region. High levels of genetic diversity (h > 85%) and significant population genetic structure (FST= 0.13, P < 0.001; AMOVA ΦST= 0.15, P << 0.001) were found. A significant genetic break was detected (ΦCT= 0.22, P << 0.001) coinciding with the transition zone between the Oregonian and Aleutian zoogeographic provinces and consistent with retention and dispersal mechanisms associated with the oceanographic circulation of the region. A correlation between geographic distance and population genetic distance supported the hypothesis of gene flow dominated by pelagic-phase dispersal. Oregonian province populations had higher haplotype diversity, with >70% of the individuals representing a recent lineage absent in the Aleutian province. This suggests a limited northward dispersal across the zoogeographic boundary. The phylogeographic stucture may be due to a founder effect in the Aleutian province or an ocean circulation driven pseudo-vicariance. These results demonstrate that organisms with protracted pelagic-phase stages and high dispersal capability can exhibit population genetic structure that reflects their historical demography and present dispersal patterns.
Evaluating biological significance of chemical exposure to fish using a bioenergetics-based stressor-response model
Authors: Beyers Daniel W , Rice James A , Clements William H
Published: April 2011

We demonstrate how contaminant exposure-response relationships can be integrated with a bioenergetics model to estimate the biological significance of sublethal exposure under fluctuating environmental conditions. The integrated bioenergetics-based stressor-response model (SRM) was evaluated by comparing observed and predicted growth of largemouth bass (Micropterus salmoides) exposed to several dieldrin concentrations and by conducting sensitivity analyses. Predictions of the SRM suggest that energetic effects of exposure of largemouth bass to ambient concentrations of dieldrin in lakes at the Rocky Mountain Arsenal National Wildlife Refuge are not biologically significant because the amount of energy lost by resident fish is small compared with variation in food consumption. Furthermore, influence of dieldrin exposure is small compared with the effects of a natural stressor like water temperature. The SRM provides a general framework for integrating laboratory-derived exposure-response relationships with ecological processes to determine the biological significance of multiple stressors in a natural environment. Comparisons of relative effects of anthropogenic and natural stressors can be used to assess potential costs and benefits of alternative ecosystem management strategies.
An alternative classification method for northern Wisconsin lakes
Authors: Emmons Edward E , Jennings Martin J , Edwards Clayton
Published: April 2011

Wisconsin has nearly 15 000 lakes with great variation in limnology, morphometry, and origin. Classification of lakes into groups is a continuing goal. This study examines two alternative approaches to lake classification, one common and the other somewhat novel. Both approaches used lake morphometry and limnological variables and were compared for ability to form groups and assign lakes to groups with a high probability of correct classification. The first approach used nonhierarchical cluster analysis to form lake groups and discriminant analysis to put lakes into these groups. The second approach formed lake groups by iterative dichotomous splitting of the sampling space into smaller and smaller subspaces. Each binary split was done using nonhierarchical cluster analyses on a subset of the original variables. This iterative splitting resulted in a hierarchical classification tree with reduced dimensionality in comparison with the original data set. At each branch, multiple logistic regression was used to place lakes into nodes of the tree. Validation of both approaches was performed with a resubstitution analysis of the model building data set as well as a separate validation data set. The decision tree method yielded significantly lower rates of misclassification and was more easily interpreted than the discriminant analysis approach.
Modeling the spatial dynamics of the U.S. purse-seine fleet operating in the western Pacific tuna fishery
Authors: Campbell H F , Hand A J
Published: April 2011

Two qualitative choice models of the location decisions of U.S. purse-seine vessels operating in a total of sixty-five 5° grids in the western Pacific tuna fishery are developed and compared. A nested logit model in which decisions are first made about where to fish in the east-west plane, followed by a choice of grid in the north-south plane, performs better than a nonnested model in which all grids are considered simultaneously. The nested model can be used for the allocation of purse-seine fishery effort in a spatially disaggregated bioeconomic model of the regional tuna fishery.
Chemical alarm signals and complex hatchery rearing habitats affect antipredator behavior and survival of chinook salmon (Oncorhynchus tshawytscha) juveniles
Authors: Berejikian Barry A , Smith R Jan F. , Tezak E Paul , Schroder Steven L , Knudsen Curtis M
Published: April 2011

