bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating delayed density-dependent mortality in sockeye salmon (Oncorhynchus nerka): a meta-analytic approach
Authors: Myers R A , Bradford M J , Bridson J M , Mertz G
Published: April 2011

Delayed density-dependent mortality can be a cause of the cyclic patterns in abundance observed in many populations of sockeye salmon (Oncorhynchus nerka). We used a meta-analytical approach to test for delayed density dependence using 34 time series of sockeye data. We found no consistent evidence for delayed density-dependent mortality using spawner - spring fry or spawner-recruit data. We did find evidence for delayed density-dependent mortality at a 1 year lag for the spawner - fall fry and the spawner-smolt data; however, effects at lags greater than 1 year were weak and not statistically significant. Between-cohort interactions at a 1-year lag are not sufficient to cause the observed cycles in adult abundance, although they will tend to reinforce patterns established by other mechanisms. Our results imply that reductions in fishing mortality in off-peak years should result in an increase in abundance.
Qualitative and quantitative sampling of lake fish communities
Authors: Jackson Donald A , Harvey Harold H
Published: April 2011

We demonstrated that estimates of the relative abundance and patterns of covariation for fish species captured in baited minnow traps, plastic traps, fine- and coarse-mesh trap nets, and multimesh gill nets from 43 lakes differed greatly among the gears; contradictory results about species' relative abundance were often provided. We conclude that simple approaches to integrate catches from gears providing an overall estimate of species abundance in communities across lakes are compromised given the inconsistency in estimates of abundance and covariation. We recommend an increased effort towards the use of presence-absence data and their adequate sampling within lake community studies. We used a resampling approach to demonstrate the relative ability of the different gears to detect the presence of species within lakes under various levels of sampling intensity. The variation among lakes and constituent species necessitates the use of multiple gears to adequately detect species composition. Many studies probably underestimate the species composition within lakes given insufficient effort and too restricted use of different sampling gears. The need for increased sampling effort is of particular concern in areas focusing on biodiversity (e.g., species losses) and ecosystem health (e.g., ecological integrity) where failing to detect species may have substantial economic and management implications.
Factors influencing organochlorine uptake in age-0 brown trout (Salmo trutta) in lotic environments
Authors: Berglund Olof , Larsson Per , Brönmark Christer , Greenberg Larry , Eklöv Anders , Okla Lennart
Published: April 2011

In 1994 and 1995, we investigated the relationship between stream morphology and water chemistry and levels of organochlorines (HCB, PCB, and DDT) in young-of-the-year brown trout (Salmo trutta) from 25 streams in southern Sweden. Contrary to earlier findings for lakes, we found a positive relationship between trophic status (total phosphorus) and uptake of persistent pollutants in stream biota (trout). This difference between benthic, stream environments and pelagic, lake environments may be related to processes affecting pollutant uptake, i.e., pollutant ``spiralling'' or the shift from heterotrophy to autotrophy in streams. Land use in the catchment area of the streams also affected pollutant levels in trout, with higher levels in agricultural landscapes and lower levels in forested areas. Size of catchment area, however, did not influence uptake of pollutants in trout. The results indicate that eutrophication of streams by agricultural activities and excessive nutrient loading may increase uptake of persistent pollutants in stream biota.
Impaired cortisol secretion in yellow perch (Perca flavescens) from lakes contaminated by heavy metals: in vivo and in vitro assessment
Authors: Brodeur Julie C , Sherwood Graham , Rasmussen Joseph B , Hontela Alice
Published: April 2011

The characteristic elevation of plasma cortisol levels in response to an acute stress of capture was impaired in both male and female yellow perch (Perca flavescens) from lakes contaminated by heavy metals. The impairment of the cortisol stress response was observed in fish 4 + years and older whereas the capacity to elevate plasma cortisol levels of fish younger than 4 + was not significantly different at contaminated and reference sites. The responsiveness to ACTH of the interrenal tissue of 4 + yellow perch was evalutated in vitro to determine whether the impairment of the cortisol stress response is caused by a dysfunction of the interrenal tissue or if the dysfunction is located elsewhere in the hypothalamo-pituitary-interrenal axis controlling the secretion of cortisol. The amount of cortisol secreted by the interrenal tissue of yellow perch from a contaminated site in response to a 10-min stimulation with 10-7 M ACTH was significantly lower compared with fish from the reference site. These results indicate that the impairment of the cortisol stress response observed in fish from polluted sites is caused, at least in part, by a dysfunction of the interrenal tissue.
Impact of water level fluctuations on St. Lawrence River aquatic vegetation
Authors: Hudon Christiane
Published: April 2011

