bluuebunny/crossref_metadata_2025 huggingface dataset:
Timing of habitat shift by Atlantic salmon parr from fluvial to lacustrine habitat: analysis of age distribution, growth, and scale characteristics
Authors: Erkinaro Jaakko , Niemelä Eero , Saari Aila , Shustov Yuri , Jørgensen Lisbeth
Published: April 2011

This study investigated the timing of a habitat shift from fluvial to lacustrine habitat of Atlantic salmon, Salmo salar, parr in a subarctic river in northern Finland and whether the individuals that shifted already had the best growth rate prior to the shift or, alternatively, whether the shift was triggered by competition-induced growth depression. The age distribution of parr indicated that most of the fish that shifted belonged to the age group 2+ and the proportion of 1+ fish was less than 3%. However, the analyses of somatic growth and scale characteristics reflected an earlier shift, at the age of 1+, for the greater part of the lacustrine fish. The growth of lacustrine fish exceeded that of their fluvial counterparts after the first year of life. Based on the growth of the first year, no indications that the lacustrine parr were recruited from the fastest growing part of the population were found. However, the growth patterns during the second year may indicate that fluvial parr with the fastest growth at age 1+ may be those that shift at age 2+. Some evidence of growth depression in fluvial fish was found.
Diel variation in trawl catchability: is it as clear as day and night?
Authors: Casey Jill M , Myers Ransom A
Published: April 2011

Diel variation in the catchability of over 50 species was examined using research vessel surveys conducted off the coast of Newfoundland and Labrador from 1972 to 1995. Catchability during the day and night was estimated for several seasons and geographic areas in the Northwest Atlantic using two generalized linear models. In general, species exhibiting diel vertical migrations, such as redfish (Sebastes sp.), northern sand lance (Ammodytes dubius), and haddock (Melanogrammus aeglefinus), were caught in higher proportions during the day. Nonmigrating species, such as flatfish, skate, and scuplin, which rely on visibility of the trawl as a means of escapement, were caught in higher proportions during the night. Analysis of the effect of depth indicated that catchability during the day, relative to the night, increased significantly with depth for 21 species. We demonstrate that the accepted methods of estimating standard errors for generalized linear models are not valid for survey trawl data and suggest alternative methods.
Diet shift in fish following competitive release
Authors: Persson Anders , Hansson Lars-Anders
Published: April 2011

We determined the diet preference of roach (Rutilus rutilus), perch (Perca fluviatilis), and bream (Abramis brama) before and after a fish removal program in Lake Finjasjön, Sweden. The biomass of roach and bream was reduced to 33 and 10%, respectively, after the program. The predominate diet change following this major reduction in fish biomass was an increased use of benthic organisms by most size-classes of roach. Also, bream shifted to benthos at an earlier ontogenetic stage. These diet shifts were most probably attributed to the drastic reduction in biomass of the benthivorous bream, resulting in underexploited benthic invertebrates. In order to test if alterations in diet choice were reflected in the composition of stable isotopes of consumer tissue, we determined the temporal changes in the 15N/14N ratio (δN) of potential fish prey as well as in fish tissue. No temporal trends were found for δN of fish, possibly due to the high temporal variability in δN of zooplankton. However, minimum and maximum δN values of major food organisms (chironomids and zooplankton) were generally reflected in the δN of both small roach and perch one sampling occasion later (3 months) and in piscivorous perch (exclusively feeding on small fish) two sampling occasions later. Hence, the stable isotope composition could be followed through food links, providing that the consumer mainly fed on one specific food item. However, several other predictions regarding connections between diet and stable isotope composition were not corroborated. We conclude that stable isotope analysis of consumer tissue cannot replace traditional methods of diet determination, but might well provide complementary data.
Ecotoxicology of metals in aquatic sediments: binding and release, bioavailability, risk assessment, and remediation
Authors: Chapman Peter M , Wang Feiyue , Janssen Colin , Persoone Guido , Allen Herbert E
Published: April 2011

Major metal-binding phases in the aerobic layer of sediments are iron and manganese oxyhydroxides (FeOOH and MnOOH) and particulate organic carbon (POC). The acid-volatile sulfide (AVS) model proposed for predicting nontoxicity from metals-contaminated sediments is only applicable to anaerobic sediments. In other sediments, normalization by POC or FeOOH and MnOOH may be predictive, but binding constants are not well understood. Metal mobilization is enhanced by ligand complexation and oxidation of anaerobic sediments. Free metal ion is the most bioavailable species, but other labile metal species and nonchemical variables also determine metal bioavailability; biotic site binding models have shown promise predicting toxicity for systems of differing chemistry. Hazard identification and ecological risk assessment (ERA) depend on determining bioavailability, from water (overlying, interstitial) and food, which can be done prospectively (e.g., normalized sediment chemistry, laboratory bioassays) or retrospectively (e.g., in situ bioassays, field studies). ERA of sediment-bound metals requires primary emphasis on toxicity and consideration of the three separate transformation processes for metals in the aquatic environment, the differences between essential and nonessential metals, the complex interactions that control bioavailability, adaptation, which may occur relatively simply without appreciable cost to the organism, weight of evidence, and causality.
Intercalibration of research survey vessels in fisheries: a review and an application
Authors: Pelletier D
Published: April 2011

