bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Actual and Potential Growth Rates of Brown Trout (Salmo trutta) in Natural Streams Based on Bioenergetic Models
Authors: Preall Richard J. , Ringler Neil H.
Published: April 2011

A ratio of specific growth rate to predicted maximum growth rate was employed as an ecological growth coefficient (EGC) in identifying major determinants of growth for brown trout, Salmo trutta, in natural streams. The coefficient may be more useful than specific growth rate when comparing trout populations from streams having diverse characteristics, since it accounts for the quantitative effects of stream temperature and mean trout weight. The maximum growth rate was generated by translating Elliott's bioenergetic equations into computer models applicable to fish weighing 5–300 g and to stream temperatures of 3.8–21.7 °C. EQMAX is the simpler model and generates only maximum growth rate. TROUT estimates the maximum ration size, maximum growth rate, and a variety of bioenergetic parameters. The EGC for Age I + trout ranged from 60 to 90% in three central New York streams. A relatively low EGC (30–60%) observed for Age II + trout in one stream may have been due to the inefficiency of feeding on small invertebrates. Temperature appears to be a dominant feature governing trout growth in streams. The bioenergetic models may provide useful predictions of the effects of foraging on prey communities by brown trout.
Effects of Elevated Winter Temperature on Seawater Adaptability, Sexual Rematuration, and Downstream Migratory Behaviour in Mature Male Atlantic Salmon Parr (Salmo salar)
Authors: Berglund I. , Hansen L. P. , Lundqvist H. , Jonsson B. , Eriksson T. , Thorpe J. E. , Eriksson L.-O.
Published: April 2011

In experiments with two different salmon (Salmo salar) stocks, elevated winter temperatures (Celsius) 4–9° above the ambient increased the degree of testicular resorption in previously mature male Atlantic salmon parr. Two-summer-old mature male parr maintained at a temperature 9° over the ambient for 5 mo (January–May) showed an increase in hypoosmoregulatory ability when challenged in seawater at the time of smoltification whereas parr kept at elevated temperature for various 2-mo periods (January–February, February–March, or March–April) failed to show this improvement. Furthermore, previously mature males kept at an elevated winter water temperature for either 2 or 5 mo showed a lower incidence of sexual rematuration, and consequently a higher mean growth rate, after one summer in sea pens. A river release experiment showed that rearing previously mature males at 4–7° above the ambient water temperature from December to April increased the number of downstream migrating fish to a level similar to that of immature smolts. We suggest the use of a simple method for enhancing the potential yield of ranched and cultured salmon from early maturing males by removing them from the stock population and rearing them over winter in heated water.
Paternal Association of Increased Susceptibility to Viral Haemorrhagic Septicaemia (VHS) in Rainbow Trout (Oncorhynchus mykiss)
Authors: Kaastrup P. , Hørlyck V. , Olesen N. J. , Lorenzen N. , Jørgensen P. E. Vestergaard , Berg P.
Published: April 2011

Farming of rainbow trout (Oncorhynchus mykiss) in Europe is hampered by unacceptably heavy losses due to the severe infectious disease viral haemorrhagic septicaemia (VHS). Strain-dependent variation of VHS resistance exists. A long-term breeding programme to increase VHS resistance in rainbow trout has been started in Denmark. This programme will be based on experimental VHS challenge of the parental fish (n = 84) as well as their normal and gynogenetic offspring (16 fullsib F1 groups). We found a paternal influence on the average VHS resistance of the offspring; partial regression coefficients for sire-offspring were estimated at 0.30 ± 0.09 and for dam-offspring at −0.1 ± 0.12.
Effects of Rosyside Dace (Clinostomus funduloides) on Microhabitat Use of Rainbow Trout (Oncorhynchus mykiss)
Authors: Grossman Gary D. , Boulé Vital
Published: April 2011

We experimentally examined the effects of competition for space between rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus funduloides) in an artificial stream. These species generally do not exhibit statistically significant differences in microhabitat use in Coweeta Creek, North Carolina, USA. Two competition (trout and dace) and two control (trout only) trials were conducted during spring and summer. Microhabitat use data indicated that the presence of dace did not produce microhabitat shifts in trout. Most behavioral changes could be attributed to acclimation effects or intraspecific competition. Based on field and laboratory results, it does not appear that interspecific competition with dace strongly affects the use of spatial resources in rainbow trout.
Meeting the Challenge of Exotics in the Great Lakes: the Role of an International Commission
Authors: Dochoda Margaret Ross
Published: April 2011

The Great Lakes Fishery Commission has traditionally supported the conservation of genetic diversity native to the Great Lakes, and counseled caution in adding new species to the Great Lakes aquatic community. Since extinction of sub-specific taxa and establishment of new species in the Great Lakes have proven irreversible, caution and conservatism are warranted. The Commission's mandate has served the Great Lakes well in preventing, controlling, and managing exotics. For example, the Commission (1) provides a forum for interjurisdictional consultation prior to planned introduction of new fish species; (2) represents fishery agency concerns for inadvertent introductions to outside interests, as in the case of ship ballast introductions; (3) champions the conservation of genetic diversity native to the Lakes; and (4) controls the exotic sea lamprey at levels which permit fishery agencies to attain their fish community objectives.
Statistical evaluation and modelling of the stomach contents of Icelandic cod (Gadus morhua)
Authors: Stefansson G , Palsson O K
Published: April 2011