Historical records of average seasonal water levels in the St. Lawrence River over the past 80 years reveal cyclic variations of up to 1 m above (1976) and 1 m below (1965) present levels. These variations are probably related to climatic conditions in the basin. Over the same period, the vertical range of seasonal water levels decreased from 2.2 to 1.5 m because of discharge regulation. Exposure of new substrate during periods of extreme low water levels may facilitate the invasion of aggressive and (or) exotic species. In Lake Saint-Pierre, a strong negative relationship was observed between seasonal water level and the percentage of emergent plant cover. Under low water levels, the lake becomes a large (387 km2) marshland that could support a high plant biomass (286 times 103 t) whereas under high water levels, the lake shifts to a vast (501 km2) open-water body with a lower predicted plant biomass (117 times 103 t). A model of the major anthropic and climatic forces acting on water levels is also presented; it describes aquatic plant biomass allocation and species diversity under different water level conditions.
Analytical models for fishery reference points
Authors: Schnute Jon T , Richards Laura J
Published: April 2011

Fishery reference points are widely applied in formulating harvest management policies. We supply precise mathematical definitions for several reference points in common use. We then derive analytical expressions for these quantities from age-structured population models. In particular, we explain how the maximum sustainable harvest rate and catch (h*, C*), two quantities of management importance, can replace the classical recruitment parameters ( alpha , beta ) in the Beverton-Holt and Ricker recruitment curves. We also demonstrate dependencies of various reference points on subsets of model parameters. Although our analysis is restricted to special cases, our models still have general utility. For example, simple calculations from analytical formulas enable checks on the output from more complex models and guide the choice of reference points for fishery management.
Relative effects of trap versus trawl fisheries on population dynamics of the northern cod (Gadus morhua) stock
Authors: Fahrig L , Pope S E , Henein K M , Rose G A
Published: April 2011

We compared the effects of the inshore trap and the offshore trawl fisheries on the population dynamics of the northern cod (Gadus morhua) stock using data analyses and simulation modelling. We first statistically characterized the catch versus stock biomass relationships for the two fisheries (1977-1986). We found a significant (P < 0.0001) relationship between the trawl catch at time t and the stock biomass at time t - 2. No temporal lag was evident in the trap catch versus stock biomass relationship. The variability in these two relationships was similar. We then modelled the catch and stock biomass dynamics of the two fisheries in parallel, incorporating the observed catch versus stock biomass relationships, but assuming equal mean catches, to examine the effects on cod population dynamics of the temporal lag and variability in the catch versus stock biomass relationships. The results suggest that, for the same amount of fish taken, a quota-based trawl fishery presents a much greater risk of collapse to the cod stock than does an inshore trap fishery. Current management methods overestimate the "safe" catch for the trawl fishery because they do not incorporate the consequences of the lag in the relationship between stock biomass and trawl catch.
Cladoceran- and copepod-dominated zooplankton communities graze at similar rates in low-productivity lakes
Authors: Cyr Hélène
Published: April 2011

Many studies suggest that the taxonomic composition of a zooplankton community should determine its grazing rate and selectivity for different types of particles. It is generally believed that copepod-dominated communities should (i) have lower grazing rates and (ii) consume larger particles than communities dominated by large cladocerans. I tested these hypotheses in situ by comparing zooplankton grazing in 19 communities from low-productivity lakes where the zooplankton ranged from >99% copepod biomass to >90% large cladoceran biomass (Holopedium gibberum, Daphnia spp.). The zooplankton grazed 1-14% of total chlorophyll per day and 0-17% of the chlorophyll in algae <35 µm per day. Grazing rates increased with increasing zooplankton biomass (r2 = 0.34, P < 0.01), but once the effect of zooplankton biomass was accounted for, similar grazing rates were found in copepod- and in cladoceran-dominated communities. The difference in grazing rates on small algae and on the whole phytoplankton assemblage, on the other hand, varied systematically with zooplankton taxonomic composition. Holopedium-dominated communities were most efficient at grazing algae <35 µm, Bosmina-dominated communities had similar grazing rates on algae <35 µm and on the whole phytoplankton assemblage, and copepod-dominated communities had similar or slightly higher grazing rates on the whole phytoplankton assemblage. Qualitative differences in grazing selectivity of different zooplankton taxa are observed in complex natural communities.
Contested stock assessment: two case studies
Authors: Starr Paul , Annala John H , Hilborn Ray
Published: April 2011

We describe two case studies where scientists representing alternative interest groups worked together to attempt to resolve scientific issues of fisheries assessments. In several fisheries in New Zealand, commercial fishing interests hired consultants to review governmental assessments. In some of these fisheries, the two sides provided alternative competing assessments; in other fisheries, there was a cooperative agreed-upon assessment. In the analysis of chinook salmon (Oncorhynchus tshawytscha) within the Pacific Salmon Treaty, scientists representing all parties agreed upon an assessment procedure and developed it over a number of years. Such contested assessments provide a number of benefits including (i) intense peer review, (ii) the ability to bring data from all parties into the assessment process, and (iii) better understanding and trust of the assessments by the different interest groups. Effective peer review requires repeating the calculations associated with data sources and assessment models. We suggest that contested assessments, despite the extra cost, are highly valuable, as they provide a substantially improved standard of assessment. Contested assessments will evolve towards cooperative analysis unless participating parties feel that the cooperative assessment is counter to their perceived interests.
Plasma levels of thyroxine, prolactin, and cortisol in migrating and resident wild arctic char, Salvelinus alpinus
Authors: Høgåsen Helga Rachel , Prunet Patrick
Published: April 2011