Fisheries stock assessments often rely on time series of abundance indices obtained from annual research surveys. It is thus important to maintain the temporal continuity of such series when vessels change. This can be achieved by estimating conversion coefficients between the two vessels through an intercalibration experiment. This paper describes such an experiment conducted from two French research vessels, including (i) a review of previous intercalibration experiments; (ii) a statistical model based on quasi-likelihood functions yielding conversion coefficient estimators; (iii) a simulation approach using both the model and previous survey data to plan the experiment; and (iv) a bootstrap procedure providing robust estimates of the conversion coefficients obtained from the model.
Stock discrimination of Atlantic walrus (Odobenus rosmarus rosmarus) in the eastern Canadian Arctic using lead isotope and element signatures in teeth
Authors: Outridge P M , Stewart R EA
Published: April 2011

Atlantic walrus (Odobenus rosmarus rosmarus) harvested from three regions of the Canadian Arctic, and by different communities within two of those regions, were distinguished using the stable Pb isotope or trace element composition of their tooth cementum. Walrus from Foxe Basin (Igloolik, Hall Beach), the High Arctic (Grise Fiord, Resolute Bay), and eastern Hudson Bay (Akulivik, Inukjuak) were each characterized by specific combinations of Pb isotope ratios and Co concentrations, and we conclude that they represent different regional stocks. Walrus landed at Akulivik and Inukjuak were further discriminated by significant differences in 208Pb/207Pb, even though the communities are only 250 km apart. There was more overlap between walrus from Igloolik and Hall Beach, which are 80 km apart, but significant differences between sites in Pb isotope ratios and in concentrations of V, Zn, and Mo suggested that more than one Foxe Basin stock was being harvested. Particularly at Hall Beach, the herds contained a few individuals with isotope ratios significantly different from the rest of the population. These "outliers" may represent either immigrants from other geological provinces or animals caught in other areas. Further investigation of the outliers could provide information regarding hunting patterns, walrus home ranges, and the rates and demographics of interstock migrations.
Evaluating uncertainty in harvest control law catches using Bayesian Markov chain Monte Carlo virtual population analysis with adaptive rejection sampling and including structural uncertainty
Authors: Patterson K R
Published: April 2011

A new method is developed for calculating Bayes posterior distributions of future catches that conform to a specified harvest control law while incorporating uncertainty in biological reference points, natural mortality, and some aspects of model structure in addition to the usual stochastic noise. A Markov chain Monte Carlo approach is used to calculate Bayesian posterior distributions for critical parameters of a Norwegian spring-spawning herring (Clupea harengus) stock assessment using an assessment model that incorporates catch-at-age, survey, and tag release and recapture observations. Exceptionally, the approach allows prior uncertainty in model structure (e.g., whether survey observation errors should be treated as normal, lognormal, or gamma variates; whether Ricker or Beverton-Holt forms are used to model recruitment). This modelling approach is a useful tool that allows management advice to be provided that takes into account uncertainty in model structures and in some parameters that, by conventional methods, need to be specified as arbitrary "best" choices. The method is also used to quantify uncertainty in some biological reference points and to calculate a probability distribution for a future catch with respect to a specified harvest control law. This has the advantage of a consistent treatment of uncertainty throughout the process of stock modelling, reference point estimation, and concomitant catch forecasting.
Protective role of ascorbic acid against damage to male germ cells in rainbow trout (Oncorhynchus mykiss)
Authors: Ciereszko Andrzej , Dabrowski Konrad , Lin Feng , Liu Li
Published: April 2011

Low antioxidant levels have been implicated in damage to sperm DNA. We used a teleost fish to test if low paternal vitamin C status may cause mutations to the sperm and birth defects. During spermatogenesis, rainbow trout (Oncorhynchus mykiss) males were fed diets with graded levels of ascorbic acid derivative that were below and severalfold higher than those required for maximum growth. This treatment resulted in corresponding changes in levels of vitamin C in seminal plasma. We found that low levels of vitamin C in seminal plasma of rainbow trout were associated with a high percentage of abnormal embryos in the offspring. Among abnormal embryos, 34.8% were haploids or aneuploids, as revealed by flow cytometric measurement of DNA content. We found that UV-irradiated sperm gave rise to progeny with abnormalities similar to those resulting from sperm with low levels of antioxidants in seminal plasma. Ascorbic acid applied directly to semen did not prevent damage due to UV irradiation. These results provide the first experimental evidence that the lack or low levels of ascorbic acid in semen correlate with damage to male germ cells.
Mitigation of harbour porpoise (Phocoena phocoena) by-catch in the gillnet fishery in the lower Bay of Fundy
Authors: Trippel Edward A , Strong Michael B , Terhune John M , Conway Jeremy D
Published: April 2011

Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz every 4 s at a level of 133-145 dB re 1 µPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1-0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.
Behavioral inferences from regulatory observer data: catch rate variation in the Scotian Shelf silver hake (Merluccius bilinearis) fishery
Authors: Gillis D M
Published: April 2011

The detailed spatial and temporal data collected for the regulation of the silver hake (Merluccius bilinearis) fishery on the Scotian Shelf provide a unique opportunity to test hypotheses about variability in catch rates on the scale of individual trawls. I used these data to examine vessel interactions and long-term temporal trends in catchability. An index of course linearity, derived from observed positions, times, and speeds of fishing vessels, indicated that interference competition was present in the fishery. However, catch rate did not decline with local vessel density. This apparent contradiction is consistent with fleet dynamic theory and suggests that the direct examination of catch rates is a poor test for interference in the retrospective analysis of fisheries data. The study of extended periods of high, localized fishing activity revealed a cycle in catch rates with periods of about 6 days. Such periods may represent an interaction between tidal, diel, and (or) technological factors. Although more study is required to identify the cause of these cycles, their existence should be considered in the design of surveys and other population studies using catch and effort data.
Application of microsatellite DNA variation to estimation of stock composition and escapement of Nass River sockeye salmon (Oncorhynchus nerka)
Authors: Beacham Terry D , Wood Chris C
Published: April 2011

Spawning escapements of individual Pacific salmon stocks returning to remote spawning locations throughout large river systems can in theory be estimated by mixed-stock analysis of appropriately weighted samples from test fisheries near the river mouth. However, the feasibility of this approach has usually been limited by practical difficulties in identifying closely related populations within the same watershed. Microsatellite DNA techniques offer new promise for overcoming these limitations as illustrated for sockeye salmon (Oncorhynchus nerka) in the Nass River of northern British Columbia. Variation at six microsatellite DNA loci (Omy77, Ots3, Ots100, Ots103, Ots107, and Ots108) was surveyed from about 1400 fish from nine stocks in the Nass River drainage as well as from 249 fish in a test fishery conducted in the lower river during 1996. Five stocks were surveyed in more than one year, and variation in allele frequencies among stocks was, on average, about 10 times greater than annual variation within stocks. Allele frequencies of stocks where the juveniles do not rear in lakes ("riverine" or "sea type") were more similar to each other compared with frequencies from lake-rearing stocks. Significant differences in allele frequencies were observed among most stocks at all loci. About 4.5% of observed variation over all loci was attributable to stock differentiation. Simulated mixed-stock samples suggested that the six microsatellite DNA loci surveyed should provide the ability to provide relatively accurate and precise estimates of stock composition when utilized for fishery management applications. The estimated proportion of Meziadin Lake sockeye salmon in the 1996 test fishery was about 73%, in close agreement with an estimate derived from direct tagging of fish in the test fishery.
Effects of water temperature on protein synthesis and protein growth in juvenile Atlantic wolffish (Anarhichas lupus)
Authors: McCarthy Ian D , Moksness Erlend , Pavlov Dimitri A , Houlihan Dominic F
Published: April 2011

The effects of water temperature (5, 8, 11, and 14°C) on the fractional rate (percent per day) of protein consumption (kr) and on white muscle and whole-body fractional rates of protein synthesis (ks), protein growth (kg), and growth efficiency (PPV, growth/consumption; kg/ks, growth/synthesis) of juvenile Atlantic wolffish (Anarhichas lupus) (initial body weight 26 g) were studied. Rates of protein consumption and white muscle and whole-body protein synthesis increased in a linear fashion between 5 and 14°C. In contrast, the relationships between temperature and white muscle and whole-body protein growth, protein growth efficiency (PPV) and protein synthesis retention efficiency (kg/ks) were parabolic. The results indicated that the optimum water temperatures for growth (Topt.G) and growth efficiency (Topt.GE) were 10-11 and 9-10°C, respectively. The maximum white muscle and whole-body protein growth rates recorded at Topt.G were 0.9 and 0.7 %·day-1, respectively. At Topt.GE, the maximum white muscle and whole-body PPV values were 28 and 34%, respectively, and kg /ks values were 92 and 51%, respectively. The growth performance data for juvenile Atlantic wolffish in comparison with published data for salmonids (rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar)) at 9-11°C further highlight its suitability as an alternative species for cold-water aquaculture in northern Europe and Atlantic Canada.
Habitat selection and clustering of a pelagic fish: effects of topography and bathymetry on species dynamics
Authors: Maravelias Christos D
Published: April 2011

