bluuebunny/crossref_metadata_2025 huggingface dataset:
Aggregation and dispersion of krill at channel heads and shelf edges: the dynamics in the Saguenay - St. Lawrence Marine Park
Authors: Lavoie Diane , Simard Yvan , Saucier François J
Published: April 2011

The spatial organization of the euphausiid (Thysanoessa raschi and Meganyctiphanes norvegica) aggregation at the head of the Laurentian Channel is examined using 120-kHz echointegration data from eight surveys in the summers of 1994 and 1995 and currents obtained from a high-resolution three-dimensional circulation model. Circulation is the main factor controlling the abundance and distribution of krill. The main aggregation pattern is U-shaped and includes an entrance corridor along the northern edge of the channel, a major accumulation zone off Les Escoumins, and an exit corridor along the southern edge. However, this mesoscale aggregation exhibits rapid fluctuations in spatial pattern and global abundance, due to the redistribution of krill within and out of the study area. The local accumulations are controlled by the interactions between the semidiurnal tidal currents, the topography, and the negative phototactism of krill. The strong vertical currents found along the channel slopes upstream of Les Escoumins and at the sills act to concentrate and pile up krill. The aggregation and dispersion mechanisms are strongly influenced by the deepwater blocking process taking place at the sills. The fortnightly tidal cycle and freshwater runoff modulate the blocking intensity. This krill aggregation dynamics is of primary importance for the trophic link with the baleen whales and fish in the Saguenay - St. Lawrence Marine Park.
Can Atlantic salmon smolt twice? Endocrine and biochemical changes during smolting
Authors: Shrimpton J Mark , Björnsson Björn Thrandur , McCormick Stephen D
Published: April 2011

Smolting is characterized by morphological and physiological changes, some of which are reversible if fish remain in freshwater. Whether fish that smolt in the first year will repeat physiological changes associated with smolting a second time is not known. To assess whether Atlantic salmon (Salmo salar) can smolt more than once, we sampled hatchery-reared Atlantic salmon at monthly intervals for 2 years beginning the fall after hatching. Fish showed differences in rate of growth and were easily differentiated by size into upper mode (UM) and lower mode (LM) by the first fall. In the first spring, gill Na+,K+-ATPase activity of UM and LM fish increased six- and three-fold, respectively. Plasma growth hormone levels in spring were significantly elevated in UM fish but not in LM. Plasma cortisol levels changed little and gill corticosteroid receptor concentration did not differ between the groups. During the summer, gill Na+,K+-ATPase activity declined in both groups and remained low until the next spring. The second spring, growth hormone levels did not increase significantly and cortisol levels increased. The increase in gill Na+,K+-ATPase activity and cortisol and high saltwater tolerance indicate that UM Atlantic salmon can smolt in two consecutive years.
Intact genetic structure and high levels of genetic diversity in bottlenecked sockeye salmon (Oncorhynchus nerka) populations of the Fraser River, British Columbia, Canada
Authors: Withler Ruth E , Le Khai D , Nelson R John , Miller Kristina M , Beacham Terry D
Published: April 2011

Analysis of six microsatellite loci in 5800 sockeye salmon (Oncorhynchus nerka) from 29 Fraser River populations provided little evidence of genetic bottlenecks or mass straying in upper Fraser sockeye salmon resulting from reduced abundances following 1913-1914 rockslides in the Fraser canyon and successive decades of high exploitation. Upper Fraser populations were not characterized by a paucity of rare alleles, a sensitive indicator of populations in which effective size has been recently reduced. Heterozygosity and allelic diversity did not differ consistently between lower and upper Fraser populations. Throughout the watershed, early-migrating populations had lower allelic diversity and a lower proportion of rare alleles than did late-migrating ones. Genetic differentiation between upper and lower Fraser populations and heterogeneity among lower Fraser populations supported the suggestion that Fraser sockeye salmon are descendants of at least two postglacial "races." Variation among lakes within regions was the strongest component of genetic structure, accounting for five times the variation among populations within lakes and more than two times the variation among regions. Extensive historical transplants of eggs and juveniles apparently resulted in lit tle gene flow among regions, but three populations were reestablished or rebuilt as the result of more recent transplants.
Aquatic macrophyte richness in Danish lakes in relation to alkalinity, transparency, and lake area
Authors: Vestergaard Ole , Sand-Jensen Kaj
Published: April 2011

We examined the relationship between environmental factors and the richness of submerged macrophytes species in 73 Danish lakes, which are mainly small, shallow, and have mesotrophic to hypertrophic conditions. We found that mean species richness per lake was only 4.5 in acid lakes of low alkalinity but 12.3 in lakes of high alkalinity due to a greater occurrence of the species-rich group of elodeids. Mean species richness per lake also increased significantly with increasing Secchi depth. No significant relationship between species richness and lake surface area was observed among the entire group of lakes or a subset of eutrophic lakes, as the growth of submerged macrophytes in large lakes may be restricted by wave action in shallow water and light restriction in deep water. In contrast, macrophyte species richness increased with lake surface area in transparent lakes, presumably due to expansion of the area colonised by submerged macrophytes. Thus, the size of the colonised area is a better predictor of species richness than lake surface area. The strong increase in species richness accompanying greater transparency can be accounted for by the combined effect of higher colonised area and higher habitat richness along gradients of deeper macrophyte growth.
Effects of stock, coded-wire tagging, and transplant on straying of pink salmon (Oncorhynchus gorbuscha) in southeastern Alaska
Authors: Thedinga J F , Wertheimer A C , Heintz R A , Maselko J M , Rice S D
Published: April 2011

