bluuebunny/crossref_metadata_2025 huggingface dataset:
Competition for Spawning Space Between Brown (Salmo trutta) and Rainbow Trout (S. gairdneri) in a Lake Inlet Tributary, New Zealand
Authors: Hayes John W.
Published: April 2008

Effect of interference competition for spawning space on spawning success of brown (Salmo trutta) and rainbow trout (S. gairdneri) was studied in the main spawning tributary of Lake Alexandrina, New Zealand. Competition was mediated through redd superimposition and severely limited the spawning success of both species. Overall spawning success, from egg deposition to fry emergence, was 2.1% for rainbow trout and 0.2% for brown trout and was dependent on time of spawning. Brown trout spawned from April to June and rainbow trout spawned from April to October. Brown trout and early spawning rainbow trout experienced poor spawning success due to severe redd superimposition by later spawning rainbows. Late spawning rainbows experienced highest spawning success. Redd superimposition by rainbow trout caused a 94% reduction in spawning success of brown trout in an experimental section of stream. Severe intraspecific competition for spawning space, through redd super-imposition, determined pattern and timing of peak rainbow fry emergence.
Density-Dependent Growth of Age 1 English Sole (Parophrys vetuls) in Oregon and Washington Coastal Waters
Authors: Peterman Randall M. , Bradford Michael J.
Published: April 2008

We tested whether English sole (Parophrys vetulus) in Oregon and Washington waters show density-dependent growth. We found that there is a significant negative effect of cohort abundance on annual growth rate of age 1 fish, but not on growth of ages 2–7. Unlike most similar studies of density dependence, this result was not confounded by time trends in abundance and growth. The multiple regression of age 1 growth on cohort abundance and temperature accounted for 91% of the interannual variation in growth, which was a significant increase in r2 over that of the previously published relation with temperature alone. However, stock assessments which take into account only the previously published temperature effect on growth for this stock will probably not seriously overestimate the impact of management regulations which increase cohort abundance.
Nutrient Enrichment Studies in a Coastal Plain Estuary: Changes in Phytoplankton Species Composition
Authors: Sanders James G. , Cibik Stephen J. , D'Elia Christopher F. , Boynton Walter R.
Published: April 2008

Natural phytoplankton assemblages from the Patuxent River estuary were maintained in outdoor, large-volume, continuous cultures and subjected to nutrient enrichment in a series of experiments over an 18-mo period. Nitrogen (either ammonium or nitrate) enrichment during summer and fall produced large changes in dominant species and patterns of species successions, yielding an assemblage much different from unenriched controls: strong, continued dominance by small centric diatoms at the expense of predominant flagellate species. Succession of dominant species occurred very rapidly, within 2–4 d after enrichment began. Increases in cell densities and the changes in successional patterns were caused by increased diatom growth rates rather than reduced growth rates of other dominant species. During winter and spring, N enrichment did not cause a response in the phytoplankton assemblage. Twice during winter experiments, assemblages exhibited a weak, delayed response to P; however, P enrichment did not affect individual species' growth rates or species succession at any time of year. Thus, further enrichment can affect phytoplankton growth and community structure, even in nutrient-enriched estuaries.
Distribution and Persistence of the Lampricide Bayer 73 Following a Control Application
Authors: Ho Kay T. Y. , Gloss Steven P.
Published: April 2008

Bayer 73 (2-aminoethanol salt of 2′,5-dichloro-4′-nitrosalicylanilide) was applied to a 41-ha delta area of Seneca Lake, New York, to control the sea lamprey (Petromyzon marinus). Concentrations of Bayer 73 in lake water samples ranged from < 10 to 573 μg/L (ppb); concentrations peaked 2.5 h after application and were generally highest near the bottom and lowest at the surface, but exceeded 40 μg/L throughout the water column. All measured concentrations were 10 μg/L (limit of detection) or less within 96 h after application. Movement of the chemical out of the treatment area, as well as drift within the treatment area, was detected. Significant mortality of one species of caged fish occurred at the station with the highest Bayer 73 concentration 14 h after application. Fish tissue residues (< 10–858 ng/g) reflected water samples in concentration and distribution patterns; they were highest 14–24 h after application and then declined. In laboratory studies performed to determine the mechanisms affecting the decline in Bayer 73 concentrations, sediment processes — specifically adsorption — enhanced the decline.
A Simple Method for Estimating the 15N Content of Dissolved Organic Matter (DO15N) in N-Cycling Studies
Authors: Axler R. P. , Reuter J. E.
Published: April 2008

A method is described for isolating the total pool of dissolved organic nitrogen (DON) from oligotrophic lake water for subsequent isotopic analysis of the15N/14N ratio in tracer experiments. The procedure involves reducing an acidified filtered sample with elemental zinc to convert nitrate + nitrite to ammonium and then analyzing and sparging with N2 to remove ammonia. The residue (DON) is evaporated to dryness, rehydrated, spotted on a filter, and vacuum ampulated for micro-Dumas conversion to N2 and isotopic analysis by optical emission spectrometry. We have used the method to accurately estimate 15N enrichments of < 1 atom-% in DON collected from 150-mL samples of [15N]nitrate-enriched mesocosms in Castle Lake, California.
Growth, Reproductive Output, and Energy Partitioning in Weathervane Scallops, Patinopecten caurinus, from British Columbia
Authors: MacDonald B. A. , Bourne N. F.
Published: April 2008