Two dynamic aspects of the ecology of pelagic fish, distribution and abundance, have been linked to topographic, bathymetric, and biotic factors. The two-stage generalized additive modelling (GAM) approach undertaken in the present study offered biological interpretations of presence/absence of a pelagic fish species as distinguished from abundance (if present) in relation to various abiotic and biotic factors. The data were collected during the ICES coordinated Atlantic herring (Clupea harengus) acoustic surveys (ICES Division IVa) of July 1992, 1994, and 1995 in the northern North Sea. The depth of the water column, the seabed substrate, and zooplankton biomass appeared to be significant factors modulating presence and relative abundance of a pelagic species within the northern North Sea. Results indicated that habitats with the higher probability of finding herring present were those located in shallower waters having a gravel/sand type of seabed that also carried the highest zooplankton abundances. Species clustering was found to be preferentially higher in these habitats. Notwithstanding their pelagic nature, herring exhibit preferences for areas with specific bathymetric, substratum, and zooplanktonic conditions. These preferences are believed to be linked to the oceanography of the North Sea ecosystem.
Age characteristics of coarse woody debris (Pinus strobus) in a lake littoral zone
Authors: Guyette Richard P , Cole William G
Published: April 2011

Littoral coarse woody debris (CWD) is a persistent class of aquatic habitat that accumulates over many centuries and provides habitat for diverse floral and faunal communities. We used dendrochronological methods to analyze residence times and age-related characteristics of eastern white pine (Pinus strobus) CWD in the littoral zone of Swan Lake in Algonquin Provincial Park, Ontario. The mean calendar date of all the annual rings in CWD samples was 1551. Annual rings dated from calendar year 1893 to 982. The mean time from carbon assimilation in a live tree to carbon loss from littoral woody debris was 443 years. Outside ring dates of the woody debris were significantly correlated with the bole's maximum and minimum diameter ratio, mass, specific gravity, length, and submergence. Negative exponential functions described the temporal structure of the CWD mass and abundance. Accelerated inputs of woody debris resulted from late nineteenth century logging and a disturbance circa 1500. No mature eastern white pine have fallen into the lake over the last 100 years.
Impacts and efficiency of scallop dredging on different soft substrates
Authors: Currie David R , Parry Gregory D
Published: April 2011

Impacts of scallop dredges and their efficiency were examined experimentally in three areas with different soft substrates in Port Phillip Bay, southeastern Australia. Physical and biological changes were measured on large (600 × 600 m) experimental plots that were dredged with an intensity and duration similar to normal fishing operations. Dredges were most efficient on soft, flat, muddy sediments (51-56% of commercial-sized scallops caught) and least efficient on firm, sandy sediments with more topographic variation (38-44%). Dredging flattened all plots, but changes to topography were most apparent on plots dominated initially by callianassid mounds. Dredges caught predominantly the scallop Pecten fumatus, and damage to bycatch species was slight, except for high mortality rates (>50%) of spider crabs and the probable mortality of many discarded ascidians. Changes to benthic community structure caused by scallop dredging were small compared with differences between study areas, and even marked reductions in the size and longevity of scallops over the last two decades may not be due entirely to dredging. The recent cancellation of all scallop dredging licences offers a unique opportunity to determine the contribution of scallop dredging to ecological changes in the bay over the past 30 years.
Modeling environmentally driven uncertainties in Baltic cod (Gadus morhua) management by Bayesian influence diagrams
Authors: Kuikka S , Hildén M , Gislason H , Hansson S , Sparholt H , Varis O
Published: April 2011

The large variability in Baltic cod (Gadus morhua) recruitment has been attributed both to environmental factors dependent on the inflow of saline water (oxygen and salinity in spawning deeps) and to the size of the spawning stock. Due to the complex interactions between hydrographic and biological processes, future recruitment levels of cod will remain highly uncertain and increase uncertainties in stock predictions and management advice. We assessed the effects of the exploitation level and mesh size used by a trawl fishery on some variables of management interest under different environmental conditions. The modeling consisted of three separate steps: (i) modeling of selectivity, (ii) estimation of uncertainties by Monte Carlo simulations, and (iii) decision analysis by Bayesian influence diagrams, focusing on the structural uncertainties and model selection. Realistic assumptions of environmental conditions and present fishing mortality rates suggest that the current Baltic cod fishery is unsustainable. We use our approach to identify robust management measures that reduce the risk of overfishing and the sensitivity to management information. The value of information analysis demonstrates the advantages of a larger mesh size as a management measure.
Estimating physiological cost of chemical exposure: integrating energetics and stress to quantify toxic effects in fish
Authors: Beyers Daniel W , Rice James A , Clements William H , Henry Catherine J
Published: April 2011