The study was performed on 14-49 cm wild arctic char, Salvelinus alpinus. Plasma thyroxine concentration was twice as high in upstream and downstream migrants (3.8 and 4.0 ng/mL, respectively) as in non-migrants (1.7 ng/mL), supporting the prevailing view that thyroid hormones are stimulatory to both upstream and downstream migration in wild anadromous salmonids. The stimulation of downstream migration by thyroid hormones is suggested to depend on the low feeding state of wild smolts. Plasma prolactin concentration was lower in downstream migrants (10.3 ng/mL) than in non-migrants sampled during the period of downstream migration (16.2 ng/mL), suggesting a possible role for this hormone in repressing seaward migration. Plasma cortisol level was twice as high in upstream migrants (464 ng/mL) as in downstream migrants (244 ng/mL) trapped in a standardized manner. Higher interrenal capacity or responsiveness in upstream migrants may increase their ability to mobilize energy stores. In upstream-migrating females, plasma prolactin concentration was positively correlated with the gonadosomatic index, suggesting a role for prolactin in early sexual maturation. Body length, which was correlated with numbers of migrations, was found to be related only to plasma thyroxine concentration in downstream migrants.
Statistical analysis of the somatic growth rate of 0+ fish in relation to temperature under natural conditions
Authors: Mooij W M , van Nes E H
Published: April 2011

The somatic growth rate of 0+ fish of the six major species in Dutch shallow eutrophic lakes, bream (Abramis brama), roach (Rutilus rutilus), pikeperch (Stizostedion lucioperca) (planktivorous and piscivorous), perch (Perca fluviatilis), ruffe (Gymnocephalus cernuus), and smelt (Osmerus eperlanus), was analysed by using a differential equation. This equation models the instantaneous growth rate of a fish as a temperature-dependent power function of body weight. Two of the model parameters were calibrated by optimising the prediction of the growth rate of the fish. Using a new method, which included a parametric bootstrap procedure, confidence limits were estimated for these two calibrated parameters and were used to test the significance of differences between species in growth performance under natural conditions. These tests revealed four groups of species: (A) smelt, (B) roach and bream, (C) ruffe and perch, and (D) piscivorous pikeperch. Growth performance of planktivorous pikeperch mainly overlapped with roach and bream (B) but showed some overlap with ruffe and perch (C). Differences and similarities are explained from the food type (D versus A, B, and C) and the phylogenetic constraints (A versus B versus C) of each species.
Stream habitat hydraulics: interannual variability in three reaches of Catamaran Brook, New Brunswick
Authors: Giberson Donna J , Caissie Daniel
Published: April 2011

The hydraulic habitat of 12 sites in a small salmon stream in central New Brunswick was investigated between 1992 and 1995 to determine patterns of habitat (substrate) stability between and within reaches. Stability was evaluated by measuring particle size distribution in replicated erosional and depositional sites in each reach and calculating the proportion of the bed predicted to be in motion at given flood flows. Erosional (riffle) sites in all reaches showed significant differences (ANOVA, p < 0.05) in substrate particle sizes from year to year, movement of embedded sediment samplers, and high predicted bedload mevement, even in small spates. In contrast, depositional sites (flats, some runs) appeared stable, showing no significant year-to-year differences in particle sizes, no movement of embedded samplers, and no increase in predicted bedload movement until high flow. The impact of the flood on the streambed depends heavily on the particle size distribution present during the flood, resulting in different levels of substrate disturbance during equal-magnitude floods in different years. Certain sites (e.g., flats) may be able to serve as hydraulic refugia to stream fauna during some floods. It is clear that year-to-year variations in substrate stability must be considered when evaluating habitat stability for stream fauna.
Growth, spatial distribution, and abundance of benthic stages of the snow crab (Chionoecetes opilio) in Bonne Bay, Newfoundland, Canada
Authors: Comeau Michel , Conan Gérard Y , Maynou Francesc , Robichaud Guy , Therriault Jean-Claude , Starr Michel
Published: April 2011

The growth and spatial distribution of postlarval snow crab (Chionoecetes opilio) from a relatively unexploitated stock in Bonne Bay, Newfoundland (Gulf of St. Lawrence), were described from the analysis of size distributions from trawls and a dredge sampled between 1988 and 1993. Immature crabs molted twice a year for instars I-V and then molted annually until females reached a terminal molt at maturity (instar X or XI) and males a juvenile stage (instar VIII). Thereafter, juvenile males could molt to another juvenile size, skip a molt, or achieve a terminal molt at the onset of the morphometric differentiation of their claws depending on the relative abundance of mature males. The life expectancy of females and males was 13 and 19 years, respectively. Males should recruit to the commercial size of 95 mm carapace width at instar XII, 9 years or more after settlement. Relative abundance of early benthic to commercial-size individuals suggests that small immature crabs (instar V) migrate from shallow rocky to deep muddy bottoms. The patchy spatial distribution observed for the snow crab appeared to be determined more by substrate and intraspecific factors than by depth. Seasonal movements to shallow waters by larger animals was related to density- and temperature-dependent factors associated with the reproductive and growth cycle.
Acquired predator recognition in juvenile rainbow trout (Oncorhynchus mykiss): conditioning hatchery-reared fish to recognize chemical cues of a predator
Authors: Brown Grant E , Smith R Jan F.
Published: April 2011