The present study examined the effects of chemical antipredator conditioning on antipredator behavior and the relative effects of antipredator conditioning and seminatural rearing environments on postrelease survival of chinook salmon (Onocrhynchus tshawytscha). Hatchery-reared juvenile chinook salmon were exposed to extracts from conspecific tissue or to comparable stimuli from green swordtail (Xiphophorus helleri). These "injured fish" stimuli were paired with water that contained the odour of predatory cutthroat trout (Oncorhynchus clarki). Chinook salmon receiving conspecific stimuli showed higher levels of several antipredator behaviors compared with chinook salmon receiving green swordtail extracts. When the two groups of chinook salmon were tested 2 days later with cutthroat trout stimulus alone, the chinook salmon that had originally received injured conspecific stimuli paired with cutthroat trout odour spent more time motionless than chinook salmon that had received green swordtail stimuli and cutthroat trout odour. In another experiment, complex rearing treatments had a negative effect on instream survival (contrary to previous studies) that was compensated for by the application of the chinook salmon extract and cutthroat trout odour prior to release. Chinook salmon, like rainbow trout (Oncorhynchus mykiss), show antipredator behavior in response to chemical stimuli from injured conspecifics and learn predator recognition when such stimuli are paired with predator odour, improving survival in the wild.
Results of pop-up satellite tagging of spawning size class fish in the Gulf of Maine: do North Atlantic bluefin tuna spawn in the mid-Atlantic?
Authors: Lutcavage Molly E , Brill Richard W , Skomal Gregory B , Chase Bradford C , Howey Paul W
Published: April 2011

Twenty giant bluefin tuna were captured in September and October 1997 and tagged and released with pop-up satellite tags programmed to jettison from March through July, 1998. Seventeen tags successfully released from the fish (12 during the known May-July spawning period), all of which were located north of 33°N latitude, in a region of the mid-Atlantic bounded by Bermuda and the Azores. Our results argue for reconsideration of current assumptions about North Atlantic bluefin tuna migration patterns, mixing rates, spawning areas, and stock structure and highlight the need for additional studies.
von Bertalanffy growth model in a random environment
Authors: Prajneshu  , Venugopalan R
Published: April 2011

The well-known von Bertalanffy growth model for describing age-length relationship is formulated in a randomly fluctuating environment. The fluctuations in the system are assumed to be described by a Gaussian white noise stochastic process. The resulting model, in terms of a stochastic differential equation, is solved analytically. It is shown that the probability density function of length of a fish is a Gaussian stochastic process. Finally, as an illustration, the methodology is applied to a set of pearl oyster (Pinctada fucata (Gould)) data.
Comparison of activity rates of 1+ yellow perch (Perca flavescens) from populations of contrasting growth rates using underwater video observations
Authors: Aubin-Horth N , Gingras J , Boisclair D
Published: April 2011

We compared the stereocinematographic (SCG) method to estimate activity rates of yellow perch (Perca flavescens) with the more traditional bioenergetic approach. We also compared activity rates of perch from two populations with contrasting growth rates to test the hypothesis that fish with lower growth rates are characterized by higher activity rates. We attempted to corroborate the SCG method by comparing values of energetic costs obtained with observations of fish movements with estimates obtained using the difference between field-derived consumption and growth rates (bioenergetic method). Independent estimates of consumption and activity rates were obtained for Lakes Hertel (average growth = 172 J·day-1) and Memphremagog (average growth = 595 J·day-1). Daily consumption rates averaged 720 J·day-1in Lake Hertel and 1457 J·day-1in Lake Memphremagog. SCG and bioenergetic methods provided similar activity estimates for Lake Hertel (<2.5% difference) and diverged by 0.4-82% for Lake Memphremagog depending on initial values of fish weight or consumption inputted in the bioenergetic equation. Regardless of the method employed, activity rates of fish from Lake Hertel were proportionally higher (24% of consumption rates) than those from Lake Memphremagog (on average 13% of consumption rates). Our work supported the suggestion that populations with slower growth rates may be associated with proportionally higher activity rates.
An assessment of light-based geoposition estimates from archival tags
Authors: Welch David W , Eveson J Paige
Published: April 2011

Archival tags record information about the environment of tagged animals over long periods of time (months to years). In theory, position can be estimated from a record of changes in light intensity with time. We describe two approaches to estimating geoposition based on estimating either the time of maximal rate of change in light intensity or the time that a reference light intensity is reached. Digital signal processing is investigated as a method of increasing the signal-to-noise ratio of the light record. Our test data suggest that the daily position of a tagged animal can potentially be estimated within an average error of about 140 km (SD's of 0.9° of longitude and 1.2° of latitude), approaching the resolution of the best eddy-resolving physical oceanographic models of ocean currents. The source of the remaining large-scale errors in geoposition appears to be extrinsic to the tags and may be related to large-scale weather systems. The accuracy of current archival tags is sufficient to permit an assessment of the open-ocean migration pathways of animals such as maturing salmon and may be sufficient for use in some parts of the continental shelf as well.
Use of simulation–extrapolation estimation in catch–effort analyses
Authors: Gould W R , Stefanski L A , Pollock K H
Published: April 2011