A model is proposed for investigating the statistical properties inherent in data on fish stomach contents of cod (Gadus morhua) taken on board Icelandic research vessels. The model explicitly incorporates components to describe the spatial distribution of prey species. It is found that combined delta-gamma (a presence-absence model and an abundance where present model, respectively) generalized additive models are useful in the analysis and explain a considerable portion of the variability in this type of data set, but a fairly large number of degrees of freedom is required to describe the behaviour of the data. A feature of the proposed model is the ability to combine information on the stomach contents from several predator length groups into a single analysis. Analytical results indicate that sampling procedures that base the analysis on the contents of individual stomachs are preferable to those based on combining the contents of several stomachs into aggregate samples.
Sedimentary phosphorus cycling and a phosphorus mass balance for the Green Bay (Lake Michigan) ecosystem
Authors: Klump J V , Edgington D N , Sager P E , Robertson D M
Published: April 2011

The tributaries of Green Bay have long been recognized as major sources of phosphorus in the Lake Michigan basin. The status of Green Bay as a sink or source of phosphorus for Lake Michigan proper has been less well defined. The bay receives nearly 70% of its annual load of phosphorus ( 700 metric tons (t) · year-1) from a single source: the Fox River. Most of this phosphorus is deposited in sediments accumulating at rates that reach 160 mg · cm-2 · year-1 with an average of 20 mg · cm-2 · year-1. The phosphorus content of these sediments varies from <5 to >70 µmol · g-1. Deposition is highly focused, with ~70% of the total sediment accumulation and at least 80% of the phosphorus burial occurring within 20% of the surface area of the bay. Diagenetic and stoichiometric models of phosphorus cycling imply that >80% of the phosphorus deposited is permanently buried. External phosphorus loading to the bay is combined with sediment fluxes of phophorus to arrive at a simple phosphorus budget. Green Bay acts as an efficient nutrient trap, with the sediments retaining an estimated 70-90% of the external phosphorus inputs before flowing into Lake Michigan.
Direct estimates of gear selectivity from multiple tagging experiments
Authors: Myers R A , Hoenig J M
Published: April 2011

A new method is introduced for estimating selectivity of fishing gear from tagging data in which data from many experiments are combined. Selectivity is modeled as a multiplicative function of length and experiment effects using a generalized linear model with a log link function and a binomial error structure. We apply this method to 137 tagging experiments on Atlantic cod (Gadus morhua) conducted from 1954 to 1991. We show that the selectivity of otter trawls changed from the 1960s to the 1980s; during the earlier period the maximum probability of capture occurred at 55 cm and declined for longer fish, whereas in recent years the maximum probability is at approximately 60 cm and remains constant for longer fish. We discuss how selectivity estimates can be used to improve stock assessments.β &  23
Fisheries in China: progress, problems, and prospects
Authors: Zhong Y , Power G
Published: April 2011

China is the leading contributor to world fisheries production. This has been achieved by intensive exploitation of territorial and distant marine waters, by considerable development of mariculture, by extensive use and manipulation of freshwater fish stocks, and by extraordinary expansion and application of better techniques to freshwater culture. Marine capture fisheries were most important until the 1980s when, in response to overexploitation of wild stocks, emphasis shifted to aquaculture. By 1993, aquaculture accounted for more than half of China's fisheries production in spite of considerable expansion of its capture fisheries. Freshwater culture was the biggest fraction, producing 7.9 million t (36.7%). The highest yields were from ponds, followed by reservoirs, lakes, and river channels. Yields per unit area greatly increased because of better rearing methods, polyculture, integrated farm - fish pond culture, introductions of new strains and species, and intensification of culture techniques. Present trends suggest that capture fisheries are approaching their limits. New investments are likely to concentrate on aquaculture. There are risks from disease, deteriorating water quality, use of suboptimal areas, and the demands of increasingly affluent Chinese people. The fisheries sector aims to maximize economic, social, and ecological benefits for Chinese society.
Bootstrap confidence limits for groundfish trawl survey estimates of mean abundance
Authors: Smith S J
Published: April 2011

Trawl surveys using stratified random designs are widely used on the east coast of North America to monitor groundfish populations. Statistical quantities estimated from these surveys are derived via a randomization basis and do not require that a probability model be postulated for the data. However, the large sample properties of these estimates may not be appropriate for the small sample sizes and skewed data characteristic of bottom trawl surveys. In this paper, three bootstrap resampling strategies that incorporate complex sampling designs are used to explore the properties of estimates for small sample situations. A new form for the bias-corrected and accelerated confidence intervals is introduced for stratified random surveys. Simulation results indicate that the bias-corrected and accelerated confidence limits may overcorrect for the trawl survey data and that percentile limits were closer to the expected values. Nonparametric density estimates were used to investigate the effects of unusually large catches of fish on the bootstrap estimates and confidence intervals. Bootstrap variance estimates decreased as increasingly smoother distributions were assumed for the observations in the stratum with the large catch. Lower confidence limits generally increased with increasing smoothness but the upper bound depended upon assumptions about the shape of the distribution.
A critical review of methods of studying fish feeding based on analysis of stomach contents: application to elasmobranch fishes
Authors: Cortés E
Published: April 2011

