bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a food web bioaccumulation model for the prediction of polychlorinated biphenyl, dioxin, and furan congener concentrations in Lake Ontario aquatic biota
Authors: Morrison Heather A , Whittle D Michael , Metcalfe Chris D , Niimi Arthur J
Published: April 2011

A previously developed benthic/pelagic food web bioaccumulation model was parameterized to predict concentrations of nine nonmetabolized polychlorinated biphenyl (PCB) congeners in invertebrates and fish from Lake Ontario. Predicted concentrations were compared with field-measured concentrations to verify the predictability of the model. Overall, 86% of model predictions were within a factor of 2 and 100% of predictions were within a factor of 10 of field-measured concentrations. The parameterized model was used to estimate chemical metabolic rates for 15 PCB, polychlorinated dibenzo-p-dioxin (PCDD), and polychlorinated dibenzo-p-furan (PCDF) congeners that are potentially metabolized. Estimated chemical metabolic rates ranged from 7.5 × 10-3 to 1.0 × 10-7·day-1 and were in general agreement with qualitative studies describing rates of metabolism of these chemicals by aquatic biota. The calibrated model was used to predict concentrations of all 24 PCB, PCDD, and PCDF congeners in invertebrates and fish commonly found in Lake Ontario but for which no field-measured data exist. These concentrations were expressed as the logarithm of the bioaccumulation factor (log BAF). The log BAF's in benthic invertebrates and salmonids ranged from 4.2 to 10.2 and from 5.1 to 11.6, respectively, and were consistent with field-measured BAF's.
Gillnet selectivity for North Sea Atlantic cod (Gadus morhua): model ambiguity and data quality are related
Authors: Hovgård Holger , Lassen Hans , Madsen Niels , Poulsen Thomas Moth , Wileman David
Published: April 2011

Gillnet selectivity curves for North Sea Atlantic cod (Gadus morhua) were fitted to catch data obtained with six different mesh sizes. The selectivity curves investigated included frequently used selectivity models following the normal, lognormal, and gamma distributions. Another group of selectivity models that take the method of capture (gilled, maxillae, or "randomly" enmeshed) into consideration was also included. The best description of the selection data was found for the latter models. Therefore, the capture processes and girth measurements should be recorded as a matter of routine and such data used when constructing and evaluating gillnet selectivity models. The shape of the selectivity curve for those size intervals where there were satisfactory catch information was well defined, while the selection curve was ambiguous outside the interval with adequate data. Ambiguities in the shape of the selectivity curve can be diminished by choosing an appropriate range in mesh sizes and ensuring that the mesh sizes match the size distribution of the population fished. It is furthermore suggested that the estimated length distribution of the fish encountering the nets be robust to misspecification of the selectivity model.
Effect of maternal growth history on egg number and size in wild white-spotted char (Salvelinus leucomaenis)
Authors: Morita Kentaro , Yamamoto Shoichiro , Takashima Yoshinobu , Matsuishi Takashi , Kanno Yasuji , Nishimura Kinya
Published: April 2011

Differences in egg number and egg size within a wild population of white-spotted char (Salvelinus leucomaenis) were examined from the perspective of maternal growth history by using a back-calculation method. Relatively greater egg size variation occurred among females (61.6%) than within females (38.4%). Larger females produced a larger number of eggs, which were also larger in size. To understand the causes of variation in egg number and egg size, several contributory factors determining maternal size were considered (initial size, growth rate for each age, total age). Egg number was not associated with maternal growth history. Contrary to egg number, egg size was strongly associated with maternal growth history; high growth in the first year was negatively associated with egg size, but high growth in the second year was positively associated with egg size. The results indicated that white-spotted char potentially exhibit phenotypic plasticity in egg size according to their growth history.
A novel method for the estimation of age and growth in rajids using caudal thorns
Authors: Gallagher M , Nolan C P
Published: April 2011

The caudal thorns of four bathyrajid species from the Falkland Islands exhibit well-defined surface ridges. The apparent periodicity of ridge deposition suggests that caudal thorns exhibiting this sculpture have potential for use as ageing devices. Caudal thorns and vertebrae were removed from selected specimens. Thorn surface band counts were compared with counts from longitudinal sections of vertebral centra. Structures were read three times by each of three readers in a double-blind study. Differences in precision were found between readers. Estimates made by the most experienced reader showed least variation. A consistent difference between thorn and centrum band counts was recorded in the males of two species, with centrum counts lower than thorn counts by one growth increment. These differences were attributed to difficulties in interpreting the centrum sections of these species. In all other groups, counts were highly correlated with no significant difference between group means. Caudal thorns represent a novel ageing structure that provides estimates with precision similar to that of more conventional vertebral ageing techniques. Centrum and thorn edge analysis, supported by evidence from a tetracycline-marked individual of a related species, confirms the nature of band formation in both structures. The use of thorns as ageing structures, where appropriate, has the potential to be of significant benefit to the resource assessment and management of skate and ray fisheries.
Cumulative effects of multiple effluent and low dissolved oxygen stressors on mayflies at cold temperatures
Authors: Lowell Richard B , Culp Joseph M
Published: April 2011