All catch-effort estimation methods implicitly assume catch and effort are known quantities, whereas in many cases, they have been estimated and are subject to error. We evaluate the application of a simulation-based estimation procedure for measurement error models (J.R. Cook and L.A. Stefanski. 1994. J. Am. Stat. Assoc. 89: 1314-1328) in catch-effort studies. The technique involves a simulation component and an extrapolation step, hence the name SIMEX estimation. We describe SIMEX estimation in general terms and illustrate its use with applications to real and simulated catch and effort data. Correcting for measurement error with SIMEX estimation resulted in population size and catchability coefficient estimates that were substantially less than naive estimates, which ignored measurement errors in some cases. In a simulation of the procedure, we compared estimators from SIMEX with "naive" estimators that ignore measurement errors in catch and effort to determine the ability of SIMEX to produce bias-corrected estimates. The SIMEX estimators were less biased than the naive estimators but in some cases were also more variable. Despite the bias reduction, the SIMEX estimator had a larger mean squared error than the naive estimator for one of two artificial populations studied. However, our results suggest the SIMEX estimator may outperform the naive estimator in terms of bias and precision for larger populations.
Assessing the toxicity of lead in sediments to Hyalella azteca: the significance of bioaccumulation and dissolved metal
Authors: Borgmann Uwe , Norwood Warren P
Published: April 2011

The relationship between bioaccumulation and toxicity of Pb to Hyalella was the same for animals exposed to Pb in water alone and for those exposed to Pb-spiked sediments, provided that the animals were gut cleared before Pb analysis. The same critical body concentration (about 126 nmol·g dry mass-1) can be used to predict Pb toxicity in both water-only and sediment exposures. Furthermore, Pb bioavailability in Pb-spiked sediments was due primarily to dissolved metal: animals caged above the sediments accumulated the same amount of Pb and had the same mortality as animals exposed directly to sediment. Increasing the water to sediment ratio from 4:1 to 67:1 resulted in a lower dissolved organic C and lower total dissolved Pb concentration in the water but no change in bioavailable Pb (i.e., bioavailable Pb was not proportional to total dissolved Pb). The overlying water concentration may be a useful indicator of bioavailable Pb in sediment tests, provided a large water to sediment ratio is used to reduce the effect of sediment on overlying water quality (i.e., Pb-complexing capacity). Although less reliable than body concentration measurements, this could provide a useful screening tool for possible Pb-induced toxicity because it can be measured without test animals present.
Density-dependent habitat selection by juvenile Atlantic salmon (Salmo salar) in experimental riverine habitats
Authors: Bult Tammo P , Riley Stephen C , Haedrich Richard L , Gibson R John , Heggenes Jan
Published: April 2011

We investigated habitat use of Atlantic salmon (Salmo salar) parr in experimental riverine enclosures made up of pool, riffle, and run habitats over a range of densities (0.1-1.25 fish·m-2) to test the implicit assumption in habitat modelling that habitat selection does not change with population density. Results indicated that habitat use changed with population density, with relatively more parr in pools and fewer in runs at higher population densities. Temperature influenced parr distribution, with relatively more parr in runs and fewer in riffles and pools at higher temperatures. Parr distribution was primarily affected by hydromorphological differences among pool, riffle, and run habitats. Effects of population density and temperature on use of pool, riffle, and run habitats were often as large as effects of hydromorphological differences among pool, riffle, and run habitats on fish distributions over the range of temperatures and densities observed. Results varied considerably, despite controlled experimental conditions. We concluded that habitat selection by juvenile Atlantic salmon parr may be density dependent and potentially quite variable.
Impacts of atypical data on Bayesian inference and robust Bayesian approach in fisheries
Authors: Chen Y , Fournier D
Published: April 2011

