bluuebunny/crossref_metadata_2025 huggingface dataset:
Ocean survival and exploitation of coho salmon (Oncorhynchus kisutch) stocks from the east coast of Vancouver Island, British Columbia
Authors: Labelle M , Walters C J , Riddell B
Published: April 2011

Juvenile tagging and escapement enumeration was conducted during 1985-1988 in nine streams within a 150-km section on the east coast of Vancouver Island. Fourteen coho salmon (Oncorhynchus kisutch) stocks of wild, hatchery, and mixed origin were monitored for ocean survival and exploitation patterns. Estimates of smolt-to-adult survival ranged from 0.5 to 23.1%. Survival rates were highly variable across years and stocks. No stock or stock type had consistently higher survival, but one hatchery stock exhibited consistently lower survival. Average exploitation rates were about 80% each year, and were as high as 96% for some stocks. Exploitation rates were not consistently higher or lower for any stock or stock type, but hatchery reared coho tended to be subject to higher exploitation. Log-linear models were used to assess the effects of various factors on survival and exploitation. Certain hatchery rearing practices had a large influence on survival. Genetic factors, run timing, and stream location had large influences on exploitation rates. An assessment of covariation in survival and exploitation rates showed no indication of a high level of similarity among stocks from adjacent streams or among stock types in this region.
Abundance and condition of larval cod (Gadus morhua) at a convergent front on Western Bank, Scotian Shelf
Authors: Lochmann S E , Taggart C T , Griffin D A , Thompson K R , Maillet G L
Published: April 2011

In November and December 1992, Atlantic cod (Gadus morhua) larvae were most abundant at a convergent front located at the periphery of a well-mixed gyrelike water mass rotating near the crest of Western Bank (outer Scotian Shelf). Zooplankton wet biomass and plankton abundance (272 and 529 µm size-classes) were also higher in the frontal region relative to the adjacent water masses. We used the frontal feature to test the hypothesis that larvae in frontal regions are in better condition than larvae elsewhere. No significant differences in triacylglycerol content (an index of nutritional condition), Fulton's K condition index, nor in the daylight feeding ratio were found between larvae in the frontal region and those in the adjacent waters. The convergent front acted as a larval collector, but exchange with other water masses eliminated measurable differences in larval condition. Our observations indicate that physically driven retention, not differential mortality (approximated by condition), was responsible for high abundances of cod larvae at this front.
Detection of migrating salmon in the Fraser River using 100-kHz sidescan sonars
Authors: Trevorrow M V
Published: April 2011

During a 10-day period in September 1995, field trials were conducted in the Fraser River near Mission, B.C., to evaluate 100-kHz side-looking sonars for salmon detection. A two-element sidescan installation looking transverse to the river flow detected echo traces due to salmon at ranges up to 250 m in water 6-13 m deep. The salmon target trajectories were identified and counted against a background of acoustic reverberation from the river surface and bottom sediments. Occasional, strong interference from boat wakes and wind-induced surface waves and bubbles was observed. Fish echo trajectory analyses allowed extraction of upstream and cross-stream swimming speeds. For some targets acoustic multipaths from surface and bottom reflections were distinguishable from direct echoes at ranges up to 150 m. Acoustic models of surface and bottom boundary backscattering, combined with bubble layer scattering and attenuation under breaking wave conditions, were able to match the observed background echo levels. Comparisons of model and data predict that under ideal conditions fish detection should be possible at ranges up to 250 m, but under windy conditions detection was limited to less than 70 m.
Spawning success of males using alternative mating tactics in sockeye salmon, Oncorhynchus nerka
Authors: Foote C J , Brown G S , Wood C C
Published: April 2011

Protein electrophoresis was used to determine the relative spawning success of jack sockeye salmon, Oncorhynchus nerka, males when they joined spawnings of larger, older individuals in experimental enclosures in the natal stream, Pierre Creek, Babine Lake, British Columbia. We attempted to relate the results to distance of the jack from female before spawning and relative size of the jack to the alpha male. Further, we measured the relationships between relative gonad size and available sperm volume to body size to determine if sperm competition could also play a role in determining the relative spawning success of males. Jack spawning success was variable (3-93%) and not significantly different from that of large males, even though they were further from the female before spawning, had smaller gonads, and had less available sperm. Jack males were adept at sneaking, usually commencing spawning within a split second of the alpha male and always on the opposite, free, side of the spawning female. The results are related to various theories on the evolution of alternative mating strategies and tactics in Pacific salmon.
Histopathology and cytogenetic evaluation of Pacific herring larvae exposed to petroleum hydrocarbons in the laboratory or in Prince William Sound, Alaska, after the Exxon Valdez oil spill
Authors: Marty G D , Hose J E , McGurk M D , Brown E D , Hinton D E
Published: April 2011