Using real data sets of elasmobranch fishes as examples, this paper presents a critical review of selected methods and statistical approaches used in fish feeding studies and makes recommendations on the application of such methodology. The percent index of relative importance is proposed as a standardized measure in dietary analyses, and a three-dimensional graphical representation of the diet is introduced. Multiway contingency table (log-linear) analysis is recommended to test for dietary variations. Caution is advised when using rank correlation to study dietary overlap and parametric tests when stomach content data do not satisfy parametric assumptions. Sampling gear type, experimental design, and statistical tests can affect results on diel feeding chronology, and stomach content weights do not suffice to interpret diel feeding chronology. On the basis of sampling requirements and model assumptions, the Diana and Olson-Mullen methods appear to be the most appropriate approaches for estimating daily ration in sharks. Use of resampling techniques is highly desirable because they provide a measure of the error in daily ration estimates. Using several criteria to evaluate the best-fitting model of gastric evacuation in fishes is also strongly advocated. Overall, increased consolidation of methods and analyses is recommended to facilitate comparative studies.
Catch-effort maximum likelihood estimation of important population parameters
Authors: Gould W R , Pollock K H
Published: April 2011

The relative ease with which linear regression models are understood explains the popularity of such techniques in estimating population size with catch-effort data. However, the development and use of the regression models require assumptions and approximations that may not accurately reflect reality. We present the model development necessary for maximum likelihood estimation of parameters from catch-effort data using the program SURVIV, the primary intent being to present biologists with a vehicle for producing maximum likelihood estimates in lieu of using the traditional regression techniques. The differences between the regression approaches and maximum likelihood estimation will be illustrated with an example of commercial fishery catch-effort data and through simulation. Our results indicate that maximum likelihood estimation consistently provides less biased and more precise estimates than the regression methods and allows for greater model flexibility necessary in many circumstances. We recommend the use of maximum likelihood estimation in future catch-effort studies.
Accumulation of domoic acid by the sea scallop (Placopecten magellanicus) fed cultured cells of toxic Pseudo-nitzschia multiseries
Authors: Douglas D J , Kenchington E R , Bird C J , Pocklington R , Bradford B , Silvert W
Published: April 2011

Sea scallops (Placopecten magellanicus) were fed Pseudo-nitzschia multiseries (formerly P. pungens f. multiseries, Nitzschia pungens f. multiseries) cells of high domoic acid (DA) content (4.0-6.7 pg DA cdot cell-1) for 22 days, followed by 14 days of feeding with nontoxic microalgae. DA was incorporated within 24 h by the scallops, with increased uptake after 6 days, and was concentrated in tissues in the following order: digestive gland >> remaining soft tissue >> adductor muscle. A maximum DA concentration of 3108 mu g cdot g-1 was recorded in the digestive gland, approximately 150 times the regulatory limit (20 mu g DA cdot g-1) and among the highest levels observed in bivalve molluscs; however, only trace amounts, 0.7-1.5 mu g cdot g-1, were found concomitantly in the adductor muscle. At the end of the exposure period, 50.9% of the DA that had been supplied to the scallops had been incorporated into the tissues. Concentrations in the digestive gland 14 days after termination of the toxic diet remained high, 752 mu g DA cdot g-1. Throughout the experiment, there was no sign of illness or mortality attributable to high DA loading, although the destructive sampling of animals did not allow us to assess the effects of the toxin in the longer term.
Evidence of density-dependent cohort splitting in age-0 yellow perch, (Perca flavescens): potential behavioural mechanisms and population-level consequences
Authors: Post J R , Johannes MRS , McQueen D J
Published: April 2011

Two sequential cohorts of age-0 yellow perch (Perca flavescens), differing approximately threefold in density, were observed for their ontogeny of spatial distribution, growth, and diet in Lake St. George, Ontario. The lower density cohort exhibited typical ontogenetic spatial behaviour patterns consisting of an early pelagic phase followed by a complete migration to the littoral zone by midsummer. The high-density cohort appeared to split into a faster growing littoral component and a slower growing pelagic component which persisted throughout the growing season and into the next spring. The differences in spatial behaviour between these two cohorts could not be explained by spatial patterns in prey availability. The overwinter mortality rate for the high-density cohort was approximately double that observed for the low-density cohort. No direct observations of behaviour were made of the two cohorts, but distribution and growth data, along with arguments from competition theory, support the hypothesis that interference competition is the density-dependent mechanism responsible for the aberrant ontogeny of spatial distribution of the high-density cohort. The occurrence of interference competition in which competitively superior individuals can monopolize optimal habitats, relegating other individuals to suboptimal habitats, infers an asymptotic stock and recruitment relationship.
Changes in size at maturity of Fraser River sockeye salmon (Oncorhynchus nerka) (19521993) and associations with temperature
Authors: Cox S P , Hinch S G
Published: April 2011