Effluents produced by pulp mills and sewage plants on northern rivers have the potential for a variety of interacting effects on downstream benthic invertebrates via increased levels of toxicants and nutrients and decreased levels of dissolved oxygen (DO) in the substratum. We experimentally measured the combined effects of these stressors at low temperature (4.5°C) on a common northern river invertebrate, the mayfly Baetis tricaudatus Dodds. Mayflies were exposed in laboratory artificial streams to one of two DO levels (low (5 mg·L-1) versus high (11 mg·L-1)) in the presence and absence of pulp mill and sewage effluent from an Alberta, Canada, mixed-effluent outfall (control river water versus 1% effluent); the DO and effluent treatments bracketed typical field concentrations. In the low-DO treatment, grazing intensity was reduced by 80%, and after 2 weeks of exposure, survival was reduced by 60-90%. Furthermore, 250-350% more mayflies in the low-DO treatment moved upward into regions of greater current velocity close to the surface of the artificial streams, a behavior that would likely make them more susceptible to fish predation in the field. In contrast, the 1% effluent treatment increased mayfly survival (possibly due, in part, to stimulation of increased mayfly grazing intensity by the effluent), although this effect only partly compensated for the pronounced negative impact of low DO levels.
Influence of organic acid site density on pH modeling of Swedish lakes
Authors: Köhler Stephan , Hruka Jakub , Bishop Kevin
Published: April 2011

A semidirect titration method was used to determine individual site densities of carboxylic acids present in natural organic matter originating from 74 Swedish lakes. The average carboxylic acid site density of natural organic matter of the studied lakes was 8.6 ± 1.6 µequiv.·mg total organic carbon-1, which is more variable than the site densities observed earlier in a set of streams. These data were then used to assess the effect on modeling pH and organic anion charge contribution caused by the natural variability in site density. Air-equilibrated pH was modeled with a median error of 0.08 pH unit, equivalent to a mean error in the charge balance of 9 µmol·L-1, using measured Cb-Caand individually determined site densities. A better prediction of pH, however, was made using this average site density and the CBALK approach, which is a different method for estimating total buffering capacity. The mean error in pH prediction was decreased to 0.05 pH unit, equivalent to a mean error in the charge balance of 5 µmol·L-1. These uncertainties in pH prediction are significantly smaller than reported in other studies. This implies that the existing natural variation in site density does not lead to significant effects on modeling pH or anion charge contribution in surface waters in the pH range of 4.5-8.5. Filtered samples (0.45 µm) did not show any significant change in pH, total organic carbon, or site density compared with unfiltered samples.
Effects of release parameters on recovery rates of tagged groundfish species
Authors: Fowler G M , Stobo W T
Published: April 2011

A compilation of groundfish mark-recapture studies conducted in the Northwest Atlantic from 1953 to 1985 was examined by analysis of deviance to determine the effects of release parameters on subsequent recoveries of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), and American plaice (Hippoglossoides platessoides). Fish length was a major determinant of recoveries for all four species, with recovery rates generally increasing with increasing fish length. Depth of capture was a significant determinant of recoveries for cod and haddock, with recovery rates decreasing as depth increased. Year of release was a significant determinant for all four species, with recovery rates declining in recent years. Declines in recovery rates of cod, haddock, and pollock occurred during certain months or seasons. Recovery rates decreased where fish were tagged in areas most distant from inhabited coastal regions, but the interpretation of this effect is complicated by changes in the fisheries over time between areas. Recovery rates also decreased with increasing catch size and varied between different tag types and capture methods. The results should prove useful in the design of tagging protocols and analysis of recovery data.
Phylogeographic lineages and differentiation pattern of Atlantic salmon (Salmo salar) in the Baltic Sea with management implications
Authors: Koljonen Marja-Liisa , Jansson Håkan , Paaver Tiit , Vasin Oleg , Koskiniemi Jarmo
Published: April 2011

The genetic structure and isolation pattern of the Atlantic salmon (Salmo salar) throughout its range in the Baltic Sea were examined as a starting point for a conservation strategy for the species in this area. The allozyme variation in seven polymorphic loci was studied in 5125 salmon from 24 rivers in four countries. A clear dichotomy was observed between stock groups from southeastern (Russia, Estonia, Latvia, southern Sweden) and northwestern (northern Finland, northern Sweden) drainage regions, corresponding to the postglacial colonisation of the Baltic Sea by two phylogeographic lineages, one from the east (the Ice Lake lineage) and one from the west (the Atlantic lineage). The geographical and genetic distances between stocks fit the one-dimensional "isolation-by-distance" model (p < 0.001). The estimated gene flow ranged from 0 to10 migrants per generation. The total diversity of hatchery stocks was 72% of that of the wild stocks. Genetically similar stock groups, phylogeographic lineages, and drainage regions are recommended for use as genetic management units in addition to stock level.
Empirical relationships between polychlorinated biphenyls in sediments and submerged rooted macrophytes
Authors: Vanier Claire , Planas Dolores , Sylvestre Michel
Published: April 2011