Major differences in population growth and reproductive characteristics of Patinopecten caurinus were related to water temperatures and food sources associated with collection sites in the Strait of Georgia and off the west coast of Vancouver Island. Inshore populations were dominated by larger, faster growing scallops that apparently live longer than offshore scallops. Individuals from the inshore site exhibited enhanced reproductive output total production, and turnover ratios compared with offshore scallops. Histological and stereological techniques were used to assess the annual reproductive cycle. Results revealed a single but protracted spawning period for inshore scallops beginning in mid-April and ending in mid-June whereas offshore scallops spawned during July and August. As scallops grew older there was a gradual shift in emphasis from growth to reproduction in addition to periods when gametogenesis proceeded at the expense of somatic tissue. The quantity of available energy invested m reproduction may restrict growth periods and limit the amount of growth for bivalve species from various habitats.
Changes in the Immune System of Coho Salmon (Oncorhynchus kisutch) during the Parr-to-Smolt Transformation and after Implantation of Cortisol
Authors: Maule Alec G. , Schreck Carl B. , Kaattari Stephen L.
Published: April 2008

The primary immune response of coho salmon (Oncorhynchus kisutch), as assessed by the production of splenic antibody-secreting cells (plaque-forming cells, PFC) after an injection of Vibrio anguillarum O-antigen, decreased during smoltification. This period was marked by increases in gill Na+-K+-adenosine triphosphatase (ATPase) activity and plasma thyroxine and cortisol titers. Numbers of leucocytes relative to erythrocytes in peripheral blood and splenic lymphocytes relative to fish body weight were also reduced. Fish reared at normal hatchery density (approximately 2 fish∙L−1) appeared to have reduced rates of development and higher numbers of PFC than fish reared at one-third normal density. Moreover, in fish changed from normal density to low density 2 wk before sampling, ATPase activity and plasma thyroxine levels were equal to those in fish reared continuously at normal density, but plasma cortisol levels and PFC were equal to those in fish reared at low density. Fish with cortisol implants had higher plasma cortisol titers, reduced numbers of splenic PFC, splenic lymphocytes, and circulating leucocytes, and greater mortality when fish were exposed to V. anguillarum.
Enzyme-linked Immunosorbent Assay for a Soluble Antigen of Renibacterium salmoninarum, the Causative Agent of Salmonid Bacterial Kidney Disease
Authors: Pascho R. J. , Mulcahy D.
Published: April 2008

A double-antibody enzyme-linked immunosorbent assay (ELISA) for detection of a soluble fraction of Renibacterium salmoninarum was developed from components extracted from the supernatant of an R. salmoninarum broth culture. The Costar® Serocluster™ EIA microplate gave the highest absorbance and signal-to-noise ratios among seven types tested. Including Tween 80 in the wash buffer resulted in higher absorbances than Tween 20 when antigen was present. Background absorbance did not increase when Tween 80 was added to the wash buffer, but did when Tween 80 replaced Tween 20 in antigen and conjugate diluents. Adsorption of coating antibody peaked within 4 h at 37 °C and 16 h at 4 °C. Antigen attachment to antibody-coated microplate wells depended more on incubation temperature than duration; we adopted a 3-h incubation at 25 °C. Conjugate incubation for longer than 1 h at 37 °C or 3 h at 25 °C resulted in unacceptable background levels. No cross-reactions resulted from heat-extracted antigens of 10 other species of bacteria. The optimized ELISA is a 6-h test that enables detection of levels of soluble antigen as low as 2–20 ng.
Aggression and Variation in Growth of Chum Salmon (Oncorhynchus keta) Juveniles in Seawater: Effects of Limited Ration
Authors: Davis Michael W. , Olla Bori L.
Published: April 2008

Chum salmon (Oncorhynchus keta) were grown in groups of 10 for 40 d on three limiting ration levels, and weight and fork length were measured at day 0 and day 40. Variation in growth of fish within a cohort was estimated from calculation of coefficients of variation for weight, fork length, condition factor, and growth rate. Average growth was significantly less at the lowest ration level than at the two higher levels, where average growth did not differ significantly. However, variation in growth (growth depensation) was significantly higher at the lowest and intermediate ration levels than at the highest ration level; we surmise that this higher variation is associated with increased competition and the disproportionate acquisition of food by larger fish. Aggressive behavior was most intense at the highest ration level. Chum salmon apparently show characteristics of a schooling fish while showing aggression, behaviors that are generally viewed as mutually exclusive.
Influence of Alternative Prey Abundance on Pelagic Fish Predation of Larval Fish: A Model
Authors: Pepin P.
Published: April 2008

In this model of predation on larval fish by pelagic fish, I postulate that variations in the abundance of the more numerous alternative prey population can determine the time required by a predator to attain its maximum ration. The model predicts that larval fish mortality should be a direct function of the abundance of their predator scaled relative to alternative prey abundance. A test of the model using data from the California Current reveals that mortality of larval northern anchovy (Engraulis mordax) shows a significant relationship with the predator-to-prey ratio (pelagic fish biomass/Zooplankton biomass). Other possible interpretations of this result and problems of model parameterization are discussed.
Acute Toxicity of Methoxychlor to Larval White Sucker (Catostomus commersoni) as Modified by Age, Food Availability, and Egg Preexposure
Authors: Holdway D. A. , Kempe E. J. , Dixon D. G.
Published: April 2008