We present empirical support for a conceptual framework in which chemical contaminants are considered as sources of physiological stress to fish. Physiological stress was quantified in terms of energy by measuring routine metabolism, food consumption, activity, and growth rates of largemouth bass (Micropterus salmoides) exposed to the organochlorine pesticide dieldrin. Regression analysis was used to estimate models that describe the response of each endpoint as a function of dieldrin concentration and duration of exposure. Metabolic rate, consumption, and growth were influenced by chemical exposure. At short durations of exposure (1-4 days), metabolic rate of exposed fish was depressed compared with controls, but at a longer duration (16 days), metabolic rate increased as a function of concentration. Food consumption and growth rates of fish exposed for 16 days declined as dieldrin concentration increased. The response of each endpoint was consistent with predictions of the general adaptation syndrome. Energetic costs of contaminant-induced changes in metabolism and food consumption can be integrated with a bioenergetics model to demonstrate biological significance of chemical exposure in a natural environment.
Courage and the management of developing fisheries
Authors: Miller Robert J
Published: April 2011

Devising a fishery management plan can be intimidating because of the diversity of issues, incomplete information, and criticism from many quarters. Here, fishery managers and scientists are encouraged to anticipate problems and to set an agenda for solving them. A guide to problems presented by developing fisheries and the order to address them are organized into four phases. In Phase I, fishers are given the opportunity to demonstrate commercial viability with a minimum of interference. In Phase II, the extent of the resource is mapped, gear-related regulations are developed, and fishers begin assuming responsibility for management decisions. In Phase III, basic biological studies are carried out, long-term management targets are set, and monitoring and regulation to achieve the targets are put into place. The fishing-down period should be extended until the long-term management plan is in place. This avoids having to pay for overfishing by underfishing. The challenge of Phase IV is staying the course laid out.
Spatial distribution of sardine (Sardinops sagax) eggs and larvae: an application of geostatistics and resampling to survey data
Authors: Fletcher W J , Sumner Neil R
Published: April 2011

The abundance of eggs and larvae of sardine (pilchard) (Sardinops sagax) off the south coast of Western Australia was investigated using geostatistical and bootstrap resampling techniques. A two-dimensional correlogram showed that the patch of newly spawned pilchard eggs had dimensions of 8 nautical miles (M) in diameter in the offshore direction and 10 M in the alongshore direction. For older stages, the size of the patch tended to increase and the level of cohesion decrease. It was more difficult to determine the size of the patch from directional variograms. The abundance of 1- and 2-day-old eggs in the study area was estimated using ordinary kriging. A bootstrapping analysis suggested that the optimal sampling design for day 1 eggs should use 4 × 10 M grids, an increase in intensity on the 5 × 15 M grids used in previous surveys.
Estimating spawning escapements from periodic counts: a comparison of methods
Authors: Hilborn Ray , Bue Brian G , Sharr Samuel
Published: April 2011

The escapement of Pacific salmon is often estimated by periodic counts of spawners, calculating the number of fish-days present and dividing by the average number of days a fish spends in the survey area. We present a maximum likelihood method to calculate the number of spawning fish and compare this approach with the most commonly used method, which relies on linear interpolation between observations. The maximum likelihood method is computationally more demanding; however, it does provide a statistical basis for describing uncertainty and can also be used to deal with data sets where the first or last counts are nonzero or where there are few observations. We compared escapement estimation methods using data from 18 experimental streams where the number of fish in the stream was evaluated by weir and carcass counts. In this comparison, the method of linear interpolation deviated from the weir count by an average of 19%, whereas the maximum likelihood method deviated by 23, 24, 30, or 40% depending upon which likelihood and arrival time model was used. We conclude that for most data sets where measures of uncertainty are not required, the linear interpolation method is adequate but recommend an examination of maximum likelihood methods when an estimate of uncertainty is required.
The effect of interannual variation in growth and condition on haddock recruitment
Authors: Marshall C Tara , Frank Kenneth T
Published: April 2011

The relationship between recruitment and spawner biomass assumes that estimates of spawner biomass are proportional to total egg production by the stock. The validity of this assumption is in question for long-lived gadoid stocks; however, estimating total egg production independently of spawner biomass is seldom feasible. An alternative approach is to examine correlations between recruitment and variables likely to be proxies for total egg production by the stock. This indirect approach was used for haddock on the Scotian Shelf. Indices of growth (mean length at age-4) and condition (weight at 50 cm) were used as proxies for the reproductive potential of individual spawners. Both variables were positively correlated with recruitment over a 3-decade period (1964-1995). During the same time period, there was no relationship between recruitment and spawner biomass estimated by Virtual Population Analysis (VPA). This is further evidence that VPA-based spawner biomass is a poor index of the true reproductive potential of the stock. The results highlight the need to develop more accurate/precise measures of total egg production for use in recruitment research.
A probabilistic analysis of decision-making about trip duration by Strait of Georgia sport anglers
Authors: Smith Barry D
Published: April 2011