Following the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, USA, Pacific herring (Clupea pallasi) larvae sampled from oiled sites had ascites, pericardial edema, and genotoxic damage. Laboratory study confirmed that these lesions were consistent with oil exposure. Pacific herring larvae were trawled from two oiled and two unoiled sites in Prince William Sound in May 1989. Larvae from oiled sites were shorter, had ingested less food, had slower growth (oiled, 0.07-0.10 mm/day; unoiled, 0.15-0.18 mm/day), and had higher prevalence of cytogenetic damage (oiled, 56-84%; unoiled, 32-40%) and ascites (oiled, 16%; unoiled, 1%) than from unoiled sites. In the laboratory experiment, Pacific herring eggs were exposed to an oil-water dispersion of Prudhoe Bay crude oil (initial concentrations of 0.0, 0.10, 0.24, 0.48, and 2.41 mg/L) and sampled for histopathology <24 h after hatching. Effects were significant at the 0.48 mg/L dose (Dunnett's procedure, P < 0.05). Lesions included ascites; hepatocellular vacuolar change; and degeneration or necrosis of skeletal myocytes, retinal cells, and developing brain cells. Lesions in field-sampled larvae were consistent with higher mortality rates documented in larvae from oiled sites.
Performance of two red king crab pot designs
Authors: Zhou S , Shirley T C
Published: April 2011

We conducted a laboratory experiment to compare effectiveness of two pot designs in reducing the bycatch of female and sublegal-sized male red king crabs (Paralithodes camtschaticus) while retaining legal males. One pot (pot A) was a simulated standard king crab pot; a newly designed pot (pot B) had smaller mesh size, lower and wider entrances, and one-way opening triggers. Pot B prevented crabs from inserting their chelipeds through the mesh, motivated crabs to search for the entrance, eased the entry for all crabs, and facilitated the escape for all crabs but legal-sized males. Given that crabs had approached the pot, the mean entry probability for all crabs was 0.63 for pot B and only 0.13 for pot A. The probability of escape for females and sublegal males averaged 0.72 for pot B compared with 0.28 for pot A. As a result, the new pot design reduced the catch probability of females and sublegal males by over 60% while it increased the catch probability of legal males by over 25%.
Correlations between pathological changes and chemical contamination in American eels, Anguilla rostrata, from the St. Lawrence River
Authors: Couillard C M , Hodson P V , Castonguay M
Published: April 2011

American eel (Anguilla rostrata) from the St. Lawrence River are heavily contaminated with chemicals that may be associated with increased incidence of diseases and reproductive impairment. The relationship between tissue mirex concentration and body mass was used to separate eels into two groups: the proportion of eels migrating from contaminated areas (Lake Ontario and upper St. Lawrence River) increased as the migration season progressed. Vertebral malformations and basophilic foci in the liver (preneoplastic lesions) were more frequent at the end of the migratory season, when the eels were more heavily contaminated with organochlorine compounds. In contrast, mesenteric nematodes were more common in the first week of the season, when eels were less contaminated. Diameters and percentages of different stages of oocytes, and density and surface area of pigmented macrophage aggregates in the spleen, did not vary among weeks. While basophilic foci are specific biomarkers of exposure to environmental contaminants, vertebral malformations may be caused by a variety of other anthropogenic or natural factors.\b Further studies are needed to confirm the observed associations between chemical contamination and pathological changes.
Effects of pH, calcium, alkalinity, hardness, and chlorophyll on the survival, growth, and reproductive success of zebra mussel (Dreissena polymorpha) in Ontario lakes
Authors: Hincks S S , Mackie G L
Published: April 2011

In 1991, field studies were conducted to determine the effects of pH, calcium, alkalinity, hardness, and chlorophyll on the survival, growth, and reproduction of zebra mussel (Dreissena polymorpha). Water from 16 south-central lakes in Ontario was collected and supplied to zebra mussels in a flow-through system. Adult zebra mussel mortality was significantly correlated with calcium and pH. Growth rates of juvenile mussels ranged from -83.3 to 200 µm ·week-1. Water buffer variables (calcium, alkalinity, and total hardness) explained 60-66% of the variation observed in the change in shell length of juvenile zebra mussel (p = 0.001-0.003). There was negative growth at calcium levels less than 8.5 mg Ca · L-1, alkalinity levels less than 17.1 mg CaCO3 · L-1 and total hardness levels less than 31 mg CaCO3 · L-1. Maximum growth occurred at calcium levels of 32 mg Ca ·L-1, alkalinity of 65 mg CaCO3 · L-1, and total hardness of 100 mg CaCO3 · L-1. Positive growth of juvenile zebra mussel only occurred at pH levels greater than 8.3. Only one veliger survived to the settling stage.
Increased abundance and depth distribution of pelagic crustacean zooplankton during hypolimnetic oxygenation in a deep, eutrophic Alberta lake
Authors: Field K M , Prepas E E
Published: April 2011

Since June 1988, the north basin of eutrophic Amisk Lake has been treated by hypolimnetic oxygenation, while the south basin has served as a reference. In summer 1989, hypolimnetic dissolved oxygen (DO) concentrations were >=>1 mg ·L-1 in the treatment basin, while they fell to <1 mg ·L-1 in the reference basin by early July. There were no apparent treatment effects on biomass, abundance, or distribution of zooplankton in surface waters (0-10 m). However, in summer 1989, hypolimnetic abundances of two of four species (Daphnia longiremis and Daphnia pulex) were greater in the treatment than in the reference basin (P < 0.03) and than in the north basin in summer 1984 (4 years pretreatment). In the hypolimnion, D. longiremis, D. pulex, Bosmina longirostris, and Diacyclops bicuspidatus thomasi were found at greater median depths (P < 0.001) in the treatment than in the reference basin. Median depths of these four species in the hypolimnion tracked species-specific DO concentrations of between 1.5 and 2.3 mg ·L-1. Coincident with enhanced DO concentrations in the treatment basin in August, D. longiremis migrated vertically in the treatment basin (median depth day versus night, P < 0.001, median migration 4 m), but not in the reference basin (P > 0.9).
Impact of hypolimnetic oxygenation on profundal macroinvertebrates in a eutrophic lake in central Alberta. II. Changes in Chironomus spp. abundance and biomass
Authors: Dinsmore W P , Prepas E E
Published: April 2011