In this study, we exposed predator-naive, hatchery-reared juvenile rainbow trout (Oncorhynchus mykiss) to the chemical stimuli from northern pike (Esox lucius) and either trout skin extract (a chemical alarm signal) or a distilled water control to test for acquired recognition of a novel predator. Trout exposed to conspecific skin extract and pike odour significantly increased antipredator behaviour (i.e., decreased foraging and area use and increased shoaling and freezing), while those exposed to distilled water and pike odour did not. Conditioned trout were exposed to pike odour alone (versus a distilled water control) either 4 or 21 days later. When presented with pike odour 4 days postconditioning, trout significantly increased antipredator behaviour (i.e., decreased foraging and area use and increased time under cover and freezing). Trout tested 21 days postconditioning still exhibited a significant increase in antipredator behaviours when presented with pike odour alone (i.e., decreased foraging and increased freezing). These data are the first to demonstrate that hatchery-reared trout can be conditioned to recognize the chemical cues of a predator and suggest that this may serve as a strategy to train hatchery-reared fish to recognize predators prior to stocking into natural waterways.
The role of olfaction in homing and estuarine migratory behavior of yellow-phase American eels
Authors: Barbin Gayle P
Published: April 2011

The role of olfaction in homing migrations of American eels (Anguilla rostrata) was examined in the Penobscot Estuary, Maine, U.S.A. Ultrasonic telemetry was used to track continuously (65 ± 12 h) 16 yellow eels displaced from a capture site. Four eels were not treated, eight rendered anosmic, and four rendered partially anosmic. All normal, only three anosmic, and two partially anosmic eels homed. Normal eels expressed a singular behavioral pattern, selective tidal stream transport (STST). STST was also displayed by three anosmic eels and one partially anosmic eel. Three alternative behavioral patterns ("sporadic vertical excursions," "sloshing," and "directed swimming") were displayed by the remainder of the anosmic and partially anosmic eels. Eels that displayed STST used the water column differently (moving at depths shallower than the thermocline, halocline, and pycnocline) from those that displayed other behaviors. Olfaction seems to be important for discrimination of the appropriate tide for transport and location of a home site but is not the only orientational mechanism used in estuaries. Mechanisms used to detect rates of change of water mass characteristics are probably important for guidance of estuarine migrations.
Relationship between growth and protein turnover rates and nucleic acids in the liver of rainbow trout (Oncorhynchus mykiss) during development
Authors: Peragón Juan , Barroso Juan B , de la Higuera Manuel , Lupiáñez José A
Published: April 2011

We have studied the nucleic acid concentrations and protein turnover rates, fractional protein synthesis (KS), degradation (KD), and accumulation (KG) rates, synthesis capacity (CS), synthesis efficiency (KRNA), synthesis per DNA unit (KDNA), and protein retention efficiency (PRE) in the liver of rainbow trout (Oncorhynchus mykiss) at different stages of development (fingerling: 7 g; juvenile: 45, 65, and 170 g; adult: 420 g; represented by 14-, 24-, 28-, 40-, and 96-week-old fish). Our results show that liver growth is characterized by linear increases in both total DNA (reflecting hyperplasia) and the protein:DNA ratio (reflecting hypertrophy); hyperplasia was more pronounced than hypertrophy. Development was accompanied by a significant decrease in KS, while KGdid not change significantly. There was a concomitant fall in RNA concentration measured as milligrams per gram of protein (CS) and as milligrams per gram of liver, while KRNAonly decreased slightly. The alterations in KSwere thus probably due to a decrease in CS. The pronounced fall in KStogether with the slight increase in the protein:DNA ratio may be responsible for the decline in KDNA. PRE increased concomitantly with an increase in whole-body weight.
Effects of surgically and gastrically implanted radio transmitters on swimming performance and predator avoidance of juvenile chinook salmon (Oncorhynchus tshawytscha)
Authors: Adams Noah S , Rondorf Dennis W , Evans Scott D , Kelly Joseph E , Perry Russell W
Published: April 2011

Radiotelemetry data are often used to make inferences about an entire study population; therefore, the transmitter attachment method should be the one that least affects the study animal. Juvenile chinook salmon (Oncorhynchus tshawytscha) <120 mm in fork length (FL) with either gastrically or surgically implanted transmitters had significantly lower critical swimming speeds than control fish 1 and 19-23 days after tagging. For fish >120 mm FL, fish with gastric implants swam as well as controls 1 day but not 19-23 days after tagging. In contrast, fish with surgical implants swam as well as controls 19-23 days but not 1 day after tagging. During predation trials, fish with gastric or surgical implants were eaten by smallmouth bass (Micropterus dolomieu) in significantly greater numbers than controls. We do not recommend implanting transmitters (representing 4.6-10.4% of the fish's body weight) in fish <120 mm FL. Furthermore, surgical implants (representing 2.2-5.6% of the fish's body weight) may be the preferred method for biotelemetry studies of juvenile chinook salmon >120 mm FL.
Partial sequence of the 24S rRNA and polymerase chain reaction based assay for the toxic dinoflagellateDinophysis acuminata
Authors: Puel O , Galgani F , Dalet C , Lassus P
Published: April 2011