Since 1984, an access-point creel survey of the Strait of Georgia, British Columbia, sport fishery has generated data on catch, effort, and attributes of effort from thousands of interviews of salmon anglers completing a daily boat-trip. I present a maximum-likelihood model for this daily bag limit (DBL) constrained fishery that estimates catch rate and variance for various angling fleets (as defined by boat-trip attributes such as the number of angling lines), estimates the probability that a boat-trip ends after a certain number of hours angling, and measures how angling success influences that probability. Most anglers targeting either chinook salmon (Oncorhynchus tshawytscha) or coho salmon (Oncorhynchus kisutch) became more likely to end a boat-trip in response to angling success, i.e., they were satiated by angling success before reaching a DBL. However, autumn and winter chinook salmon anglers tended to extend a boat-trip in response to angling success, i.e., they were motivated by angling success. Variability in angling success could not be attributed to variability in angler skill. Coho salmon catch rates increased by about 42% with each additional angling line per boat-trip up to three. The model can be used to judge the effectiveness of a DBL in reducing daily catch.
Water quality prediction and probability network models
Authors: Reckhow Kenneth H
Published: April 2011

It is a common strategy in surface water quality modeling to attempt to remedy predictive inadequacies by incorporating additional mechanistic detail into the model. This approach reflects the reasonable belief that enhanced scientific understanding of basic processes can be used to improve predictive modeling. However, nature is complex, and even the most detailed simulation model is extremely simple in comparison. At some point, additional detail exceeds our ability to simulate and predict with reasonable error levels. In those situations, an attractive alternative may be to express the complex behavior probabilistically, as in statistical mechanics, for example. This viewpoint is the basis for consideration of Bayesian probability networks for surface water quality assessment and prediction. To begin this examination of Bayes nets, some simple water quality examples are used for the illustration of basic ideas. This is followed by discussion of a set of proposed probability network models for the eutrophication of the Neuse River estuary in North Carolina. The presentation concludes with consideration of applications and opportunities for Bayes nets in predictive water quality modeling.
BUGS in Bayesian stock assessments
Authors: Meyer Renate , Millar Russell B
Published: April 2011

This paper illustrates the ease with which Bayesian nonlinear state-space models can now be used for practical fisheries stock assessment. Sampling from the joint posterior density is accomplished using Gibbs sampling via BUGS, a freely available software package. By taking advantage of the model representation as a directed acyclic graph, BUGS automates the hitherto tedious calculation of the full conditional posterior distributions. Moreover, the output from BUGS can be read directly into the software CODA for convergence diagnostics and statistical summary. We illustrate the BUGS implementation of a nonlinear nonnormal state-space model using a Schaefer surplus production model as a basic example. This approach extends to other assessment methodologies, including delay difference and age-structured models.
Exceptions to semelparity: postmaturation survival, morphology, and energetics of male chinook salmon (Oncorhynchus tshawytscha)
Authors: Unwin M J , Kinnison M T , Quinn T P
Published: April 2011

Between 2.1 and 6.8% of fall-run male chinook salmon (Oncorhynchus tshawytscha) reared in two New Zealand hatcheries matured as yearling parr, of similar size to immature siblings. The incidence of mature parr in 58 half-sib families ranged from 0 to 69% of the available males. Although chinook salmon are normally semelparous, about 80% of mature parr survived to mature again at age 2, and all fish held for another year matured again at age 3. All three ages produced milt that successfully fertilized eggs. Morphological development in mature parr and repeat-maturing males was consistent with that of older, first time maturing males. The gonadosomatic index for mature age-2 males was 11.7, 7.2, and 5.4% for repeat-maturing males, freshwater-reared males, and sea-run males, respectively. Muscle energy density for repeat-maturing males (4.45 kJ/g) was lower than for normal males (5.20-5.45 kJ/g) and negatively correlated with the gonadosomatic index. Although we think it unlikely that repeat maturation occurs regularly in the wild, our results indicate that under favorable conditions, chinook salmon can exhibit some iteroparous traits. We hypothesize an evolutionary continuum between semelparity and iteroparity in salmonids, primarily characterized by modifications in a few key energetic and physiological thresholds.
Limnological succession in reservoirs: a paleolimnological comparison of two methods of reservoir formation
Authors: Hall Roland I , Leavitt Peter R , Dixit Aruna S , Quinlan Roberto , Smol John P
Published: April 2011

Analysis of diatoms, algal pigments, and chironomids in sediment cores from two otherwise similar prairie reservoirs demonstrated that differences in reservoir formation (river valley impoundment versus lake inundation) and hydrological regime (variable versus stable water level) resulted in distinct patterns of aquatic community change. Lake Diefenbaker, a 500-km2 reservoir created by damming the South Saskatchewan River in 1968, experiences water level fluctuations of 6 m·year-1. In contrast, impoundment of Buffalo Pound Lake in 1952 flooded a natural lake, raised mean water levels ~2.0 m, and reduced water level fluctuations from ~3 to <1 m·year-1. Comparison of fossil records showed that reservoir formation did not inevitably lead to eutrophication. Lake Diefenbaker exhibited typical reservoir ontogeny with three trophic periods, including an initial ~4-year period of eutrophy, a decade of mesotrophy, and a gradual shift to modern productive conditions. Planktonic taxa dominated diatom communities at all times, whereas benthic chironomid and algal remains were rare. In contrast, pigment analyses suggested that phytoplankton standing crops declined after impoundment in Buffalo Pound Lake but that chironomid and macrophyte populations expanded. Such site specificity in trophic development appears to result from differences in the extent of inundation (500 versus ~5 km2) and the magnitude of subsequent water level fluctuations (6.3 versus <1 m).
Habitat factors controlling Pacific herring (Clupea pallasi) egg loss in Prince William Sound, Alaska
Authors: Rooper Christopher N , Haldorson Lewis J , Quinn II Terrance J
Published: April 2011

