bluuebunny/crossref_metadata_2025 huggingface dataset:
Mercury and methyl mercury in freshwater seston: direct determination at picogram per litre levels by dual filtration
Authors: Morrison Kenneth A , Watras Carl J
Published: April 2011

Here, we describe a method for directly determining sestonic mercury in lake waters at concentrations ranging down to 0.12 ng Hg/L (total Hg) and 0.01 ng MeHg/L (monomethyl mercury) in a 250-mL water sample. Detection limits for the method are 30 pg of Hg and 3.0 pg of MeHg, reported as three times the standard deviation of a procedural blank. The method involves dual filtration using ultraclean 47-mm-diameter, 0.45-µm pore size cellulose nitrate filters in an all-Teflon® filter stack. Lake water is pumped directly through a primary filter that traps suspended seston particles and then through a secondary filter that is used to estimate the integrated reagent, filter, and sorption blank. Both filters are analyzed for Hg or MeHg and the primary filter is corrected by subtracting the secondary blank. Sestonic Hg is determined after acid digestion and wet oxidation of the filters with BrCl, reduction with NH2OH-HCl followed by SnCl2, and purging via N2 onto dual gold traps for detection via cold-vapor atomic fluorescence spectroscopy. Sestonic MeHg is determined after acid distillation of the filters, aqueous-phase ethylation, purging onto Tenax®, isothermal gas chromatography separation, and detection by cold-vapor atomic fluorescence spectroscopy. The method was tested on a variety of lakes in Wisconsin, Florida, and Washington. The blank-corrected mass of sestonic mercury collected from these lakes onto primary filters ranged from 30 to 340 pg Hg and from 3 to 23 pg MeHg. The corresponding concentrations of mercury in the seston were 22-790 ng Hg/g dry weight and 3-75 ng MeHg/g dry weight. The method allowed us to demonstrate a clear negative dependence of sestonic mercury concentrations (weight:weight) on pH in Wisconsin lakes.
Effect of solar ultraviolet radiation (280–400 nm) on the eggs and larvae of Atlantic cod (Gadus morhua)
Authors: Béland France , Browman Howard I , Rodriguez Carolina Alonso , St-Pierre Jean-François
Published: April 2011

In the Gulf of St. Lawrence, Canada, solar ultraviolet B radiation (UV-B, 280-320 nm) penetrates a significant percentage of the summer mixed-layer water column: organisms residing in this layer, such as the eggs of Atlantic cod (Gadus morhua), are exposed to UV-B. In outdoor exposure experiments, Atlantic cod eggs were incubated in the presence versus the absence of UV-B and (or) UV-A (320-400 nm). We tested two hypotheses: H1, UV-B induces mortality in Atlantic cod eggs, and H2, UV-A either exacerbates or mitigates any such UV-B-induced mortality. Hypothesis H1 was supported: there was a significant mortality effect on Atlantic cod eggs exposed to UV-B at the surface and at a depth of 50 cm. Hypothesis H2 was not supported: there was no effect of UV-A. These experiments indicate that Atlantic cod eggs present in the first metre of the water column (likely only a small percentage of the total egg population) are susceptible to UV-B. However, UV-B must be viewed as only one among many environmental factors that produce the very high levels of mortality typically observed in the planktonic early life stages of marine fishes.
Attenuation of ultraviolet radiation in a large lake with low dissolved organic matter concentrations
Authors: Smith REH , Furgal J A , Charlton M N , Greenberg B M , Hiriart V , Marwood C
Published: April 2011

Solar radiation spectra were measured in mesotrophic Lake Erie in 1997 to determine the principal factors influencing ultraviolet radiation (UVR) attenuation. Water clarity ranged widely, with the diffuse vertical attenuation coefficient for photosynthetically active radiation (KdIPAR) varying from 0.26 to 17.2 m-1, and UVR attenuation varied positively and significantly with KdIPAR. Particle concentration (total suspended solids, TSS) was the single most useful water quality characteristic for predicting broadband UVB (305-320 nm) and UVA (320-400 nm) attenuation. Dissolved organic carbon concentration (DOC) and fluorescence were much less important than TSS in predicting UVR attenuation over the typical range of water clarity (KdIPAR < 2 m-1). The predominant role of TSS in UVR attenuation could not be explained by phytoplankton or other absorbing organic matter in the particulate phase, suggesting instead an important role for scattering. Attenuation spectra through the UV region were not monotonic at the higher particle concentrations and could not be modelled solely as a function of DOC as previously reported for other lakes. Attenuation at 310 and 320 nm confirmed the conclusion from spectrally integrated measurements that particles are the dominant agents of variable UVR attenuation in Lake Erie.
Effects of oil sands related aquatic reclamation on yellow perch (Perca flavescens). II. Chemical and biochemical indicators of exposure to oil sands related waters
Authors: van den Heuvel M R , Power M , MacKinnon M D , Dixon D G
Published: April 2011