Bayesian inference is increasingly used in fisheries. In formulating likelihood functions in Bayesian inference, data have been analyzed as if they are normally, identically, and independently distributed. It has come to be believed that the first two of the assumptions are frequently inappropriate in fisheries studies. In fact, data distributions are likely to be leptokurtic and (or) contaminated by occasional bad values giving rise to outliers in many fisheries studies. Despite the likelihood of having outliers in fisheries studies, the impacts of outliers on Bayesian inference have received little attention. In this study, using a simple growth model as an example, we evaluate the impacts of outliers on the derivation of posterior distributions in Bayesian analyses. Posterior distributions derived from the Bayesian method commonly used in fisheries are found to be sensitive to outliers. The distributions are severely biased in the presence of atypical values. The sensitivity of normality-based Bayesian analyses on atypical data may result from small "tails" of normal distribution so that the probability of occurrence of an event drops off quickly as one moves away from the mean a distance of a few standard deviations. A robust Bayesian method can be derived by including a mixture distribution that increases the size of tail so that the probability of occurrence of an event does not drop off too quickly as one moves away from the mean. The posterior distributions derived from this proposed approach are found to be robust to atypical data in this study. The proposed approach offers a potentially useful addition to Bayesian methods used in fisheries.
Cyclic dynamics of a yellow perch (Perca flavescens) population in an oligotrophic lake: evidence for the role of intraspecific interactions
Authors: Sanderson Beth L , Hrabik Thomas R , Magnuson John J , Post David M
Published: April 2011

Understanding the extent to which repeated oscillations in fish populations are driven by external factors or internal processes within the population is an important challenge. We document cyclic dynamics in a population of yellow perch (Perca flavescens) in oligotrophic Crystal Lake. Since 1981, we have observed three cases of cohort dominance in which two age-classes dominated the population for roughly 5 years. Young-of-the-year (YOY) perch were caught in 1981-1982, 1986-1987, and 1990-1991, whereas few to no YOY were caught during the midyears. The presence of YOY was negatively related to juvenile perch abundance and positively related to adult perch abundance. Mechanisms that may be responsible for these patterns include cannibalism of YOY by either juveniles or adults, potential for reproduction by adults, and competition between YOY and juveniles. YOY were abundant primarily in years when reproductively mature fish were in the lake, suggesting that the repeated oscillations are driven predominantly by pulses of abundant, reproductive, adult perch. As these young perch grow to juveniles, they exclude the possibility of survival by successive cohorts through cannibalistic and competitive interactions. This exclusion occurs until they themselves become reproductively mature and the cycle then repeats. Ultimately, long-term patterns in Crystal Lake suggest that cyclic dynamics are generated by intraspecific interactions.
Effect of velocity on the filter feeding of dreissenid mussels (Dreissena polymorphaandDreissena bugensis): implications for trophic dynamics
Authors: Ackerman Josef Daniel
Published: April 2011

Fluid dynamic forces were found to significantly affect the ability of freshwater dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) to clear plankton. Tests conducted in a flow chamber at <1 cm·s-1were consistent with published clearance rates from standard tests involving unstirred containers (i.e., 60-70 mL· mussel-1·h-1for 11-mm-long mussels). Increasing ambient velocity up to ~10 cm·s-1led to clearance rates at least twice those of standard testing methods. Higher velocities (~20 cm·s-1) were inhibitory and resulted in reduced clearance rates. There were no detectable differences in the clearance rates of D. polymorpha and D. bugensis of equal size tested at ~10 cm·s-1, but large mussels had greater clearance rates than small ones. These results were found to be consistent with observations from marine bivalves and indicate that fluid dynamic issues are of importance in freshwater ecosystems, especially those that are shallow and (or) flowing. The trophic dynamics of these ecosystems will be better understood when the effects of fluid dynamics on the organism's ability to filter feed and the local delivery of seston through turbulent mixing are considered.
Temperature-related loss of smolt characteristics in Atlantic salmon (Salmo salar) in the wild
Authors: McCormick Stephen D , Cunjak Richard A , Dempson Brian , O'Dea Michael F , Carey Judith B
Published: April 2011

Atlantic salmon (Salmo salar) that had previously been released as fry in tributaries of the Connecticut River were captured from 1993 to 1997 during their normal spring smolt migration 198 km from the mouth of the river. Smolts had peak levels of gill Na+,K+-ATPase activity and salinity tolerance early in migration (early May), indicating physiological readiness to enter seawater. Significant decreases in gill Na+,K+-ATPase activity (29-66%) and salinity tolerance were seen in smolts at the end of the migratory period (late May and early June). Reduced gill Na+,K+-ATPase activity occurred earlier in warm years and was directly related to the degree-days during migration (r2 = 0.75). Reduced gill Na+,K+-ATPase activity was found at the end of migration in warmer, southern rivers (Connecticut River and Penobscot River, Maine) but not in northern rivers (Catamaran Brook, New Brunswick, and Conne River, Newfoundland). Both hatchery- and stream-reared fish held in the laboratory exhibited a more rapid loss of physiological smolt characteristics when held at higher temperature. The results indicate that late migrants in southern rivers lose physiological smolt characteristics due to high temperatures during spring migration. Delays in migration, such as those that occur at dams, may have negative impacts on smolt survival in warmer rivers.
A simple and precise method for measuring ammonium in marine and freshwater ecosystems
Authors: Holmes Robert M , Aminot Alain , Kérouel Roger , Hooker Bethanie A , Peterson Bruce J
Published: April 2011