In this study, we use empirical relationships to model accumulation of polychlorinated biphenyls (PCBs) in submerged rooted macrophytes sampled in the upper St. Lawrence River (Canada - United States). The correlations between PCB congener concentrations in sediments, in macrophyte shoots, and in their roots were all significant (P < 0.001). However, the PCB congener concentrations in macrophyte shoots were better predicted by concentrations in sediments (top 5 cm) than by those in the roots of plants (R2= 0.839 and 0.704, respectively). Our results suggest that models based on the phase partitioning concept are applicable to submerged macrophytes. The lipids in shoots and the organic fraction in sediments are likely the phases involved in PCB partitioning between these two compartments. Between shoots and roots, the lipid phase also appears to be involved in the congener partitioning. However, between roots and sediments (5- to 10-cm depth interval), the correlation was weaker using organic weight standardisation of congener concentrations in sediments than using dry weight standardisation (R2= 0.852 and 0.778, respectively).
Fisheries assessment: what can be learned from interviewing resource users?
Authors: Neis Barbara , Schneider David C , Felt Lawrence , Haedrich Richard L , Fischer Johanne , Hutchings Jeffrey A
Published: April 2011

Fishers have detailed knowledge of their resources, their environment, and their fishing practices that is rarely systematically collected. We conducted three types of interviews with coastal Newfoundland fishers to identify the range of information available, to see if it could be quantified, and to explore its potential for reconstructing trends within fisheries. These fishers have many terms for Atlantic cod (Gadus morhua), each associated with characteristic patterns of seasonal movement and availability to gear and indicating the location of several coastal spawning areas. They described a variety of changes in fishing practice. Of the four changes that could be quantified, all contributed to decadal-scale increases in catch efficiency prior to 1992, while change in catch per unit of effort for cod was consistently negative at decadal scales. For these fishers' lumpfish (Cyclopterus lumpus) roe fishery, catch per unit of effort was consistently negative in the 1990s. We describe ways to access the large reservoir of information held by fishers, the use of several cross-checks to identify consistent patterns, and the use of trends and patterns to broaden the basis for interpreting quantitative surveys used in fisheries assessment. Local information from resource users can be assembled in forms usable in quantitative stock assessments.
New perspectives on the growth and longevity of the European lobster (Homarus gammarus)
Authors: Sheehy MRJ , Bannister RCA , Wickins J F , Shelton PMJ
Published: April 2011

The natural rate of lipofuscin accumulation in an eyestalk ganglion was determined from microtagged European lobsters, Homarus gammarus, of known age, recaptured from the Yorkshire fishery (United Kingdom). This calibration, in combination with supporting data from shorter-lived astacideans (freshwater crayfish), was used to age wild lobsters from the fishery. A unique perspective of age-at-size in a clawed-lobster population was obtained, which circumvented some difficulties associated with conventional methods for estimating generalized growth and natural mortality. The exceptional ages attained by some of the largest lobsters (males: average 31 years, maximum 42 ± 5 years; females: average 54 years, maximum 72 ± 9 years) are explained by ageing theory, indicate natural mortality rates, M, of 0.15 and 0.08 for males and females, respectively, and point to the existence of an offshore refuge. Age-at-size is highly variable: at least seven year-classes enter the fishery at 85 mm carapace length. This limits resolution of annual cohorts in size compositions, complicates development of recruitment indices, and may explain past size composition stability. The new age-length data suggest potential selective fishing impacts and past early recruitment variations. The study highlights the need for age data in order to obtain accurate crustacean stock assessments.
Should depensation be dismissed as a possible explanation for the lack of recovery of the northern cod (Gadus morhua) stock?
Authors: Shelton Peter A , Healey Brian P
Published: April 2011

After 7 years of a moratorium on northern cod (Gadus morhua), there is no convincing evidence that recovery has commenced. Under the simple assumption of linear density dependence, rapid population growth is predicted. That this has not transpired leads to consideration of less simple assumptions regarding density dependence, such as depensation.
Concordance of taxonomic composition patterns across multiple lake assemblages: effects of scale, body size, and land use
Authors: Allen Andrew P , Whittier Thomas R , Larsen David P , Kaufmann Philip R , O'Connor Raymond J , Hughes Robert M , Stemberger Richard S , Dixit Sushil S , Brinkhurst Ralph O , Herlihy Alan T , Paulsen Steven G
Published: April 2011

We assessed environmental gradients and the extent to which they induced concordant patterns of taxonomic composition among benthic macroinvertebrate, riparian bird, sedimentary diatom, fish, and pelagic zooplankton assemblages in 186 northeastern U.S.A. lakes. Human population density showed a close correspondence to this region's dominant environmental gradient. This reflected the constraints imposed by climate and geomorphology on land use and, in turn, the effects of land use on the environment (e.g., increasing lake productivity). For the region as a whole, concordance was highest among assemblages whose taxa were relatively similar in body size. The larger-bodied assemblages (benthos, birds, fish) were correlated most strongly with factors of broader scale (climate, forest composition) than the diatoms and zooplankton (pH, lake depth). Assemblage concordance showed little or no relationship to body size when upland and lowland subregions were examined separately. This was presumably because differences in the scales at which each assemblage integrated the environment were obscured more locally. The larger-bodied assemblages showed stronger associations with land use than the diatoms and zooplankton. This occurred, in part, because they responded more strongly to broad-scale, nonanthropogenic factors that also affected land use. We argue, however, that the larger-bodied assemblages have also been more severely affected by human activities.
Effects of the spawning migration on the nutritional status of anadromous Atlantic salmon (Salmo salar): insights from stable-isotope analysis
Authors: Doucett R R , Booth R K , Power G , McKinley R S
Published: April 2011