We describe the polymerase chain reaction (PCR) amplification of an 805 base pair fragment of 24S rRNA from the toxic dinoflagellate Dinophysis acuminata and the sequence of this fragment. We also describe a PCR-based assay for the specific detection of D. acuminata in seawater samples. Conserved primers, starting at positions 711 and 1489 of the 24S rRNA from the dinoflagellate Prorocentrum micans, were used for the PCR. The PCR product was cloned and sequenced. The fragment was aligned with rRNA sequences from other protists. Two oligonucleotides in variable domains of the sequence from D. acuminata were chosen and a protocol was defined for PCR-based detection of D. acuminata (30 cycles, 50°C). Experiments conducted with seawater samples led to the detection of D. acuminata in naturally contaminated samples. The PCR enabled us to detect down to 30 cells/L seawater. The problem of interference from large concentrations of other phytoplankton species may be solved using nested PCR.
Influence of fish density on the energy allocation pattern of juvenile brook trout (Salvelinus fontinalis)
Authors: Marchand François , Boisclair Daniel
Published: April 2011

Our objectives were (i) to assess the influence of fish density on the energy allocation pattern of juvenile brook trout (Salvelinus fontinalis) and (ii) to define the mechanism by which this influence occurs. We estimated growth, consumption, and activity rates of brook trout held in 8-m3 enclosures characterized by two different densities (four or eight fish per enclosure; D4 and D8 enclosures, respectively). Eight experiments designed to estimate these variables were performed during a 27-day period. Fish from D4 enclosures ( DELTA W bar = 0.46 g) grew twice as much as those from D8 enclosures ( DELTA W bar = 0.24 g). For any given experiment, consumption rates were not significantly different between the two fish densities (0.434-1.09 g dry ·100 g wet-1 ·day-1). However, fish stocked in D8 enclosures displayed more aggressive behavior, executed 5.5 times more movements, and swam at speeds 13% faster than fish in D4 enclosures. These differences resulted in activity rates fourfold higher in D8 enclosures than in D4 enclosures. Empirical analyses combining our results with published values of growth, consumption, and activity rates supported the hypothesis that competition can have a negative effect on growth through a decrease in consumption rates and an increase in activity costs.
Methyl mercury dynamics in littoral sediments of a temperate seepage lake
Authors: Krabbenhoft David P , Gilmour Cynthia C , Benoit Janina M , Babiarz Christopher L , Andren Anders W , Hurley James P
Published: April 2011

The sites and rates of methyl mercury (MeHg) production and transport in littoral zone sediments were investigated at Pallette Lake in northern Wisconsin. In littoral areas where groundwater inflow occurs, sulfate supply from groundwater creates profiles of electron acceptors (sulfate) and donors (methane, sulfide) that are reversed from those found in sediments whose sulfate supply is delivered from overlying water. The highest MeHg concentrations in porewaters and the maximal advective MeHg flux rates (4.5-61.7 ng ·m-2 ·day-1) were observed in the spring, while highest bulk phase concentrations occur later in the summer. These estimated MeHg fluxes are greater than the mean areal production rates estimated previously for the water column and are similar to the atmospheric flux. Gross MeHg production was measured using the addition of 203Hg as a tracer to sediments. The depth at which maximal 203Hg methylation occurred coincided with the observed maximums in solid-phase and porewater MeHg concentrations. Because input, advection, and accumulation of MeHg in these sediments were measured directly, an independent estimate of MeHg production could be made and compared with 203Hg-derived rates. This comparison suggests that that the 203Hg tracer method provides reasonable estimates of gross methylation rates and that a substantial fraction of solid-phase Hg is available for methylation.
Effects of ration on the maturation and fecundity in captive Atlantic herring (Clupea harengus)
Authors: Ma Y , Kjesbu O S , Jørgensen T
Published: April 2011

We examined the effects of amount of food on vitellogenic oocyte size and number (fecundity) between two experimental groups of Atlantic herring (Clupea harengus) kept in separate but identical compartments of a large seawater tank. Growth and maturation were monitored for 1.5 years. Each group of 200 fish was fed exclusively on krill. At the end of the experiment, a high-ration group, fed 12 mg ·g fish-1 ·day-1, had similar weights-at-length as wild specimens of the same stock. A low-ration group fed about half the amount of the high-ration group had significantly lower weights-at-length. Ration had no effect on oocyte size and relative potential fecundity (oocytes per gram), but mean potential fecundity (oocytes per fish) of the low-ration fish was 26% lower than that of the high-ration fish. The relative intensity of early stages of atresia was quantified histologically. Atresia is a common phenomenon in Atlantic herring and increases markedly with suboptimal feeding. Mean relative atretic intensities were estimated at about 3 and 6% for the high- and low-ration groups, respectively, but with large intragroup variation. Modeled realized fecundity (spawned eggs per fish) indicated a 9 and 40% reduction compared with the measured potential fecundities, respectively.
Lungworm (Nematoda: Metastrongyloidea) infections in Canadian phocids
Authors: Gosselin Jean-François , Measures Lena N , Huot Jean
Published: April 2011

