bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection of Dosages of Oxytetracycline for Age Validation Studies
Authors: McFarlane G. A. , Beamish R. J.
Published: April 2008

Oxytetracycline (OTC), injected to mark the otoliths of sablefish (Anoplopoma fimbria), causes mortality directly in proportion to the dosage administered. The selection of an appropriate dosage requires minimizing mortality while maximizing the number of fish that have a usable OTC mark. Laboratory studies could not be used to determine appropriate dosages. Dosages that substantially increased mortality in the ocean did not cause any mortality in the laboratory. For sablefish, we recommend a dosage of 25–35 mg OTC/kg fish.
Analysis of 2-Methylisoborneol in Water, Mud, and Channel Catfish (Ictalurus punctatus) from Commercial Culture Ponds in Mississippi
Authors: Martin J. F. , McCoy C. P. , Greenleaf W. , Bennett L.
Published: April 2008

We describe a new method for the isolation of 2-methylisoborneol (MIB) from channel catfish (Ictalurus punctatus) that have been declared "off-flavor" organoleptically. The method involves microwave cooking fish under a nitrogen stream and trapping the condensate at −80 °C. The fish condensate was extracted with hexane which was reduced to 100 μL and analyzed by gas chromatography. Concentrations as low as 5 ng MIB∙g fish−1 were routine detected. A bioconcentration value for MIB in off-flavored fish flesh was 28.1 ± 14.0 (±SD) concentration water/concentration fish. Analysis of off-flavored fish collected at the processing plant consistently showed elevated concentrations of MIB. Geosmin, another compound known to cause flavor and odor problems in fish flesh, was not detected.
A General Fishery Model for a Size-Structured Fish Population
Authors: Schnute Jon
Published: April 2008

This paper describes a fishery model based on size, rather than age, as the fundamental population variable. The model's key ingredient is a density function related to number of fish within any given size range. A key assumption is that selectivity in the fishery is determined by size, not age, and that fish can reach recruitment size at various ages. The theory easily yields moment equations comparable with those obtained recently by Fournier and Doonan; for example, the general moment equation here is derived in a four-line proof. The paper gives detailed recommendations for tailoring the new model to a specific fishery, where model complexity is determined by the available data. The new theory places earlier models of Deriso and Schnute in the context of generalized cohort analysis, where size-dependent mortality is allowed. In particular, the paper identifies a potential problem with these earlier models and proposes a solution. All results are interpreted biologically to provide both conceptual and analytical tools for stock assessment.
Determination of Population Discreteness in Two Species of Shrimp, Pandalus jordani and Pandalopsis dispar, from Coastal British Columbia Using Parasite Tags and Other Population Characteristics
Authors: Thompson A. B. , Margolis L.
Published: April 2008

Two digenean metacercariae, Neolebouria tinkerbellae and an unidentified species (Metacercaria A), parasitizing Pandalus jordani, and Metacercaria A parasitizing Pandalopsis dispar, were used as naturally occurring biological markers to determine intraspecific population discreteness. Shrimp were sampled from Imperial Eagle Channel and Trevor Channel, Barkley Sound (west coast of Vancouver Island, British Columbia), and from an adjacent offshore area. The mean size at age and the age composition of P. jordani and P. dispar were also estimated. Many differences occurred among samples in the abundances of the metacercariae, in the mean size at age, and in the age composition for each shrimp species, demonstrating that separate shrimp populations existed. In some cases, natural boundaries separated populations of shrimp, for example, the island chain and shallow waters which lie between Imperial Eagle Channel and Trevor Channel. In other cases, such as occurred for the separate populations identified within Imperial Eagle Channel, there were no apparent topographic barriers. No evidence for the occurrence of offshore or onshore migrations of P. jordani or P. dispar was obtained.
Empirical Models for Zoobenthic Biomass in Lakes
Authors: Rasmussen Joseph B. , Kalff Jacob
Published: April 2008

Estimates of macrozoobenthos from the literature were regressed against a series of limnological variables to yield empirical models for zoobenthic biomass in the profundal, sublittoral, and littoral zones of lakes. Variables indicative of phytoplankton biomass (chlorophyll concentration, total phosphorus concentration, and Secchi disk transparency) explained between 14 and 57% of the variance of zoobenthic biomass ((g/m2)0.1). Other factors such as humic colour, morphometry (slope, mean depth, ratio of mean to maximum depth, and lake area), and mean annual air temperature substantially increased the amount of explained variance. In the profundal and sublittoral zones, the best models explain 70% of the variance in zoobenthic biomass. Littoral zone models explained less than 50%, and this deficiency was attributed to sampling difficulties and to high local variability of slope and wave exposure in the littoral zone.
Equilibrium Models for Seasonal Dynamics of Plankton Biomass in Four Oligotrophy Lakes
Authors: Walters Carl J. , Krause Edith , Neill William E. , Northcote Thomas G.
Published: April 2008