Unlike other Canadian Pacific salmon (Oncorhynchus spp.), long-term declines in the size at maturity of Fraser River sockeye salmon (O. nerka) have not been reported in past studies. Using data specific for 10 Fraser River sockeye stocks, we demonstrate that size at maturity has generally declined over the past 42 yr for females in all stocks and for males from eight stocks. Independent of this temporal trend, we found that size at maturity of both sexes in all stocks was smaller in years when sea surface temperatures were relatively warm. Slower growth in warmer years may be caused directly by increased metabolic demand, or indirectly by oceanic changes that influence food acquisition. We speculate that fitness of Fraser River sockeye will be reduced in the future if sea surface temperature increases and salmon abundance remains near present levels.
Fertilization of an oligotrophic lake with a deep chlorophyll maximum: predicting the effect on primary productivity
Authors: Gross H P , Wurtsbaugh W A , Luecke C , Budy P
Published: April 2011

We investigated how epilimnetic fertilization would affect chlorophyll levels and light penetration of oligotrophic sockeye salmon (Oncorhynchus nerka) lakes and how the resulting self-shading would affect primary production of the prominent deep chlorophyll maxima (DCM) of the lakes. Epilimnetic nutrient additions to large mesocosms (330 m3) in Redfish Lake, Idaho, increased levels of primary productivity and chlorophyll a but decreased Secchi depths and light available in the metalimnion and hypolimnion. Redfish Lake and other Sawtooth Valley (Idaho) lakes had DCM in which the mean chlorophyll a peaks were 240-1000% of mean epilimnetic chlorophyll a concentrations. The DCM existed at low light levels and accounted for 36-72% of the lakes' primary production. Simulations using photosynthesis-irradiance (P-I) curves demonstrated that fertilization would increase predicted water column primary production by 75-101%. Most of this increase occurred in the epilimnion, with only a slight decrease occurring in the DCM as the result of increased shading.
Accuracy and precision in sampling hyporheic fauna
Authors: Fraser B G , Williams D D
Published: April 2011

A series of interstitial faunal samples was taken from a riffle in the Speed River, southern Ontario, Canada, to compare the field performance of four hyporheic samplers: the standpipe, colonization, and freeze corers and a pump sampler. Each of the samplers proved useful for collecting purely qualitative data, but statistical differences in some of the measured quantitative parameters were identified. The colonization corer significantly underestimated invertebrate density at each of the depths tested (20, 40, and 60 cm below the surface of the river bed). Taxonomic richness did not differ among the samplers. A sampling bias in the pump sampling method was identified in terms of both the proportion of insect larvae captured and the mean chironomid body size and is probably the result of a filtering effect of the interstices. Sampling precision estimates of density, richness, and organismal size ranged from 20 to 40%, but no pattern among the four samplers for any of the measures was observed. We conclude that, whereas the standpipe and freeze coring methods most effectively characterize the hyporheos, one of the other methods might prove acceptable under specific field circumstances or under certain practical constraints.
Toxicological mechanisms of a multicomponent agricultural seed protectant in the rainbow trout (Oncorhynchus mykiss) and fathead minnow (Pimephales promelas)
Authors: Greene Michael W , Kocan Richard M
Published: April 2011

Ethylene glycol (EG) and thiram, an aldehyde dehydrogenase inhibitor, are components of the seed protectant Vitavax-200. EG is a common solvent, thought to be nontoxic, whereas thiram, a dithiocarbamate known to be toxic to fish, is an active ingredient in Vitavax-200. When the\i toxicities of EG and thiram were investigated individually and as a mixture in rainbow trout (Oncorhynchus mykiss) and fathead minnow (Pimephales promelas), a strong synergistic toxic effect was observed. Using a constant sublethal concentration of thiram, a 5- to 19-fold increase and a 2- to 2.4-fold increase in EG toxicity was observed in fathead minnow and rainbow trout, respectively. The toxicity of EG following pretreatment of rainbow trout with pyrazole, an alcohol dehydrogenase inhibitor, was decreased by 22% whereas pretreatment with cyanamide, an aldehyde dehydrogenase inhibitor, increased toxicity 3.4-fold. The results indicate that thiram inhibits the complete metabolism of EG, resulting in the buildup of a toxic aldehyde intermediate and increasing the toxicity of EG.
The Laurentian Great Lakes experience: a prognosis for the fisheries of Atlantic Canada
Authors: Kerr S R , Ryder R A
Published: April 2011

The fish production systems of Atlantic Canada are in a state of crisis, in the social, political, economic, and biological senses. We doubt that the true scope and provenance of the crisis have yet been apprehended by the responsible managers. Our view is that the obvious overfishing that precipitated the problem is but the first major instance of further devastation that will visit the fishery. We find numerous parallel behaviours among the various Atlantic fisheries and the patterns of demise of the fish production systems of the Great Lakes basin ecosystem. Unless management regimes awaken to these realities, the fisheries of Atlantic Canada are doomed to the same dismal scenarios as were witnessed in the Great Lakes. Properly understood, remedial measures painfully learned in the Great Lakes could usefully inform responsible management agencies in Atlantic Canada. A new institutional structure is required in Atlantic Canada to deal with the requirements of ecosystem management.
Latitudinal variation in vertebrate number has a genetic basis in the Atlantic silverside, Menidia menidia
Authors: Billerbeck J M , Ortí G , Conover D O
Published: April 2011