Methoxychlor is currently pulsed into several western Canadian rivers at 0.30 mg∙L−1 to control the emergence of blackflies (Diptera: Simuliidae). A 2-h exposure of white sucker (Catostomus commersoni)) eggs to 4.83 mg methoxychlor∙L−1 at 1, 3, or 6 d postfertilization increased the incidence of deformities in both 1-d-old and pooled 3- and 6-d-old eggs (2.9 and 3.1%, respectively) compared with control eggs(1.1%). Larvae from exposed eggs showed a 2-d delay in the onset of exogenous feeding. Exposure as eggs increased methoxychlor tolerance. Respective 168-h PE LC50s (the 2-h pulse-exposure concentration causing 50% mortality over 168 h) for 2-d-old larvae from control eggs and eggs exposed for 2 h to methoxychlor at 1, 3, or 6 d postfertilization were 0.36, 1.04, 2.05, and 2.67 mg∙L−1 Methoxychlor toxicity in control larvae was modified by age; 10-d-old larvae were less tolerant than 2-, 18-, and 26-d-old larve, with respective PE LC50s of 0.04, 0.36, 0.34, and 0.20 mg∙L−1. After the onset of feeding, food availability modified toxicity. The96-h PE LC50sfor 18-d-oldfedand unfed larvae and 26-d-old fed and unfed larvae were 0.34, 0.032, 0.20, and 0.038 mg∙L−1, respectively. Swimbladder development was arrested in 2-d-old larvae exposed for 2 h to 0.10 mg methoxychlor∙L−1 at 9 d of age. White sucker survival may be at risk in methoxychlor-treated rivers.
Influence of the Abundance, Size, and Yolk Reserves of Juvenile Chum Salmon (Oncorhynchus keta) on Predation by Freshwater Fishes in a Small Coastal Stream
Authors: Fresh Kurt L. , Schroder Steven L.
Published: April 2008

Predator–prey interactions between juvenile chum salmon (Oncorhynchus keta) and piscivores were studied in a small coastal stream and in sections of a controlled-flow channel. The predators were primarily large [Formula: see text] rainbow trout (Salmo gairdneri) and large [Formula: see text] coho salmon (O. kisutch). The relationship between chum salmon fry abundance and the quantity consumed by predators suggested a type II functional response. Neither prey size nor prey abundance influenced predation, but predators did select fry with relatively high yolk reserves. Our results suggest that the numbers of juvenile chum salmon needed to satiate predators and to enhance fry survival are attainable by enhancement projects located on smaller rivers and streams.
Effect of Stocking Density on the Survival, Growth, and Dispersal of Steelhead Trout Fry (Salmo gairdneri)
Authors: Hume Jeremy M. B. , Parkinson Eric A.
Published: April 2008

In a coastal British Columbia stream a stocking density of between 0.3 and 0.7 fry/m2 maximized the production of steelhead trout (Salmo gairdneri) parr and smolts. A severe autumn flood doubled the mortality rates of fry stocked at densities of 0.7 fry/m2 or higher but had little effect on fry stocked at lower densities (<0.15 fry/m2). Overall survival to smolts appeared to be lower than measured elsewhere for wild fish (2 vs. 4.5 – 18%). The proportion (<10%) of surviving fry found below the stocked sections was considered to be an indicator of potential displacement mortality in streams with no vacant downstream areas. This downstream dispersal was not density dependent and was small in comparison with the mortality of nondispersing fish. Although initial fry and parr sizes were density dependent, there was no detectable density effect on older parr or smolt sizes.
New Graphical Techniques for Analyzing Salmon Migration in Mark–Recapture Experiments
Authors: Green Philip E. J.
Published: April 2008

New graphical techniques are applied to study the migration of chinook salmon (Onchorynchus tshawytscha). The techniques are based on plots of median recapture dates, log of the number of recaptures, and drawings of fish on grid maps. Under certain assumptions, the graphs can be used to generate hypotheses about the direction of movement of the salmon at different ages and brood years. The techniques developed are shown to adhere to the established principles of graphical design and could be extended for other similar studies.
Critical Swimming Speed of Fraser and Thompson River Pink Salmon (Oncorhynchus gorbuscha)
Authors: Williams I. V. , Brett J. R.
Published: April 2008

Critical swimming speeds were determined for male and female pink salmon (Oncorhynchus gorbuscha) captured from the Fraser and Thompson rivers and Seton Creek, British Columbia. The fish were categorized into two basic groups. Lower river fish were captured from the Fraser River at Fort Langley and Yale, and up-river fish were captured from the Thompson River at the Canyon and at Ashcroft and from Seton Creek near Lillooet, British Columbia. The critical swimming speeds of males and females in various stages of maturation were compared. In general, the up-river fish were stronger swimmers than the lower river fish. Gravid fish were stronger swimmers than spawning fish, which in turn were stronger swimmers than fish which were spawned out. Standardized critical swimming speeds ranged from a mean of 1.73 ± 0.35 (SE) body lengths/s for spawned females up to 3.39 ± 0.48 lengths/s for up-river gravid males.
Food Selection by Yellowtail Flounder (Limanda ferruginea) on Georges Bank
Authors: Collie Jeremy S.
Published: April 2008