Plankton biomass dynamics were monitored over an 11-yr period in four coastal British Columbia lakes while they were disturbed by salmonid introductions, fertilization, and zooplankton harvesting. Except for dramatic zooplankton responses to fertilization, the lakes had relatively simple and stable seasonal biomass patterns, with midsummer zooplankton peaks and no clear seasonal cycles in biomass of unicellular phytoplankton. Simple models predict that equilibrium biomasses should follow the observed pattern, provided zooplankton grazing and metabolic rates are temperature independent; experimental measurements of these rates did not show clear temperature dependence. Enclosure studies showed that phytoplankton biomass can return quickly (48 – 72 h) to equilibrium after disturbance, but zooplankton biomass responds more slowly (2- to 3-wk recovery times), yet fast enough to track a seasonally varying equilibrium. We conclude that the biomass equilibrium of unicellular phytoplankton is set by grazing and metabolic rates of zooplankton, while the zooplankton biomass equilibrium is set by phytoplankton productivity.
Reproductive Responses of Five White Sucker (Catostomus commersoni) Populations in Relation to Lake Acidity
Authors: Trippel Edward A. , Harvey Harold H.
Published: April 2008

White sucker (Catostomus commersoni) in three acid lakes (pH 4.90, 5.56, and 5.58) frequently matured at older ages and larger sizes and had shorter reproductive life spans than white sucker in two circumneutral lakes (pH 6.30 and 6.35). Reproductive life span was positively correlated in females (r = 0.97) and males (r = 0.85) with lake pH. In the acid lakes, elevated mortality rates coincided with the onset of sexual maturity whereas in circumneutral lakes, mortality rates did not change at maturity. Ovarian weight and ovarian somatic index values were not significantly different between females from two acid and two circumneutral lakes. Values of fecundity, ova dry weight, testicular weight, and testicular somatic index of fish in acid lakes were either significantly greater than or equal to values in white sucker from circumneutral lakes. Results are discussed within the context of life history theory.
Modeling and Forecasting Primary Production Rates Using Box–Jenkins Transfer Function Models
Authors: Keller Aimee
Published: April 2008

Box–Jenkins transfer function models were developed for time series of integrated hourly primary production rates. A 28-mo record of 56 biweekly measurements collected from seven mesocosms during a nutrient addition experiment was analyzed. Incorporation of two input variables (phytoplankton biomass and hourly light) significantly improved the fit of the models. When compared with standard regression models, the time series models all had reduced residual variance. The forecasting ability of the final fitted model for a control system was demonstrated with independent data from the two replicate control mesocosms.
Binational Management of Pacific Hake (Merluccius productus): A Stochastic Modeling Approach
Authors: Swartzman Gordon L. , Getz Wayne M. , Francis Robert C.
Published: April 2008

We use an age-structured stochastic recruitment model to examine a stock managed by two nations: the Pacific Hake (Merluccius productus) fishery. The model computes the mean and variance in stock and yield and the probability (risk) that the stock falls into a critically low condition. An optimization algorithm finds effort quotas that maximize expected yield over a short-term planning horizon while constraining the risk of critically low stock conditions. Yields produced exceed those of constant effort alternatives, but with year-to-year fluctuations in fishing effort including fishery closures. These occur in different years for the United States and Canadian fisheries depending on the condition of the stock and the incoming year class. Binational management of fishing effort is also presented as a two-person game with a weighted difference between fishery catch and effort as payoff. Nash (rational players), maxi–min (self-protecting), and Pareto (cooperative optimizing) strategies are examined. There are striking shifts in relative effort between United States and Canadian fisheries as the cost of effort changes relative to catch. This approach shows potential benefits to both players in playing a long-term cooperative strategy.
Microbial Communities on Leaf Material Protected from Macroinvertebrate Grazing in Acidic and Circumneutral Streams
Authors: Palumbo Anthony V. , Mulholland Patrick J. , Elwood Jerry W.
Published: April 2008

To determine how low pH and high aluminum concentrations directly affect microbial activity on decomposing leaves in streams, we examined microbial communities on leaf surfaces using in situ flow-through chambers which exclude macroinvertebrates. Bacterial production (thymidine incorporation) on leaf material was significantly higher at pH 6.4 than at 4.9 after 4 wk of incubation, and this difference persisted for the last 5 wk of the experiment. Microbial respiration was greater at the high pH site after 6 wk, and there were no significant differences in ATP standing stock. Concentrations of oxalate-extractable aluminum on the leaf material increased significantly within the first 4 wk of incubation and stabilized at significantly greater levels at low pH (4.66 mg∙g−1) than at high pH (1.70 mg∙g−1). Transferring leaf material from the high-pH to the low-pH stream had negative effects after only 1 wk of incubation. However, transferring from low pH to high pH did not result in significant positive effects until 4 wk after the transfers. The reduced microbial production and respiration in the low-pH stream imply that decomposition rates may be slower in acidified systems due, at least in part, to direct effects of acidification on microbial activity.
Testing of Male Sockeye Salmon (Oncorhynchus nerka) and Steel head Trout (Salmo gairdneri) for Infectious Hematopoietic Necrosis Virus
Authors: Mulcahy D. , Pascho R. J. , Batts W. N.
Published: April 2008