Adult yellow perch (Perca flavescens) were stocked into experimental ponds designed to emulate possible aquatic reclamation alternatives of the oil sands mining industry. After 5 and 11 months, mixed-function oxygenase (MFO) activity, liver conjugation enzymes, bile polycyclic aromatic hydrocarbon (PAH) equivalents, and plasma sex steroids were measured. Liver MFO activity and bile PAH equivalent concentration were closely correlated and showed the highest levels in the experimental ponds but also demonstrated a gradient of exposure among reference locations. Levels of steroid hormones in fall-captured fish did not show major differences among sites. However, during winter, yellow perch from three sites, including the experimental ponds, showed low levels of sex steroids in both males and females. Multivariate regressions showed no relationship between steroid hormone concentrations and gonad size or fecundity. Similarly, steroid hormones did not parallel the gradient of exposure as measured by MFO and bile PAH metabolites. Gonad size and fecundity also were not directly correlated with the gradient of exposure observed in this study. Although MFO activity and bile PAH equivalents were good indicators of exposure to oil sands related waters, they were not predictive of physiological endpoints, suggesting that the latter were influenced primarily by ecological and not by chemical factors.
Effects ofGammarus lacustris(Crustacea: Amphipoda) on plankton community structure in an alpine lake
Authors: Wilhelm Frank M , Schindler David W
Published: April 2011

The amphipod Gammarus lacustris is generally considered as a herbivore or a detritivorous scavenger, but we and others have observed it preying on pelagic zooplankton in fishless alpine lakes of the Canadian Rockies. We tested the hypothesis that G. lacustris predation alters the plankton community structure of alpine lakes by manipulating G. lacustris density in large (2800 L) in situ enclosure experiments. Compared with control enclosures (no Gammarus), Daphnia middendorffiana abundance was reduced 49, 85, and 100% in the low, medium, and high (40, 200, and 400 individuals·m-2) Gammarus density enclosures, respectively. Hesperodiaptomus arcticus density was not significantly related to G. lacustris density. Comparison of mesocosm results with lake data showed that G. lacustris predation on D. middendorffiana in the lake was lower, possibly because a pelagic deepwater refugium allows Daphnia to escape predation. The results show that G. lacustris predation can affect the plankton community structure in small fishless alpine lakes.
Effect of temperature on the P4501A response in winter- and summer-acclimated Arctic char (Salvelinus alpinus) after oral benzo[a]pyrene exposure
Authors: Jørgensen Even H , Wolkers Johannes
Published: April 2011

In this study, the time-dependent P450 response to oral benzo[a]pyrene exposure at 1 and 10°C was investigated in winter- and summer-acclimated Arctic char (Salvelinus alpinus). In both seasons, a strong induction of CYP1A activities and protein levels (measured only in the winter experiment) were seen at both 1 and 10°C. At 1°C, the responses were delayed and more long-lasting than at 10°C. No within-season difference between 1 and 10°C in the magnitude of the induction response was found, but due to elevated baseline CYP1A activities, the induction response was seven times lower in winter- as compared with the response in summer-acclimated Arctic char. The results show that the CYP1A enzymes of the Arctic char respond to temperature changes in a compensatory way, and they are promising with respect to the applicability of the P450 enzyme system of the Arctic char as a biomarker for monitoring polycyclic aromatic hydrocarbon contamination in high-latitude environments. More studies are needed, however, to reveal seasonal differences in the biomarker response to pollutants.
Is it possible to predict habitat use by spawning salmonids? A test using California golden trout (Oncorhynchus mykiss aguabonita)
Authors: Knapp Roland A , Preisler Haiganoush K
Published: April 2011

It is widely believed that stream salmonids select spawning sites based on water depth, water velocity, and substrate size. Attempts to predict spawning locations using these habitat features have met with little success, however. In this study, we used nonparametric logistic regression to determine what habitat features were associated with the locations chosen by spawning California golden trout (Oncorhynchus mykiss aguabonita). From this nonparametric model, we developed a parametric model that incorporated the habitat features most strongly associated with spawning sites and used this model to calculate the probability of use by spawning golden trout for specific stream locations. The overall nonparametric model was highly significant and explained 62% of the variation in spawning location. Four of the eight habitat variables, substrate size, water depth, water velocity, and stream width, had highly significant effects and alone explained 59% of the variation in spawning location. The results of a cross-validation procedure indicated that the parametric model generally provided a good fit to the data. These results indicate that location-specific probabilities of use were predictable based on easily measured habitat characteristics and that nonparametric regression, an approach still rarely used in ecological studies, may have considerable utility in the development of fish-habitat models. Given the escalating pace at which fish habitats are being altered, such models are increasingly important in predicting the effects of these alterations on populations.
Mixing and migration of overwintering Atlantic cod (Gadus morhua) stocks near the mouth of the Gulf of St. Lawrence
Authors: Campana S E , Chouinard G A , Hanson J M , Fréchet A
Published: April 2011

Millions of Atlantic cod (Gadus morhua) migrate distances of up to 500 km each fall to aggregate together in a small overwintering area off eastern Canada. Synoptic research vessel surveys carried out each January between 1994 and 1997 documented dense aggregations of cod along both flanks of the Laurentian Channel in each year, with estimated biomasses exceeding 100 000 metric tons. Using the trace element composition of the otolith ("otolith elemental fingerprint") as a natural tag, we found members of four populations to be present on the overwintering grounds in significant numbers, yet large-scale mixing among the populations was minimal. Individual trawl samples were often composed of a single population, suggesting that population integrity was maintained at a scale of <20 km. Cod from the southern Gulf of St. Lawrence dominated the population composition along the southern flank of the Channel, while cod from the northern Gulf dominated the northern flank; the distributions of both of these populations extended well to the east of their summer habitats and were remarkably similar across years. There was no evidence of large-scale mixing across the Channel. In light of the substantive migration of northern Gulf cod into the management area for the southern Newfoundland population, fishing effort off southern Newfoundland has the potential to reduce the size of the northern Gulf population.
Retinoic acid hydroxylation and teratogenesis in lake sturgeon (Acipenser fulvescens) from the St. Lawrence River and Abitibi region, Quebec
Authors: Doyon Christian , Fortin Réjean , Spear Philip A
Published: April 2011