Straying of pink salmon (Oncorhynchus gorbuscha) from two wild stocks (intertidal and upstream) in southeastern Alaska was estimated. Secondary factors (coded-wire tagging and transplanting of the intertidal stock) that may influence straying were also evaluated. In 1996, 321 494 fry were marked with either coded-wire tags or pelvic-fin clips. A total of 3828 marked adults were recovered in their natal streams and 79 strays were recovered in streams within 60 km of the release sites. The overall estimated straying rate was 5.1%. Estimated straying for the intertidal stock (9.2%) was higher than straying of the upstream stock (3.7%) but was not statistically different due to high variance of the estimates. The proportion of fish straying was significantly greater (P = 0.01) for coded-wire-tagged than for pelvic-fin-clipped fish for the upstream but not for the transplanted stock. Straying and distribution of the transplanted stock were more similar to those of the upstream stock, which was endemic to the natal watershed and release site of the transplant, than to those of the intertidal stock, which was the donor stock for the transplant. Although tagging may influence straying, incubation and initial estuarine environment appear to be major determinants of the natural straying of pink salmon in southeastern Alaska.
Effects of sea ice cover on the swarming behaviour of Antarctic krill, Euphausia superba
Authors: Brierley Andrew S , Watkins Jonathan L
Published: April 2011

Much of the distribution range of Antarctic krill, Euphausia superba, is covered by permanent or seasonal sea ice. Sea ice extent has been implicated as a major factor affecting reproductive success of krill and krill dispersal, but little is known of the way in which ice cover may influence krill behaviour. This is largely because the under-ice environment is difficult to study. Ship-borne echosounders have, however, detected krill aggregations in midwater in ice-covered regions. We used 120-kHz echograms collected underway during three cruises that crossed ice-covered and adjacent open waters in the Bellingshausen, Weddell, and Scotia seas to compare morphological and next-neighbour characteristics of krill swarms within and without ice cover. No significant differences were detected between the horizontal and vertical extent of swarms or swarm next-neighbour distance in ice-covered or open waters. Distributions of swarm mid-depths did, however, differ significantly between ice-covered and open areas in all three seas, although the direction of difference was not the same in each instance: swarms in the Weddell and Scotia seas were generally shallower under ice than in open water, whereas in the Bellingshausen Sea the opposite prevailed.
Is social aggregation in aquatic crustaceans a strategy to conserve energy?
Authors: Ritz D A
Published: April 2011

Antarctic krill, Euphausia superba, is preeminently a gregarious animal. It lives for almost the whole of its existence from the late furcilia stage in aggregations. Despite this, laboratory study of schooling and swarming behaviour has been seriously neglected and critical emergent properties of group dynamics may have been overlooked. Using different-sized groups of gregarious mysids, I show that weight-specific oxygen uptake is reduced by about seven times when they form cohesive aggregations compared with when they are in uncohesive small groups. If this is true for E. superba, it casts doubt on all previous measurements of metabolic rate and suggests that estimates of the metabolic cost of swimming and perhaps feeding are much too high. The reason that groups conserve energy compared with isolates or small groups is hypothesised to be at least partly due to hydrodynamic processes, which serve to minimise sinking rates. Dye plumes revealed updrafts generated by mysid swarms, which could be exploited by individuals to reduce their sinking rate. These circulation patterns might also increase the efficiency of particle capture by aggregations. I propose that aggregation in aquatic crustaceans is a strategy to optimise energy expenditure and maximise food capture. Measuring behavioural and physiological rate processes in isolated animals will produce only artifacts.
Molecular phylogenetics of circumglobal Euphausia species (Euphausiacea: Crustacea)
Authors: Jarman Simon N , Elliott Nicholas G , Nicol Stephen , McMinn Andrew
Published: April 2011

The speciation history of members of the krill genus Euphausia with continuous circumglobal distributions was investigated by phylogenetic and molecular clock analyses of their mitochondrial DNA. Molecular clock estimates for divergence times of Antarctic and sub-Antarctic species of Euphausia of ~15 million years ago were fairly close to the time of formation of the Antarctic Convergence, consistent with their vicariant speciation. However, the confidence limits quantified for these time estimates were large at ~11 million and ~25 million years. A divergence time of between ~10 million years for Euphausia triacantha and Euphausia longirostris suggested that migration across oceanographic fronts like the Antarctic Convergence may also lead to speciation in krill. Genetic differentiation between Euphausia vallentini and Euphausia lucens was found to be relatively minor and occurred between 0.76 million and 1.65 million years ago. These species have overlapping ranges, suggesting that there is potential for sympatric genetic differentiation in krill.
Krill (Euphausiacea) demography and variability in abundance and distribution
Authors: Siegel Volker
Published: April 2011