Infectious hematopoietic necrosis (IHN) virus has been isolated only rarely from whole milt samples of male sockeye salmon (Oncorhynchus nerka). In 3 yr of testing, virus incidences in males ranged from 0 to 13% when milt was sampled but were 60–100% with spleen or kidney. When IHN virus was isolated from sockeye salmon milt at titers less than 3.00 log10 plaque-forming units (pfu)/mL, the level of virus in the kidney or spleen exceeded 7.00 log10 pfu/g. Higher rates of IHN virus isolation from kidney or spleen than from milt were also generally found in steelhead trout (Salmo gairdneri), although the differences were less pronounced than in sockeye salmon. Furthermore, virus was sometimes isolated from steelhead trout milt when the level of virus in kidney or spleen samples was very low, and was recovered from some milt samples when none was isolated from the corresponding spleen sample. When male salmonids are tested for IHN virus, kidney or spleen samples are superior to whole milt, but milt should be included for critical examinations.
Preexposure and Subsequent Resistance to Lead in Yearling Brook Trout Salvelinus fontinalis
Authors: Tang Yong , Garside E. T.
Published: April 2008

Potential for acclimation of brook trout, Salvelinus fontinalis, at sublethal levels of dissolved lead was measured. Samples of yearlings (19.2 ± 6.1 g) were preexposed continuously to environmentally realistic sublethal levels (10, 24, and 37 μg Pb/L) for 10, 20, 30, and 40 d and subsequently exposed to a lethal level (2 mg Pb/L), during which the incidence of mortality was recorded. Survival intervals of fish preexposed to 10 μg Pb/L were not significantly different from those preexposed to tap water (<2 μg Pb/L) in each preexposure interval. Fish preexposed to 24 μg Pb/L for 10 and 20 d were less resistant but returned to normal resistance after 30 and 40 d of preexposure. Fish preexposed to 37 μg Pb/L had significantly shorter survival intervals than those preexposed to tap water in each preexposure interval. The maximum acceptable toxicant concentration (MATC) of lead for brook trout is set between 24 and 37 μg Pb/L.
Oxygen Conditions in Two Prairie Pothole Lakes During Winter Ice Cover
Authors: Baird D. J. , Gates T. E. , Davies Ronald W.
Published: April 2008

Winter oxygen depletions rates (WODR) from two small southern Alberta prairie lakes were much higher than reported in 1979 for similar lakes in Manitoba. Depletion of oxygen was nonlinear, and the most appropriate regression model used a log transformation indicating that depletion was exponential. A correlation between WODR and sediment organic content was found both within and between the two lakes studied. Spatial variation in WODR indicated that whole-lake WODR based on single-point vertical profiles may be highly inaccurate. Oxygen concentrations in the water column stabilized at low (0.5–2.0 mg∙L−1) levels although an anoxic water layer may occur over the sediment.
Empirical Hypothesis to Explain the Restricted Distribution of Hyalella azteca (Amphipoda) in Anthropogenically Acidified Lakes
Authors: France Robert L. , LaZerte Bruce D.
Published: April 2008

A simple and speculative model is proposed to explain the restricted distribution of Hyalella azteca (Amphipoda) within acidified Ontario lakes. The model integrates field chemical and ecological data with results from laboratory toxicological experiments. Frequent spring depressions of pH to below 5.0, measured in the littoral zone of Plastic Lake during 1982, were predicted to cause a mortality of 35.2% to a theoretically constructed amphipod population. A time trend simulation suggested that population decline of H. azteca in similar anthropogenically acidified lakes could be caused by such direct mortality due to short-term pH fluctuations. Assumptions and factors not considered by the model which could exacerbate or mitigate the effects of acidic snowmelt to H. azteca are discussed.
Assessment of Pacific Skipjack Tuna (Katsuwonus pelamis) Resources by Estimating Standing Stock and Components of Population Turnover from Tagging Data
Authors: Kleiber P. , Argue A. W. , Kearney R. E.
Published: April 2008

More than 140 000 tagged skipjack tuna (Katsuwonus pelamis) were released during 3 yr over a large portion of the central and western Pacific. Tag returns exceeded 6000. We developed a set of tag attrition models to analyze tag release and return data and catch and effort statistics for the study area. We used these models to assess the status of the skipjack resource in the whole study area and within subdivisions thereof. Total standing stock was estimated at 3 million metric tons (Mt), (95% confidence range 2.5–3.7 Mt). Overall attrition rate (including losses to natural mortality, fishing mortality and emigration) was 0.17 mo−1 (0.15–0.20∙mo−1). Total throughput was estimated at 6.2 Mt∙yr−1 (5.5–7.1 Mt∙yr−1) compared with catch of < 0.3 Mt∙yr−1. Overall harvest ratio was 0.04. Harvest ratios for seven subareas for which detailed catch and effort statistics were available ranged from 0.02 to 0.46; only one exceeded 0.17. Low harvest ratios over most of the study area during the period tags were at large imply a potential for increased skipjack catches in many subareas and in the whole study area.
Abundance of Larval Tanner Crabs (Chionoecetes spp.) in Relation to Adult Females and Regional Oceanography of the Southeastern Bering Sea
Authors: Incze Lewis S. , Armstrong David A. , Smith Sharon L.
Published: April 2008