Variation in the number of vertebrae was examined in field and laboratory populations of the Atlantic silverside, Menidia menidia, drawn from across the species' range along the Atlantic coast of North America. Vertebral counts of wild fish increased and were tightly correlated (r = 0.995) with latitude in accordance with Jordan's rule. This strong correlation persisted in laboratory stocks reared for multiple generations in a range of common environments, revealing a genetic basis to Jordan's rule. Selection over the winter in the field increased mean vertebral number in the northern population, intensifying the latitudinal trend in vertebral number that existed in the fall. The combined field and laboratory data support the hypothesis that vertebral number in fishes is adaptive. Moreover, these data implicate natural selection as opposed to random genetic drift as the cause of Jordan's rule.
Phylogenetic analysis of Pacific salmon (genus Oncorhynchus) using nuclear and mitochondrial DNA sequences
Authors: Domanico M J , Phillips R B , Oakley T H
Published: April 2011

Recent phylogenetic analyses of Pacific salmon of genus Oncorhynchus based on sequences from mitochondrial DNA and one nuclear growth hormone intron supported two subgroups:one with chinook (O. tshawytscha) and coho (O. kisutch) salmon and the other with pink (O. gorbuscha), sockeye (O. nerka), and chum (O. keta) salmon. In the latter group, a sister relationship was indicated between pink and chum salmon. Previous studies based on morphological and allozyme data had suggested a closer relationship between pink and sockeye salmon. In this paper we present a combined analysis of 4365 base pairs aligned sequence from nuclear and mitochondrial genes including new sequence data from the internal transcribed spacers (ITS1 and ITS2) of the nuclear ribosomal DNA, the sequences of three growth hormone introns (GH1C, GH2C, GH2D) and the sequences of the ATPase6 and ND3 genes of the mtDNA. Phylogenetic analysis of the combined data set gives strong support to a close relationship between pink and chum salmon and between coho and chinook salmon.
Taxon diversity in the genus Holopedium (Crustacea: Cladocera) from the lakes of eastern North America
Authors: Hebert P DN , Finston T L
Published: April 2011

Although the genus Holopedium contains only two recognized species, the taxonomic status of many North American populations has been uncertain. By exploiting allozyme analysis to clarify taxonomic assignments, this study shows that Holopedium populations in the lakes of eastern North America are separated into two genetically distinct lineages. Component populations of each group show both low levels of genetic polymorphism and high genetic similarity. Aside from their genetic divergence, morphological and ecological differences among the groups support their recognition as distinct species. Holopedium gibberum is broadly distributed in the cool temperate regions of North America, while H. amazonicum occurs in the southern and eastern portions of the continent. The latter pair of species co-occur at some sites without hybridization, confirming their reproductive isolation.
Timing of spawning and assessment of a degree-day model to predict the in situ embryonic developmental rate of white sucker, Catostomus commersoni
Authors: Hamel P , Magnan P , Lapointe M , East P
Published: April 2011

We sampled eggs and larvae of white sucker, Catostomus commersoni, on six spawning grounds to (i) determine the influence of water temperature and discharge on spawning and (ii) assess the reliability of four degree-day equations developed to predict the attainment of organogenesis, eyed egg, hatching, and swim-up phases. We estimated a threshold temperature for spawning of 13°C at four sites and 10°C at two colder sites. A delay of 2 or 3 days was observed between the threshold and the onset of spawning. On average, the degree-day equations predicted the attainment of the developmental phases with an accuracy of 1.6 days, except at the two colder sites, where developmental rates were faster than predicted. The lower spawning temperatures and faster developmental rates observed at the colder sites were interpreted as adaptations to the reduced growing season. Finally, at one site the drift of swim-up larvae occurred over a 6-day period even though spawning lasted 24 days; it was not possible to determine the exact duration of drift at the other sites. This synchronization could be an adaptation lowering the risk of predation on individual larvae, as all the larvae enter the lake within a few days.
Impact of hypolimnetic oxygenation on profundal macroinvertebrates in a eutrophic lake in central Alberta. I. Changes in macroinvertebrate abundance and diversity
Authors: Dinsmore W P , Prepas E E
Published: April 2011

Hypolimnetic oxygenation from 1988 to 1991 in the north basin of Amisk Lake increased mean summer (June-August) dissolved oxygen (DO) concentrations in the deep hypolimnion (25 m) from <0.4 mg ·L-1 during pretreatment years (1980-1987) to 2.7 mg ·L-1 during treatment. Mean summer hypolimnetic temperatures at 25 m also increased from 6.3 (pretreatment) to 8.1°C (treatment). Profundal (15-25 m) Chironomus spp. abundance in the treated basin increased from <100 to >2000 ·m-2 from 1988 to 1991 whereas Chaoborus spp., Tubificidae, and other taxa remained uncommon at similar depths. Shannon-Weaver indices of diversity decreased as oxygenation progressed, in contrast with previous studies. Similar patterns in densities and diversity were observed in the south basin of Amisk Lake, although the increase in DO concentrations was smaller relative to the north basin. The impact of increased water temperature on macroinvertebrates appeared minor relative to the effects of increased DO concentrations. No changes in macroinvertebrate communities were noted in a nearby reference lake during the study period. Responses to hypolimnetic oxygenation in Amisk Lake differed markedly from those reported for smaller, single-basined water bodies.
Population dynamics and fishery policy for migratory resources with two migration paths
Authors: Yamauchi A , Matsumiya Y
Published: April 2011