Among euphausiids, there are many species that are represented by enormous numbers of individuals and are of considerable importance to various ecosystems, as well as to human exploitation. Considerable progress has been made regarding quantitative aspects of krill biology. This detailed knowledge about krill population parameters is necessary to answer questions about the importance of euphausiids to energy flow through certain ecosystems. This information also helps in assessing the importance of seasonal or long-term climate effects on variation in euphausiid populations because variability is not simply noise. Hypotheses have been developed as to how large seasonal or latitudinal environmental changes affect species survival strategies in poor conditions and maintenance of a stable population level. This paper discusses aspects of the spatial distribution with regard to seasonal and interannual changes, developments to define genetically distinct populations, and results of long-term variability in krill abundance and biomass for various species in different geographical locations.
Ecosystem changes and the effects on capelin (Mallotus villosus), a major forage species
Authors: Carscadden J E , Frank K T , Leggett W C
Published: April 2011

Capelin (Mallotus villosus), an important forage and commercial fish in the Northwest Atlantic, has exhibited dramatic changes in its biology during the 1990s, coincident with extreme oceanographic conditions and the collapse of major groundfish stocks. Commercial exploitation has not been a serious factor influencing the population biology of capelin in the area. The overall consumption of capelin has declined as predator stock abundances have changed. Data on plankton are sparse, but there appears to have been a decline in zooplankton abundance during the 1990s, and at the same time, a phytoplankton index increased. The impact of the changes in the physical environment has been the subject of previous studies and these are reviewed. The relative impacts of four factors, commercial exploitation, predation, food availability, and the physical environment, on the changes in capelin biology are discussed in the context of capelin as a single species and in the context of the ecosystem. The overall patterns suggest the existence of a "trophic cascade" within the distributional range of capelin in the Northwest Atlantic during the 1990s primarily driven by declines in major finfish predators.
Variations in the isotope composition of mercury in a freshwater sediment sequence and food web
Authors: Jackson Togwell A
Published: April 2011

Analysis of a sediment core and food-web animals from the Niagara Basin of Lake Ontario yielded the first recorded evidence for systematic variations in the stable-isotope composition of mercury (Hg) in natural environments on Earth. The sediments comprised younger strata enriched in Hg by recent pollution overlying older strata containing background Hg only. Several Hg isotope ratios, including 199Hg/201Hg, 201Hg/204Hg, and 202Hg/204Hg, varied significantly with the Mn/Fe ratio of the extractable readily reduced oxyhydroxide fraction of the sediment and with the concentrations of extractable Mn or Fe fractions, or both, in the sediment, and the zone of recent Hg pollution gave strikingly different results than the zone of background Hg. Food-web animals displayed a progressive increase in the 202Hg/204Hg ratio from lower to higher trophic levels in the order crustaceans < forage fish < trout; but superimposed on this trend were secondary trends owing to systematic decreases in the ratio from planktonic to benthic crustaceans and, correspondingly, from plankton-eating to benthos-eating forage fish. The results of the research suggest fractionation of Hg isotopes by natural processes, including Hg methylation, with effects linked to temporal variations in the oxidation-reduction potential of the sediments. These findings show that Hg isotopes could provide valuable but as yet untapped information about the sources and biogeochemical cycling of natural and anthropogenic Hg.
Genetic monitoring of supportive breeding in brown trout (Salmo truttaL.), using microsatellite DNA markers
Authors: Hansen Michael M , Nielsen Einar E , Ruzzante Daniel E , Bouza Carmen , Mensberg Karen-Lise D
Published: April 2011

Stocking with offspring of local wild fish, so-called supportive breeding, is often advocated as an alternative to stocking domesticated fish. However, it is important to ensure that supportive breeding does not result in inbreeding and loss of genetic variability. We analysed eight microsatellite loci in samples of wild and hatchery-reared brown trout (Salmo trutta) from three populations subject to supportive breeding. For calibrating statistical procedures, we included two test samples of reared offspring for which the precise number of parent fish was known and a sample from a further wild reference population. Three different statistical procedures were used to detect population bottlenecks and loss of variability: (i) a randomization test for comparing allelic diversity between samples; (ii) estimates of effective number of breeders from gametic-phase disequilibrium; and (iii) a test for assessing population bottlenecks based on detecting deviations from mutation-drift equilibrium. All three procedures were useful but they also exhibited different strengths and limitations, with the test for population bottlenecks probably being the single most useful procedure for routine monitoring. In two populations subject to supportive breeding, there were strong indications of reduced effective population sizes, and significant genetic differentiation was observed between different samples from the same population.
Zooplankton production in Lake Ontario: a multistrata approach
Authors: Kuns Michelle M , Sprules W Gary
Published: April 2011