Abundances of larval Chionoecetes bairdi and C. opilio in the southeastern Bering Sea are compared for springs of 1978 through 1981. Geographical subareas of the shelf were designated for statistical analysis of results to accommodate variations in hydrographic conditions and circulation, distribution of benthic populations, and distribution of planktonic sampling effort. Maximum observed abundances of first-stage zoeae were 1230 and 12 697∙m−2 for C. bairdi (during May) and C. opilio (during April), respectively. Numbers exceeding 10% of these values were common over some portions of the shelf during all years of study. Significant (P < 0.001) interannual differences in larval abundance were detected: in three subareas for C. opilio and in one for C. bairdi. The sharp decline in abundance of larval C. opilio after 1979 in two of the subareas could be accounted for by regional declines in numbers of adult female crabs. This was not true of the remaining subarea where two weak larval year-classes of C. opilio (1980 and 1981) and one of C. bairdi (1980) occurred despite an abundance of adult females. Vertical distribution of larval crabs is shown and the potential roles of advection, planktonic conditions, and reproductive output are evaluated with respect to observed patterns of larval abundance.
Embryonic Development and Energetic Investment in Egg Production in Relation to Size of Female Lobster (Homarus americanus)
Authors: Attard Jean , Hudon Christiane
Published: April 2008

The egg development index, dry weight, and energy content were measured on eggs from 148 ovigerous female lobsters (Homarus americanus) caught off îles de la Madeleine (Québec). Two modes of embryonic development were observed at stages 3 and 8 (Perkins. 1972. Fish. Bull. 70: 95–99). Stage 3 predominated among females of 71–82 mm and stage 8 among those of 83–110 mm carapace length (CL), indicating that larger females both extrude and hatch their eggs earlier than smaller females. Energy content per egg increased with female size and ranged from 4.6 cal∙egg−1 for females 72–76 mm CL to 5.2 cal∙egg−1 for females 107–110 mm CL. Females between 82 and 90 mm CL invested 0.155 kcal per gram of their own weight in egg production, which was the maximum value in the size range. Females smaller than 82 mm CL and larger than 90 mm CL expended proportionately less on egg production, with the difference allocated to either somatic growth in the smaller or maintenance in the larger animals. Large females produce proportionately more eggs, containing more calories per egg which hatch at an earlier time than small females. The higher energy content of eggs from large females and their earlier hatching are probably factors that enhance larval growth and survival. If so, large females contribute relatively more to recruitment than their greater fecundity.
Factors Affecting the Distribution, Abundance, and Measurement of Pacific Herring (Clupea harengus pallasi) Spawn
Authors: Hay D. E. , Kronlund A. R.
Published: April 2008

Records of the date, location, and magnitude of Pacific herring (Clupea harengus pallasi) spawnings in British Columbia, collected since 1928, were compiled and analysed. In the early years of spawn surveys, adjacent spawnings were often reported as single events. Gradually, this practice has changed so that each spawning has a separate record. As a consequence of this change in methods, the mean length of spawnings has decreased in recent years but the total numbers of records has increased. Estimates of mean spawning width and intensity have also changed, partly due to changing survey methods as well as changing spawning distributions. A spawn abundance index is developed to account for these temporal changes. Abiotic factors affecting the distribution and abundance of spawn deposition include sea surface temperatures and the fishery. Biological factors affecting spawn distribution and abundance are not as well defined, but it is shown that in some situations, spawn dimensions may change as a function of stock abundance.
Role of Environment and Stock on the Elemental Composition of Sockeye Salmon (Oncorhynchus nerka) Vertebrae
Authors: Yamada S. Behrens , Mulligan T. J. , Fournier D.
Published: April 2008

Individual spawning populations, or stocks, of salmon differ in the elemental composition of their scales and bone. These stock-specific differences have a pronounced environmental component, since elevated concentrations of certain elements in fish tissue can be induced by feeding hatchery fish food enriched in these elements. This study tests the hypothesis that both genetic and environmental factors contribute to the stock-specific elemental composition of salmon vertebrae. Four stocks of sockeye salmon (Oncorhynchus nerka) were raised under identical conditions and each stock was subjected to four environmental treatments. The elemental composition of the vertebrae were analysed using X-ray spectroscopy; nine elements were measured. The resulting elemental composition data were analysed by multivariate analysis of variance. Evidence is presented for both a stock and a treatment factor contributing to the vertebral composition.
Separable Virtual Population Analysis of Pacific Salmon with Application to Marked Chinook Salmon, Oncorhynchus tshawytscha, from California's Central Valley
Authors: Kope Robert G.
Published: April 2008

A separable virtual population analysis model is developed for Pacific salmon which utilizes aged catch and spawning escapement data. This model is applied to marked chinook salmon, Oncorhynchus tshawytscha, from California's Central Valley hatcheries using weighted least squares criteria for goodness of fit. Structural inadequacies of the model apparently produce discrepancies between predicted values and observed data that are of about the same magnitude as the observational errors in estimating the recoveries of marked fish. Some of the inadequacy of the model may be due to environmentally induced variability in population parameters, but for the marked fish used in this analysis, some of the variability is probably due to year-to-year variability in hatchery practices. From this analysis it appears that although nominal fishing effort has been relatively stable or even declining in recent years, fishing mortality has been increasing with the exception of 1983 and 1984.
Experimental Enrichment of a Coastal Stream in British Columbia: Effects of Organic and Inorganic Additions on Autotrophic Periphyton Production
Authors: Perrin Chris J. , Bothwell Max L. , Slaney Pat A.
Published: April 2008