Otostrongylus circumlitus (Railliet, 1899) was found in 5% (16/308) of grey seals (Halichoerus grypus), 6% (1/17; intensity = 38) of harbour seals (Phoca vitulina), and none of 100 harp seals (Phoca groenlandica) from eastern Canada and none of 31 ringed seals (Phoca hispida) from Holman, Northwest Territories. Eighty-two percent of these infections were observed in young-of-the-year seals. Filaroides (Parafilaroides) gymnurus (Railliet, 1899), detected in nodules in the superficial parenchyma of the lungs, infected 24% (5/16) of grey seals, 27% (4/15) of harbour seals, 57% (29/51) of harp seals, 81% (25/31) of ringed seals, and one stranded bearded seal (Erignathus barbatus) (new host report for harp, ringed, and bearded seals; new locality report for Holman). Filaroides (Parafilaroides) hispidus Kennedy, 1986 was found in systematically sliced lungs of grey seals (2/3; new host report) and ringed seals (2/7) but not in harp seals (n = 11) or harbour seals (n = 5). Intensity ranged from 37 to 3570 for F. (P.) gymnurus and from 295 to 1196 for F. (P.) hispidus. No detrimental effect on body condition of seals could be associated with infection by lungworms.
Sperm competition and paternity assurance during the first breeding period of female snow crab (Chionoecetes opilio) (Brachyura: Majidae)
Authors: Urbani Nicola , Sainte-Marie Bernard , Sévigny Jean-Marie , Zadworny David , Kuhnlein Urs
Published: April 2011

Two highly polymorphic microsatellite DNA loci were used to determine paternity of larvae of primiparous Chionoecetes opilio females. In addition, female spermathecal contents were genotyped at the two loci and histological analysis of the organs was carried out to elucidate patterns of sperm competition. Females carrying their first brood from controlled laboratory matings and from matings in the wild were examined. Spermathecal contents from wild-caught females were cut into several cross sections and each section genotyped individually. Both wild and laboratory females commonly mated with several males whose ejaculates were stored and stratified in the spermathecae. Genetic typing of the offspring of laboratory-mated females revealed single paternity and indicated that the last mate to inseminate a female before oviposition gained paternity of the clutch. The predominant mechanism ensuring single paternity appeared to be sperm stratification. In wild-caught females, the microsatellite typing of the offspring also revealed single paternity, but larvae appeared to be sired by males whose genotypes were found in the spermathecal cross sections towards the dorsal end (blind end) of the spermathecae. This suggested that they were the first males to mate with females that they guarded until oviposition, and females remated with other males thereafter.
Does annual variation in growth and sexual maturation of white sucker (Catostomus commersoni) confound comparisons between pulp mill contaminated and reference rivers?
Authors: Bussières Dany , Gagnon Marthe Monique , Dodson Julian , Hodson Peter V
Published: April 2011

A previous study on the effect of pulp and paper effluents on white sucker (Catostomus commersoni), conducted in 1991 and 1992, in both effluent-exposed and reference rivers showed that fish grew faster at downstream sites than at upstream sites. However, in contrast with fish from a reference river, fish exposed to effluent showed no decrease in age or size at first maturity or increase in gonad size or fecundity in response to greater growth. The objective of the present study, conducted in 1993, was to test if differences in measures of growth and sexual maturation between fish populations in exposed and reference rivers would vary from year to year and whether such variation would affect conclusions concerning the effects of pulp mill effluents. Although size at age, fecundity, and age at first maturity varied between the two studies, patterns of demographic responses to pulp mill effluents, relative to reference populations, remained the same, i.e., conclusions about effects of pulp mill effluents did not change despite variation in demographic variables between years and sites. This study reaffirmed the view that only by including the fish populations in a reference river could effects due to bleached kraft mill effluent be separated from effects due to nutrient gradients.
Use of lipofuscin for resolving cohorts of western rock lobster (Panulirus cygnus)
Authors: Sheehy Matt , Caputi Nicolavito , Chubb Christopher , Belchier Mark
Published: April 2011

We evaluated lipofuscin age pigment as an approach to age determination of western rock lobster (Panulirus cygnus). Lipofuscin was measured using fluorescence image analysis of olfactory lobe sections from 184 juvenile lobsters from coastal nursery reefs at Seven Mile Beach, Western Australia. Modal analysis of a lipofuscin concentration-frequency histogram for this sample suggested the presence of additional age-classes, not apparent in conventional size-frequency distributions but expected to be present from earlier tag-recapture studies. Modal progression suggested a remarkably constant average lipofuscin accumulation rate of 0.31% by volume per year in the wild lobsters, which was supported by blind-trial measurements of lipofuscin in known-age laboratory-reared specimens. Lipofuscin-based age estimates, indicating that most juvenile lobsters are 3-5 years old immediately prior to recruitment to the fishery at 76 mm carapace length, agree with the long-established relationship between puerulus settlement and lobster catch 3-4 years later. Results indicate that the lipofuscin ageing technique will permit independent assessment of current population parameter estimates and be useful for determining sexual and regional differences in these for the western rock lobster.
Ecological relationship between freshwater sculpins (genus Cottus) and beach-spawning sockeye salmon (Oncorhynchus nerka) in Iliamna Lake, Alaska
Authors: Foote Chris J , Brown Gayle S
Published: April 2011