Anadromous Atlantic salmon (Salmo salar) were collected during their spawning migration along the Exploits River, Newfoundland, in 1996 and analyzed for stable-isotope ratios (δ13C and δ15N) and tissue concentrations of protein and lipid. Fish became progressively more 13C enriched during the spawning migration (about -24 to -19), and the degree of enrichment was dependent on tissue type (red muscle: +4.1, liver: +2.6, white muscle: +1.3). Only liver showed consistent changes in δ15N, as overwintering kelts (13.5 ± 0.8) were about +2 more enriched than upstream migrants (11.4 ± 1.5). Isotopic enrichment in migrating salmon appeared to result from mobilization, reorganization, and catabolism of stored lipid and protein reserves associated with the cessation of feeding upon entering freshwater. The most significant correlations existed between lipid content and δ13C in red muscle (r2 = 0.67) and protein content and δ15N in liver (r2 = 0.32). This study shows that fasting affects the stable-isotope ratios of both carbon and nitrogen in anadromous fishes and that nutritional status should be considered when inferring food web relationships from the isotopic compositions of migrating salmonids.
Temperature- and size-dependent growth of larval and early juvenile Atlantic cod (Gadus morhua): a comparative study of Norwegian coastal cod and northeast Arctic cod
Authors: Otterlei Erling , Nyhammer Gunnar , Folkvord Arild , Stefansson Sigurd O
Published: April 2011

Norwegian coastal (NC) and northeast Arctic (NA) Atlantic cod (Gadus morhua) larvae were reared on live zooplankton to investigate temperature- and size-specific growth. Larval and juvenile growth was temperature and size dependent. Growth in length and weight increased with increasing temperature from 4 to 14°C, with a corresponding reduced larval stage duration. Maximum growth rate occurred at a larval size of 0.1-1.0 mg dry weight, followed by a declining trend during the juvenile stage. The temperature optimum of larval cod fed in excess is estimated to be between 14 and 16°C, with a maximum weight-specific growth potential exceeding 25%·day-1. Temperature- and stock-specific growth curves of dry weight at age are well described by a generalized Gompertz model. A stock-specific difference in mean weight at age was observed, with NC growing better than NA. Neither countergradient latitudinal variation in growth capacity of the two larval cod stocks nor temperature adaptation across latitudes was indicated. A stock-specific difference in weight at length was observed in early juveniles, with NC being heavier than NA. Overall, a positive correlation between temperature and condition level was found. No distinct temperature- or stock-specific differences in survival were observed.
Phylogeny of the lamprey genusLampetrainferred from mitochondrial cytochromeband ND3 gene sequences
Authors: Docker Margaret F , Youson John H , Beamish Richard J , Devlin Robert H
Published: April 2011

Mitochrondrial DNA analysis resolved many previously unanswered questions concerning the phylogeny of the lamprey genus Lampetra (comprising the subgenera Entosphenus, Lethenteron, and Lampetra). A total of 735 base pairs were sequenced from the cytochrome b and NADH dehydrogenase subunit 3 (ND3) genes in 11 lamprey species. With the exception of L. (E.) hubbsi from California, species of the Entosphenus subgenus formed a tight-knit clade that was very distinct from the other two subgenera. Lampetra hubbsi clustered with species of the Lampetra subgenus from the west coast of North America (L. ayresii and L. richardsoni) whereas species of the Lampetra subgenus from Atlantic drainages, namely the North American L . aepyptera and European L. fluviatilis, formed a third cluster. A fourth cluster included two species from the Lethenteron subgenus (L. japonica and L. appendix). Inclusion of published data from a third Lethenteron species, L. zanandreai, showed it to group with the L. (L.) fluviatilis lineage rather than with the other two Lethenteron species. Within each subgenus, members of paired and satellite species were closely related to one another (e.g., L. japonica and L. appendix) or were genetically indistinguishable (e.g., L. ayresii and L. richardsoni). Using rates of molecular evolution estimated in other fish taxa, these genetically indistinguishable species diverged less than 70 000 years ago.
Can reduced salmonid population abundance be detected in time to limit management impacts?
Authors: Ham Kenneth D , Pearsons Todd N
Published: April 2011

We evaluated eight populations of native salmonids to determine if rapid, sensitive detection of a reduction in abundance is possible in the Yakima River basin, Washington, where a large-scale test of hatchery supplementation is being conducted. Prospective power to detect impacts to abundance was estimated from 3-16 annual baseline surveys conducted by electrofishing, trapping, or snorkeling. High interannual variation in abundance estimates (CV = 26-94%) prevented detection of small impacts for most taxa. For three taxa, models of environmental and biological influences accounted for between 42 and 49% of temporal variation, increasing our ability to detect impacts of other influences. Detectable impacts for a t test with alpha = 0.1 and beta = 0.1 were >18% for all eight taxa and >54% for four of eight taxa. We suggest that population abundance monitoring may not provide feedback sufficiently sensitive or rapid enough to implement corrective actions that prevent impacts from causing harm or exceeding an acceptable level, especially for rare or highly valued taxa with small acceptable impacts.
A neural network model for forecasting fish stock recruitment
Authors: Chen D G , Ware D M
Published: April 2011