Effects of hypolimnetic oxygenation on profundal (15-25 m depth) Chironomus spp. in double-basined Amisk Lake were studied from 1988 to 1991. Responses were species specific. Mean densities and biomasses of C. anthracinus at 25 m increased 55- and 109-fold, respectively, in the treated north basin over the study period. Densities also increased in the reference south basin, but mean larval weights and biomasses were significantly lower than in the treated basin (P < 0.001). Anoxic conditions in the hypolimnion (dissolved oxygen concentrations <1 mg ·L-1), rather than low hypolimnetic temperatures, appeared to limit C. anthracinus distribution in Amisk Lake. Major changes in C. anthracinus abundance were not apparent until 2 years after the treatment commenced. Densities and biomasses of C. cucini were higher in the reference basin than in the treated basin of Amisk Lake. Densities of the C. decorus and C. plumosus groups increased in the treated basin but remained of minor importance. In comparison, densities of the C. cucini and C. plumosus groups at 25 m in the reference south basin of nearby Baptiste Lake declined over the study period. Increased profundal Chironomus spp. abundance in Amisk Lake suggested an increase in potential fish food.
Impact of hypolimnetic oxygenation on the vertical distribution of cisco (Coregonus artedi) in Amisk Lake, Alberta
Authors: Aku PMK , Rudstam L G , Tonn W M
Published: April 2011

Using hydroacoustics and vertical gill nets, we evaluated the efficacy of hypolimnetic oxygenation as a lake management tool by quantifying summer vertical distributions of cisco (Coregonus artedi) in a treated and untreated basin of Amisk Lake, Alberta, during and after oxygenation (1988-1993) and in untreated Baptiste Lake, Alberta. In Baptiste Lake, the hypolimnion remained anoxic and cisco were restricted to epilimnetic waters. Oxygenation increased hypolimnetic dissolved oxygen (DO) concentrations in Amisk Lake, expanding habitat by up to 9 m. During oxygenation, hypolimnetic DO remained above concentrations avoided by cisco (<1.3 mg ·L-1) in the treated basin, but fell below this level by midsummer in the reference basin. Consequently, cisco were distributed up to 8 m deeper in the treated than in the reference basin. In August 1990, a metalimnetic oxygen minimum in the reference basin confined >70% of the cisco to the epilimnion, while >60% of the fish inhabited the metalimnion and hypolimnion in the treated basin. Although DO remained above avoidance concentrations throughout most of the treated basin, the highest densities of cisco occurred in water with mean ( ± SD) DO concentration and temperature of 3.1 ± 1.3 mg ·L-1 and 11.8 ± 2.1oC, respectively. Thus, the extent of habitat expansion for fish during oxygenation programs will also depend on the availability of suitable temperatures.
A Bayesian interpretation of target strength data from the Grand Banks
Authors: Hammond T
Published: April 2011

Knowledge of the target strength (TS) distribution of the fish being surveyed is necessary for accurate acoustic biomass estimates. Although dual-beam and split-beam transducers can measure TS in situ, these measurements are usually misleading because fish with higher TS are detected more readily, measurements are coming from several fish species, and measurements are made on the total echo from several unresolved targets. A Bayesian method of analysis was developed to extract information from TS data despite these problems. The first problem was addressed using a model of fish detection that was calibrated with data from a survey of northern cod (Gadus morhua) on the Grand Banks. The second problem, species composition, was dealt with by incorporating information about the relative abundance of species groups. Prior information about the concentration profile of the species assemblage was used to take into account the third problem, multiple detection. Results suggested that the difficulties mentioned above are serious sources of bias that should not be ignored. The method also indicated how research effort can be directed to improve acoustic surveys.
A tracer investigation of nitrogen cycling in a pristine tundra river
Authors: Peterson B J , Bahr M , Kling G W
Published: April 2011

The fate of nitrogen (N) in drainages depends in part on N storage and transformation within the river network. The addition of an [15N]NH4+ isotopic tracer to a tundra river provided information on the uptake, food web transfer, and ecosystem retention of N. The fourth-order Kuparuk River ecosystem took up 60% of the NH4+ within 1 h and 1 km of the point of tracer addition. Long-lived biota and epilithon retained measurable amounts of the added 15N for up to 2 years. These transformations and storages within rivers exert control over the timing of N export, the chemical form of exported N, and, consequently, its ecological impact on downstream aquatic ecosystems.
Lungworm (Otostrongylus circumlitus) infections in ringed seals (Phoca hispida) from eastern Arctic Canada
Authors: Bergeron E , Measures L N , Huot J
Published: April 2011