Periphyton accumulation rates and alkaline phosphatase activity were examined in reaches of the Keogh River, British Columbia, following additions of grain and inorganic fertilizer as separate treatments during spring–summer 1981. Two different levels of N and P addition were used: one to attain ambient N and P concentrations of 200 and 15 μg∙L−1, respectively, and the other to attain 400 and 20 μg∙L−1, respectively. Grain (rolled barley) was added monthly at 280 g∙m−2. N and P additions increased chlorophyll a accrual rates by more than an order of magnitude. Diatoms dominated the periphyton community until midsummer. In July and most of August, the relative importance of chlorophytes increased and biomass levels declined markedly in spite of continued nutrient additions. Grain additions resulted in no detectable change in periphyton accrual, but alkaline phosphatase activity increased by 35% over control levels. These results suggest that additions of labile organic matter to nutrient-deficient coastal streams can increase autotrophic P deficiency. Based on responses of juvenile salmonids, additions of inorganic nutrients to increase autotrophic production can maximize trophic enhancement in nutrient-deficient streams.
Acoustical Assessment of Squid (Loligo opalescens) off the Central Oregon Coast
Authors: Jefferts Katharine , Burczynski Janusz , Pearcy William G.
Published: April 2008

Squid (Loligo opalescens) were surveyed acoustically in an area off the Oregon coast using dual-beam and echo integrator techniques. The method developed is shown to be feasible for in situ estimation of target strength, distribution, and abundance of midwater squids. Average target strength was estimated both while drifting with a squid school and cruising over one. The values derived, −58.6 to −58.7 dB, are much lower than previous estimates, but more realistic in relation to the target strength of fishes. Schools judged to be fish or squid showed little difference in depth or size, but varied significantly in geographic distribution. Density estimates ranged from 9.9 t/km2 in a known spawning area to 0.93 t/km2 in an adjacent area.
Induced Cytochrome P450 in Winter Flounder (Pseudopleuronectes americanus) from Coastal Massachusetts Evaluated by Catalytic Assay and Monoclonal Antibody Probes
Authors: Stegeman John J. , Teng Frances Y. , Snowberger Elisabeth A.
Published: April 2008

Levels of hepatic microsomal ethoxyresorufin O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) activities and sensitivity to inhibition by α-naphthoflavone in winter flounder (Pseudopleuronectes americanus) from Deer Island flats in Boston Harbor, off Plymouth Beach, off Nantucket, and at the outer New Bedford Harbor in Buzzards Bay, Massachusetts, suggested induction of cytochrome P450 by environmental chemicals. Levels of activity were higher in fish from Boston Harbor and Plymouth Bay than from Nantucket and Buzzards Bay. In fish from Buzzards Bay the levels of EROD and AHH activities were closely correlated, with some fish there apparently uninduced. Immunoblot analysis of flounder liver microsomes with a monoclonal antibody (1-12-3) against β-naphthofiavone-inducible scup cytochrome P450E revealed a single cross-reacting protein in untreated fish from all four field sites. A similar protein was induced by β-naphthoflavone treatment. Levels of this flounder protein correlated positively with levels of AHH and EROD activity in Buzzards Bay fish, consistent with a conclusion that some fish there were uninduced. The results demonstrate the induction of a P450E counterpart in flounder in Massachusetts waters and indicate its identity as the AHH and EROD catalyst. The results also establish the use of monoclonal anti-P450E in analysis of environmental induction.
Comparison of Six Models for Nutrient Limitations on Phytoplankton Growth
Authors: Morrison K. A. , Thérien N. , Marcos B.
Published: April 2008

Equations and responses of six formulations for expressing nutrient limitation on phytoplankton growth are examined, including a scenario of no limitation. The Monod and internal storage formulations are representative of current applications, while the others have not been applied previously to phytoplankton. The general forms of growth responses under laboratory-type conditions are compared. The Contois formulation is found to be very flexible and is capable of describing the Monod and logistic formulations purely through selected parameter values. It can also generate a type of response not given by the other formulae. The different expressions are calibrated in a model applied to one station in the LG-2 reservoir. Validation is attempted using data from other stations. The Contois and logistic formulations gave the best results, but failures of the other formulations may be due in part to unavailability of much of the nutrients due to such things as complexing, while available data was only on total nutrients. Our results suggest that the Contois formulation is a valid alternative for representing nutrient limitation and may be robust in situations where data may be inadequate for the more rigourous internal storage formulations.
Inverse Correlation between Ovarian Development of Atlantic Salmon (Salmo salar) Smolts and Sea Age
Authors: Chadwick E. Michael P. , Claytor Ross R. , Léger Claude E. , Saunders Richard L.
Published: April 2008

In order to understand the factors which determine sea age of Atlantic salmon (Salmo salar), ovarian development of smolts was examined in 14 groups which varied in parental sea age, smolt age, and size. Parental sea age of smolts explained most of the variation in ovarian development. Smolts from one-sea-winter parents had a higher percentage of the more advanced oocyte stages in their ovaries, while smolts from two-sea-winter parents had a low percentage, and those from three-sea-winter parents had none. Annual within-stock variation and covariance with freshwater age were not significant. Hatchery-reared smolts had similar ovarian development to their wild counterparts. There was also a significant, positive correlation between fork length of smolts and ovarian development within groups.
Patterns of Larval Emergence and Their Potential Impact on Stock Differentiation in Beach Spawning Capelin (Mallotus villosus)
Authors: Fortier Louis , Leggett William C. , Gosselin Serge
Published: April 2008