A neural network model is developed to forecast the recruiting biomass of fish. The west coast of Vancouver Island, British Columbia, Pacific herring (Clupea pallasi) stock is selected as an example application based on data compiled from long-term ecosystem research and stock assessment programs. A fuzzy logic decision procedure was used to evaluate all possible neural networks. The output from the two "optimal" networks was compared with the output from a multiple regression analysis and a standard Ricker climate stock-recruitment model. The performance of the neural network models in reproducing a 41-year time series was far superior (R2 between the fitted and observed recruitment is about 60-70%) to the multiple linear regression model (R2 = 0.29) and the Ricker climate stock-recruitment model (R2 = 42%). This pilot study demonstrates how artificial neural networks can be used to improve the accuracy of fishery stock forecasts and hence the management of the fishery resources by making the actual harvest rate (catch/stock biomass) closer to the target harvest rate (desired catch/stock biomass).
Impact of Ca(OH)2 treatment on macroinvertebrate communities in eutrophic hardwater lakes in the Boreal Plain region of Alberta: in situ and laboratory experiments
Authors: Yee K A , Prepas E E , Chambers P A , Culp J M , Scrimgeour G
Published: April 2011

Ca(OH)2 treatment has been recently used to remediate water quality problems associated with eutrophication in lakes on the Boreal Plain of western Canada. This study examines how Ca(OH)2 treatment affects the survival of Hyalella azteca and larvae of Chironomus spp. in laboratory microcosms and the abundance and seasonal dynamics of macroinvertebrates in two eutrophic hardwater lakes. Macroinvertebrate data for three reference lakes sampled during the same time period are also presented. Additions of 225 and 295 g Ca(OH)2·m-2 (74 and 107 mg·L-1) to two lakes resulted in lake water pH remaining within its natural range (<10) and had no discernable effects on macroinvertebrate density or biomass up to 2 years after treatment. Macroinvertebrate response to Ca(OH)2 in hardwater lakes differed markedly from results reported for softwater lakes. After 4 days, no detectable influence was observed on survivorship of Chironomus spp. with laboratory dosages of 0-300 g Ca(OH)2·m-2 (0-1781 mg·L-1), but survivorship of H. azteca was reduced by >= 50% at dosages that raised water pH to >=10 (300 g Ca(OH)2·m-2). The sensitivity of H. azteca, but not Chironomus spp., could be a result of singular or combined effects of Ca(OH)2 levels, precipitate, or changes in pH. It may also reflect the greater dependence of H. azteca than Chironomus spp on the water above, rather than below, the sediment-water interface.
Stable carbon isotopes as pelagic food web tracers in adjacent shelf and slope regions off British Columbia, Canada
Authors: Perry R Ian , Thompson Peter A , Mackas David L , Harrison Paul J , Yelland Douglas R
Published: April 2011

Surveys were conducted in spring 1992 to examine the use of 13C/12C ratios to differentiate pelagic food webs and to trace food web interactions between adjacent continental shelf and slope/deep ocean environments off southwestern British Columbia, Canada. Salinity was used to define shelf or slope/deep ocean water masses and their productivity conditions because eddies and meanders at the shelf break were observed to draw water off the shelf. The 13C/12C ratio of plankton was related to the mean upper layer (0-50 m) salinity. 13C abundance was enriched (relative to 12C) in the shelf water mass compared with the slope water mass. This enrichment persisted up the food web from particulate organic matter through three size-classes of zooplankton to larval fish. The cross-shelf spatial scale separating these food webs, as determined from spatial semivariograms of 13C/12C and the upper layer mean salinity, was 40-45 km, similar to the Rossby radius for eddies at this location (50 km). Larval fish may provide a means to monitor exchanges of plankton between geographically adjacent food webs if time scales for incorporation of new isotope signatures from diets into tissues are determined.
A modelling study of the 1976 climate regime shift in the North Pacific Ocean
Authors: Wu Julia Qiuying , Hsieh William W
Published: April 2011

Around 1976, the North Pacific Ocean underwent a climate regime shift, with significant biological consequences. To model the changes in the ocean, an ocean general circulation model was forced by the wind stress and sea surface temperature monthly climatology of the 1952-1975 period in one numerical experiment and the 1976-1988 period in another. Changes in the ocean model between the two experiments revealed how the ocean might have changed under the 1976 climate regime shift. In winter, the intensified post-1976 Aleutian Low spun up the subarctic gyre and the subtropical gyre, except in the Gulf of Alaska, where the circulation weakened. Upwelling was generally enhanced in the subarctic and downwelling enhanced in the subtropical region, with temperature changes down to 600 m. In the post-1976 period, the meridional heat transports were also enhanced: poleward in the low latitudes, equatorward in the midlatitudes, and poleward in the high latitudes.
Intra- and inter-specific competition and the reproductive success of sympatric Pacific salmon
Authors: Essington Timothy E , Quinn Thomas P , Ewert Victor E
Published: April 2011