Otostrongylus circumlitus, a metastrongyloid nematode found in the lungs of ringed seals (Phoca hispida) and other pinnipeds, may affect the health of seals and reduce diving capacity. Of five sites sampled in eastern Arctic Canada (190 seals examined), Salluit, Que., is an important enzootic zone (prevalence 48.2%, n = 27). Maximum intensity of O. circumlitus was 32 worms. Infection is restricted to young-of-the-year seals and may have an impact on recruitment of the population. Local geographic conditions may influence transmission of the parasite and thus prevalence and intensity of O. circumlitus among populations of ringed seals. No condition index used showed any significant relationship to infection, but prevalence and intensity were related to sternal blubber thickness (0.01 < p < 0.05) indicating that this parasite may have an effect on the physical condition of seals. Otostrongylus circumlitus may have an indirect effect on seals by modifying their diving behavior. Severe infections may lead to death, but light infections could be lost after a certain time with subsequent development of protective immunity.
Downstream migrations of juvenile Pacific salmon (Oncorhynchus spp.) in a glacial transboundary river
Authors: Murphy Michael L , Koski K V , Lorenz J Mitchel , Thedinga John F
Published: April 2011

Migrations of juvenile Pacific salmon (Oncorhynchus spp.) in the glacial Taku River (seventh order) were studied to assess movement from upriver spawning areas (in British Columbia) into lower-river rearing areas (in Alaska). Differences between fyke-net catches in the river and seine catches in the river's estuary indicated that many downstream migrants remained in the lower river instead of migrating to sea. In particular, age-0 coho salmon (O. kisutch) and chinook salmon (O. tshawytscha) moved downriver from May to November but were not caught in the estuary. Age-0 sockeye salmon (O. nerka), coho presmolts, and other groups delayed entry into the estuary after moving downriver. We tagged groups of juvenile coho (ages 0-2) from the fyke net with coded-wire to determine when they left the river. One-third of all tags recovered from sport and commercial fisheries occurred 2-3 years later, showing that many coho remained in fresh water for 1-2 years after moving to the lower river. Lower-river areas of large glacial rivers like the Taku River can provide essential rearing habitat for juvenile salmon spawned upriver and are important to consider in integrated whole-river management of transboundary rivers.
A strategy to detect fish discarding by combining onboard and onshore sampling
Authors: Allard Jacques , Chouinard Ghislain A
Published: April 2011

Discarding of small fish is considered to be an important conservation problem and has become illegal in some fisheries. We present a cost-efficient strategy to help enforce regulations against discarding. A discarding indicator is defined using the change in slope between two reference points on the empirical length-frequency density of the catch. This discarding indicator is then used according to the external distribution concept: the sampling distribution of the discarding indicator, when no discarding occurred, is obtained directly from samples taken by onboard observers; the value of the discarding indicator observed by onshore observers from a boat not covered by onboard observers is then compared with this sampling distribution. This procedure offers a nonparametric test for discarding. Application of the strategy is illustrated using data from the 1991 Atlantic cod (Gadus morhua) fishery in the southern Gulf of St. Lawrence. We describe several enforcement frameworks within which the method can be applied. The cost efficiency of the strategy comes from shifting resources from high-cost onboard observation to lower cost onshore observation.
Geographic and environmental factors affecting the distribution of kelp beds and barren grounds and changes in biota associated with kelp reduction at sites along the Norwegian coast
Authors: Sivertsen Knut
Published: April 2011

Sites at 244 locations along the west and north Norwegian coasts were investigated to evaluate whether kelp (Laminaria hyperborea) beds had been overgrazed by the sea urchins Strongylocentrotus droebachiensis and Echinus esculentus in the years 1981-1992. Barren ground communities were found in sheltered and moderately wave-exposed areas mainly in the inner and middle archipelago from Nordmøre (63°N) northwards. Densities of large-sized (adult and intermediate) L. hyperborea were 20.7 individuals ·m-2 in kelp beds and 9.7 individuals ·m-2 in transition areas. Juvenile Laminaria spp. were present at densities of 23.9 individuals ·m-2 in kelp beds, 3.6 individuals ·m-2 in transition areas, 0.0 individuals ·m-2 in barren grounds, and 59.1 individuals ·m-2 in kelp-harvested locations. Both the densities and the mean size of S. droebachiensis in barren grounds decreased northwards. The mean densities were 52.2 and 26.1 individuals ·m-2 for the areas south and north of the Arctic Circle, respectively. Multivariate analysis (CANOCO) showed that seven ``environmental'' factors (i.e., kelp depth gradient, distance (latitude), time of sampling, nematode infection in S. droebachiensis, wave exposure, coastal gradient, and substratum) contributed significantly to variability in the distribution of kelp beds and barren grounds. Species in hard-bottom communities in shallow waters could be divided into three distinct BIOTA.
Contaminant levels in St. Lawrence River yellow perch (Perca flavescens): spatial variation and implications for monitoring
Authors: Ion J , Lafontaine Y de , Dumont P , Lapierre L
Published: April 2011

Yellow perch (Perca flavescens) (n = 50) were collected from five geographic sectors between 1991 and 1992 to assess the spatial variability in trace metal and PCB (10 congeners) levels along the St. Lawrence River. Spatial differences among the five sectors were analyzed using two-way ANOVA and were significant only for PCBs. Both Hg and total congener concentrations were significantly and positively correlated with fish age, but not with mass or length. The relative proportions of the PCB congeners did not vary among sites. The bioaccumulation factor (BAF) of 3700 for total congeners compared favourably with previously reported results. Since 1975, Hg and PCB levels in St. Lawrence River yellow perch have decreased by factors of 2-3 and 30, respectively. Power analyses revealed that future monitoring studies may require large sample sizes to successfully detect the small spatial differences found for many contaminants. For example, to detect, at a power level of 90%, a 33% difference in Hg levels in yellow perch (i.e., the maximum difference found in this study) among the five sectors, 80 fish per sector would be required.
Population dynamics, production, and prey consumption of fathead minnows (Pimephales promelas) in prairie wetlands: a bioenergetics approach
Authors: Duffy W G
Published: April 2011