All-trans-retinoic acid (RA) is an extremely active form of vitamin A; however, excessive or insufficient concentrations elicit anomalies including those associated with limb and craniofacial development. Lake sturgeon (Acipenser fulvescens) from the St. Lawrence River and tributaries were estimated to have a 2.9% incidence of fin and craniofacial malformations. Among larvae raised in artificial streams, a greater incidence of fin malformations (6.3%; p < 0.001) occurred in St. Lawrence River sturgeon compared with larvae from the Abitibi region. To test the hypothesis that the differences in rate of malformations may be associated with metabolic imbalances of RA, cytochrome P-450 dependent conversion to 4-hydroxyretinoic acid (4-OH-RA) was investigated. Optimal assay conditions are described for in vitro 4-OH-RA production in liver microsomes. Enzyme activity tended to decrease with increasing age and gonadal development in fish collected from Abitibi, but no statistically significant effects of sex, age, length, or gonadal development were discerned. The rate of 4-OH-RA formation was 3.5-fold greater (p < 0.0001) in the St. Lawrence sturgeon while the concentrations of cytochrome P-450 inducing PCBs (expressed as dioxin toxic equivalents) were 20-fold greater in a composite liver sample of the St. Lawrence sturgeon. Liver retinoid concentrations were negatively correlated (p < 0.0001) with RA hydroxylation rate. These results are consistent with the possibility that cytochrome P-450 dependent RA metabolism increased by chemical contaminants is associated with developmental anomalies in the St. Lawrence sturgeon.
Bioavailability and acute toxicity of copper to rainbow trout (Oncorhynchus mykiss) in the presence of organic acids simulating natural dissolved organic carbon
Authors: Marr J CA , Lipton J , Cacela D , Hansen J A , Meyer J S , Bergman H L
Published: April 2011

Copper bioavailability and toxicity to early life stage rainbow trout (Oncorhynchus mykiss) were evaluated by laboratory toxicity testing performed using organic acid mixtures. Geochemical modeling was used to design exposure solutions that simulate dissolved organic carbon (DOC) of a natural aquatic system and to determine the fractions of total Cu present as inorganic species (e.g., Cu2+) and as individual Cu-organic complexes. Failure time modeling indicated that mortality was best predicted by a combination of total inorganic Cu and distinct Cu-organic complexes. The Cu-organic complexes that contributed to toxicity are characterized as low-affinity Cu-ligands, and our results support the hypothesis that Cu toxicity in nature is a function of the binding characteristics of individual ligands. Estimates of time-independent median lethal concentration thresholds determined at widely varying equivalent concentrations of DOC (0-16 mg/L) were constant (7.9-8.6 µg Cu/L) when modeled using the sum of inorganic Cu and Cu bound to the two low-affinity ligands as predictors of toxicity. Our results indicate that Cu bound to organic complexes may be available to fish and that acute toxicity of Cu is determined by the binding affinities of specific DOC components relative to Cu-binding affinity of fish gill.
Chance fluctuations and the survival of small salmon stocks
Authors: Routledge Richard D , Irvine James R
Published: April 2011

In this paper, we use a Markovian approach to demonstrate that stocks with modest growth potential at low abundance can be driven quite rapidly to extinction. Under relatively benign conditions, stock survival rates may be high, but even a modest increase to the amount of chance variation in recruitment can reduce survival rates dramatically. Survival rates also depend on the form of the stock-recruitment curve, including depensation that takes hold only at extremely low abundances. Fortunately, small amounts of straying among adjacent populations can push the survival rate substantially toward the value for a combined, homogeneous unit. Our analysis also suggests modifications to existing approaches of establishing minimum target levels for spawning densities and the near impossibility of reliably estimating extinction rates.
Genetic structure and differentiation among populations of two cyprinids,Leuciscus cephalusandRutilus rutilus, in a large European river
Authors: Laroche J , Durand J D , Bouvet Y , Guinand B , Brohon B
Published: April 2011

The aim of this investigation was to compare the genetic responses of two common cyprinids, chub (Leuciscus cephalus) and roach (Rutilus rutilus), to various habitat and pollution regimes within the same river basin, the Rhone, using allozyme data. Over the three main portions of the River Rhone, lower genetic polymorphism and lower heterozygosity were detected for the chub in the Saone, which is characterized by lower environmental diversity than in the Lower and Upper Rhone. On a local scale, no detectable decrease in polymorphism or heterozygosity was observed in populations of both species living in heavily polluted sites of the Rhone's Chemical Corridor. Significant differentiation was detected between populations of both chub and roach localized upstream and downstream from the dams of Donzère Mondragon, which were erected 45 years ago. The F statistics and neighbor-joining analysis of genetic distances suggested that the Upper Rhone populations were unique in comparison with the other populations for both species; this situation could be the result of historical factors and (or) a selective pressure in a variable environment. Isolation by distance was observed for chub in the less perturbed river system over a range of 100 km. By contrast, there was no relationship between geographic distance and genetic distance for roach, whatever the subsystem tested.
Effets des métaux (Ag, Cd, Cu) sur la composition biochimique et compartimentation de ces métaux chez deux microalgues Skeletonema costatum et Tetraselmis suecica
Authors: Perrein-Ettajani H , Amiard J C , Haure J , Renaud C
Published: April 2011