Individual female Pacific salmon fight for breeding space with conspecific and heterospecific females. We evaluated the consequences of this competition on the reproductive success of sockeye (Oncorhynchus nerka), chum (Oncorhynchus keta), and pink salmon (Oncorhynchus gorbuscha) in the Weaver Creek spawning channel, British Columbia. We hypothesized that differences in body size, relative abundance, and spawning date would influence the magnitude of interspecific interactions. Reproductive success (survival rate of eggs to emigrating fry) of the most abundant species, sockeye, was strongly and inversely correlated with conspecific abundance but not with the abundance of the other, less abundant species. Chum reproductive success was inversely correlated with sockeye abundance but not with the abundance of the scarce and smaller pink. Surprisingly, pink reproductive success was not correlated with sockeye abundance and only marginally correlated with chum abundance despite the fact that pink are smaller and spawn earlier than sockeye. Thus, intra- and inter-specific competition can substantially affect salmon reproductive success, but the magnitude of the competitive effects may depend on relative abundance, size, spawning date, and microhabitat preferences.
Comparative examination of scale-explicit biological and physical processes: recruitment of Pacific hake (Merluccius productus)
Authors: Horne John K , Smith Paul E , Schneider David C
Published: April 2011

The creation, maintenance, and destruction of aquatic organism distributions result from biological and physical processes that operate at different spatial and temporal scales. Rate diagrams plot and contour ratios of process rates as a function of spatial and temporal scale to summarize the relative importance of demographics, growth, and kinematics. We demonstrate the utility of this approach by examining physical and biological processes that influence the distribution and survival of larval and juvenile Pacific hake (Merluccius productus) in the California Current region. Processes that influence changes in hake biomass switch from mortality and drift among larvae to somatic growth and active locomotion among juveniles. Comparison of hake rate diagrams with those of capelin (Mallotus villosus) and Atlantic cod (Gadus morhua) show that dominant processes differ across scales, across life history stages, and across species.
Lake Ontario: the predominant source of triazine herbicides in the St. Lawrence River
Authors: Pham T -T , Rondeau B , Sabik H , Proulx S , Cossa D
Published: April 2011

To estimate triazine herbicide concentrations and sources in the St. Lawrence River, water samples were collected at its two major inlets (from the Great Lakes, Cornwall station, and from the Ottawa River, Carillon station) and at the outlet (Quebec City station) of the fluvial section. Sampling was carried out over an 18-month period between 1995 and 1996. Triazines were detected only in the dissolved phase at concentrations ranging from 2 to 91, from <0.4 to 15, and from <0.4 to 13 ng·L-1 for atrazine, cyanazine, and simazine, respectively. Dilution models show that, despite the presence of sporadically high concentrations of herbicides in St. Lawrence tributaries during periods of their application, loading from the tributaries is minor. Mass balance calculations show that Lake Ontario is clearly the main source of triazines (~90%) to the St. Lawrence River. During the 1995-1996 hydrological year, Lake Ontario contributed 15.1 × 103 of the 16.6 × 103 kg of atrazine outflowing the St. Lawrence River to the estuary. The difference (1.5 × 103 kg·year-1) can be attributed to tributaries in Quebec, which represent 0.75% of the amount of atrazine spread on farmlands. There is no evidence of the degradation of triazine compounds during their transit time in the river.
Reaction field, capture field, and search volume of 0+ nase (Chondrostoma nasus): effects of body size and water velocity
Authors: Flore L , Reckendorfer W , Keckeis H
Published: April 2011

The reaction field, capture field, and search volume of four size-classes of 0+ nase (Chondrostoma nasus) were investigated at two water velocity regimes using flow-tank experiments. Reactive and capture distances, measured in three dimensions, increased linearly with fish size and were larger in flowing water than in calm water. The 0+ nase reacted almost exclusively to prey that were situated in their forward-directed hemisphere. In flowing water, 0+ nase systematically drifted and (or) swam downstream with the current in pursuit of prey that had drifted past their stations. Captures thus occurred in their backward-directed hemisphere. Based on the fish's swimming speed and its reaction field, we propose a modified method for estimating search volume of 0+ nase and other rheophilic cyprinid species with a similar feeding mode. Search volume also increased linearly with fish size and was larger in flowing water than in calm water. We argue why the foraging mode of 0+ nase in flowing water is the effect of a constraint imposed by water current rather than the result of an economic strategy.
Mercury speciation in the Lower St. Lawrence Estuary
Authors: Cossa Daniel , Gobeil Charles
Published: April 2011

Mercury speciation was determined in the water column and sediment pore waters of the Lower St. Lawrence Estuary, and total Hg (HgT) was measured in seven biological species, including pelagic and demersal fish and crustaceans. In water, HgT concentrations ranged from 1.8 to 7.8 pM, with the highest levels in surface waters and the lowest in deep waters (1.8-2.9 pM). HgT concentrations in sediment pore waters were 10 times as high, with methyl mercury levels of 5.1-14.4 pM. Reactive Hg (HgR) generally accounted for around 20% of HgT in the water column and <30% in pore waters. The distribution of elemental Hg and HgR suggests that Hg(II) is reduced in surface waters and that inorganic Hg is mobilized during remineralization of organic matter at the sediment surface. In the biota, concentrations ranged between 0.05 and 0.89 nmol·g-1 (wet weight). Feeding habits and habitats account for these observations. Results suggest that the sediment is the main source of Hg contamination for the biota. A mass balance calculation showed that the Hg flux entering the lower estuary from the St. Lawrence River is equivalent to the amount buried in estuarine sediments.
Sediment dynamics and the transport of suspended matter in the upstream area of Lake St. Francis
Authors: Lepage Serge , Biberhofer Johann , Lorrain Stéphane
Published: April 2011