I assessed the population dynamics of fathead minnows (Pimephales promelas) in prairie wetlands and developed a bioenergetics model to estimate their production and prey consumption. I sampled populations in four wetlands weekly from late May through June and biweekly during July and August using a Kushlan 1-m2 throw trap. I imposed commercial harvest on two populations; the other two populations served as controls. Weekly population density estimates ranged from 52 000 to 356 000 ·ha-1 during early June and from 5400 to 19 700 ·ha-1 in late August. Simulated commercial harvest did not influence population density, mortality rates, or size of fathead minnows. Standing stock biomass differed among wetlands sampled, ranging from 144 to 482 kg ·ha-1 in early June and from 1 to 33 kg ·ha-1 during late August. However, differences were attributed to differential predation pressure rather than harvest pressure. Net production during the period ranged from 71.5 to 202.7 kg ·ha-1. Daily net production was greatest in early June (2.6-13.5 kg ·ha-1 ·day-1) and then declined during July and August (0.1-1.2 kg ·ha-1 ·day-1). Total mass of prey consumed by fathead minnows ranged from 332.7-1104.8 kg ·ha-1 among wetlands.
Interlake variation in growth and size structure of bluegill (Lepomis macrochirus): inverse analysis of an individual-based model
Authors: Nibbelink Nathan P , Carpenter Stephen R
Published: April 2011

Habitat structure alters food availability and predation risk, thereby directly affecting growth, mortality, and size structure of fish populations. Size structure has often been used to infer patterns of resource abundance and predation. However, food availability and predation risk in contrasting habitats have proven difficult to measure in the field. We use an inverse modeling approach to estimate food availability and habitat choice parameters from changes in length distributions of bluegill (Lepomis macrochirus). The model suggests that dynamics of bluegill length distributions primarily reflect food availability and habitat choice. Bluegill behavior minimized effects of size-selective predation on size structure. Parameters for food availability and habitat choice were correlated. It was therefore not possible to attain unique estimates of food availability and habitat selection when both were free parameters. However, when one parameter was estimated independently, the other could be identified. In five Wisconsin lakes, seining studies were used to estimate the size at which bluegill switched from littoral to pelagic habitats. Using this measure of switch size in the model, we estimated food availability for bluegill in each lake. These estimates were positively correlated with observed growth (r2 = 0.91), demonstrating the model's ability to estimate food availability.
An improved Fabens method for estimation of growth parameters in the von Bertalanffy model with individual asymptotes
Authors: Wang You-Gan
Published: April 2011

In the analysis of tagging data, it has been found that the least-squares method, based on the increment function known as the Fabens method, produces biased estimates because individual variability in growth is not allowed for. This paper modifies the Fabens method to account for individual variability in the length asymptote. Significance tests using t-statistics or log-likelihood ratio statistics may be applied to show the level of individual variability. Simulation results indicate that the modified method reduces the biases in the estimates to negligible proportions. Tagging data from tiger prawns (Penaeus esculentus and Penaeus semisulcatus) and rock lobster (Panulirus ornatus) are analysed as an illustration.
Interpreting Pacific halibut catch statistics in the British Columbia individual quota program
Authors: Sullivan Patrick J , Rebert Suzanne Dyner
Published: April 2011

An individual quota management program was implemented on Pacific halibut (Hippoglossus stenolepis) in Canada in 1991. Subsequent changes in fleet behavior influenced the interpretability of catch-per-unit-effort (CPUE) statistics. A regression analysis on Pacific halibut CPUE statistics collected from 1986 to 1994 indicates that year, season, area, vessel class, and gear type all significantly influence CPUE and that there are significant year x season, year x area, and other interactions. CPUE as an annual index of abundance appears to be influenced by changes in fish distribution and fleet behavior. Effort-weighted global CPUE estimates indicate a 38% increase in halibut density in years following implementation of the quota program, while seasonally adjusted area-weighted estimates show only a 16% increase. Two systematic scientific surveys conducted on a portion of this area in 1986 and 1993 showed a 132% increase in density, although high variation and bias in these estimates limited their significance. The composition of the fleet remained relatively stable over this period making interactions involving the factors of gear type and vessel size-class less significant. Results of this analysis proved useful in planning survey and assessment programs prior to implementing a similar quota program in Alaska.
Food and foraging behavior in relation to microhabitat use and survival of age-0 Atlantic salmon
Authors: Nislow Keith H , Folt Carol , Seandel Marco
Published: April 2011