Yellowtail flounder (Limanda ferruginea) stomachs and benthic grab samples were collected concurrently at three sites on four quarterly dates from August 1982 to May 1983. Stomach contents and grab samples were sorted and weighed and important prey species measured. Yellowtail flounder feed mainly on benthic macrofauna; in most cases a few amphipod and polychaete species constituted the bulk of the diet. I calculated selection indices to compare the species and size composition of the stomach contents with that of the benthic macrofauna. The selection indices are consistent among the four sampling dates and can largely be explained by prey life history and prey size. A lognormal curve, fitted by least squares, accounts for 87% of the variation in the mean size-selection indices. According to this curve, the preferred prey size of 3-yr-old yellowtail flounder is 13 mg.
L'incidence d'Aerococcus viridans var. homari dans le stock naturel de homards (Homarus americanus) des îles de la Madeleine (Québec), suite à une épidémie de gaffkémie dans un élevage in situ
Authors: Ménard Jacques , Myrand Bruno
Published: April 2008

In 1982, gaffkemia appeared in a private lobster (Homarus americanus) culture facility located in House Harbour lagoon in Magdalen Islands (Quebec, Canada). It caused the death of about 40 000 lobsters. The outbreak did not expand to the natural stock despite the fact that conditions seemed favourable for the spread of gaffkemia. In June 1983, only 2% of the lobsters sampled around the islands (6/300) were contaminated. By June 1984, no infected individuals were found either in the natural stock or from the private facility. Lobster fishing data from 1979 to 1985 confirm that gaffkemia did not affect natural stock.
Fluctuations of a Fortnightly Abundance Index of the Ivoirian Coastal Pelagic Species and Associated Environmental Conditions
Authors: Mendelssohn Roy , Cury Philippe
Published: April 2008

In this paper we analyze time series of catch per unit of effort (CPUE) from 1966 to 1982 of small pelagic species off the Ivory Coast using sea surface temperature (SST) collected by merchant ships. A fill-in model is used to estimate missing values of CPUE and SST in the areas in which the fishery operates. A multivariate time series model of the fortnightly data is able to explain 43% of the observed variance in CPUE from 1966 to 1982. A model estimated by using only the data from 1966 to 1980 produced reasonable forecasts of the fortnightly CPUE for 1981–82. A new approach for estimating optimal transformations of variables in the model is used to examine the form of the relationships between CPUE and its predictors. The biological interpretation of the estimated transformations is consistent with previous results on the dynamics of zooplankton in the same area.
A Length-Based Stock Assessment Method Utilizing a Generalized Delay-Difference Model
Authors: Fournier David A. , Doonan Ian J.
Published: April 2008

We present a length-based stock assessment method based on a generalization of the delay-difference methods of Deriso. Data inputs to the model include the estimated weight of the catch, the estimated fishing effort, the estimated mean weight of the catch, and the estimated central moments of the length distribution of the catch. The model's performance is demonstrated by applying it to data from a simulated exploited fish population exhibiting biomass-dependent catchability which would cause conventional catch–effort models to seriously underestimate the extent of stock depletion. The model was generally able to detect the presence of the biomass-dependent catchability and to correctly estimate the optimal level of fishing effort.
Wind-Forced Hydrodynamics and Their Interaction with Larval Fish and Plankton Abundance: A Time-Series Analysis of Physical–Biological Data
Authors: Taggart Christopher T. , Leggett William C.
Published: April 2008

We evaluated methods to measure simultaneously biological and physical properties essential for estimating short-term mortality of larval fish. We used the data to test Templeman's watermass exchange hypothesis and the associated safe-site hypothesis. Synoptic estimates of larval capelin (Mallotus villosus) and microzooplankton particle density were obtained simultaneously with a scale resolution of 200 m (horizontal), 2–4 m (vertical) and 6–8 h (temporal) in a 1-km2 coastal embayment in eastern Newfoundland. Statistically significant population estimates were derived from multiple regression models incorporating a limited number of samples. Spectral analysis of wind and current time-series and analysis of large-scale temperature oscillations were consistent with Templeman's hypothesis. Nearshore current responded to cross-shore wind forcing at periods of 2–6 d. Larval capelin abundance oscillations were coherent with wind and with current at periods of ~5 d, consistent with the watermass exchange and safe-site hypotheses. Although larvae and microzooplankton abundances showed similar spectral density and were in phase, their coherence was weak. Integrated measures of onshore wind and of the onshore–offshore wind spectrum were correlated, and either can be used as a composite measure of the considerable interannual variation evident in the frequency, magnitude, and duration of onshore winds, and hence of watermass exchange.
Energy Reserves of Three Zooplankton Species from Two Lakes with Different Metal Concentrations
Authors: Arts Michael T. , Sprules W. Gary
Published: April 2008

Dry weight and lipid content of three zooplankton species in two lakes differing in concentrations of copper, nickel, and aluminum were assayed for two consecutive summers. Epischura lacustris and Holopedium gibberum had lower lipid levels and were generally lighter in the lake with elevated metals. The lipid droplet in eggs of H. gibberum was 21% smaller in the lake with elevated metal levels. Total body burdens of copper in H. gibberum were twice as high in the lake with elevated metals. There was no difference in dry weight and levels of energy reserves of Diaptomus minutus between the lakes. Lower lipid content and decreased weight of E. lacustris and H. gibberum from Round Lake could not be explained by lowered food availability, since both the edible portion of phytoplankton biomass and abundance of small Bosmina were similar in the two lakes. Since there were no differences in food levels for E. lacustris and H. gibberum in the two lakes, we attributed lower energy reserves in these species to effects of heavy metal contamination.
Life History and Abundance of Young Adult Lampetra ayresi in the Fraser River and Their Possible Impact on Salmon and Herring Stocks in the Strait of Georgia
Authors: Beamish Richard J. , Youson John H.
Published: April 2008