We present evidence that estimates of annual zooplankton production in Lake Ontario based on stratified plankton net tows are preferable to those based on single, integrated tows through the whole water column. Samples were collected roughly every 2 weeks during 1993 and 1994 at a deep midlake station and at a shallower nearshore station. Stratified net tows were taken through each of the epilimnion, metalimnion, and hypolimnion and the mean temperatures of these strata used in production calculations. Integrated net tows were taken through the whole water column and the mean temperature of the column used in production calculations. Production estimates based on stratified samples were consistently higher (up to 310%) than those based on integrated samples. We show that higher stratified estimates are partly due to higher plankton net filtering efficiency over the shorter stratified hauls and partly due to the lower mean temperatures used in integrated hauls. Our analyses provide a basis for approximating the error in integrated production estimates caused by temperature stratification, water column depth, and plankton net efficiency.
Methyl mercury in pristine and impounded boreal peatlands, Experimental Lakes Area, Ontario
Authors: Heyes A , Moore T R , Rudd J WM , Dugoua J J
Published: April 2011

Methyl mercury (MeHg) concentrations were measured in peat and peat porewater of pristine wetlands and an impounded riparian wetland at the Experimental Lakes Area in northwestern Ontario, Canada. In pristine wetlands, MeHg concentrations in peat ranged from 0.1 to 60 ng·g-1 and in peat porewater from 0.02 (the detection limit) to 7.3 ng·L-1, with higher concentrations in wetlands that received upland runoff. Impoundment increased the average MeHg concentration in the near-surface peat porewater from 0.2 to 1.0 ng·L-1. As the increase was most dramatic near the peat - surface water interface, we suggest that the elevated MeHg concentrations resulted from an increase in net MeHg production associated with the decomposition of inundated vegetation. Impoundment increases the area of potential Hg methylation by imposing anoxia over the entire wetland surface and by facilitating the exchange of nutrients and MeHg between the peat surface and the surface water. No clear chemical control on MeHg concentration was observed among the pristine wetlands or in the impounded wetland. However, in laboratory incubations of peat, porewater MeHg concentration increased upon the addition of sulfate. We propose that sulfate availability is an important variable in Hg methylation in pristine northern wetlands.
Interpopulation differences in growth rates and food conversion efficiencies of young Grand Banks and Gulf of Maine Atlantic cod (Gadus morhua)
Authors: Purchase Craig F , Brown Joseph A
Published: April 2011

Geographically separated Atlantic cod (Gadus morhua) stocks in the northwest Atlantic exhibit life history variation and have been shown to differ genetically. The genetic and environmental contributions to phenotypic differences, however, have not yet been measured. We used common environment experiments to evaluate the importance of temperature on the observed growth variation between Grand Banks (GB) and Gulf of Maine (GOM) cod stocks. Larvae from the GB grew faster than GOM larvae at both 7 and 12°C. Growth rates of juveniles were not different, but GB juveniles had higher food conversion efficiencies than those from the GOM (at both ambient and warm temperatures). The results indicate that faster growth of GOM cod in the wild is not due to a higher genetic capacity for growth rate in GOM than in GB fish. The findings give evidence of genetically based phenotypic variation, which is in agreement with molecular studies on population differentiation in cod, and support the theory of countergradient variation in growth rates of larval fish.
Impacts of outliers and mis-specification of priors on Bayesian fisheries-stock assessment
Authors: Chen Y , Breen P A , Andrew N L
Published: April 2011

Bayesian inference is increasingly used in estimating model parameters for fish-stock assessment, because of its ability to incorporate uncertainty and prior knowledge and to provide information for risk analyses in evaluating alternative management strategies. Normal distributions are commonly used in formulating likelihood functions and informative prior distributions; these are sensitive to data outliers and mis-specification of prior distributions, both common problems in fisheries-stock assessment. Using a length-structured stock-assessment model for a New Zealand abalone fishery as an example, we evaluate the robustness of three likelihood functions and two prior-distribution functions, with respect to outliers and mis-specification of priors, in 48 different combinations. The two robust likelihood estimators performed slightly less well when no data outliers were present and much better when data outliers were present. Similarly, the Cauchy distribution was less sensitive to prior mis-specification than the normal distribution. We conclude that replacing the normal distribution with "fat-tailed" distributions for likelihoods and priors can improve Bayesian assessments when there are data outliers and mis-specification of priors, with relatively minor costs when there are none.
Estimability of natural mortality and other population parameters in a length-based model: Pandalus borealis in Kachemak Bay, Alaska
Authors: Fu Caihong , Quinn II Terrance J
Published: April 2011