A long-term project was initiated in autumn 1994 to monitor the suspended matter (SM) in the upstream area of Lake St. Francis. Over a 32-month period, 190 SM samples were collected at six study sites while conductivity and current velocity measurements were made to study resuspension and transport of SM. Weather data from a nearby station and daily discharge rates for the St. Lawrence River were also utilised. Overall, the study shows that the SM load in the central portion of Lake St. Francis is not evenly distributed. On the northern side of the lake, the SM load is mainly a function of the SM load carried by the St. Lawrence River waters coming from the Great Lakes. On the southern side, an important contribution to the SM load comes from sediment resuspension and from the local tributaries. Calculations show that wave action is likely to resuspend surficial sediments in depths shallower than 2 m, a surface area estimated to be 32-35 km2 between Cornwall Island and Thompson Basin. Also, important fluctuations of the south shore tributaries' winter discharge are thought to contribute to sediment resuspension and redistribution of contaminants such as mercury and polychlorinated biphenyls.
Defining the sources of airborne polychlorinated biphenyls: evidence for the influence of microbially dechlorinated congeners from river sediment?
Authors: Chiarenzelli Jeff , Bush Brian , Casey Ann , Barnard Ed , Smith Bob , O'Keefe Patrick , Gilligan Eileen , Johnson Glenn
Published: April 2011

Sampling on Akwesasne Mohawk Nation lands during 1993 yielded elevated polychlorinated biphenyl (PCB) concentrations comparable with those of other areas impacted by the discharge of PCBs. The summer air PCB congener- specific pattern in proximity to three Superfund sites along the St. Lawrence River suggests that the volatilization of Aroclor 1248, used extensively at all three downwind sites, is the dominant source. A dechlorinated source, presumably from river sediment and waters, is a minor contributor (~12%) to the pattern. These two sources can account for ~80% of the observed pattern. At a small cove adjacent to an industrial landfill, summer concentrations exceeded those measured in the winter by a factor of 27. At all sample sites during the summer months (June-August), concentrations and chlorine to biphenyl ratios increased, and similar congener-specific PCB patterns were observed. During the colder months, PCB concentrations at all sites decreased but were elevated with respect to those measured elsewhere in the Great Lakes region during the same time period.
Acute temperature elevation in tap and Rhine water affects skin and gill epithelia, hydromineral balance, and gill Na+/K+-ATPase activity of brown trout (Salmo trutta) smolts
Authors: Nolan D T , Hadderingh R H , Spanings F AT , Jenner H A , Wendelaar Bonga S E
Published: April 2011

The effects of a 3-h temperature elevation of 7°C were studied for 29 days on the brown trout (Salmo trutta) smolt in tap water and in water from the lower Rhine. The effects in the skin were apparent at 3 h and included depletion of electron-dense vesicles and increased numbers of heavily stained desmosomes in the filament cells of the upper epidermis. Increased levels of apoptosis and necrosis occurred and were associated with leukocyte infiltration of the epidermis. Similar effects in the gill epithelium were mainly confined to the chloride cells. Highest levels of necrosis in skin and gill epithelia occurred in fish that were temperature shocked in Rhine water. Effects of exposure to Rhine water alone were intermediate between those of temperature shock in tap water and in Rhine water. At 29 days, recovery was good in tap water, partial in Rhine water, and poor for the fish temperature shocked in Rhine water. Although disruption of hydromineral balance was not indicated in plasma electrolytes, specific Na+/K+-ATPase activities in the gill were higher for all treatments at 24 h and for the groups temperature shocked in Rhine water at 8 days. Overall, temperature shock in Rhine water gives additive stress effects and poor recovery at 29 days.
Some secrets of a great river: an overview of the St. Lawrence River supplement
Authors: Lean D RS
Published: April 2011

The present issue attempts to cut across discipline boundaries and examines many of the suspected pollution problems in an ecological context. Each of the papers provides a rich literature on relevant issues so that the present studies can be placed in context with historical observations. The papers provide information on changes in plankton populations, macrophyte distribution, mixing rates of the water column, and the dynamics of sediments, where many of the metals and persistent organic pollutants reside. Papers on metals and persistent organic pollutants follow with special emphasis on the polychlorinated biphenyl problems of the Massena area of the Upper St. Lawrence River. Further downstream reliable models to predict polychlorinated biphenyl levels in whales were developed. Indicators for bioavailable metals in sediments were introduced and new information was provided on aspects of global mercury transport.
Detecting pan-Atlantic migration in salmon (Salmo salar) using 137Cs
Authors: Tucker Strahan , Pazzia Ivano , Rowan David , Rasmussen Joseph B
Published: April 2011