The interaction between two sculpin species, Cottus cognatus and Cottus aleuticus, and island beach spawning sockeye salmon (Oncorhynchus nerka) was examined in Iliamna Lake, Alaska. We conclude that sculpins actively move to specific spawning beaches and that the initiation of their movements precedes the start of spawning. Sculpin predation on sockeye eggs is positively dependent on sculpin size and on the state of the eggs (fresh versus water hardened), with the largest sculpins able to consume nearly 50 fresh eggs at a single feeding and 130 over a 7-day period. The number of sculpins in sockeye nests is greatest at the beginning of the spawning run, lowest in the middle, and high again at the end, with peak numbers of over 100 sculpins per nest (1 m2). We discuss the results in terms of energy flow of marine-derived nutrients into an oligotrophic system and in terms of the coevolution of sockeye spawning behavior and the predatory behavior of sculpins.
The ontogeny of piscivory and its ecological consequences
Authors: Mittelbach Gary G , Persson Lennart
Published: April 2011

In this study, we review the wealth of ecological information available for 27 species of freshwater piscivores from Europe and North America and examine the factors that determine variation in the diet ontogeny of piscivores and consider some of the ecological consequences of this variation. Focusing on interspecific variation, we found that species that were born larger and had larger mouth gapes became piscivorous at younger ages and at smaller sizes. However, there was no relationship between time of spawning (measured by average spawning temperature) and size at age 1 or size when becoming piscivorous. Species that became piscivorous at smaller sizes were also larger by age 1, and size differences expressed by piscivores in their first year of life tended to carry over to later ages. Not surprisingly, maximum and mean prey size eaten increased with predator size in all species. However, while piscivore species differed in morphologies and feeding efficiencies, prey sizes in the diets were remarkable similar for piscivores of similar body length. These data suggest that most of the variation found in the sizes of prey eaten by piscivores is due to differences in piscivore body size.
Otolith and fish size relationships, measurement error, and size-selective mortality during the early life of Atlantic salmon (Salmo salar)
Authors: Meekan M G , Dodson J J , Good S P , Ryan DAJ
Published: April 2011

The development of the relationship between otolith and body size in Atlantic salmon (Salmo salar) between hatching and emergence was examined by repeatedly measuring individually identified fish. Otolith growth increments were deposited daily in the period between hatching and emergence. Comparison of back-calculated otolith size and standard length using least squares regression analyses revealed a weak relationship between these variables at each of the 5-day sampling intervals. However, when data sets were pooled among intervals, variation in otolith size accounted for 98% of the variation in alevin length. A computer simulation demonstrated that levels of measurement error similar to those documented in our study resulted in the failure of regression analyses to detect strong relationships between otolith and fish size. Mortality that occurred during the experiment was strongly size selective. This truncated the size ranges of fish in cross-sectional data sets and thus reduced the ability of regression analysis to detect relationships between otolith and fish size. We propose that the weak relationship between otolith and fish size at emergence recorded in previous studies was an artifact of measurement error and the truncation of size ranges in regression analyses. Differences in alevin size at emergence were present at hatching and had been propagated by growth.
Predation by juvenile piscivorous bluefish (Pomatomus saltatrix): the influence of prey to predator size ratio and prey type on predator capture success and prey profitability
Authors: Scharf Frederick S , Buckel Jeffrey A , Juanes Francis , Conover David O
Published: April 2011

Capture success, handling time, prey vulnerability, and prey profitability were examined as a function of prey length/predator length ratio for age-0 juvenile bluefish (Pomatomus saltatrix) feeding on juvenile striped bass (Morone saxatilis) and Atlantic silverside (Menidia menidia). For each prey species, bluefish capture success declined linearly and handling time increased exponentially with increasing length ratios between 0.20 and 0.65. However, bluefish capture success was lower and handling times increased at a faster rate when feeding on juvenile striped bass compared with Atlantic silverside. Prey vulnerability, measured as bluefish predation rate, declined exponentially with increasing length ratios for each prey species. Profitability curves were dome shaped for each prey species; however, profitability values and the location of dome peaks differed between prey species. Capture success functions were combined with field length distributions to generate expected frequency distributions of length ratios included in bluefish diets. Comparisons resulted in good agreement between expected and observed sizes in bluefish diets, illustrating the importance of capture success in determining piscivore diets. Our results indicate that, for juvenile fishes, prey-specific morphological and behavioral differences can have significant effects on the outcome of predator-prey interactions and that size-based predation components are best represented as continuous functions of relative fish size.
Partitioning total size selectivity of gill nets for walleye (Stizostedion vitreum) into encounter, contact, and retention components
Authors: Anderson Charles S
Published: April 2011