The environmental cues triggering larval capelin (Mallotus villosus) emergence in the St. Lawrence estuary and in coastal Newfoundland are different. In the estuary, emergence from the intertidal and subtidal spawning grounds starts with dusk and ends with dawn, indicating an active response to low light intensity. In the laboratory, emergence from undisturbed sediments collected in the field is perfectly synchronized with the dark phase of the illumination cycle. Nocturnal emergence would represent an adaptation reducing vulnerability to visual predators. Previous work has shown that in Newfoundland, capelin emergence from intertidal beaches is triggered by abrupt changes in water temperature following the sporadic advection to the coast of surface water masses characterized by low predator and high prey abundances. We argue that regional differences in the emergence pattern of the species represent different strategies to avoid predation at the onset of the planktonic drift when the vulnerable yolk sac larvae are densely aggregated. Selection acting on the behaviour of the early larval stages could contribute to stock differentiation in capelin.
Evaluation of Total Phosphorus as a Predictor of the Relative Biomass of Blue-green Algae with Emphasis on Alberta Lakes
Authors: Trimbee Annette M. , Prepas E. E.
Published: April 2008

The relative biomass of blue-green algae in freshwater (total dissolved solids < 500 mg∙L−1) Alberta lakes was consistently underestimated by two recent empirical models based on total nitrogen (TN), total phosphorus (TP), Secchi disc depth (SD), and depth of the mixed layer (Zm). We regrouped the data used in these empirical models to eliminate the potential biases introduced by including data from lakes not in dynamic equilibrium and generated a new model based on TP. This new model accounted for 11% more of the variation in relative blue-green algal biomass than the original model based on TN, TP, SD, and Zm and 21% more than the model based on TN to TP ratios and SD to Zm ratios. This new model was also a much better predictor of the relative biomass of blue-green algae in Alberta lakes than the original models. In addition, for lakes in Alberta, TP was a much better predictor of total blue-green algal biomass than TN or the TN to TP ratio. Our analyses suggest that for large numbers of lakes, TP may be as good or better an indicator of relative and total biomass of blue-green algae than TN or TN to TP ratios.
Plasma Testosterone Concentration Predicts the Ovulatory Response of Coho Salmon (Oncorhynchus kisutch) to Gonadotropin-Releasing Hormone Analog
Authors: Fitzpatrick Martin S. , Redding J. Michael , Ratti Frank D. , Schreck Carl B.
Published: April 2008

Plasma concentrations of testosterone, 17α-hydroxy-20β-dihydroprogesterone (DHP), and estradiol-17β were determined in hatchery populations of adult female coho salmon (Oncorhynchus kisutch) before and after the fish were injected with gonadotropin-releasing hormone analog (GnRHa) to accelerate ovulation. Treatment with GnRHa significantly accelerated maturation over that observed in saline-injected controls; however, a number of females that received GnRHa did not ovulate for as long as 8 wk after treatment. Before treatment, the mean plasma levels of DHP did not differ between early- and late-ovulating females; estradiol differed sometimes, but not always; and testosterone was always higher in the early-ovulating fish. Thus, plasma concentrations of testosterone appear to be useful for predicting the sensitivity of coho salmon to GnRHa treatment for induced ovulation.
Depression of Primary Production by Humic Matter and Suspended Sediment in Limnocorral Experiments at Southern Indian Lake, Northern Manitoba
Authors: Guildford S. J. , Healey F. P. , Hecky R. E.
Published: April 2008

Eroding and flooded shoreline materials were added to a series of limnocorrals in Southern Indian Lake (northern Manitoba) to simulate their effects on the phytoplankton following impoundment of the lake. Inorganic clays depressed primary productivity and phytoplankton biomass but relieved phosphorus deficiency. These effects appeared to be primarily due to reduction of light penetration; release of available phosphorus was small. Organic moss–peat material initially increased and then lowered primary productivity and biomass, while phosphorus deficiency was lowered. The initial stimulation could be traced to the release of soluble nitrogen and phosphorus. Enrichment experiments indicated that the depression was due to the binding of iron or some other metal by dissolved humic material. Responses of phytoplankton in the lake could be understood as a composite of responses seen in the limnocorrals to the two eroding shoreline materials.
Empirical Models of Fish Response to Lake Acidification
Authors: Reckhow Kenneth H. , Black Robert W. , Stockton Jr. Thomas B. , Vogt J. David , Wood Judith G.
Published: April 2008

A large historical data set from the Adirondack region of New York was compiled to study the relationship between water chemistry variables associated with acid precipitation and the presence/absence of selected fish species. The data set was used to examine simple statistical models for fish presence/absence, as a function of the water chemistry variables, for brook trout (Salvelinus fontinalis), lake trout (Salvelinus namaycush), white sucker (Catostomus commersoni), and yellow perch (Perca flavescens). Of these models, only those for brook trout and lake trout were found to be acceptable based on statistical goodness-of-fit criteria; thus, parameters for models of these two species alone were estimated using maximum likelihood logistic regression. Candidate models for brook trout and lake trout were then examined, with particular consideration for the problems associated with model misspecification, errors-in-variables, and multicollinearity. For each of the two species, a model was recommended that may be used to predict the effect of changes in lake acidification on species presence/absence in lakes in the Adirondack region.
Effect of Dietary Cadmium on Growth, Survival, and Tissue Concentrations of Cadmium, Zinc, Copper, and Silver in Juvenile American Lobster (Homarus americanus)
Authors: Chou C. L. , Uthe J. F. , Castell J. D. , Keanz J. C.
Published: April 2008