Effects at sublethal silver, cadmium, and copper concentrations on growth and biochemical composition of two marine microalgae Tetraselmis suecica and Skeletonema costatum revealed that growth is by far the most sensitive factor, whereas cellular content of polysaccharides, proteins, lipids, and pigments are not significantly affected. This suggests that the first target of these metals is cell division and processes related to it. Heavy metal concentrations in algal cells were lower in S. costatum than in T. suecica, and the study of metal partitioning showed that for both algal species, Cd was firmly bound onto the cell wall or had entered the cell, whereas 40% of the initially adsorbed Cu was easily released after treatment by the chelating agent. However, in both algal species, Cd and Cu were predominantly present in the insoluble fraction, and in the cytosol, thermoresistant metal-chelating polypeptids are involved. For this study, the major metal detoxification process in algae exposed to sublethal concentrations is therefore their binding to insoluble components. The strong stability of the later suggests less bioavailability and maybe a limited transfer of these metals to higher trophic levels.
Contribution of Gammarus lacustris to phosphorus recycling in a fishless alpine lake
Authors: Wilhelm Frank M , Hudson Jeff J , Schindler David W
Published: April 2011

We estimated the net P transport by Gammarus lacustris from the benthic to pelagic regions of a fishless alpine lake and compared it with P regeneration by the entire plankton community. Gammarus lacustris released between 5.2 and 18.1 ng P·L-1·h-1 (adults only and adults plus immatures, respectively) in the pelagic region during nighttime vertical migration. Additional P released into and removed from the water column due to predation on zooplankton was estimated at 1.87 and 2.3 ng P·L-1·h-1, respectively. The net daily regeneration of 52.2-181.4 ng P·L-1·day-1 by the G. lacustris population represented 9.5-32.9% of the total P regenerated by the planktonic community. The majority of the P released by G. lacustris represents "new" P to the pelagic zone because it originated in sediments. We conclude that G. lacustris can represent an important link in benthic-pelagic coupling in oligotrophic mountain lakes.
Water quality requirements of smolting Atlantic salmon (Salmo salar) in limed acid rivers
Authors: Kroglund Frode , Staurnes Magne
Published: April 2011

Groups of Atlantic salmon (Salmo salar) smolts were held 1-13 days in soft water with a pH range of 5.0-6.6, concentrations of labile inorganic monomeric Al (Ali) of 10-90 µg·L-1, and 0.7-2.3 mg Ca·L-1. Fish were exposed to either naturally acidic water from a river in southwestern Norway, limed water from the same river, mixtures of acidic and limed river water, acidic river water with sulfuric acid and Al added, or limed river water with additional lime. Mortality was observed in all groups exposed to water with pH < 5.8 and containing 30-90 µg Ali·L-1. No fish died in water with pH > 5.8 and 15-20 µg Ali·L-1, but fish in water with pH 5.8-6.2 had lower plasma Cl- concentration and gill Na+,K+-ATPase activity than fish in water with pH > 6.5. Smolts exposed to pH < 5.8 were unable to survive in seawater, and smolts exposed to water with pH 5.8-6.2 had lower hypoosmoregulatory capacity than smolts exposed to water with pH > 6.5. These results show that even moderately acidified water with low Al concentrations impairs smoltification and reduces the seawater tolerance of Atlantic salmon smolts.
Narrow size regime among individuals favors rapid growth in Arctic char (Salvelinus alpinus) juveniles
Authors: Seppä Teija , Peuhkuri Nina , Hirvonen Heikki , Laurila Anssi , Piironen Jorma , Ranta Esa
Published: April 2011

We studied whether social environment in the form of different body size regimes in rearing groups affects the growth of juvenile Arctic char (Salvelinus alpinus) in hatchery conditions. Young-of-the-year Arctic char were divided into groups of three different compositions (a wide, a bimodal, and a narrow size-frequency distribution) in which individuals would be subjected to different dominance and competitive relationships. After a 9-month growth period the fish in the narrow size distribution had grown the fastest in both length and weight. Also, total biomass gains were highest for fish originating from the narrow size distribution treatment. The adjusted mean biomasses for wide, bimodal, and narrow size regime treatments were 5400, 5000, and 5900 g, respectively. Our results give support to the hypothesis that individuals in size-sorted groups should show enhanced growth compared with individuals originating from a wider size-frequency distribution where more aggressive interactions are to be expected.
Population differences in antifreeze production cycles of juvenile Atlantic cod (Gadus morhua) reflect adaptations to overwintering environment
Authors: Goddard Sally V , Kao Ming H , Fletcher Garth L
Published: April 2011