Because stock-assessment models have become more complex, the question of estimability of population parameters is important. We conducted simulation-estimation experiments with a length-based model of the pink shrimp (Pandalus borealis Krøyer) population in Kachemak Bay, Alaska, to compare the robustness of various modeling approaches to specifications of natural mortality (M), catchability (q), a survey gear selectivity parameter (L50), and data imprecision. Our goal was to determine the estimability of various parameters, particularly M, q, and L50. Simulation results suggest that interannual variations in M and L50 could be estimated, if the underlying values have a trend over time. However, parameter q should be fixed at a chosen value, even when it varies over time. Estimated M for the Kachemak Bay P. borealis population increased in the 1980s, perhaps owing to increased predation mortality by groundfish.
Comparison between consumption rates of yellow perch (Perca flavescens) estimated with a digestive tract model and with a radioisotope approach
Authors: Gingras Jérôme , Boisclair Daniel
Published: April 2011

We compared consumption rates of yellow perch (Perca flavescens) obtained from surveys of complete digestive tract contents (CDTC) with two radioisotope approaches using 137Cs as a biological tracer. We sampled fish of age 1+, 2+, and 3+ from three lakes for a total of six lake - age-class combinations. The two radioisotope methods provided very similar estimates of consumption rates. The relative differences between the CDTC approach and the radioisotope approaches ranged from 67 to 128% when the sampling interval length was 28-35 days. At the time scale of 70 days, the relative differences between the approaches ranged from 15 to 20%. We propose that the ratio of the sampling interval length to the biological half-life of the contaminant determines the discrepancy between consumption estimates obtained using CDTC and radioisotopic approaches. Our analyses suggest that, under the specific conditions encountered in our study, a minimum value for this ratio to obtain adequate consumption rates may be 45%. Although our work represents a corroboration of the radioisotope approach in systems where 137Cs is present at trace levels, it also suggests that consumption rates obtained for time periods shorter than 70 days should be interpreted with caution.
The drift-retention dichotomy on Browns Bank: a model study of interannual variability
Authors: Hannah Charles G , Shore Jennifer A , Loder John W
Published: April 2011

Interannual variability in drift and retention in the Browns Bank region in spring was investigated by tracking particles in numerical-model estimates of the seasonal mean circulation and monthly mean flow anomalies computed using wind and sea-level data. The circulation changes associated with the variable forcing tend to reinforce either drift to the Bay of Fundy or retention in the vicinity of Browns Bank. Regular spring spawning can lead to widely different distributions of 1-month-old larvae, supporting the concept of a drift-retention dichotomy for Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae in the region. Analysis of interannual variability indicates that retention has bounded properties that must be accounted for when relating retention variability to forcing indices. As well, the nonlinearities associated with calculating particle trajectories from velocity fields contribute about 10% of the variance in retention indices. Comparison with biologically based indices of haddock survival indicates that circulation variability alone is not the dominant influence on survival to ages 1 and 2 years. However, it can be expected to have a significant influence in conjunction with biological factors such as the location and timing of peak spawning and the variable vertical position of eggs and larvae.
Optimal swimming speeds and forward-assisted propulsion: energy-conserving behaviours of upriver-migrating adult salmon
Authors: Hinch Scott G , Rand Peter S
Published: April 2011

Anadromous salmon migrations are energetically expensive. Long-distance migrants should be efficient in their use of energy and minimize swimming costs wherever possible. We explore swimming strategies and energy-saving tactics employed by three long-distance-migrating sockeye salmon (Oncorhynchus nerka) stocks in the Fraser River watershed, British Columbia. We used stereovideography and bank-side observations to estimate swimming speeds (from tailbeat frequency) and ground speeds (using distance traveled and duration) for individuals at several sites. Salmon were highly efficient at migration (i.e., ground speeds equaled or exceeded swimming speeds) through reaches with relatively low encountered currents (<0.25 m·s-1). We speculate that salmon exploit small reverse-flow vortices to achieve this feat. With low encountered currents, most salmon migrated according to an optimal swimming speed model: migrants minimized transport costs per unit distance traveled. Generally, salmon were less efficient at migration with fast currents, although the Chilko stock were superoptimal migrants, possibly owing to unique morphology and (or) behaviours. The risk of significant delays is enhanced when fast currents are encountered. Under these conditions, relatively fast swimming speeds could minimize travel time, despite high costs. Migrants may be balancing energetic costs of migration against the fitness costs of spawning delays.
Predicting the recruitment strength of an annual squid stock: Loligo gahi around the Falkland Islands
Authors: Agnew David J , Hill Simeon , Beddington John R
Published: April 2011

Two cohorts of Loligo gahi recruit to the fishery around the Falkland Islands, the first in summer and the second in autumn-winter. We investigated factors affecting recruitment to these cohorts using 13 years of data (1987-1999). The first evidence for density-dependent effects on recruitment in a squid population is reported, with very high spawning stock biomass leading to a reduction in recruitment in both cohorts. October sea surface temperature was negatively correlated with recruitment to the second cohort 6 months later, and a linear model explained 66% of the variance in recruitment strength. A model combining sea surface temperature and spawning stock size explained 77% of the variance. Thus, low October temperatures and moderate stock sizes lead to higher recruitment the following year than high October temperatures and high stock sizes. A strong negative relationship was also found between sea surface temperature in May and the timing of recruitment to the first cohort the following January-February, suggesting that higher temperatures lead to faster development of embryos or paralarvae and earlier recruitment to the fishery. A predictive model of recruitment size and timing should enable better management of L. gahi.
Density and size of juvenile salmonids in response to placement of large woody debris in western Oregon and Washington streams
Authors: Roni Philip , Quinn Thomas P
Published: April 2011