The accurate measurement of ammonium concentrations is fundamental to understanding nitrogen biogeochemistry in aquatic ecosystems. Unfortunately, the commonly used indophenol blue method often yields inconsistent results, particularly when ammonium concentrations are low. Here, we present a fluorometric method that gives precise measurements of ammonium over a wide range of concentrations and salinities emphasizing submicromolar levels. The procedure not only solves analytical problems but also substantially simplifies sample collection and preservation. It uses a single working reagent (consisting of orthophthaldialdehyde, sodium sulfite, and sodium borate) that is stable for months when stored in the dark. The working reagent and sample can be mixed immediately after sample collection and the reaction proceeds to completion within 3 h at room temperature. Matrix effects and background fluorescence can be corrected without introducing substantial error. This simple method produces highly reproducible results even at very low ammonium concentrations.
Biogeochemical influences on the carbon isotope signatures of Lake Ontario biota
Authors: Leggett M F , Servos M R , Hesslein R , Johannsson O , Millard E S , Dixon D G
Published: April 2011

Particulate organic matter (POM), zooplankton, and benthic invertebrates were sampled seasonally at a midlake and east basin site in Lake Ontario. The δ13C values of POM samples were compared with measurements of chlorophyll a concentrations, areal rates of primary productivity, concentrations of dissolved free CO2 (CO2(aq)), and the δ13C of zooplankton and benthic invertebrates. The δ13C of POM was significantly correlated with the concentration of CO2(aq) at the east basin site. No correlation was found between chlorophyll a concentrations, areal rates of primary productivity, and the δ13C of POM. The δ13C of zooplankton was not always similar to the δ13C of the POM fraction collected, indicative of the complexity of food web interactions within the lower trophic levels. The δ13C of benthic invertebrates feeding on the sediment surface was similar to that of POM produced prior to stratification, indicating the importance of the spring bloom as a food source for benthic primary consumers.
Predator-induced life history shifts inDaphnia: a synthesis of studies using meta-analysis
Authors: Riessen Howard P
Published: April 2011

Daphnia respond to kairomones from a variety of predators by altering their morphology, behavior, and life history. I use the statistical technique of meta-analysis to quantitatively evaluate the results of 27 independent studies that examine various life history responses of Daphnia to kairomones released from three common predators: Chaoborus, Notonecta, and planktivorous fish. Daphnia exhibit a fundamentally different set of life history responses to Chaoborus (delayed reproduction, decreased size of first clutch, slight tendency toward increased size at maturity) than they do to Notonecta and fish (earlier reproduction, increased clutch size, smaller size at maturity). These opposite responses appear to be related to different patterns of prey selection exhibited by the predators. Food level does not affect the life history responses of Daphnia to Chaoborus kairomones; however, the length of exposure to these kairomones does influence the degree of delay in reproduction. In addition, changes in size at maturity in response to predator kairomones are positively correlated with changes in both age at maturity and size of the first clutch. While the life history shifts exhibited by Daphnia in the presence of Notonecta and fish appear to be clearly adaptive, the fitness consequences of Chaoborus-induced responses are unclear.
Estimating the probability of exceeding elevated pH values critical to fish populations in a hypereutrophic lake
Authors: Kann Jacob , Smith Val H
Published: April 2011

Current eutrophication models typically are used to predict seasonal mean conditions. However, the risk of summer fish kills in hypereutrophic lakes is likely to be more closely dependent on periodic extreme events, such as potentially lethal peaks in pH driven by algal photosynthesis. In hypereutrophic Upper Klamath and Agency lakes, Oregon, peak summertime pH values frequently exceed critical levels that can reduce fish growth and survival (pH > 9.50, a likely sublethal tolerance limit for two resident endangered fish species). We developed two empirical models, one parametric and one nonparametric, that predict the likelihood of exceeding user-defined critical values of pH from concentrations of chlorophyll a in these lakes. Separate models were derived to incorporate seasonal dynamics and differences between the two lakes, and the behavior of these models was tested under four different critical pH scenarios. Both parametric and nonparametric models performed similarly, suggesting that management efforts to reduce chlorophyll a in these lakes from 200 to 100 µg·L-1 should decrease the probability of exceeding pH 9.5 by 45%. We suggest that this general approach potentially can be applied to the management of fish populations in other hypereutrophic lakes as well.
A multivariate approach for defining fishing tactics from commercial catch and effort data
Authors: Pelletier Dominique , Ferraris Jocelyne
Published: April 2011