137Cs is a globally dispersed radioisotope that is transferred efficiently through the food chain. There is a strong east-west gradient of 137Cs in the waters of the North Atlantic due to anthropogenic inputs from Europe, with levels exceeding 10 Bq·m-3 in the Irish Sea and concentrations <1.5 Bq·m-3 in the West Atlantic. This range in values is subsequently reflected in fish, including Atlantic salmon (Salmo salar), caught in those waters. 137Cs concentrations in adult salmon, which had returned to the Ste. Marguerite River, Canada, reflected the entire range of values seen previously across the North Atlantic. In fact, 43% of fish had concentrations characteristic of the Faroe, Norwegian, North, and Irish seas. These results are in sharp contrast with what is generally believed about the migration of salmon and suggest that their marine life history is more panoceanic than previously thought.
Influence of ultraviolet-B radiation, stratospheric ozone variability, and thermal stratification on the phytoplankton biomass dynamics in a mesohumic lake
Authors: Xenopoulos Marguerite A , Prairie Yves T , Bird David F
Published: April 2011

Terrestrial ultraviolet radiation (UVR) is highly variable in both space and time, and phytoplankton in the mixed layer may be exposed at irregular intervals to significant daily doses. The influence of the natural UVR on phytoplankton dynamics was investigated in a small mesohumic lake, Lac Cromwell, in the Laurentian Hills by means of a time-intensive (about 60 days) daily study of the relationship between UVR flux and phytoplankton biomass. Following the onset of lake stratification, at which time the epilimnion became shallower than 2.5 m, the study revealed a strong negative relationship between ultraviolet-B radiation (UVB) and algal biomass at the surface (r 2 = 0.61) and at 1 m (r 2 = 0.38). Although this relationship held throughout the stratified period, chlorophyll a concentration declined particularly rapidly (-65%) during a short-lived ozone-thinning period. There was a major shift in the community taxonomic composition during the same period from a typical diatom-chrysophyte spring bloom towards a dinoflagellate-dominated community that was followed by cyanobacteria. Here, we present evidence that the impact of the temporary increase in UVB was intensified by a concurrent lack of mixing, indicating that turbulence and thermal stratification are key components modulating UVB effects in lakes.
Analysis of an estuarine striped bass (Morone saxatilis) population: influence of density-dependent mortality between metamorphosis and recruitment
Authors: Kimmerer W J , Cowan, Jr. J H , Miller L W , Rose K A
Published: April 2011

Compensation due to density-dependent mechanisms is essential for the maintenance of an exploited fish stock. Understanding compensation is important for understanding population regulation and responses to added mortality. We examined possible density-dependent effects on striped bass (Morone saxatilis) in the San Francisco Estuary. Three sets of data from sampling programs for young striped bass showed density-dependent mortality between 1 month of age and 8-12 months. The relationships between two indices of young striped bass abundance and recruitment at age 3 fit a Beverton-Holt function, also indicating density dependence. The carrying capacity, as determined by the asymptote of the Beverton-Holt curves, has declined over the last two to three decades. These results are consistent with a compensatory mechanism based on food limitation occurring after metamorphosis and with the decline in food resources observed in the estuary over the same period. The decline in striped bass over the last two to three decades may be partly due to this declining carrying capacity.
Influence of moon phase on acoustic estimates of the abundance of fish performing daily horizontal migration in a small oligotrophic lake
Authors: Gaudreau Nathalie , Boisclair Daniel
Published: April 2011

We tested the influence of the moon phase on the relative number of fish performing daily horizontal migrations and we used this information to develop a sampling strategy that accounted for expected effects of the moon phase on fish behavior. Hydroacoustic surveys were performed over 3 days at each moon phase for the months of July and August (from the day before to the day after the new moon, the first and last quarter moon, and the full moon). Dace (Phoxinus eos × Phoxinus neogaeus) migrated from the littoral towards the pelagic zone at dusk and returned to the littoral zone at dawn. Their relative abundance (FRA) in the pelagic zone averaged 0.1 fish echo·m-3during midday and 17.0 fish echoes·m-3at night. The number of dace performing horizontal movements was eightfold larger during new-moon than full-moon nights. Simulations indicated that sampling fish populations six times during a 2-month period (once at full, new, and quarter moon; once during the day and once during the night) provided the most accurate estimates of FRA.
Effects of whole-lake manipulations of nutrient loading and food web structure on planktonic respiration
Authors: Pace Michael L , Cole Jonathan J
Published: April 2011

We assessed planktonic respiration in whole-lake manipulations of nutrient loading and food web structure in three manipulated and one unmanipulated lake over 7 years. The manipulations created strong contrasts in zooplankton body size across a series of nutrient loads. Large-bodied zooplankton were suppressed by planktivorous fish in one lake, while in the other two manipulated lakes, large-bodied zooplankton dominated community biomass. Nutrients were added as inorganic N and P. Nutrient loads ranged from background to conditions resembling eutrophic lakes. Planktonic respiration was measured weekly in each lake by dark bottle oxygen consumption. Respiration was low when lakes were not fertilized (average 8.5 µmol O2·L-1·day-1) and was correlated with differences in dissolved organic carbon among the lakes. Respiration increased with nutrient addition to a mean range of 12-25 µmol O2·L-1·day-1; however, respiration differed among lakes at the same nutrient loading. Further, respiration was independent of dissolved organic carbon in the fertilized lakes. Differences in the intensity of zooplankton grazing as determined by food web structure strongly regulated primary and bacterial production across the range of nutrient loads. Consequently, respiration was positively related to primary production, phytoplankton biomass, and bacterial production and inversely related to the average size of crustacean zooplankton.