Four groups of juvenile Atlantic cod (Gadus morhua) were collected in summer (1992) from four coastal sites of northeast Newfoundland. They were held together at seasonally ambient temperature and photoperiod and monitored over one winter for variation in a biochemical phenotype, antifreeze production capacity. Our results show that population differences in antifreeze production capacity reflect the severity of overwintering conditions faced. Cod from three bays along the northeast coast (49.5°-47.5° N) exhibited very similar patterns of antifreeze production, suggesting that these environments demand from their cod inhabitants approximately the same high level of freeze resistance. However, cod from the most exposed northerly site at the tip of the Great Northern Peninsula (51.5° N) developed antifreeze levels about 50% higher than those of the other three groups, confirming that the more extreme high-latitude environment demands even greater freeze protection for survival. Since 34% of Great Northern Peninsula cod produced antifreeze levels outside the range of all other juveniles, we suggest that the physiological distinctness of this population has evolved by genetic amplification of antifreeze production capacity rather than by selective mortality. The existence of physiological population structure should be factored into strategies for sustainable fishing of this species in northern waters.
Sonar estimates of daytime activity levels of Euphausia pacifica in Saanich Inlet
Authors: Jaffe Jules S , Ohman Mark D , Robertis Alex De
Published: April 2011

A three-dimensional multibeam tracking sonar system (FishTV) was deployed in the stratified waters of Saanich Inlet in July-August of 1996 and 1997 to assess the swimming behavior of euphausiids in situ. Here, a new algorithm is used to estimate swimming velocities of animals from the uncorrelated displacements of acoustic targets in pairs of sonar frames with increasing time delays between frames. Assuming isotropic motions of euphausiids, the superior spatial resolution of the sonar in one dimension (range) is used to infer the three-dimensional motions. We applied the algorithm to sonar tracks of groups of 10 000 - 25 000 euphausiids recorded in the daytime at depths just above the oxycline on six different occasions. The animal movements were described with a probability density function for velocity which suggests that about 60-70% of the animals were moving less than or equal to 0.3-1.2 cm·s-1. These distributions imply remarkably low swimming speeds and quiescent behavior. Limited motility in the daytime would confer two major advantages on the euphausiids: reduction of encounter rates with ambush predators and decreased metabolic costs.
Individual-based model simulations of a zebra mussel (Dreissena polymorpha) induced energy shunt on walleye(Stizostedion vitreum) and yellow perch (Perca flavescens) populations in Oneida Lake, New York
Authors: Rutherford Edward S , Rose Kenneth A , Mills Edward L , Forney John L , Mayer Christine M , Rudstam Lars G
Published: April 2011

Zebra mussels (Dreissena polymorpha) recently invaded North American aquatic ecosystems and are hypothesized to impact lakes by increasing water clarity through filtration and shunting energy from pelagic to benthic pathways (ES effect). We used an individual-based model of Oneida Lake, New York, walleye (Stizostedion vitreum) and yellow perch (Perca flavescens) populations to simulate ES effects on percids by lowering zooplankton density and production rates and increasing benthos rates. We performed 50-year simulations involving both zooplankton and benthos changes together and each change alone. We also performed simulations to determine robustness of model predictions under different assumed levels of zooplankton and benthos, increased forage fish and mayflies, and walleye stocking. Predicted ES effects were elimination of walleye high-recruitment years, resulting in a 30% reduction in adult walleye abundance. Yellow perch adult abundance increased by 6% due to reduced walleye predation. Neither component (zooplankton or benthos) of ES generated the same total response for yellow perch as both components together. Simulated walleye stocking and increased forage fish density had little effect on model predictions. Increased mayfly densities offset predicted ES effects by buffering predation on juvenile percids. Model predictions of ES impacts on percids generally were consistent with observed changes in Oneida Lake since zebra mussel arrived.
Survival of pink salmon (Oncorhynchus gorbuscha) fry to adulthood following a 10-day exposure to the aromatic hydrocarbon water-soluble fraction of crude oil and release to the Pacific Ocean
Authors: Birtwell I K , Fink R , Brand D , Alexander R , McAllister C D
Published: April 2011

Saltwater-acclimated, coded-wire tagged, and adipose fin clipped pink salmon (Oncorhynchus gorbuscha) fry were exposed for 10 days to seawater (control) or 25-54 μg·L-1 (low dose) or 178-349 μg·L-1 (high dose) of the water-soluble fraction (WSF) of North Slope crude oil. The WSF was composed primarily of monoaromatics and was acutely lethal to the fry: 96-h LC50 ranged from 1 to 2.8 mg·L-1. After exposure the fry (30 000 per treatment) were released into the Pacific Ocean to complete their life cycle. The experiment was replicated in 1990, 1991, and 1992. There was no consistent significant dose-dependent effect of the 10-day exposure to the crude oil WSF on growth of the pink salmon prior to their release. Adult pink salmon from this experiment were captured in fisheries and also recovered from their natal Quinsam River, British Columbia. Pink salmon from each treatment group were recovered in similar numbers. Exposure of populations of fry to the WSF of crude oil and release to the Pacfic Ocean did not result in a detectable effect on their survival to maturity. Fry from all treatment groups incurred typically high mortality following release, and there were no discernible effects on survival that were attributable to exposure to the WSF of crude oil.
Les métaux (Mn, Cu, Cd, Zn et Hg) des meuniers noirs (Catostomus commersoni) et des grands brochets (Esox lucius) de l'amont et de l'aval du barrage Moses-Saunders sur le fleuve Saint-Laurent près de Cornwall (Ontario) et Massena (New York)
Authors: Lalonde Janick D , Chapleau François , Brind'Amour Anik , Ridgway Lara Louise
Published: April 2011