Fishing tactics correspond to fishing practices at the scale of the fishing operation. In the case of mixed fisheries, they are defined as a combination of target species, gear, and fishing location, at a given time of the year. This paper proposes an approach to determine fishing tactics from the analysis of commercial catch and effort data. The approach is based on typologies of fishing operations involving multivariate descriptive methods like factorial analyses and classification techniques. The obtained types of fishing operations are considered as fishing tactics. The approach is applied to two contrasting examples, a small-scale Senegalese fishery and a Celtic Sea fishery that operates at a larger scale. Catch per species and fishing effort are computed per tactic. Results emphasize the importance of fishing location and seasonal effects for characterizing fishing tactics.
Effect of time of day, time of year, and life history strategy on time budgeting in juvenile Atlantic salmon, Salmo salar
Authors: Valdimarsson Sveinn K , Metcalfe Neil B
Published: April 2011

Traditionally, behavioural studies on juvenile Atlantic salmon, Salmo salar, have been conducted during the day in summer. It is known that Atlantic salmon become nocturnal in winter, but very little is known about their behaviour at that time. Therefore, observations in a seminatural stream were carried out during the day and night, from February to June, comparing diel and seasonal differences in behaviour between fish adopting alternative life history strategies. The results showed a general trend for more activity in spring than in winter, and the fish were found to be foraging at surprisingly low light levels. There were differences in relative feeding rate between the life history strategies; the early migrant fish foraged mostly during the day whereas the delayed migrant fish did more foraging at night. There is some evidence that the early migrant fish made fewer feeding attempts over the winter, which is surprising, since they grow faster over that period. This suggests differences in foraging efficiency, which could contribute to the separation into these two life history strategies.
Recovery of fish populations in Lake 223 from experimental acidification
Authors: Mills K H , Chalanchuk S M , Allan D J
Published: April 2011

The fish populations of Lake 223, a lake previously acidified to pH 5.1, were monitored during 13 years of gradual pH recovery to preacidification pH 6.7. During acidification, recruitment ceased for all fish species in this lake and two were extirpated. During pH recovery, successful recruitment resumed for all fish species that remained in the lake. One of the extirpated species, fathead minnow (Pimephales promelas), successfully colonized the lake. Lake trout (Salvelinus namaycush) abundance decreased during acidification and remained low during pH recovery due to very low recruitment. Growth curves, condition factor, and annual survival of lake trout decreased during acidification and quickly increased to preacidification values during pH recovery. During the early years of pH recovery, white sucker (Catostomus commersoni) abundance increased to almost 10 times the number at the start of the experiment but decreased during the final years due to decreased annual survival and recruitment. Pearl dace (Margariscus margarita) became abundant during acidification and their abundance decreased during pH recovery as fathead minnow abundance increased. Other fish species that were caught infrequently prior to acidification, brook stickleback (Culaea inconstans), lake chub (Couesius plumbeus), and finescale dace (Phoxinus neogaeus), were caught frequently during pH recovery.
Using nonlinear functional relationship regression to fit fisheries models
Authors: Kimura Daniel K
Published: April 2011

Functional relationship regression refers to that class of statistical model where a functional relationship is assumed to exist between two arithmetic variables, but the two arithmetic variables can only be viewed with measurement error and (or) natural variability. The goal is to estimate the underlying functional relationship when observing only the variables containing error or natural variability. While statistical details need to be worked out, some general approaches to this class of problem can be recommended. First of all, nonlinear least squares can provide maximum likelihood estimates when the error variance ratio, λ;, is assumed known. Furthermore, the usual estimates of standard errors from nonlinear least squares, while theoretically flawed for this class of model, appear to provide usable estimates for many practical problems. Next, a K-sample F test, for testing the equality of nonlinear functional relationship regression curves, is proposed. Finally, computer memory-saving algorithms are suggested for situations where sample sizes are large. Methods proposed here are applied to three types of functional curves commonly estimated in fisheries biology: a stock-recruitment curve, allometry, and the von Bertalanffy growth curve.
Maximum reproductive rate of fish at low population sizes
Authors: Myers Ransom A , Bowen Keith G , Barrowman Nicholas J
Published: April 2011

We examine a database of over 700 spawner-recruitment series to search for parameters that are constant, or nearly so, at the level of a species or above. We find that the number of spawners produced per spawner each year at low populations, i.e., the maximum annual reproductive rate, is relatively constant within species and that there is relatively little variation among species. This quantity can be interpreted as a standardized slope at the origin of a spawner-recruitment function. We employ variance components models that assume that the log of the standardized slope at the origin is a normal random variable. This approach allows improved estimates of spawner-recruitment parameters, estimation of empirical prior distributions for Bayesian analysis, estimation of the biological limits of fishing, calculation of the maximum sustainable yield, and impact assessment of dams and pollution.
Bacterial carbon production in Lake Erie is influenced by viruses and solar radiation
Authors: Wilhelm Steven W , Smith Ralph EH
Published: April 2011