The population dynamics and fishery policy for a migratory resource with two migration paths are analyzed, based on the supposition that the resource separates into two groups, each migrating along and caught on a different path, after reproduction in a limited area. Two possible mechanisms determining individual migration paths are considered: (i) ``nongenetically controlled'' migration and (ii) ``genetically controlled'' migration. Initially, the relationships between the resource population dynamics and the fishery are analyzed for both these cases. Based on these results, the optimal fishery policy for each migration path is analyzed. Two criteria to be maximized were considered: (i) the ``game situation,'' which aims to maximize catches on each fishery path, and (ii) the ``cooperative situation,'' which aims to maximize the total, overall catch on both paths. In the case of genetically controlled migration, a fishery based on one path negatively affects recruitment on that path but positively affects recruitment on the alternative path. In both the nongenetically controlled and genetically controlled migration cases, the cooperative policy resulted in higher overall maximum catch, especially in the latter case. In the genetically controlled migration case, convergence to equilibrium is often slow, the rate being affected by density dependence of mortalities.
Temperature-dependent allometric models to estimate zooplankton production in temperate freshwater lakes
Authors: Stockwell J D , Johannsson O E
Published: April 2011

Empirical relationships between body size and temperature, and daily P/B of temperate freshwater zooplankton species were derived from the literature. Body size explained 81% of the variation in daily P/B of zooplankton at temperatures <<= 10°C and 48% at temperatures >10°C. The two relationships did not differ in slope but significantly differed in elevation. The regression models were then applied to zooplankton samples collected from a midlake station in Lake Ontario to predict zooplankton seasonal production. Production estimates from the regression models, when compared with estimates from the egg ratio method for the same data set, were similar for cladoceran species, four and 10 times higher for two copepod species, and two times higher for total zooplankton production. In general, these differences are within the range expected based on previous studies that compared different production models. The regression models can provide quick, independent estimates of zooplankton production to complement estimates based on traditional, species-specific methods. Furthermore, the models can be used in conjunction with automated synoptic instruments, such as optical plankton counters and temperature probes, to provide production estimates that better represent large, complex systems such as the Great Lakes.
Organic contaminants in submersed macrophytes drifting in the Detroit River
Authors: Lovett-Doust J , Lovett-Doust L , Biernacki M , Mal T K , Lazar R
Published: April 2011

Macrophytes drifting in the Detroit River were sampled and analysed for contaminants at monthly intervals from September 1990 to September 1991. Twelve species of submersed macrophytes were identified, as well as algae and leaves of terrestrial plants. Drifting plant debris was greatest in August-September, when Potamogeton spp. and Najas sp. predominated. Over the study period, a total of 60.57 times 106 kg fresh mass (3.0285 times 106 kg ash-free dry mass) of plant debris drifted out of Lake St. Clair into the Detroit River annually. Organochlorine content differed between plant taxa and according to the time of year. Annual contaminant burden of the Detroit River by upriver contributions was carried mostly by Potamogeton spp. and Najas sp. Total annual load of organochlorines in drifting plant debris was estimated to be 155 g, including 124 g of PCBs. These bioavailable contaminants may enter the detrital compartment of aquatic food webs, following plant senescence, or may be taken up directly by herbivores. Contaminants associated with plant debris drifting from Lake St. Clair and the Detroit River contribute a significant burden of bioavailable organic contaminants to the western basin of Lake Erie.
Influence of biomass and ocean climate on the growth of Pacific herring (Clupea pallasi) from the southwest coast of Vancouver Island
Authors: Tanasichuk R W
Published: April 2011

I examined the growth of Pacific herring (Clupea pallasi) from the southwest coast of Vancouver Island using data for over 83 000 fish seined between 1975 and 1996. Size-at-age (length, total mass) of recruits (age 3) was negatively related to parental biomass. Length was also negatively related to sea temperature over the first growing season and positively related to salinity later in the third growing season. Prerecruit effects explained variations in mass and length for adult herring ages 4 and 5, respectively. Growth of adults was described as growth increments (growth rates). Seasonal growth in length for adults was assumed to be a linear function of time, and growth in mass an exponential function. Daily growth rates for length were negatively related to initial length. Instantaneous daily growth rates in mass were a negative function of initial mass, adult biomass, and sea temperature in August. Interannual variations in condition suggest that adults grow differently in mass than they do in length. I suggest that length is not synonymous with mass as a measure of adult growth. Consequently, it provides little, if any, information on surplus energy accumulation by adults and therefore adult fish contribution to stock productivity.
Ascorbic acid in the gonads of North Sea dab (Limanda limanda) during the reproductive cycle
Authors: Saborowski Reinhard , Koprivnjak Jean-François , Sisak Mitchell M , Sahling Gerrit , Buchholz Friedrich , Lum Ken R , Schneider Rolf
Published: April 2011