We examined, using underwater snorkeling observations and field experiments, the influence of food availability on foraging behavior, habitat use, and survival of age-0 Atlantic salmon (Salmo salar) during the critical first-summer growth period. While most feeding attempts were directed at drifting invertebrate prey, we found a higher rate of benthic feeding forays than previously reported for salmon. Greater food abundance was associated with higher feeding foray rates, more time allocated to foraging, occupancy of higher microhabitat velocities, and greater first-year survival between two study streams. Experimental drift reduction reduced drift foray rates and triggered a change in behavior to increased benthic feeding. In contrast, within a single stream, greater predicted invertebrate drift in high-velocity microhabitats (1 m2) was unrelated to either microhabitat occupancy or drift foray rates of age-0 salmon. We suggest that, in some situations, salmonid foraging is related more directly to overall prey density than to the availability of high-velocity, high drift rate microhabitats. Differences in resource tracking (increased foraging, growth, or survival with increased food abundance) at different scales, along with the use of alternative predation modes, underscore the importance of considering behavior when linking food resources to growth and survival of stream salmonids.
Fish tissue metals and zooplankton assemblages of northeastern U.S. lakes
Authors: Stemberger Richard S , Chen Celia Y
Published: April 2011

Temperature, chlorophyll a, proportion of forest cover on the watershed, and fish tissue Pb, Zn, and Hg concentrations were the primary gradients that best explained the patterns of distribution of zooplankton assemblages in 38 northeastern U.S. lakes. Different zooplankton assemblages were associated with lakes that contained trout or cool-water species of minnows and systems dominated by a variety of warmwater fish species. Heavy metals in fish varied widely with geographic location and proximity to urban areas. Regression models indicated that Zn and Hg in fish were significantly and positively associated with chain length of the zooplankton web. In contrast, these metals and As showed a significant negative correlation with the number of feeding links between species. Structurally complex pelagic webs, comprising many lateral links, may significantly attenuate the transfer of heavy metals to higher trophic levels. Stepwise regression models that included structural variables significantly improved the amount of explainable variance in the fish metal concentrations over those with only physicochemical and land use variables. This study suggests that the high variability of metals in fish observed between adjacent lakes and across the region is explained in part by the structural features of the zooplankton web.
Increment formation in otoliths of slow-growing winter flounder (Pleuronectes americanus) larvae in cold water
Authors: Casas Maria C
Published: April 2011

Known-age winter flounder (Pleuronectes americanus) larvae were reared in large outdoor mesocosms where the temperatures were <5°C for the first 40 days and increased slowly after this and in field enclosures where the temperature ranged between 12.3 and 19.6°C. In the cold-water group, somatic and otolith growth were suppressed at the low initial temperatures and no increments were visible. After temperatures increased, somatic growth was evident and a variable number of initial narrow increments (0.2-0.6 µm) was observed. As larvae emerged from this initial period of slow growth, they began to develop rapidly and otolith increment widths increased to 1.0-3.0 µm. In contrast, larvae reared at the warmer temperature grew rapidly and laid down daily increments beginning 5 days after hatching.
Exchange of water and oxygen between the two basins of Amisk Lake
Authors: Lawrence Gregory A , Burke J M , Murphy T P , Prepas E E
Published: April 2011

Amisk Lake was artificially oxygenated year-round by bubbling oxygen through a diffuser installed at the deepest point of its north basin. The hypolimnion of both basins became anoxic in summer before operation of the system whereas anoxia was never observed while it was fully operational (July 1990 until October 1993). The system increased the average hypolimnetic oxygen content of the south basin by an average of 83 tonnes (t) more than under natural conditions between 2 September and 18 May. This considerable increase is approximately accounted for by the transport of dissolved oxygen (DO) through the connecting channel by currents driven by the bubble plume ( approx 52 t) and by internal seiche pumping ( approx 17 t): both mechanisms are contingent on the thermocline depth being less than that of the connecting channel. Internal seiche pumping was possible because the connecting channel is shorter than the maximum distance across which hypolimnetic fluid moved between flow reversals. Other factors that may have been important include changes in the replenishment of DO during turnover, oxygen transfer during winter through the ice-free patch created by the bubble plume, and an increase in DO consumption.
Response of temperate sea anemones to butyltin contamination
Authors: Mercier Annie , Pelletier Émilien , Hamel Jean-François
Published: April 2011

Two common species from the North Atlantic, Metridium senile and Bunodactis stella, were used to assess the response of temperate sea anemones toward tributyltin (TBT) contamination. Sea anemones M. senile exposed to a nominal TBT concentration of 50 ng ·L seawater-1in a continuous-flow system for 5 days accumulated 0.33 ± 0.02 ng TBT ·mg dry mass-1and 0.49 ± 0.02 ng dibutyltin (DBT) ·mg dry mass-1, a TBT derivative that dominates in seawater. The daily ingestion of 10 mg of mussel homogenate, contaminated with 10 ng TBT ·mg wet mass-1, for 5 days led to comparable accumulations in M. senile and B. stella of 0.52 ± 0.09 ng TBT ·mg dry mass-1(0.61 ± 0.01 ng DBT ·mg dry mass-1) and 0.47 ± 0.10 ng TBT ·mg dry mass-1(0.62 ± 0.12 ng DBT ·mg dry mass-1), respectively. Total burdens to the tissues after 5 days, combining TBT and DBT as Sn, represented 35 ± 6 and 42 ± 15% of ingested TBT in M. senile and B. stella, respectively. Adsorption and degradation processes are apparently involved in butyltin regulation. The two cold-water species metabolized TBT almost as efficiently as a previously studied tropical symbiotic species, but they accumulated lower levels of butyltins and therefore seem less vulnerable to TBT contamination.
Potential for dispersal of Gyrodactylus salaris (Platyhelminthes, Monogenea) by sea-running stages of the Atlantic salmon (Salmo salar): field and laboratory studies
Authors: Soleng Arnulf , Bakke Tor A , Hansen Lars P
Published: April 2011