Bacterial production is an integral recycling mechanism that facilitates carbon flow through aquatic food webs. Factors influencing bacterial activity therefore impact carbon flow. Although ecologists consider grazing and dissolved organic carbon flux to be the major regulators of bacterial activity, we explored two other important pressures. Virus-like particle abundance ranged from 3.7 × 1010to 37.9 × 1010·L-1in samples collected during August 1997 and July 1998. Bacterial abundance during these periods ranged from 1.8 × 109to 4.6 × 109·L-1. Based on electron microscopic analysis, viruses in Lake Erie would have been responsible for 12.1-23.4% of bacterial mortality and, in quasi-steady-state conditions, a comparable loss of bacterial productivity. In the central basin, solar radiation was also demonstrated to regulate bacterial productivity. Ultraviolet radiation (295-400 nm) was shown to inhibit bacterial productivity according to a cumulative exposure kinetic model, and biological weighting functions were derived to enable calculation of time- and depth-integrated photoinhibition. The daytime photoinhibitory loss of bacterial carbon production was estimated to be 14-30% over the upper 5 m, primarily due to ultraviolet radiation >320 nm. Viruses and sunlight are therefore of comparable importance as regulators of bacterial activity in this system.
Spatial patterns in relations among brown trout (Salmo trutta) distribution, summer air temperature, and stream size in Rocky Mountain streams
Authors: Rahel Frank J , Nibbelink Nathan P
Published: April 2011

Stream size interacted with mean July air temperature to influence the distribution of brown trout (Salmo trutta) in southeastern Wyoming streams. The geographic range of brown trout was positively associated with mean July air temperatures of 19-22°C. Within this thermal zone, brown trout were more likely to occur in large streams (>4 m wetted width) than in small streams. We used a geographic information system to examine spatial patterns in the distribution of anomalous sites (i.e., sites predicted to have brown trout but which lacked this species). Sites that lacked brown trout but contained brook trout (Salvelinus fontinalis) tended to be on small streams at the cold margin of the 19-22°C thermal window. Sites lacking both brown trout and brook trout tended to be on small streams clustered in three of the six study drainages. The spatial aggregation of these sites suggests that additional regional factors influence the occurrence of brown trout in southeastern Wyoming. It is hypothesized that these factors could involve land-use practices interacting with basin geology and geomorphology. Classification models that incorporate a few general habitat factors are useful for identifying stream reaches with the potential to support brown trout and for directing management efforts to sites where this potential is not realized.
Mortality, movement, and body size: critical scales for Atlantic cod (Gadus morhua) in the Northwest Atlantic
Authors: Schneider David C , Bult Tammo , Gregory Robert S , Methven David A , Ings Danny W , Gotceitas Vytenis
Published: April 2011

The problem of scaling spatially and temporally limited data to larger scale questions can no longer be ignored as evidence accumulates that the importance of any given process, relative to another, depends on spatial and temporal scale. A recently developed graphical technique allows identification of critical space and time scales, which separate scales at which one rate prevails from scales at which another rate prevails. We used data from the literature to test a series of hypotheses concerning change in critical scales with change with life history stage in Atlantic cod (Gadus morhua). The critical scales for mortality relative to kinematics increased slightly for pelagic juveniles relative to drifting eggs, decreased substantially for demersal juveniles relative to pelagic juveniles, increased again in adults, and, contrary to expectation, remained high in large adults ("mother fish"). Critical time and space scales were found to be linked and cannot be taken as constants.
Field evaluation of a bioenergetics-based foraging model for kokanee (Oncorhynchus nerka)
Authors: Stockwell Jason D , Johnson Brett M
Published: April 2011