Total ascorbic acid was measured in the gonads of North Sea dab (Limanda limanda) throughout one reproductive cycle. In the ovaries, the concentration of ascorbate began to increase during the resting period in summer and reached maximum values of 400 μg .g fresh weight (fw)-1 at the onset of ovary maturation in fall. Concentrations declined rapidly towards the spawning period in spring and reached the lowest values of 80-100 μg .g fw-1. The maximum deposition of ascorbate in the ovaries amounted to 2.5 mg .organ-1 and occurred in late winter, corresponding to the beginning of the spawning period. In the testes, ascorbate concentrations were lower than in the ovaries, reaching a maximum of 170 μg .g fw-1 in early fall. The lowest values of 20-60 μg .g fw-1 appeared in winter and spring. In the testes the highest deposition of ascorbate amounted to 110 μg .organ-1 and appeared at the beginning of maturation. The sexual differences and seasonal variations are discussed in relation to the reproductive biology of dab.
Diurnal and nocturnal feeding activity in Arctic char (Salvelinus alpinus) and rainbow trout (Oncorhynchus mykiss)
Authors: Alanärä Anders , Brännäs Eva
Published: April 2011

When food is limited and competition for it is high, individual fish may adopt different diel activity patterns. We followed individual feeding activity in groups of 10 Arctic char (Salvelinus alpinus) and rainbow trout (Oncorhynchus mykiss) using a combined self-feeding and PIT-tag system. Food was supplied at low and high rewards to five replicate groups of Arctic char and rainbow trout. Four categories were identified in both species: high-triggering diurnal (diurnal fish with the highest self-feeding activity), low-triggering diurnal, nocturnal, and nontriggering fish. On average, the photophase proportion of the total daily activity was approx 90% in diurnal and approx 20% in nocturnal individuals. Rainbow trout offered high rewards did not show any diel preferences. Diurnal Arctic char and rainbow trout with the highest self-feeding activity were initially larger and had the highest growth rates, indicating a high social position. Nocturnal fish were initially smaller and their proportion of trigger actuations much lower than the high-triggering diurnal fish. These still grew successfully whereas nontriggering fish grew significantly less. Thus, some individuals with a low social status may apply an alternative strategy to attain adequate growth by feeding at night when dominant individuals are less aggressive. This may be referred to as concurrent dualism (diurnalism and nocturnalism).
Implications of interference among fishing vessels and the ideal free distribution to the interpretation of CPUE
Authors: Gillis D M , Peterman R M
Published: April 2011

Despite recognized biases, catch per unit effort (CPUE) statistics remain widely used for the estimation of fish abundance. Previous workers have shown that CPUE can be a misleading index of abundance due to fish behavior, the nominal effort units used, and increases through time in efficiency of fishing (catchability). We examine the theoretical implications of a different factor, interactions among fishing vessels, for the relationship between abundance and CPUE. Our model simulates a fishery that occurs in several adjacent fishing grounds. The spatial distribution of catch and effort is based on a simplification of the Baranov catch equation, the relationship between fishing efficiency and local fishing effort (interference), and the assumptions of the ideal free distribution. Our results indicate that (i) even low levels of interference among fishing vessels can cause a breakdown in the correlation between CPUE and local abundance and (ii) the influence of interference on this relationship is dependent on the correlation of abundances among adjacent areas. Our model suggests an alternative index of abundance, based on the proportion of fishing effort on a ground, that would be appropriate for cases where interference occurs among fishing gear.
Distribution of gill parasite (Lernaeocera branchialis) infection in Northwest Atlantic cod (Gadus morhua) and parasite-induced host mortality: inferences from tagging data
Authors: Jones Megan EB , Taggart Christopher T
Published: April 2011

We describe geographic and host size related trends in the prevalence of the gill parasite Lernaeocera branchialis (Copepoda, Pennellidae) infecting Atlantic cod (Gadus morhua) in coastal Newfoundland and Labrador and assess the effect of parasitism on cod survival in the wild. Using cod-tagging studies conducted between 1962 and 1989, we test three null hypotheses: (1) parasite prevalence in the Northwest Atlantic is latitudinally invariant, (2) infected cod have the same survival probability as parasite-free cod, and (3) parasite prevalence is independent of fish length. The first hypothesis is rejected given a significantly negative relationship between prevalence and latitude. The second hypothesis is rejected in one geographic region where 8% fewer infected cod from northeast Newfoundland were recaptured relative to uninfected cod. This implies that parasitized cod can suffer an 8% differentially higher mortality relative to nonparasitized cod. The third hypothesis is rejected because the proportion of cod infected was generally greatest in the 43-49 cm length-class and decreased significantly with increasing length. Differential survival between infected and uninfected cod within length-classes was not observed. The use of L. branchialis as a population marker warrants caution. The parasite has the potential to affect the recovery of depleted Northwest Atlantic cod stocks in a geographically differential manner.
Anomalous migrations of anadromous herrings revealed with natural chemical tracers
Authors: Limburg Karin E
Published: April 2011