The addition of as much as 45 mg Cd/kg to a crab-based diet did not significantly affect growth or survival of juvenile American lobster (Homarus americanus) fed for 17 wk. The addition of Cd to the crab-based diet destroyed the highly significant relationship observed in nature between Cu and Ag concentrations in the digestive gland. Cd, Zn, and Cu in the crab-based diet were taken up by the digestive gland more efficiently than these metals added to the casein-based diet. Cu, Zn, and Ag concentrations in tail muscle were not affected by dietary Cd. Tissue mean molar ratios of metals (normalized to Cu and Ag) and dietary Cd ic crab-based diets showed a significant (p < 0.05) logarithmic relationship between dietary Cd levels and Cu/Ag (or Ag/Cu) ratios in both the tail muscle and digestive gland and Cd/Cu and Cd/Ag ratios in the digestive gland. A linear relationship was observed between Cd levels in crab-based diets and Cd/Cu, Cd/Ag, and Zn/Ag ratios in tail muscle. The absence of ascorbic acid (vitamin C) in the diet increased the uptake of Cd by the digestive gland and had an interactive effect on mean molar ratios of Cd, Cu, and Ag in the digestive gland.
Photoperiod Control of Parr–Smolt Transformation in Atlantic Salmon (Salmo salar): Changes in Salinity Tolerance, Gill Na+,K+-ATPase Activity, and Plasma Thyroid Hormones
Authors: McCormick Stephen D. , Saunders Richard L. , Henderson Eugene B. , Harmon Paul R.
Published: April 2008

Atlantic salmon (Salmo salar) were subjected to artificial photoperiods to determine the manner and extent of photoperiod control of the parr–smolt transformation. Exposure to continuous light (L24) at first feeding and maintained throughout the rearing period inhibited increases in salinity tolerance and gill Na+,K+-ATPase activity that occurred in spring in fish raised under simulated natural photoperiod (SNP). Fish reared under continuous light and returned to SNP in October (L24OCT) underwent normal increases in salinity tolerance and gill Na+,K+-ATPase activity, whereas those returned in December (L24DEC) underwent delayed and intermediate increases. Plasma thyroxine peaks occurred simultaneously in all groups but were diminished in the L24 and L24DEC groups. Plasma 3,5,3′-triiodo-L-thyronine levels were not affected by any photoperiod treatment. Inhibition of the parr–smolt transformation decreased the potential for growth in seawater. In spite of changes in the timing of the transformation induced by photoperiod treatment, salinity tolerance and gill Na+,K+-ATPase activity were strongly correlated; correlation between changes in salinity tolerance and plasma thyroid hormones were, by comparison, weak. The results demonstrate that continuous light applied early in ontogeny and maintained throughout the rearing period inhibits osmoregulatory changes associated with parr–smolt transformation, whereas increasing day length during winter–spring stimulates transformation.
Population and Production Dynamics of an Enchytraeid Worm in a Subtropical Blackwater River
Authors: Stites David L.
Published: April 2008

Population and production dynamics of Barbidrilus paucisetus Loden and Locy (Oligochaeta: Enchytraeidae) in a sixth-order blackwater river are described. This worm was the dominant member of the meiofauna of the sand habitat, accounting for 50–90% of the total density. Population density varied seasonally, increasing from < 20 000/m2 in the winter to 60–120 000/m2 in the summer. Biomass averaged 145 mg dry mass/m2 with a range of 8–326 mg/m2. Density peaked in the clean coarse sand of the center channel areas and was lower where the sand was finer and where more organic matter was present. Size frequency histograms indicated that there were three recruitment peaks during the sampling year, with mature and new individuals present in all seasons. Annual production (2.12 g dry mass/m2, SE = 0.15 g/m2), was estimated using the size frequency method and a cohort production interval correction of 3. Annual production was low compared with that of terrestrial Enchytraeidae and comparable with that of many aquatic insect species. Annual production/biomass ratio (14.3) was higher than terrestrial Enchytraeidae, due to the comparatively short generation time of this species.
Responses of Juvenile Atlantic Salmon (Salmo salar) to Episodic Increases in Acidity of Nova Scotia Rivers
Authors: Lacroix Gilles L. , Townsend Donald R.
Published: April 2008