Thirty streams in western Oregon and Washington were sampled to determine the responses of juvenile salmonid populations to artificial large woody debris (LWD) placement. Total pool area, pool number, LWD loading, and LWD forming pools were higher in treatment (LWD placement) than paired reference reaches during summer or winter. Juvenile coho salmon (Oncorhynchus kisutch) densities were 1.8 and 3.2 times higher in treated reaches compared with reference reaches during summer and winter, respectively. The response (treatment minus reference) of coho density to LWD placement was correlated with the number of pieces of LWD forming pools during summer and total pool area during winter. Densities of age-1+ cutthroat trout (Oncorhynchus clarki) and steelhead trout (Oncorhynchus mykiss) did not differ between treatment and reference reaches during summer but were 1.7 times higher in treatment reaches during winter. Age-1+ steelhead density response to treatment during summer was negatively correlated with increases in pool area. Trout fry densities did not differ between reaches, but the response of trout fry to treatment was negatively correlated with pool area during winter. Our research indicates that LWD placement can lead to higher densities of juvenile coho during summer and winter and cutthroat and steelhead during winter.
Why are dwarf fish so small? An energetic analysis of polymorphism in lake whitefish (Coregonus clupeaformis)
Authors: Trudel Marc , Tremblay Alain , Schetagne Roger , Rasmussen Joseph B
Published: April 2011

Sympatric populations of dwarf lake whitefish (Coregonus clupeaformis) (DLW) and normal lake whitefish (NLW) commonly occur in north temperate and subarctic lakes. DLW have a much lower growth, mature earlier, and have a shorter life span than NLW. Furthermore, they are usually not found when cisco (Coregonus artedi) are present, possibly due to competitive exclusion. In this study, we compared the energy budget of DLW, NLW, and cisco using food consumption rates estimated with mass balance models of chemical tracers (i.e., mercury and radiocesium). These chemicals are globally distributed and can be readily detected in fish and their prey. Our analysis showed that the energy budget of DLW and cisco was similar. DLW and cisco consumed on average 4050% more food than NLW. The conversion efficiency of DLW and cisco was two to three times lower than that of NLW. These results suggest that DLW and cisco allocated a larger fraction of their energy budget to metabolism than NLW. Our analysis also suggests that the earlier maturation and shorter life span of DLW and cisco may be due to their higher metabolic rates.
Forest harvest impacts on water quality and aquatic biota on the Boreal Plain: introduction to the TROLS lake program
Authors: Prepas E E , Pinel-Alloul B , Planas D , Méthot G , Paquet S , Reedyk S
Published: April 2011

Eleven headwater lakes in Alberta's Boreal Plain were monitored for nutrients and plankton 2 years before and 2 years after variable watershed harvesting (harvesting mean 15%, range 0-35%). After harvesting, variations in annual precipitation resulted in lake water residence times that differed by an order of magnitude from one year to the next. During the first posttreatment year, total phosphorus concentrations increased (overall 40%) in most lakes; however, response was most consistent in lakes that were shallow and the water column mixed or weakly thermally stratified. Chlorophyll a, cyanobacteria (Aphanizomenon-Anabaena), and cyanotoxins (microcystin-LR) increased after harvesting, primarily in shallow lakes. Zooplankton abundance and biomass decreased after harvesting, particularly in stratified lakes where edible phytoplankton biomass declined. In the weakly or nonstratified lakes, declines in zooplankton biomass were associated with higher cyanobacterial biomass and cyanotoxins. Posttreatment change in total phosphorus concentration was strongly related to weather (greatest response in a wet year) and relative drainage basin size (drainage basin area to lake volume, r2 = 0,78, P << 0,01). There was no evidence that buffer strip width (20, 100, and 200 m) influenced lake response. These results suggest that activities within the entire watershed should be the focus of catchment-lake interactions.
Hierarchical interpretation of nonlinear relationships linking yellowfin tuna (Thunnus albacares) distribution to the environment in the Atlantic Ocean
Authors: Maury Olivier , Gascuel Didier , Marsac Francis , Fonteneau Alain , Rosa Anne-Laure De
Published: April 2011