Metamorphosis in Lampetra ayresi begins in July but is not completed until approximately April of the following year when the oesophagus opens. The prolonged period of metamorphosis differs from that of other lamprey species and may have evolved in response to the pattern of discharge of the Fraser River. Prior to the opening of the oesophagus, some metamorphosing L. ayresi congregate just upstream of the salt water that moved into the river from the ocean. Soon after the oesophagus opens, lampreys are able to osmoregulate in salt water and enter the Strait of Georgia from May to July. Maximum numbers go to sea in early June, correlated with the maximum discharge from the Fraser River. Laboratory studies indicated that there was a relatively short period during which it was possible for the lampreys to go to sea. The mortality of L. ayresi held in fresh water in the laboratory greatly increased after mid-June, with few surviving beyond mid-July. These mortalities indicate that most L. ayresi must go to sea. In the laboratory a small number grew and reproduced normally in fresh water. A population estimate of the number of downstream migrants in 1979 indicated that L. ayresi were very abundant in the Fraser River. Three additional estimates of density and abundance were used to corroborate this observation. Even though L. ayresi feed for only about 10 wk in the Strait of Georgia, they are an important source of direct or indirect mortality to herring and young salmon. If L. ayresi was uncommon in British Columbia in the past, as previously described, then this present level of predation is an important new source of mortality to herring and salmon.
Intercalibration of Two Echo Integration Systems based on Acoustic Backscattering Measurements
Authors: Kieser R. , Mulligan T. J. , Williamson N. J. , Nelson M. O.
Published: April 2008

A joint Canada/U.S. survey for Pacific hake (Merluccius productus) was performed in 1983. As part of this survey two vessels made 350 pairs of acoustic backscattering strength measurements while the vessels steamed along side-by-side. A stochastic model was developed to analyse these data and to test for any departure from the null hypothesis of equal measured backscattering strengths. The null hypothesis was rejected. Several possible explanations for the observed differences are examined.
Influence of Water Temperature and Nitrogen to Phosphorus Ratios on the Dominance of Blue-Green Algae in Lake St. George, Ontario
Authors: McQueen D. J. , Lean D. R. S.
Published: April 2008

Data collected at Lake St. George, Ontario, over five summers spanning a period of 13 yr showed that there was no correlation between percent blue-green algal composition and the ratio of total nitrogen (TN) to total phosphorus (TP), However, percent blue-green algae was positively correlated with temperature and negatively correlated with nitrate nitrogen (NO3-N), total inorganic nitrogen (TIN), and the ratio of NO3-N:TP. Multiple correlations involving percent blue-green algae (dependent variable) with respect to temperature, in combination with one of NO3-N, TIN, NO3-N:TP, or TIN:TP, were also significant. In all cases, temperature effects accounted for most of the explained variation. The strongest correlation was found for the multiple regression involving percent blue-green algae versus temperature and the NO3-N: TP ratio. The pattern that emerged from the Lake St. George data set was that when temperature exceeded 21 °C and the ratio of NO3-N:TP was below 5:1, the likelihood of a blue-green algal bloom was high. When temperature was below 21 °C and NO3-N:TP exceeded 5:1, blue-green blooms never occurred.
Effects of Water and Substratum Nutrient Supplies on Lotic Periphyton Growth: An Integrated Bioassay
Authors: Pringle Catherine M.
Published: April 2008

Effects of substratum and water nutrient perturbations on periphyton growth were assessed in a nutrient-poor stream by combining a substratum enrichment technique with a flow-through bioassay system. Periphyton growth (chlorophyll a, total biovolume) responded to combined influences of water and substratum enrichment in an additive manner when both compartments were amended with N and P to yield an optimal ratio [Formula: see text]. When NO3-N was added to the substratum and PO4-P to the water, algal growth response was synergistic. Analysis of the vertical distribution of P fractions in cores taken from nutrient-diffusing substrata indicates that attached microorganisms mediate P release from underlying substrata, acting as a filter or temporary sink. Nutrient-diffusing substrata are useful detectors of limiting nutrients in aquatic systems; however, their function and application differ from water enrichment assays where nutrients are added at a constant rate. Differences are partially attributed to spatial and temporal variability of nutrient release and the strictly localized influence of substratum flora on ambient water chemistry.
Responses of Arctic Grayling (Thymallus arcticus) to Acute and Prolonged Exposure to Yukon Placer Mining Sediment
Authors: McLeay D. J. , Birtwell I. K. , Hartman G. F. , Ennis G. L.
Published: April 2008