Toxicity of different pH levels to Atlantic salmon (Salmo salar) parr held in floating pens for 54 d was assessed in four acidic streams of Atlantic Canada during the autumnal episode of increasing acidity. All parr died in the two streams where pH levels decreased below pH 4.7. Mortality was related to the rate of pH change and to parr size. Plasma sodium and chloride concentrations decreased by about 50–70 mmol∙L−1in parr of these two streams, and the rate of electrolyte loss was related to the rate and severity of pH change. In the other two streams, pH levels were never lower than pH 4.8 and no fish died. Plasma sodium and chloride concentrations in these parr decreased by 20–30 mmol∙L−1, but only after 30 d of exposure. Increased hematocrit, increased respiratory–cough response, and decreased feeding response, especially for parr in the most acidic streams, were also the result of stress apparently related to decreasing pH levels. Concentrations of labile aluminum were usually less than 10% of total dissolved aluminum and always less than 50 μg∙L−1in the four streams. Accumulation of aluminum in the gills of parr was not a significant factor in the lethal effects observed, which were more likely due to low pH.
Lack of a Depth Effect on the Growth of the Air-Breathing Catfish, Clarias macrocephalus
Authors: Bevan David J. , Kramer Donald L.
Published: April 2008

In juvenile Clarias macrocephalus, distance travelled to breathe air increased strongly with depth, but growth rate was not significantly affected. Forty-seven fish (4.60 ± 0.12 g, 8.4 ± 0.07 cm, mean ± SE) were initially raised for 28 d in individual cages (30, 60, 90, and 118 cm deep) at 27 °C and 0.72 mg O2∙L−1, with a daily ration of 6% body weight. Distance travelled increased from 15.5 m∙h−1 at 30 cm to 51.2 m∙h−1 at 118 cm. When fish were subsequently maintained without food for a further 14 d, at 0.15 mg O2∙L−1, distance travelled averaged 6.6 and 22.7 m∙h−1 at 30 and 118 cm, respectively. Despite the increase in activity, depth had no significant effect on specific growth rate of either fed (3.62 ± 0.08%∙d−1) or fasting (−0.70 ± 0.03%∙d−1) fish. Strong effects of depth on the growth of air-breathing fishes may not be as general as previously suggested.
Aggregation in Littoral Amphipod Populations: Transformation Controversies Revisited
Authors: France R. L.
Published: April 2008

Spatial variability in amphipod (Hyalella azteca) density was examined in 17 Canadian Shield Lakes in south-central Ontario. Aggregation was measured by the exponent of the power relationship between density and variance. The average b index was 1.45, although this value varied depending on lake and habitat type. Whereas this should indicate the use of a fourth-root transformation, neither this nor the logarithmic transformation was as effective as the square-root in stabilizing variance. A literature review suggests that if a universal transformation is sought for benthos data, it should not be the commonly used log transformation. The observation that the square-root transformation seemed to work better on average than the fourth-root transformation, even in the region suggested by theory for the latter, suggests that complications may arise in the uncritical use of Taylor's Power Law.
Statistical Interrelation of Length, Growth, and Scale Circulus Spacing: Appraisal of a Growth Rate Estimator for Fish
Authors: Doyle Roger W. , Talbot A. J. , Nicholas R. R.
Published: April 2008

Biological and statistical properties of spacing of the marginal circuli of scales (CIRC) were examined in an experimental population of tilapia (Oreochromis mossambicus/hornorum) hybrids. Biological, or "causal," interrelationships of body length, growth, and CIRC were analysed by maximum likelihood solution of a simultaneous equation model involving the three variables. Spacing varies directly with growth rate and inversely with fish length, and growth varies inversely with length. Consequently, spacing is relatively constant along the radial axis of the scale except where variation in ration level or other factors varies the rate of growth as a function of length. The correlation of CIRC with current growth rate in populations of mixed parentage, sizes, and ages is sufficiently high (r = 0.65–0.71) to render it a useful growth estimator in aquaculture and natural situations where ages are unknown and sequential size measurements are difficult to obtain. Statistical and procedural conditions for maximizing the utility of the growth estimator in several applications are examined: (a) comparison of individual growth rates within a population, (b) comparison of mean growth of populations in different environments, (c) indirect selection for growth in aquaculture genetic programs, and (d) response of growth to exogenous variables such as parasite load, behaviour, and microhabitat.
Interpreting Selectivity Indices Calculated from Field Data or Conditions of Prey Replacement
Authors: Confer John L. , Moore Marianne V.
Published: April 2008

Indices of prey selection are compared empirically to clarify the kind of information each can provide and when the indices can be used appropriately. Emphasis is given to Chesson's alpha (α) and Strauss' Linear index (Li) because they are commonly used and represent two mathematically dissimilar approaches to measuring selection. Neutral selection for α and Li is not equivalent. For Li, neutral selection for a prey type occurs when selectivity equals the weighted (by relative abundance) average selectivity for all other prey types. For α, neutral selection equals the unweighted average for all prey types, which is equivalent to 1 divided by the number of prey types. Li and α respond differently to rare prey types. This is especially evident in field samples having large differences in relative prey abundances. Li values decrease as abundance of a prey type decreases in the environment, in contrast, α values often increase greatly as the proportional abundance of a prey type in the environment decreases. Consequently, α values, but not Li values, are often strongly influenced by the values for very rare prey, α values are sensitive to changes in the number of prey types, but not to changes in prey proportion. When the number of prey types is constant, α may be the most meaningful indicator of prey type preference. In contrast, Li values are sensitive to changes in prey proportions in the environment. When prey proportions are constant among experiments, Li is appropriate for measuring changes in the impact of a predator on a prey type and changes in selectivity relative to the average prey item. If number of prey types and prey proportions vary among experiments, Vanderploeg and Scavia's W or E* may be most appropriate.