Contact and retention components were estimated by indirect methods for walleye (Stizostedion vitreum) in Lake Erie, Dexter Lake (Ontario), and nine Minnesota lakes. In all 11 lakes, the retention function was well described by a unimodal function of fish size/mesh perimeter, and the addition of a contact component significantly improved model fit. A plausible range of models was identified for Lake Erie by considering the contact component to be constant or proportional to mesh size. Total catchabilities were estimated for two lakes by direct methods and encounter probabilities estimated by comparison of direct and indirect selectivities. Encounter probabilities estimated for Dexter Lake increased proportionately to fish length. Encounter probabilities estimated for Mille Lacs had a more complex form and were not well described by allometric power functions such as those sometimes used to describe swimming speed and encounter rates.
Impact of environmental perturbation on a tropical fish community
Authors: Piet G J
Published: April 2011

Tissawewa is a tropical reservoir in which annually recurring water level fluctuations are the main source of environmental variations. Aspects of a major perturbation studied related to (i) a progressive water level decrease that ultimately caused the reservoir to (ii) dry completely and a radical change of environment after refilling. The first aspect caused a decrease in the abundance of small pelagic fish but an increase in large bottom-dwellers. Main causes responsible for these changes are a decrease in the food available to the fish community resulting in weight loss and increased mortality of smaller bodied species. Also, the concentration of suspended silt and seston increased, probably damaging fish gills, thereby adversely affecting oxygen intake of the fish. Apparently, bottom-dwellers are better adapted to these conditions than pelagic species. The second aspect caused the composition of the food source to change, resulting in diet shifts and changes in relative abundance of some fish species (often compensated for by an inverse change of another species of the same feeding guild). In contrast with the annually recurring minor perturbations, the major perturbations caused the species composition and size structure of the fish community to change.
Do different predators affect distance, direction, and destination of movements by a stream mayfly?
Authors: McIntosh Angus R , Townsend Colin R
Published: April 2011

We observed the directions and distances travelled by Nesameletus ornatus mayfly nymphs in stream channels (current velocity 18 cm·s-1) with either Eldon's galaxias (Galaxias eldoni), brown trout (Salmo trutta), or no fish. Short (<20 cm) upstream movements were most common, but movements up to 90 cm in both directions were recorded. Predators had no significant impact on movement direction or distance compared with controls when all movements were considered. Only movements in direct response to galaxias were significantly longer and more likely to be in a downstream direction than movements not directly associated with galaxias. In most cases the frequency of downstream drift distances fitted a negative exponential model. Our results showed that when current and turbulence were low, N. ornatus could have considerable control over their movement.
Partitioning the influence of physical processes on the estimation of ichthyoplankton mortality rates. I. Theory
Authors: Helbig J A , Pepin P
Published: April 2011

This paper examines the effects of natural spatial-temporal variability in ichthyoplankton concentration and in currents on the estimation of mortality rates. We derive expressions for the biases and variances of mortality estimates computed from the change in plankton concentration between successive surveys as well as estimates of the corrections due to the advection of plankton. We demonstrate that estimate bias depends primarily on how well the mean current and mean ichthyoplankton fields are sampled whereas the variance depends on the variability about the mean in currents and plankton concentration and on the time and length scales on which this variability occurs. Simplified versions of the theoretical expressions provide an easily implemented framework for evaluating the quality of field sampling plans.
Hepatic mixed function oxygenase activity and vitellogenin induction in fish following a treatment of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM)
Authors: Hewitt L M , Munkittrick K R , Van Der Kraak G J , Scott I M , Schleen L P , Servos M R
Published: April 2011

Recent laboratory studies with nontarget fish species have shown that the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) exhibits estrogenic activity through binding to rainbow trout (Oncorhynchus mykiss) hepatic estrogen receptors and induction of vitellogenin in hepatocyte cultures. In addition, mixed function oxygenase (MFO) activity associated with exposure to field formulations has been attributed in part to the presence of chloro-nitro-trifluoromethyl-dibenzo-p-dioxin impurities. To investigate the environmental effects associated with these findings, the temporal and spatial patterns of MFO activity and vitellogenin induction were monitored in three nontarget fish species following a TFM field treatment. Elevated MFO activity was detected as early as 1 day in caged rainbow trout and activity in trout, wild white sucker (Catostomus commersoni), and longnose dace (Rhinichthys cataractae) peaked 2 or 3 days after treatment. Highest activities were observed in fish exposed closest to lampricide application points and declined with increasing distance downstream. After 18 days, MFO activity was reduced but remained almost sevenfold reference values at several sites. Plasma vitellogenin was not detected in caged trout sampled 6 and 18 days post-treatment, and dioxin impurities were not detected in sediments after treatment. It was concluded that laboratory testing underestimated the duration of MFO activity under field conditions and that an assessment of formulation exposure during sensitive life stages represents an area for further study.