Population growth of Gyrodactylus salaris increased exponentially on Atlantic salmon (Salmo salar) smolts in laboratory experiments conducted at 12.0°C. Furthermore, G. salaris was transmitted successfully from salmon smolt to parr at 0.0, 7.5, 10.0, and 20.0%° salinity and reproduced in fresh water after direct transfer from 7.5%° (16 days), 20.0%° (4 and 8 h), and 33.0%° (5, 15, and 30 min). No G. salaris were observed on salmon parr exposed to 33.0%° for 60 min. The prevalence of G. salaris on wild salmon smolts caught approximately 25 km from the river mouth in the Drammensfjord (surface salinity 2.0-3.5%°) was 71.2% compared with 88.0% on those from the neighbouring River Lierelva. Adult wild salmon caught as prespawners, spawners, and postspawners (kelts) in the River Drammenselva were infected with G. salaris. The prevalence and abundance increased from autumn to spring, in contrast with earlier studies on salmon parr, demonstrating the possible importance of adult salmon as reservoirs for G. salaris during winter. The results support the hypothesis of brackish water dispersal of G. salaris by infected salmonids migrating in estuaries and fjords. The use of salt as a disinfectant against G. salaris in hatcheries, and the stocking of possibly infected fish into brackish and seawater, should also be reexamined.
Dynamics of salmonine diets and foraging in Lake Ontario, 1983-1993: a test of a bioenergetic model prediction
Authors: Rand Peter S , Stewart Donald J
Published: April 2011

We tested the hypotheses that (1) reductions in individual size and energy density of adult alewife (Alosa pseudoharengus) in Lake Ontario over the past decade have caused reductions in mean size of consumed alewife and compensatory increases in frequency of feeding by salmonines and (2) perceived recent reductions in the alewife and rainbow smelt (Osmerus mordax) prey base in recent years have resulted in shifts in diets of salmonines to less preferred prey items. Data from a diet survey conducted on sport-caught salmonines during 1983-1988 and 1993 indicated significant reductions in the mean size of consumed alewife across all predator species over time and an increased frequency of feeding among some predators (reflected by a decline in the proportion of empty stomachs observed). We found evidence of increased ration levels in coho salmon (Oncorhynchus kisutch) and lake trout (Salvelinus namaycush) and an increase in the number of adult alewife in stomachs of all predator species that was accurately predicted by an earlier bioenergetic model analysis. We found evidence of a shift in diet across years away from rainbow smelt and other fishes to adult alewife. Results point toward possible sources of bioenergetic stress on salmonines in Lake Ontario.
Estimation of eggs lost from superimposed pink salmon (Oncorhynchus gorbuscha) redds
Authors: Fukushima M , Quinn T J , Smoker W W
Published: April 2011

This study investigated whether repeated use of limited spawning grounds (i.e., redd superimposition) by pink salmon (Oncorhynchus gorbuscha) can cause density-dependent mortality. Loss of eggs from part of Auke Creek, Alaska, was estimated from a series of mark-recapture experiments and maximum likelihood models. The number of eggs lost per day during the 5-week spawning season and for 2 weeks afterward was roughly proportional to spawner abundance and weakly related to stream discharge. Freshets after cessation of spawning induced negligible egg loss. The maximum daily egg loss estimated by one model was 398 000 eggs (80% CI = 267 000 - 1 581 000) or equivalently a loss of about 300 female spawners when the daily spawner abundance (both male and female) in the study area was at most 1000.
Body size and reproductive allocation in a multiple spawning centrarchid
Authors: Fox Michael G , Crivelli Alain J
Published: April 2011

Reproductive allocation in the multiple-spawning pumpkinseed (Lepomis gibbosus) was estimated in two non-native populations in southern France and one native Canadian population with experiments conducted in artificial enclosures, supplemented with data collected from wild populations. Reproductive allocation, estimated as the sum of mass lost over weeks when fish spawned, averaged 24 and 27% of prespawning body mass in the two French populations and 11.5% in the Canadian population. Estimates generated from a bioenergetics model and from batch fecundity in field-caught females gave similar results. Females from the French populations averaged 2.9 and 3.1 spawning periods, whereas the Ontario females averaged 2.1 spawning periods over a shorter spawning season. Body size was weakly correlated with reproductive allocation in one French and one Canadian population. The level of reproductive allocation in pumpkinseeds is considerably lower than that estimated in other multiple-spawning fishes. We suggest that multiple spawning can evolve solely to allocate the production of young in a variable environment and not necessarily to increase the total reproductive output of the female.
Population genetic studies of northern shrimp, Pandalus borealis, in Icelandic waters and the Denmark Strait
Authors: Jónsdóttir Ólöf DB , Imsland Albert K , Nævdal Gunnar
Published: April 2011