We examined the effect of a dam on concentrations of metals (Mn, Cu, Cd, Zn, and Hg) in white sucker (Catostomus commersoni) and in northern pike (Esox lucius). Fish were caught upstream and downstream of the Moses-Saunders Power dam on the St. Lawrence River near Cornwall, Ontario, and Massena, New York. Upstream of the dam, Lake St. Lawrence is a 136-km2 reservoir resulting from the flooding of 90 km2 of agricultural land in 1958, and downstream is Lake St. Francis. In northern pike, no difference in the mean concentrations of metals was found between upstream and downstream fish. Hg concentrations increased with length in upstream and downstream pike, whereas Zn showed an inverse relationship with length downstream. For a particular length, Hg concentration was higher in downstream northern pike. On average, white sucker were five times more contaminated by Hg upstream than downstream. The levels of Mn and Cu were also found to be higher upstream. No bioaccumulation of metals was observed in white sucker. Based on the results obtained for the northern pike, after 37 years, it seems that the high metal concentrations observed in Lake St. Lawrence after the creation of the reservoir have now disappeared. We believe that the high level of contamination of the white suckers in this lake is linked with this species' habit of being in constant contact with the sediments, which could be locally highly contaminated.
The role of copepod-dominated meiofauna in the mineralization of organic matter in a cold marine mesocosm
Authors: Parent Serge , Morin Antoine
Published: April 2011

Large populations of meiofauna are found in the sand filters of the St. Lawrence mesocosm at the Montreal Biodome. Three 30-day experiments were conducted in heterotrophic microcosms to quantify how populations of micro- and meio-faunal organisms affect mineralization using the apparent mineralization rate (AMR), i.e., nitrate production, as a proxy. Tryptone, mesocosm detritus, and fishmeal were used as organic substrates (C:N ratios 4-8). Harpacticoid copepods dominated the meiofauna in numbers (87%) and biomass (90%). AMR was inversely related to meiofaunal mass and not related to ciliate density. Through grazing, 1 g meiofaunal dry mass·m-2 reduced the AMR of tryptone by 42%, of detritus by 9.4%, and of fishmeal by 2.7%. Particle size affected the effect of meiofauna, whereas the C:N ratio affected the AMR. The scarcity of nematodes, which are known to stimulate mineralization, may explain these results. Copepod-dominated meiofauna decrease nutrient regeneration rates in heterotrophic habitats when C:N ratios are low.
Evaluation of the flood-pulse concept based on statistical models of growth of selected fishes of the Upper Mississippi River system
Authors: Gutreuter Steve , Bartels Andrew D , Irons Kevin , Sandheinrich Mark B
Published: April 2011

The flood-pulse concept (FPC) states that annual inundation is the principal force responsible for productivity and biotic interactions in river-floodplain systems. Somatic growth is one component of production, and we hypothesized that, if the FPC applies, growth of fishes that use the moving littoral zone should differ among years with differing flood pattern, whereas nonlittoral fishes would show no such response. Growth of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus), species that exploit littoral resources, increased during a year having an unusual warm-season flood in the Upper Mississippi River system and was reduced during low-water years. Growth of white bass (Morone chrysops), which do not rely heavily on the littoral zone, did not differ significantly between the extreme-flood and low-water years. Patterns of growth of black crappie (Pomoxis nigromaculatus), which have intermediate dependence on the moving littoral zone, were somewhat ambiguous. These results are consistent with the hypothesis that the FPC applies, at least under certain conditions, to this temperate river system. Our results can also provide an important basis from which to assess some costs and benefits of water level management strategies in large regulated temperate rivers.
Timing of the metamorphic molt of the American lobster (Homarus americanus) is governed by a population-based, photoperiodically entrained daily rhythm
Authors: Waddy S L , Aiken D E
Published: April 2011

The metamorphic molt of the American lobster (Homarus americanus) occurs in the form of a population-based, recurring daily rhythm that is photoperiodically entrained. Molting occurs predominantly in the scotophase (dark period) at temperatures of 11, 15, and 20°C and in both normal and reversed photoperiod cycles. Molting is arrhythmic in larvae reared in continuous illumination (LL), but when larvae reared in LL are transferred to cyclic photoperiod conditions (LD 12:12), the rhythm is reinstated in a stepwise manner over 3 days. When larvae are transferred from LD 12:12 to LL, the molting rhythm continues for 3 days before dampening. The rhythm appears to be phase-set by the onset of darkness: similar proportions of larvae (79-89%) reared in scotophase lengths of 6, 10, and 12 h molted in the 12-h period following lights-off. The results demonstrate that the synchrony of the metamorphic molt with the scotophase is not fortuitous and suggest that the molting rhythm may result from a gated event under the influence of an endogenous pacemaker.
Relative importance of stream-borne particulate and dissolved phosphorus fractions to Lake Tahoe phytoplankton
Authors: Hatch Lorin K , Reuter John E , Goldman Charles R
Published: April 2011