Underyearling Arctic grayling (Thymallus arcticus) from the Yukon River system were expsed for 4 d to suspensions of fine inorganic (≤ 250 g∙L−1) and organic (≤ 50 g∙L−1) sediment and for 6 wk to inorganic sediment (≤ 1000 mg∙L−1) under laboratory conditions. The test sediments were collected from an active placer mining area near Mayo, Yukon Territory. The exposures evoked sublethal responses but did not cause gill damage. Mortalities (10 and 20%) occurred only in experiments at 5 °C with inorganic sediment concentrations ≤ 20 g∙L−1. Six weeks of exposure to sediment concentrations > 100 mg∙L−1impaired feeding activity, reduced growth rates, caused downstream displacement, colour changes, and decreased resistance to the reference toxicant pentachlorophenol, but did not impair respiratory capabilities. Stress responses (elevated and/or more varied blood sugar levels, depressed leucocrit values) were recorded after short exposure (1–4 d) to organic sediment concentrations as low as 50 mg∙L−1. Inorganic sediment strengths ≥ 10 g∙L−1caused fish to surface. The lethal and sublethal responses of Arctic grayling to pentachlorophenol were similar to those determined for other healthy salmonid fishes.
Strategies for the Cultivation of European Oysters (Ostrea edulis) in the Maritime Provinces of Canada: Preliminary Analyses
Authors: Cross Melvin L. , Newkirk Gary F. , Johnson Graham
Published: April 2008

Eight Nova Scotia Companies have been producing and marketing the oyster Ostrea edulis on a pilot scale. They have obtained seed oysters from pilot hatcheries at Dalhousie University and Pleasant Point, Nova Scotia. Calculations of net present values show that plausible scenarios can be produced in which the hatchery would be commercially viable, but they require important technological and market targets to be reached. These targets pertain not only to the production of seed oysters, but also to the sale of mature oysters by aquaculturists.
Evidence for Size-Selective Mortality of Juvenile Sockeye Salmon (Oncorhynchus nerka) in Babine Lake, British Columbia
Authors: West Cameron J. , Larkin P. A.
Published: April 2008

Otolith – body length relations and back-calculation procedures were used to test the hypothesis that mortality of juvenile sockeye salmon (Oncorhynchus nerka) in Babine Lake, British Columbia, is size selective. Samples of the 1978 brood of sockeye were collected as fry from spawning tributaries as juveniles in the main basin, and as smolts at the outlet. Total otolith length was chosen as the most useful otolith dimension for back-calculation of fork length at emergence. Sockeye from the various tributaries show different fork length – otolith length relationships necessitating a weighting procedure for comparisons involving samples of mixed stocks from the lake. Instantaneous daily growth rate and In fork length during the early lake-rearing period were significantly correlated. Smaller juveniles grew more slowly than larger individuals in mid-july, and a hierarchy of sizes was maintained. The distributions of total otolith length at emergence for fry, surviving juveniles, and smolts indicate selective mortality of fish with smaller otoliths, hence of small size at emergence. Survivals from the lower and upper halves of the initial total otolith length distribution were 8.9 and 63.6%, respectively. Comparable estimates for back-calculated fork lengths at emergence were 27.2 and 43.4%. Size-selective mortality is most intense in the late summer and early autumn, and may be associated with predation and parasitism.
Separation of Aquatic Lipid Classes by Chromarod Thin-Layer Chromatography with Measurement by latroscan Flame Ionization Detection
Authors: Parrish Christopher C.
Published: April 2008

Lipid classes in solvent extracts of marine dissolved and particulate matter, benthic invertebrates, net-caught zooplankton, and freshwater sediment trap material were measured with the Chromarod–latroscan (thin-layer chromatography (TLC/flame ionization detector (FID)) system. As many as 11 classes were identified in these samples by combining multiple development schemes with the partial scanning facility in the latroscan. Part of the latroscan's circuitry was modified to include a scan-interruptor switch to further facilitate partial scanning. Quantitative aspects of the TLC/FID system were improved with the use of a syringe fitted with a repeating dispenser for sample application, and by maximizing the detector's response. High FID responses were obtained with double developments and high hydrogen flow rates and FID scan rates. Under these conditions an analytical precision of 10% was attained for most compounds with only about five analyses on different Chromarods, and the range in mean FID response to different compounds was significantly narrowed. An intercalibration was performed to test TLC/FID accuracy: the latroscan gave lipid values which were about 85% of true gravimetric values.
Prey Choice among Piscivorous Juvenile Walleyes (Stizostedion vitreum)
Authors: Lyons John
Published: April 2008

In order to examine prey selection by walleyes (Stizostedion vitreum), I compared prey electivities for walleyes in Sparkling Lake, Wisconsin, with the results of species-preference experiments in the laboratory. Before young-of-the-year (YOY) yellow perch (Perca flavescens) were present in the littoral zone of Sparkling Lake, juvenile walleyes fed significantly less on minnows and more on darters than expected based on the relative abundance of these two taxa in the lake. After large numbers of YOY yellow perch appeared in the littoral zone, walleyes fed primarily on the abundant yellow perch, although their diet was not significantly different from that predicted based on the relative abundance of minnows, darters, and YOY yellow perch in the lake. In laboratory experiments, juvenile walleyes ate more bluntnose minnows (Pimephales notatus) than YOY yellow perch, and almost never ate johnny darters (Etheostoma nigrum). Walleyes were more successful at capturing bluntnose minnows than YOY yellow perch, but even when this was taken into account, walleyes ate more bluntnose minnows and fewer YOY yellow perch than expected, indicating that walleyes preferred bluntnose minnows to YOY yellow perch. Differences in prey selection between walleyes in the field and in the laboratory may have been related to differences among prey in distribution and movement patterns in Sparkling Lake.
Chlorophyll–Phosphorus Relationships for Subarctic Lakes in Western Canada
Authors: Ostrofsky M. L. , Rigler F. H.
Published: April 2008