The aim of this study was to describe the population structure of northern shrimp, Pandalus borealis, in Icelandic waters and the Denmark Strait, based on genetically determined and electrophoretically detectable protein variants. Muscle samples of 4417 specimens were collected from 24 sampling locations in three areas: inshore and offshore areas in Icelandic waters and Dohrnbank in the Denmark Strait. The samples were analysed by starch gel electrophoresis (Tris-citrate buffer, pH 7.0) and isoelectric focusing (pH ranging from 3.5 to 9.5 and from 4.0 to 6.5). Three enzymes displayed sufficient activity and allele variation to be used in the routine work: glucose phosphate isomerase, malate dehydrogenase, and phosphoglucomutase. The analyses revealed low mean heterozygosity and proportion of polymorphic loci, as is common for decapods in general. The results displayed significant genetic differences among shrimps inhabiting the three areas, especially between inshore shrimp on one hand, and shrimp from the offshore area and Denmark Strait on the other. For management purposes, the northern shrimp in the three areas should preferentially be treated as three biological units.
A multiple-reach model describing the migratory behavior of Snake River yearling chinook salmon (Oncorhynchus tshawytscha)
Authors: Zabel Richard W , Anderson James J , Shaw Pamela A
Published: April 2011

A multiple-reach model was developed to describe the downstream migration of juvenile salmonids in the Columbia River system. Migration rate for cohorts of fish was allowed to vary by reach and time step. A nested sequence of linear and nonlinear models related the variation in migration rates to river flow, date in season, and experience in the river. By comparing predicted with observed travel times at multiple observation sites along the migration route, the relative performance of the migration rate models was assessed. The analysis was applied to cohorts of yearling chinook salmon (Oncorhynchus tshawytscha) captured at the Snake River Trap near Lewiston, Idaho, and fitted with passive integrated transponder (PIT) tags over the 8-year period 1989-1996. The fish were observed at Lower Granite and Little Goose dams on the Snake River and McNary Dam on the Columbia River covering a migration distance of 277 km. The data supported a model containing two behavioral components: a flow term related to season where fish spend more time in regions of higher river velocity later in the season and a flow-independent experience effect where the fish migrate faster the longer they have been in the river.
Larval condition and vulnerability to predation: an analysis based on mixed-prey experiments
Authors: Elliott Joel K , Leggett William C
Published: April 2011

Many recent studies in larval fish ecology measure larval nutritional condition (e.g., RNA/DNA ratios), with the ultimate goal of assessing future survival probabilities. Larvae of intermediate or poor condition are generally considered to be more vulnerable to predators than larvae in good condition. The objective of our study was to experimentally test whether larvae in poor condition have lower relative survival rates when exposed to a predator. We conducted mixed-prey experiments with larval capelin (Mallotus villosus) on days 6, 8, and 10 posthatching by putting 75 fed and 75 starved larvae in 38-L containers with (treatments) and without (controls) predators (juvenile lumpfish, Cyclopterus lumpus). There were no significant differences in the mean condition (RNA/DNA ratios) or dry weights of larvae recovered from controls and treatments. These results suggest that RNA/DNA ratios are not useful indicators of vulnerability to predation for larval capelin.
DNA adducts and histopathological lesions in perch (Perca fluviatilis) and northern pike (Esox lucius) along a polycyclic aromatic hydrocarbon gradient on the Swedish coastline of the Baltic Sea
Authors: Ericson G , Lindesjöö E , Balk L
Published: April 2011

DNA adducts, histopathological abnormalities, and organosomatic indices were used to study contaminant effects on fish along a polycyclic aromatic hydrocarbon (PAH) gradient, leading away from an aluminum smelter on the Swedish Baltic coast. The level of DNA adducts, analysed using the 32P-postlabelling method, was at least 145 times higher in the liver of female perch (Perca fluviatilis) from the innermost site on the gradient, closest to the suspected point source of PAHs, than at a distant reference site. Of the DNA adducts analysed, a relatively small number accounted for a very high proportion of the total level of adducts (30-60% at the innermost site and close to 100% at the outermost site). These particular adducts could also be observed in extrahepatic tissues, such as trunk kidney and head kidney, along the entire gradient. Similar patterns of adducts were also observed in northern pike (Esox lucius). Focal hepatocellular degeneration in perch was about 15 times more extensive at the innermost site than at the next site in the gradient and absent in perch from the two outermost sites. Body size relative to age was also significantly reduced in perch from the three innermost sites compared with the outermost site.
Nearshore settlement and localized populations of age 0 Atlantic cod (Gadus morhua) in shallow coastal waters of Newfoundland
Authors: Grant Scott M , Brown Joseph A
Published: April 2011

Mark-recapture experiments and seasonal sampling were carried out to examine the nearshore movements, abundance, and behaviour patterns of age 0 Atlantic cod (Gadus morhua) in eelgrass (Zostera marina) and no-eelgrass habitat in Trinity Bay, Newfoundland, during 1994 and 1995. Cod remained localized, not moving further than a few hundred metres in eelgrass and no-eelgrass habitats for several weeks after settling from a pelagic habit, and may remain localized during their first winter. Observations from this study of bulk movements of marked and unmarked cod, high within-site variation in catch rates during the day, and significant day-night differences in the mean and variance of catch data, combined with results from related studies, provide indirect evidence that age 0 cod shoal during the day and disperse at night within the study area. Behaviour patterns exhibited by age 0 cod (restricted nearshore movements, diurnal shoaling, and preference for structurally complex habitat) are mechanisms for predator avoidance, suggesting that predation risk is high in coastal Newfoundland. A significant increase in abundance of age 0 cod in less suitable habitat (no-eelgrass cover) when settlement strength was high is consistent with the hypothesis of density-dependent habitat selection.