Using generalized additive models, we show evidence for nonlinear relationships between various hydrological factors and age-structured catch per unit effort of Atlantic yellowfin tuna (Thunnus albacares) for two fishing fleets. Catchability effects are distinguished from tuna environmental preference effects in the catch per unit effort variability. With respect to catchability, an important nonlinear effect of local fishing effort is highlighted for each fleet. It is interpreted as resulting from a local overfishing phenomenon of adult yellowfin tuna and from vessel fishing tactics (cooperation/spying). The environmental preferences obtained facilitate the interpretation of the hierarchical spatial distribution and age-dependent movements of the yellowfin population. We show that, on a large spatiotemporal scale (the whole ocean), low salinity is a good predictor of yellowfin habitat. Juveniles are mainly distributed in low-salinity waters (<0.035 kg·kg1) when adults extend their range to waters of 0.036 kg·kg1. On a mesoscale, adult population annual reproductive transatlantic displacements are probably driven by temperature and salinity gradients to warm and low-salinity locations that are favorable for juveniles. Northsouth seasonal movements of the population are clearly related to warmwater seasonal oscillations. On a small scale, ocean thermic stability and gradients of sea surface temperature are important physical factors determining yellowfin concentration.
II: THE EFFECTS OF POLLUTED WATERS ON FISH LIFE.
Authors: KNIGHT A. P.
Published: April 2011

not available
III: THE CLAM FISHERY OF PASSAMAQUODDY BAY.
Authors: STAFFORD M.A., Ph. D. J.
Published: April 2011

not available
V: FOOD OF THE SEA-URCHIN (Strongylocentrotus dröbachiensis.)
Authors: Scott Ph.D. Dr. F. H.
Published: April 2011

not available
Life cycle of Calanus finmarchicus in the lower St. Lawrence Estuary: the imprint of circulation and late timing of the spring phytoplankton bloom
Authors: Plourde Stéphane , Joly Pierre , Runge Jeffrey A , Zakardjian Bruno , Dodson Julian J
Published: April 2011

The life cycle of Calanus finmarchicus in the lower St. Lawrence estuary is described based on observations of female egg production rate, population stage abundance, and chlorophyll a biomass collected over 7 years (19911997) at a centrally located monitoring station. The mean seasonal pattern shows maximum abundance of females in May, but peak population egg production rate and naupliar (N3N6) abundance occur in early July just after onset of the late spring  early summer phytoplankton bloom. The population stage structure is characterized by low summer abundance of early copepodite stages C1C3 and high stage C5 abundance in autumn. Between 1994 and 1997, there was important interannual variation in both timing (up to 1 month) and amplitude (five- to eight-fold) of population reproduction. Patterns of seasonal increase of C5 abundance in autumn suggest interannual variations of both timing and magnitude of deep upstream advection of this overwintering stage. Thus, the main features of C. finmarchicus population dynamics in the central lower St. Lawrence Estuary are (i) late reproduction resulting from food limitation prior to the onset of the summer phytoplankton bloom, (ii) probable export of early developmental stages during summer, and (iii) advection into the central lower St. Lawrence Estuary of overwintering stage C5 in autumn from downstream regions. These results support the hypothesis that circulation, mainly driven by discharge from the St. Lawrence River and its tributaries, is a key factor governing population dynamics of C. finmarchicus in this region.
Life cycles and seasonal distributions of Calanus finmarchicus on the central Scotian Shelf
Authors: McLaren Ian A , Head Erica , Sameoto D D
Published: April 2011

The life cycle of Calanus finmarchicus on and around Western Bank, 19911992, was essentially annual; the overwintered generation (G0) produced G1 that developed at temperature-dependent rates and then largely disappeared after June to winter as late copepodids at depth. However, a small fraction of G1 matured to spawn a less rapidly developing G2 that outnumbered G1 in the depths of Emerald Basin in autumn 1990. Estimated mortality on the central Scotian Shelf for G1 from egg to copepodid stage 5 in June was ~4%·day1 but subsequently for G1 and G2 was nearly constant at ~1%·day1. Populations on Western Bank mostly derived from reproduction by overwintered G2 on the Scotian Shelf. Larger populations in Emerald Basin in 19871988 were augmented from advected animals enabled to diapause there at depth and on Emerald Bank by inputs from beyond the shelf break, ultimately from farther north. Our observations and analyses match the physical circulation in the region.
I: THE PLANKTON OF EASTERN NOVA SCOTIA WATERS.: AN ACCOUNT OF FLOATING ORGANISMS UPON WHICH YOUNG FOOD-FISHES MAINLY SUBSIST.
Authors: Wright M.A., LL.D. R. Ramsay
Published: April 2011

not available
VII: THE SEAWEEDS OF CANSO.: Being a Contribution to the Study of Eastern Nova Scotia Algæ
Authors: ROBINSON B.A. C. B.
Published: April 2011

not available
In situ studies with Asian clams (Corbicula fluminea) detect acid mine drainage and nutrient inputs in low-order streams
Authors: Soucek David J , Schmidt Travis S , Cherry Donald S
Published: April 2011