Algal bioassays using stream water additions from seven Lake Tahoe basin mountain creeks were used to assess short-term bioavailability of stream P to Lake Tahoe phytoplankton during the 1996 spring snowmelt. Results indicate that 75-90% of bioassay response is due to nutrients in the <0.45-µm range. Lake Tahoe phytoplankton are primarily P limited, although N colimitation has been observed during summer. Bioassay response did not correlate well with particulate P > 0.45 µm but was highly correlated with dissolved inorganic P. Dissolved organic P may also be stimulatory to Lake Tahoe phytoplankton. Bioassay response was relatively constant for each treatment during the study, due in part to a consistent diatom dominance of the phytoplankton community. The bioassay technique utilized is not sensitive enough to detect changes in land use along a single stream. Dissolved inorganic P was determined to best represent Lake Tahoe short-term (several days) stream bioavailable P at the present time. Physical bioavailability factors such as lake thermal dynamics and biological factors such as lake microbial dynamics should be addressed in addition to the chemical factors when considering lake biologically available P.
Bayesian state-space modeling of age-structured data: fitting a model is just the beginning
Authors: Millar Russell B , Meyer Renate
Published: April 2011

Explicit modeling of process variability in the dynamics of fisheries is motivated by a desire to incorporate more realism into stock assessment models, and much recent research effort has been devoted to the computational features of fitting state-space models for this purpose. Here, we extend the Bayesian application of nonlinear state-space modeling to sequential population analysis of age-structured data using a model formulation that allows for unreported catches and incidental fishing mortality. It is shown that, once a familiarity with the general-purpose Bayesian software BUGS is acquired, implementing a state-space model is a relatively simple task. Indeed, this application requires just 18 lines of code in its entirety and does not require the programmer to know the formulae for any prior density functions or likelihoods. Consequently, we suggest that this methodology may permit the implementation phase of nonlinear state-space modeling to be relegated, thereby allowing more effort to be devoted to the challenging issues of model checking, selection/averaging, sensitivity, and prior specification.
Simulated and observed response of the southwest Vancouver Island pelagic ecosystem to oceanic conditions in the 1990s
Authors: Robinson Clifford KL , Ware Daniel M
Published: April 2011

In this paper, we discuss changes in the ocean climate around La Perouse Bank off southwestern Vancouver Island, British Columbia, and its influence on the functioning of the pelagic ecosystem. We compare results of a one-dimensional simulation model of plankton and fish production and biomass dynamics with empirical data collected in the 1990s. Comparisons of simulation results with empirical data indicate that the La Perouse model can account for relative interannual changes in copepod biomass, euphausiid biomass and production, the consumption of Pacific herring (Clupea pallasi) by Pacific hake (Merluccius productus), and the growth condition factor of Pacific hake. The model is less successful at capturing changes in spring diatom biomass, the proportion of euphausiids in the Pacific hake diet, and interannual variability in the Pacific herring condition factor. A measure of overall model performance suggests that the La Perouse ecosystem model performs equally well in both strong and weak upwelling periods. The La Perouse ecosystem model has been used to generate an annual index of net phytoplankton and macrozooplankton production for the coastal upwelling region off southwestern Vancouver Island from 1967 to 1998.
Particulate light absorption and the prediction of phytoplankton biomass and planktonic metabolism in northeastern Spanish aquatic ecosystems
Authors: Duarte C M , Agustí S , Kalff J
Published: April 2011

Examination of particulate light absorption and microplankton metabolism in 36 northeastern Spanish aquatic ecosystems, ranging from alpine rivers to inland saline lakes and the open Mediterranean Sea, revealed the existence of general relationships between particulate light absorption and the biomass of phytoplankton and microplankton metabolism. The particulate absorption spectra reflected a dominance of nonphotosynthetic, likely detrital, particles in rivers and a dominance of phytoplankton in coastal lagoons. There was a strong relationship between the light absorbed by phytoplankton and the chlorophyll a (Chl a) concentration of the systems, which indicated an average (±SE) Chl a specific absorption coefficient of 0.0233 ± 0.0020 m2·mg Chl a-1 for these widely diverse systems. Chl a concentration was a weaker predictor of the total particulate light absorption coefficient, pointing to an important role of nonphytoplanktonic particles in light absorption. Gross production was very closely related to the light absorption coefficient of phytoplankton, whereas community respiration was strongly correlated with the total particulate light absorption coefficient, indicating the optical signatures of sestonic particles to be reliable predictors of planktonic biomass and metabolism in aquatic ecosystems.
Utility of storage lipid volumes in inferring recent trophic history of copepods
Authors: Reiss C S , McLaren I A , Avendaño PA
Published: April 2011

We were able to estimate lipid oil-sac volumes of Pseudocalanus spp. copepodids c3 to c5 on and around Western Bank, Scotian Shelf, during three cruises (October and November 1997 and January 1998) at stations on (<60 m depth) and off (>60 m depth) the bank. We test the hypothesis that storage lipid volume was not significantly different between locations during these three months. Pseudocalanus spp. are an important prey for Atlantic cod (Gadus morhua) larvae that are spawned and persist on the bank. However, in contrast with the greater concentration of Pseudocalanus spp. on relative to off the bank, size-adjusted oil-sac volumes were on average larger and less variable at off-bank stations. We conclude that the greater copepod concentration on the bank does not result from enhanced and uniform nutrition on the bank. Lipid volumes averaged larger in winter than in the autumn, indicating that nutritional condition of Pseudocalanus spp. copepodids does not decline subsequent to the autumn bloom. Although biochemical techniques are available to quantify the level of storage lipids in individual copepods, simple measurements of oil sacs and body sizes permit a rapid real-time assessment of their recent trophic history in relation to oceanographic structure.
Recruitment variation related to fecundity in marine fishes
Authors: Rickman S J , Dulvy N K , Jennings S , Reynolds J D
Published: April 2011