Concentrations of total phosphorus and chlorophyll a were measured weekly in 49 lakes in the vicinity of Yellowknife, N.W.T., Canada, from May to September 1977. The relationship between [TPspr] and [Chl asu] was significantly different from the Dillon–Rigler model, but similar to relationships developed for lakes in Alberta, British Columbia, and the Yukon Territory. Empirical relationships were developed between [TPspr] and maximum chlorophyll a concentrations and the probability of exceeding critical concentrations of chlorophyll a. These models may be potentially more useful than models which predict only a mean summer chlorophyll concentration.
Transfer of Organochlorine Residues from Blubber through the Circulatory System to Milk in the Lactating Grey Seal Halichoerus grypus
Authors: Addison R. F. , Brodie P. F.
Published: April 2008

Residues of the DDT group of insecticides and the polychlorinated biphenyls (PCBs) were measured in maternal blubber, milk, and blood or serum and in pup blubber and blood or serum of grey seals (Halichoerus grypus) from Sable Island, N.S. sampled in 1984 and 1985. DDT-group and PCB concentrations in blubber samples were lower in 1984 than in a sample of this population taken in the mid-1970's, but not lower than those in a sample taken in 1982. Concentrations in 1985 samples were slightly higher than those in the 1984 samples, for unknown reasons. On a lipid weight basis, residue concentrations in blood or serum were consistently about 50% of those in blubber lipid. The more highly chlorinated and therefore more lipid-soluble PCB components were transferred less efficiently from blubber to the circulatory system. Net transfer of residues from maternal blubber to maternal milk was about 70% efficient; this implies considerable degradation of circulatory lipid and resynthesis, probably to milk carbohydrates and other compounds. There was some selection against movement of especially the lower chlorinated PCB congeners from circulatory lipids into milk lipids, compared with transfer of the DDT group. Thus, a nonselective barrier exists to quantitative transfer of residues from blubber lipid to circulatory lipid, and a partially selective barrier exists against PCBs in the transfer of residues from circulatory to milk lipids; at least the latter barrier seems to involve lipid solubility.
Genetic Changes in Pink Salmon (Oncorhynchus gorbuscha) Following Their Introduction Into the Great Lakes
Authors: Gharrett A. J. , Thomason M. A.
Published: April 2008

Pink salmon (Oncorhynchus gorbuscha) previously thought to require salt water for completion of their life cycle, have been firmly established in the Great Lakes following an accidental introduction into Lake Superior. We compare allelic frequencies at 27 protein-coding loci from collections of pink salmon from the Great Lakes with those from the anadromous population (Lakelse River, British Columbia) from which they were derived. Although the allelic frequencies in the Great Lakes collections are consistent with a single introduction, the frequencies observed in these collections differ substantially from those of the Lakelse River population. Alleles of G3p-1 and Ck-1, rarely observed (frequency < 0.005) in British Columbia population, are present in Great Lakes pink salmon at frequencies between 0.06 and 0.27. Smaller changes were observed at 11 other loci; 14 loci were monomorphic in all collections. Loss of variability in the Great Lakes was reflected by a decrease in average number of alleles per locus. Selection for physiologically tolerant phenotypes may have been necessary to establish this unique, self-perpetuating, freshwater population. The biochemical genetic changes we observed, however, can be adequately explained by genetic drift resulting from bottlenecks occurring at the first and at subsequent generations. Any decreases in survival resulting from freshwater intolerance would have exacerbated the bottlenecks. This adaptively distinct lineage produced by the ecological change coupled with the bottlenecks may be a major step toward speciation.
Density and Size Estimates of Cisco (Coregonus artedii) Using Analysis of Echo Peak PDF from a Single-Transducer Sonar
Authors: Rudstam Lars G. , Clay Clarence S. , Magnuson John J.
Published: April 2008

We estimated size and density of fish in three Wisconsin lakes from echo peak probability density functions (PDFs) obtained at night with a single-transducer 70-kHz echosounder. At night, cisco (Coregonus artedii) dominated the pelagic zone in all three lakes. The beam pattern effect was removed with a deconvolving filter technique. Fish size was estimated by fitting a combination of Rice PDFs to the deconvolved fish scattering PDF. Vertical density profiles and size estimates obtained acoustically corresponded to distributions and lengths of fish caught in vertical gill nets. The proportion of different size classes caught in gill nets agreed fairly well with the proportions determined acoustically. This analysis can be applied to signals from noncalibrated sonars and can be used to calibrate simultaneously obtained echo squared integration values. With calibrated sonars, target strength can be estimated in situ. For Cisco, TS = 21.9 log10L − 67.2, where TS is target strength in (decibels) and L is fish length (centimetres). The average number of Cisco in the three lakes ranged from 89 to 1551 fish/ha, corresponding to a biomass of 2–223 kg/ha. Maximum densities range from 12 to 49 fish/1000 m3.
Vertical Transport of Oxygen into the Hypolimnion of Lakes
Authors: Cornett R. J. , Rigler F. H.
Published: April 2008