We used a bioenergetics-based foraging model to determine if bioenergetic and foraging constraints could explain kokanee (Oncorhynchus nerka) diel vertical migration in Blue Mesa Reservoir, Colorado. We compared model predictions of daily growth and migration strategies with observed growth and diel vertical distributions on three dates during the summer. Results suggest that bioenergetic and foraging constraints were not sufficient to explain diel vertical migration early in the summer, when thermal stratification was weak. However, these constraints could explain observed patterns later in the summer, when optimal thermal habitat for kokanee was spatially segregated from food-rich surface waters. The onset of a strong thermocline, and its exclusion of piscivorous lake trout (Salvelinus namaycush) from surface waters, appeared to determine the relative importance of predation risk for kokanee diel vertical migration patterns. Our observations and modeling results suggest that the relative importance of various factors driving diel vertical migration changes seasonally. Furthermore, the relative importance of each factor likely varies from system to system and may have caused the variety of single-factor hypotheses proposed to explain kokanee diel vertical migration. The model provides a framework for studying diel vertical migration across systems of differing thermal regimes, productivity, and predation pressures.
Density-dependent habitat selection and the modeling of sperm whale (Physeter macrocephalus) exploitation
Authors: Whitehead Hal
Published: April 2011

The monitoring and management of sperm whale (Physeter macrocephalus) populations have proved problematic. Studies of living animals indicate that movements are largely determined by resource availability, thus suggesting that density-dependent habitat selection may be a realistic framework within which to study sperm whale populations. A model, in which animals migrate between 2 × 2° squares at rates that depend on relative resource availability, was used to examine the effects of whaling on measures of sperm whale abundance. The model simulated four types of whaling: shore-based whaling, pelagic open-boat whaling by many boats, pelagic whaling by a fleet based around one factory ship, and pelagic whaling by a fleet sequentially exploiting different parts of the study area. Catch per unit effort was found to have little relationship with population size in any part of the study area for shore-based whaling and for pelagic whaling when the study area was sequentially exploited. Thus, in these circumstances, catch per unit effort should not be used as a measure of depletion. To give a reasonable assessment of depletion, visual or acoustic surveys must extend well beyond the areas being exploited.
Relationships between total mercury in sediments and methyl mercury in the freshwater gastropod prosobranch Bithynia tentaculata in the St. Lawrence River, Quebec
Authors: Désy JC , Archambault J -F , Pinel-Alloul B , Hubert J , Campbell P GC
Published: April 2011

Total Hg concentrations in sediment and methyl mercury (MeHg) levels in the gastropod species Bithynia tentaculata were evaluated at 21 stations in the fluvial corridor of the St. Lawrence River (Quebec, Canada). In the sediments (n = 21), total Hg concentrations ranged from 34 to 2790 ng·g dry weight-1. In the gastropods, MeHg concentrations varied from 15 to 290 ng·g dry weight-1 in undepurated gastropods (n = 20) and from 41 to 420 ng·g dry weight-1 in depurated gastropods (n = 13; without gut contents). The southern sector of Lake St. Louis, located near the Îles-de-la-Paix, had significantly higher Hg concentrations than any other sectors under study, both for total Hg in the sediments and MeHg in the gastropods. We established linear models to describe the relationships between Hg contamination in sediments and molluscs for the fluvial corridor of the St. Lawrence River and for the Lake St. Louis sector. Total Hg in sediments and MeHg in gastropods were highly correlated for all pooled stations (r = 0.83), and the relationship was even stronger for the Lake St. Louis stations (r = 0.92). Our study suggests that the gastropod B. tentaculata is a promising biomonitor species for assessing Hg contamination in the fluvial corridor and lakes of the St. Lawrence River.
Biotransformation of polychlorinated biphenyls in St. Lawrence River sediments: reductive dechlorination and dechlorinating microbial populations
Authors: Cho Y -C , Kim J , Sokol R C , Rhee G -Y
Published: April 2011

Polychlorinated biphenyl dechlorinating microbial populations in St. Lawrence River sediments were fractionated and estimated based on the dechlorination pattern using a combination of serial dilution and most probable number techniques. Two distinctive dechlorination patterns were found in most probable number sediments spiked with Aroclor 1248. A high-dilution inoculum decreased the average number of chlorines per biphenyl from 4.0 to 3.4 but was unable to dechlorinate meta-substituted congeners consisting mainly of 2,5,2',5'-, 2,4,2',5'-, and 2,5,2'-chlorobiphenyl (pattern B). On the other hand, a low-dilution inoculum did dechlorinate the meta-rich congeners and reduced the average number of chlorines to 2.9 (pattern A). These results indicate that there are at least two populations. While pattern B was produced by pattern B producing dechlorinators, pattern A was produced by a combination of pattern B producers plus another population that dechlorinates the meta-substituted congeners. When the population size was calculated based on the frequency of respective dechlorination patterns, the populations yielding pattern B were approximately 2.4 × 106cells·g dry weight sediment-1whereas the dechlorinators of the meta-rich congeners were two orders of magnitude less at 3.5 × 104cells·g dry weight sediment-1. Despite lower numbers, these meta-dechlorinators in pattern A increased the overall dechlorination by almost twofold.