In situ Asian clam (Corbicula fluminea [Müller]) studies may effectively mirror resident community responses to both acute toxicants and nutrient inputs in low-order streams. Clam survival and growth after 30 days in situ were compared with benthic macroinvertebrate community structural changes caused by acid mine drainage (AMD) and nutrient loading (measured as nitrate) in a small subwatershed of the North Fork Powell River, Virginia, U.S.A. Clam survival distinguished between two different levels of impact due to acidic, neutralized, and intermittent AMD inputs and was positively correlated with water column pH and negatively correlated with conductivity and metal con centrations. Survival was also positively correlated with relative abundance of the order Ephemeroptera, the most sensitive macroinvertebrate taxonomic group to AMD in this system. Clam growth was not related to AMD inputs but was positively correlated with nitrate concentrations and the relative abundance of the collector-filterer functional feeding group. These results suggest that transplanted clam studies accurately reflect benthic macroinvertebrate community responses to multiple stressors from point and nonpoint sources.
Male competition and breeding success in captively reared and wild coho salmon (Oncorhynchus kisutch)
Authors: Berejikian B A , Tezak E P , Park L , LaHood E , Schroder S L , Beall E
Published: April 2011

In the Pacific Northwest, releasing captively reared adult salmon (Oncorhynchus spp.) for natural spawning is an evolving strategy for the recovery of imperiled populations. However, the ability of captively reared fish to spawn naturally may be compromised by their artificial rearing environments. In this study, wild coho salmon (O. kisutch) males outcompeted captively reared males and controlled access to spawning females in 11 of 14 paired trials in laboratory stream channels. In two cases where satellite males were observed participating in spawning, DNA genotyping results determined that they did not sire any of the progeny. When spawning occurred at night and was not observed, DNA results confirmed behavior-based determinations of dominance made before dark. Dominance was established soon after the males were introduced into a common arena containing a sexually active female. We hypothesize that decisions by subordinate males to avoid direct competition may have minimized conflict. The competitive inferiority of captively reared coho salmon in this and a previous study probably reflects deficiencies in rearing environments, which fail to produce appropriate body coloration and body shape and perhaps alter natural behavioral development.
Changes in polyphosphate sedimentation: a response to excessive phosphorus enrichment in a hypereutrophic lake
Authors: Kenney William F , Schelske Claire L , Chapman Andrew D
Published: April 2011

Historic changes in lake phosphorus (P) loading are often determined in paleolimnological investigations by assessing stratigraphic changes in sediment total P. Polyphosphate (poly-P) in sediments may provide additional information on historic lake trophic status, because phytoplankton store surplus P intracellularly as poly-P when supplies exceed growth requirements. We hypothesize that phytoplankton (i.e., cyanobacteria and diatoms) with stored poly-P can remain intact and viable for many decades after sedimentation and that sedimented poly-P is not geochemically reactive. We tested our hypotheses with sediment cores from Lake Apopka, Fla., U.S.A., where P loading has increased ~7-fold since the 1920s and phytoplankton biomass is nitrogen limited owing to excessive P enrichment. We show that sedimented poly-P is mobilized by sample drying (i.e., becomes water soluble, geochemically reactive, and bioavailable); that anthropogenic P enrichment is expressed in the sediment record as increasing concentrations of poly-P; and that, consequently, sedimentary poly-P is a sensitive indicator of historic excessive P enrichment. Sedimentary poly-P is not geochemically reactive; thus, it represents biological attenuation that may partially ameliorate the effects of excessive P loading.
Patterns in abundance of fishes in main channels of the upper Mississippi River system
Authors: Dettmers John M , Gutreuter Steve , Wahl David H , Soluk Daniel A
Published: April 2011

Abundance of fishes of the main channels of the upper Mississippi River system and of other large North American rivers is largely unknown because historic sampling methods have been inadequate. We used a bottom trawl to estimate spatial and temporal patterns in abundance in the navigation channels of Pool 26 of the Mississippi River and the lower Illinois River. Total biomass density averaged 21 and 29 kg·ha1in the navigation channels of Pool 26 and the lower Illinois River, respectively. We identified spatial and temporal patterns in catches of key species using a generalized linear model based on the negative binomial distribution. Some species, including shovelnose sturgeon (Scaphirhynchus platorynchus), are persistent residents of the main channel. Multiple-season residents, including freshwater drum (Aplodinotus grunniens), rely heavily on the main channel during most of the year but leave it briefly, for example to seek thermal refugia in backwaters during winters. We suggest revision of the prevailing notion that main channels of large temperate rivers serve mainly as corridors for movement among other habitat types.
Stability of physiological and behavioural determinants of performance in Arctic char (Salvelinus alpinus)
Authors: Cutts C J , Adams C E , Campbell A
Published: April 2011

The physiological and behavioural mechanisms that confer behavioural dominance are poorly understood. Although recent studies have shown a link between metabolism and dominance, these studies relied on single measurements of both, and assumed that inter-individual variation of physiology and behaviour were repeatable over time. This paper demonstrates that standard metabolic rate is a repeatable trait in Arctic char (Salvelinus alpinus L.) and that relative differences between individuals are consistent across a range of environmental conditions. Furthermore, there were positive associations between metabolic rate, aggression, and competitive ability that were also repeatable over time. However, there was no relationship between competitive ability (measured as feeding attempts) and subsequent growth. This may be due to an energetic cost of dominance: high rates of food capture were only attainable through high rates of effort. This, in addition to elevated aggression, was thought to exert an energetic cost that could not be fully offset by the increased food intake.