Recruitment for many marine fishes is believed to be determined at an early life history stage. Pacific herring (Clupea pallasi) spawn in the intertidal and shallow subtidal zones and have a demersal egg stage that is susceptible to egg removals during incubation. Data were collected by the Alaska Department of Fish and Game in four years in Prince William Sound, Alaska, to identify important factors contributing to egg removals. We constructed analysis of variance models based on physical and biological variables to determine which environmental factors control egg loss rates. The habitat variables examined at each study transect were depth, wave exposure, north-south location, substrate, vegetation, mean bird abundance, abundance of loose eggs, and fish predation. Depth of spawn was the primary factor determining egg loss. Cumulative time of air exposure over incubation was substituted into the model for depth. Using the model, the total estimated egg loss from spawning to hatching ranged from 67 to 100% with an average of 75% (SE = 3.3%) in 1995. Eggs were originally deposited from 4 to -6 m depth relative to mean low water. The majority of eggs that remained in the spawning beds to hatching were deposited from 1 to -4 m depth. Egg removals due to avian predation were probably responsible for extreme egg loss rates at shallow depths.
Large-scale spatial heterogeneity of macrozooplankton in Lake of Geneva
Authors: Pinel-Alloul Bernadette , Guay Catherine , Angeli Nadine , Legendre Pierre , Dutilleul Pierre , Balvay Gérard , Gerdeaux Daniel , Guillard Jean
Published: April 2011

Spatial distribution of macrozooplankton was studied during spring in Lake of Geneva to evaluate the influence of abiotic (water temperature and stability, nutrients) and biotic (bacteria, chlorophyll a, fish biomass) factors on macrozooplankton distribution. Mapping and spatial analyses revealed that abiotic factors, as well as crustacean abundances, were structured along a gradient in the great lake basin. Chlorophyll a biomass, bacteria density, cyclopoid abundance, and fish biomass showed more patchy or inshore-offshore distribution patterns. Using canonical analyses, we determined the relative contribution of the spatial and environmental factors to the distribution of macrozooplankton species and of trophic groups based on herbivory and omnivory/carnivory. The distribution of macrozooplankton can be explained by small-scale variations and lake gradients in abiotic and biotic factors, with a dominant contribution of the abiotic factors. Water temperature and stability, as well as ammonium, are the main factors related to macrozooplankton distribution in Lake of Geneva during spring. Chlorophyll a biomass was also related to the distribution of cyclopoids. The canonical models explained 35-72% of the variance in the distribution of total crustaceans, species, and trophic groups. However, 28-65% of the macrozooplankton variance remained unexplained, which may be due to fine-scale variations in other environmental factors.
Influence of turbidity on piscivory in largemouth bass (Micropterus salmoides)
Authors: Reid Scott M , Fox Michael G , Whillans Thomas H
Published: April 2011

In situ and laboratory feeding trials coupled with stomach content analysis of largemouth bass (Micropterus salmoides) were performed to examine how turbidity influences the size selectivity and capture rates of prey. No significant differences in the capture success of adult largemouth bass preying on northern redbelly dace (Phoxinus eos) were observed during in situ feeding trials in two Lake Ontario coastal wetlands differing in turbidity level (2.3 and 20 nephlometric turbity units (NTU)). During 1-h laboratory feeding trials, the overall number of fathead minnows (Pimephales promelas) captured was not significantly different among 1-, 18-, and 37-NTU treatments. However, at 70 NTU, the number of fathead minnows captured was significantly lower than that at the lowest turbidity treatment. Selection by juvenile largemouth bass of the smallest size-class of fathead minnow decreased as turbidity increased. No significant differences in piscivory were apparent between juvenile largemouth bass collected from turbid and clear habitats. Stomach content comparisons of juvenile largemouth bass seined from six clear and turbid habitats suggest that piscivory is primarily regulated by the availability of vulnerable size-classes of prey fish, as opposed to water clarity.
Spatial and temporal heterogeneity of an epilithic streambed community in relation to the habitat templet
Authors: Eisenmann Heinrich , Burgherr Peter , Meyer Elisabeth I
Published: April 2011