An understanding of the processes that control recruitment variation is central to explaining the population dynamics of fishes and predicting their responses to exploitation. Theory predicts that interannual variation in recruitment should be positively correlated with the fecundity of fish species, but empirical studies have not supported this hypothesis. Here, we adopt a phylogenetic comparative approach, which accounts for evolutionary relatedness among stocks and species, to investigate this relationship. We calculated the mean fecundity of fishes from 52 stocks at the mean length of maturity and related this to interannual recruitment variation. We found that in 13 of 14 comparisons between stocks or closely related species, the stocks with higher fecundity have higher recruitment variation. This was true whether or not we controlled for spawning stock size. However, when the analyses were repeated using a traditional cross-species approach, which did not account for the evolutionary relatedness of stocks, the relationships were not significant. This is the first empirical study to link fecundity with recruitment variation and suggests that fecundity is an important component of fish stock dynamics.
Relating spatial distributions of acoustically determined patches of fish and plankton: data viewing, image analysis, and spatial proximity
Authors: Swartzman Gordon , Brodeur Richard , Napp Jeffrey , Walsh Danny , Hewitt Roger , Demer David , Hunt George , Logerwell Elizabeth
Published: April 2011

We developed a point-and-click acoustic data viewer (FishViewer) for exploratory comparison of up to three acoustic survey transects (or three frequencies) at a time and other environmental and biological data (e.g., surface temperature and seabird abundance). FishViewer also contains image-processing tools (e.g., morphological and threshold filters) for distinguishing between fish shoals and plankton patches and for patch identification. These tools and methods are illustrated using survey data collected at three frequencies (38, 120, and 200 kHz) near the Pribilof Islands, Bering Sea, during September 1995. Data were also visualized by converting the patches identified in the acoustic images to polygons, showing the boundaries of each patch using a connected component algorithm. Proximity between these fish shoal and plankton patch polygons was examined statistically using an interval-based nonparametric regression model (generalized additive models) and a distance-based proximity measure. The methods presented for data refinement, visualization, and the establishment of fish-plankton patch proximity serve as a paradigm for scale-robust hypothesis formulation and testing of spatial patterns of fish and plankton.
Hyperaggregation of fish and fisheries: how catch-per-unit-effort increased as the northern cod (Gadus morhua) declined
Authors: Rose G A , Kulka D W
Published: April 2011

Misinterpretations of elevated catch-per-unit-effort (CPUE) in the northern cod (Gadus morhua) fishery contributed to overestimations of stock size, inflated quotas, and unsustainable fishing mortality in the 1980s and early 1990s. We hypothesize that concentration of the fish and fishery led to extreme hyperstability in the CPUE-abundance relationship. In the late 1980s, migrant cod began to concentrate within the Bonavista corridor, their most southerly cross-shelf migration route. By the spring of 1990, approximately 450 000 t was concentrated within 7000 km2 at densities quadruple those of the 1980s. Densities remained high through 1992, while abundance declined fivefold. During this period, cod hyperaggregated (local densities increased with decreasing biomass) in the Bonavista corridor and CPUE increased. To the north, no hyperaggregation occurred, and densities and CPUE declined with biomass. In the Bonavista corridor from 1990 to 1993, CPUE was hyperstable with local cod density. Areas of high cod densities (>0.1 fish·m-2) shrunk as regional estimates of cod biomass declined. The spatial extent of the fishery contracted proportional to the shrinkage in area occupied by the fish. Hence, CPUE was related to abundance at the local scales of a fishing set (local acoustic density) but not to abundance at regional or stock scales.
Under-ice diel vertical migrations of Oncorhynchus nerka and their zooplankton prey
Authors: Steinhart Geoffrey B , Wurtsbaugh Wayne A
Published: April 2011

We used stationary hydroacoustics and measures of environmental conditions (water temperature, dissolved oxygen, light levels, and zooplankton) to determine what factors, foraging or predation risk, influenced diel vertical migrations of Oncorhynchus nerka during winter in three high-mountain lakes. The Sawtooth Valley lakes are deep, oligotrophic, glacial lakes located in central Idaho, U.S.A., and historically contained populations of anadromous O. nerka. In general, low light intensities limited foraging opportunities of O. nerka under ice, especially at night. In Stanley Lake, O. nerka underwent diel vertical migrations to exploit available light to feed. Oncorhynchus nerka occupied shallow water at night, where there was still sufficient light to feed, but were found in deep water during the day. It is unknown whether O. nerka occupied deep depths during the day to feed on high densities of zooplankton or to avoid predators. In Alturas Lake, O. nerka remained in the top 25 m both day and night to feed high densities of zooplankton found near the surface. In Redfish Lake, O. nerka also showed little migration: O. nerka stayed in shallow water both day and night and occupied the same depths with the highest zooplankton densities. The vertical distribution of O. nerka during the winter appears to be determined by available food and light, but the deep daytime distribution found in Stanley Lake is still unexplained.