Anadromous herrings of the genus Alosa are generally thought to leave their natal river or estuary at the end of the first growing season and return as mature adults to spawn. Nevertheless, immature yearling alosines have been observed in large numbers in the Hudson River estuary during and after the spring spawning run. I analyzed the stable isotopic ( delta 13C, delta 15N) compositions of 26 blueback herring (Alosa aestivalis), eight American shad (Alosa sapidissima), and 10 alewife (Alosa pseudoharengus) collected from 55-225 km above the estuary mouth during April-July and compared them with isotopic compositions of young-of-year (resident) alosines, as well as adults (marine phase). delta 13C of the May-caught American shad and alewife indicated a marine origin (greater than -22.5omicron); blueback herring split into both marine and freshwater ( delta 13C less than -25.5omicron) groups. June-caught fish had intermediate values. Microprobe traces of Sr in these fishes' otoliths helped further to discriminate between resident fishes and those that had migrated to sea (or brackish water) and then moved back upriver for a period of several weeks. The combination of biogeochemical tracer methods holds promise for elucidating complex life histories of fishes and helps to pose questions about plasticity of migration.
Decision-making for the restoration of Atlantic salmon populations damaged by acid precipitation: the interplay of biology and economics
Authors: Power M
Published: April 2011

Acidification of Atlantic salmon (Salmo salar) rivers represents a major threat to salmon production in much of Nova Scotia, Canada. Efforts at understanding the efficacy of proposed remedial strategies have concentrated on estimating the biological parameters of the acidification issue. However, the dominance of societal values in the allocation of resources to fisheries management problems demands alternative strategies for the remediation of acidity in salmon rivers be developed that account for both the biological and cost constraints on remedial strategy selection. A theoretical framework incorporating biological and cost detail is developed that demonstrates the dependence of optimal remedial strategy selection on the biological, physical, and cost parameters of acidification and responses to it in the juvenile portion of the life history. Marine smolt survival is also shown to have an influence on the selection of the optimal remedial strategy. Only when all relevant biological and cost parameters are appropriately estimated, validated and included in decision-making can useful strategies promising to optimize the restoration of Atlantic salmon stocks in acidified waters be developed.
Genetic changes in Atlantic salmon (Salmo salar) populations of Northwest Irish rivers resulting from escapes of adult farm salmon
Authors: Clifford S L , McGinnity P , Ferguson A
Published: April 2011

A study was made of rivers in Northwest Ireland where escapes of adult Atlantic salmon (Salmo salar) are known to have occurred from adjacent sea cages. Two markers that showed substantial frequency differences between these farm and wild populations were used: an Ava II-B mtDNA haplotype and allele E at minisatellite locus Ssa-A45/2/1. Farmed populations also showed a significant reduction in mean heterozygosity over the three minisatellite loci examined. Independent occurrence of mtDNA and minisatellite DNA markers in several juvenile samples indicated interbreeding of escaped farm salmon with wild salmon. The proportion of juveniles of maternal farm parentage in two rivers ranged from 18% in 1993 to 2% in 1995 with an average of 7% in both rivers (1993-1995) and a maximum frequency of 70% in an individual sample. Only a small proportion of 29 000 adult farm salmon that escaped in spring 1992 appear to have bred successfully in the rivers studied. Juveniles of farmed parentage survived to at least the 1+ summer stage, but the subsequent fate of these fish could not be determined in the time period of the study.
Characterization of the photoautotrophic algal and bacterial communities in a large, shallow, subtropical lake using HPLC-PDA based pigment analysis
Authors: Steinman Alan D , Havens Karl E , Louda J William , Winfree Nancy M , Baker Earl W
Published: April 2011

Pigment abundances of the oxygenic and anoxygenic photoautotrophic communities from sediments and the water column in Lake Okeechobee, Florida, were estimated using reverse-phase high-performance liquid chromatographic (RP-HPLC) and photodiode array (PDA) UV/VIS (350-800 nm) spectrophotometric analyses. Thirty lipophilic pigments were identified and measured in the samples, with the most abundant overall (sediment and open-water samples combined) being chlorophyll a (38.1%), fucoxanthin (12.6%), pheophytin a (7.6%), zeaxanthin (6.6%), and pyropheophytin a (3.6%). Relative abundance of chlorophyll a was greater in the water column than in the sediments (58.3 versus 24.3% of all pigments) whereas pheophytin a comprised 9.1% of the total pigments in the sediments but only 3.7% of the total pigments in the water column. Principal component analysis (PCA) separated the sediment samples from those collected in the water column; this discrimination appears to be a function of pigment integrity in that sediment assemblages had much greater relative abundances of degraded pigments. Different regions of the lake were weakly separated by PCA based on pigments. The relatively weak degree of separation may reflect the overwhelming abundance of chlorophyll a at all sites. Overall, the pigment assemblage in Lake Okeechobee suggests cyanobacteria-diatom dominance. Out of 65 sampling events, pigments from anoxygenic photoautotrophs (e.g., bacteriochlorophylls) were detected 17 times but accounted for >20% of total chlorophyll only five times. Bacteriochlorophylls were observed only in the sediments and were most abundant during June and September, when winds were calm and temperatures warm, and at relatively shallow sites.