Rates of vertical transport of oxygen into the hypolimnion were calculated by multiplying the vertical eddy diffusivity coefficients, determined from the heat budget, by the measured gradients in oxygen concentration. In 12 lakes, transport ranged from 0 to 70 mg O2∙m−2∙d−1and was insensitive to the depth defining the upper boundary of the hypolimnion. Oxygen was transported into the hypolimnion of lakes with a thinner hypolimnion and out of the hypolimnion of lakes with a thick hypolimnion. Transport averaged 4% of the measured total rate of hypolimnetic oxygen depletion and < 10% of the depletion rate in individual strata. Pooling these results with published estimates of oxygen gradients and eddy diffusivities suggests that in lakes with different trophic status (phosphorus levels 4–100 μg∙L−1) and size (areas from 0.4 to 70 km2), vertical oxygen transport accounts for less than 15% of the hypolimnetic oxygen deficit. Oxygen depletion models will gain relatively little precision by including a vertical transport flux parameter.
Stock Identification with the Maximum-Likelihood Mixture Model: Sensitivity Analysis and Application to Complex Problems
Authors: Wood C. C. , McKinnell S. , Mulligan T. J. , Fournier D. A.
Published: April 2008

Simulations were performed to evaluate the bias and precision of stock composition estimates from the maximum-likelihood mixture model using hypothetical multilocus characters. Bias and precision were examined in relation to the number of stocks being resolved, the number of loci available, and the difference in allelic frequency among stocks at each locus, using Monte Carlo simulations with different levels of sampling error in the mixture and learning samples. Model performance improved with increasing stock separation and number of loci available. Bias was not affected by the number of stocks resolved in simulations where mixture contributions from individual stocks remained constant. These results provide guidelines for reducing the complexity of genetic stock-identification problems by summing estimated mixing proportions for individual stocks within groupings based on stock similarity. The trade-off between improved accuracy and level of grouping can be examined graphically to determine the most useful level of grouping for the problem at hand. We illustrate this procedure with a real example from mixed-stock fisheries on sockeye salmon (Oncorhynchus nerka) along the British Columbia – Alaska coast.
Recruitment Dynamics of Spring-Spawning Herring in the Northwest Atlantic
Authors: Winters G. H. , Wheeler J. P.
Published: April 2008

Recruitment patterns of the seven major spring-spawning herring populations in the Northwest Atlantic were found to be determined largely by annual variations in overwintering temperatures and salinities associated with the Labrador Current, and the patterns were therefore synchronous. Removal of the environmental component of recruitment variability revealed dome-shaped stock–recruit curves with sharply ascending left limbs and relatively high degrees of compensatory density dependence in recruitment as measured by the Ricker parameter, β. The degree of such density dependence was positively correlated with recruitment variability which was itself negatively associated with mean stock size, i.e. large herring stocks tended to have less recruitment variability but lower levels of density dependence in recruitment than smaller stocks. In addition, environmental variability was positively associated with recruitment variability, and for stocks of the same size, the more northern populations of spring-spawning herring, inhabiting a more variable environment, have a higher level of density dependence on recruitment. Simulation studies showed that larger herring stocks could sustain higher levels of fishing mortality than smaller herring stocks, due mainly to reduced recruitment variability. We suggest that the most appropriate fishing strategy for herring is to maintain fishing mortality at a level of F = 0.20 with the option of closure when parent stock size falls below the critical level. A surprising finding from our study was the high level of density dependence of recruitment in herring stocks which we attributed to several features: (1) a large egg size and the ability of herring populations to adapt to a wide range of spawning conditions, (2) a density-dependent mortality associated with egg hatching success, and (3) a strong homing tendency ensuring that changes in spawning population sizes are spread evenly throughout the spawning area, thereby optimizing larval production.
Age Validation for the Mountain Brook Lamprey, Ichthyomyzon greeleyi
Authors: Medland T. E. , Beamish F. W. H.
Published: April 2008

Larval mountain brook lamprey, Ichthyomyzon greeleyi, were collected from Bent Creek in western North Carolina to provide information on the age structure of the population and to validate statolith banding patterns as an aging technique. Larvae were injected with oxytetracycline in winter and held in the laboratory at seasonally adjusted temperatures for 1 yr. Statoliths from these larvae were examined over the course of the study for the presence and persistence of oxytetracycline, and banding patterns which appeared after marking. Oxytetracycline persisted in all statoliths over the course of the study, and one complete annulus was formed on each statolith during the winter period when growth was slow. The larval period of I. greeleyi commences after hatching in late June and persists for 4.2–5.2 yr, with the oldest individuals being predominantly female.
An Alternative Perspective on Recruitment Overfishing and Biological Reference Points
Authors: Sissenwine M. P. , Shepherd J. G.
Published: April 2008

Biological reference points are used to guide fisheries management decisions. The reference points most often used are expressed in terms of fishing mortality rate (F). Fmsy relates to the maximization of sustainable yield. In principle, it is a most useful reference point, but in practice it is difficult to estimate. Fmax and F0.1 relate to certain levels of yield per recruit and are easily estimated, but they ignore conservation of the resource. Recruitment overfishing has usually been understood to occur when a population has been fished down to a point where recruitment is substantially reduced or fails. It has not been used as a basis for a biological reference point because the definition is vague and cannot be readily related to fishing mortality. Levels of spawning biomass below which recruitment seems to be reduced have been used, but their determination from available data is usually difficult and controversial. We propose an alternative definition of recruitment overfishing in terms of the level of fishing pressure that reduces the spawning biomass of a year class over its lifetime below the spawning biomass of its parents on average. Conventional models and types of data can be used to determine this level of F, denoted as Frep, which clearly relates to the replacement of spawning biomass and thus to sustainability of a population and yield in the long term.