The microbial community of river sediments and their relationship to environmental factors is largely unknown. In this study, the abundance of bacteria, flagellates, ciliates, and Micrometazoa was investigated for eight different sediment types. The sediment types were classified by discharge (stable versus flood period), location (upper versus lower reach), and depth (superficial versus deep sediment layer). Abundances in the lower reach were more than two times higher than in the upper reach but decreased markedly at both sites after flooding. Organism densities were similar between the two sediment layers, although deeper habitats served as potential refugia, as indicated by reduced transport of coarse particles into the deep sediment layer. The organism abundances correlated with concentration of fine organic particles. A habitat templet model was used to classify favourableness and disturbance of the sediment types. For an empirical placement of sediment types in the model, results on abundances, fine organic particles, nutrient concentrations, particle transport, and flood frequency were integrated. Local processes, mainly related to sediment transport, decreased the predicticability of the habitat templets.
Lake sturgeon (Acipenser fulvescens) growth chronologies
Authors: LeBreton Gregory T , Beamish F William H. , Wallace Robert G
Published: April 2011

We used annual increments in the pectoral fin rays of lake sturgeon (Acipenser fulvescens) to assess growth synchrony. We based our decision criteria on correlation among individual chronologies developed from samples collected in the Saskatchewan River, Saskatchewan, and Lake St. Clair and the Mattagami River, Ontario. Initially, correlations among chronologies were not significant within these three populations. However, as mean ageing error was reduced, correlations among chronologies increased to significant levels in samples from the Saskatchewan River and Lake St. Clair. Correlations were not significant among consistently aged fish sampled from the Mattagami River. We conclude that interannual growth variation in lake sturgeon is influenced by population-wide extrinsic factors in some populations. Our results suggest that both growth synchrony and ageing error should be quantified during the construction of growth chronologies for all organisms.
Temperature and the recruitment of Atlantic cod (Gadus morhua)
Authors: Planque B , Frédou T
Published: April 2011

Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock has proven to be problematic and has resulted in recurrent controversy between studies supporting either hypothesis. In the present study, we examine the relationship between interannual changes in temperature and variation in recruitment for nine Atlantic cod (Gadus morhua) stocks in the North Atlantic. We show that for individual stocks, the relationship often appears weak and statistically not significant. On the other hand, by combining in a single metaanalysis the results from individual stocks, we demonstrate that recruitment of Atlantic cod is linked to interannual fluctuations in temperature in such a way that for stocks located in warm water the relationship is negative, for stocks located in cold water the relationship is positive, and there is no relationship for stocks located in the middle of the temperature range.
A method for nitrate collection for δ15N and δ18O analysis from waters with low nitrate concentrations
Authors: Chang Cecily CY , Langston James , Riggs Mike , Campbell Donald H , Silva Steven R , Kendall Carol
Published: April 2011

Recently, methods have been developed to analyze NO3- for δ15N and δ18O, improving our ability to identify NO3- sources and transformations. However, none of the existing methods are suited for waters with low NO3- concentrations (0.7-10 µM). We describe an improved method for collecting and recovering NO3- on exchange columns. To overcome the lengthy collection loading times imposed by the large sample volumes (7-70 L), the sample was prefiltered (0.45 µm) with a large surface area filter. Switching to AG2X anion resin and using a coarser mesh size (100-200) than previous methods also enhanced sample flow. Placement of a cation column in front of the anion column minimized clogging of the anion column by dissolved organic carbon (DOC) accumulation. This also served to minimize transfer of unwanted oxygen atoms from DOC to the 18O portion of the NO3- sample, thereby contaminating the sample and shifting δ18O. The cat-AG2X method is suited for on-site sample collection, making it possible to collect and recover NO3- from low ionic strength waters with modest DOC concentrations (80-800 µM), relieves the investigator of transporting large volumes of water back to the laboratory, and offers a means of sampling rain, snow, snowmelt, and stream samples from access-limited sites.
Spatial ontogeny of lentic age-0 rainbow trout, Oncorhynchus mykiss: whole-lake manipulations of population size structure
Authors: Landry François , Post John R , Parkinson Eric A
Published: April 2011

We assessed the influence of the presence of larger-bodied conspecifics on the spatial ontogeny of age-0 rainbow trout, Oncorhynchus mykiss. We created populations with three different size structures in experimental lakes: age-0 and larger-bodied conspecifics, age-0 only, and an initially age-0 only population into which we added larger-bodied conspecifics midexperiment. In the continuous presence of larger conspecifics, age-0 rainbow trout spatial distribution was skewed toward littoral and benthic habitats which had low abundances of their primary prey (zooplankton). The opposite pattern was observed in the experimental lake devoid of larger-bodied conspecifics where the largest proportion of the age-0 class was found in the open-water limnetic habitat where their prey was most abundant. The change in spatial distribution of age-0 rainbow trout in the lake with a midseason addition of larger-bodied conspecifics was consistent with a treatment effect. This addition effect was weakened by a significant ontogenetic change in spatial distribution from littoral to benthic to pelagic habitats as the age-0 rainbow trout grew, and the strength of the change was inversely related to the intensity of interactions with conspecifics. This study provides experimental evidence that the risk of interactions with larger-bodied conspecifics is the process that controls the ontogeny of habitat use by young fish in lakes.