bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of rearing conditions on growth and mortality of juvenile chum salmon (Oncorhynchus keta) infected with Ichthyobodo necator
Authors: Urawa Shigehiko
Published: April 2011

Chum salmon (Oncorhynchus keta) juveniles, experimentally infected with the bodonid flagellate Ichthyobodo necator (Henneguy, 1883), were reared in 18-L tanks at three densities (300, 600, and 1200 fish) for 5 weeks. Water inflow rates were adjusted to give five combinations of crowding and flow rate. The parasite density on the fish body surface increased to 2700–4100 parasites-mm−2 over the course of the experiment and did not differ significantly among the groups. Total mortality was 76–90% in infected groups kept under the most unfavorable conditions (crowding or low water supply) but 11–15% in the other infected groups. The former groups also showed apparent growth reductions. In the uninfected controls, mortality was low (0.7–2.6%) and the degree of crowding or water supply had no significant effect on growth or mortality. Infected salmon were also much less resistant to seawater challenge; all fish kept at high stocking density or low inflow rate died in seawater. These results indicate that Ichthyobodo infections have marked effects on both host growth and survival when infections are combined with environmental stress induced by overcrowding and (or) inadequate water supply, although the parasite density is not affected by these factors.
Allopodocotyle margolisi n.sp. (Digenea: Opecoelidae) from the deep-sea fish Coryphaenoides (Chalinura) mediterraneus in the northeastern Atlantic
Authors: Gibson David I.
Published: April 2011

An opecoelid digenean parasite, Allopodocotyle margolisi n.sp., is described from the macrourid fish Coryphaenoides (Chalinura) mediterraneus from benthopelagic waters of the North Rockall Trough, NE Atlantic Ocean. This is the first member of the genus to be recorded from deep-sea fishes. It is distinguished from its neritic congeners on the basis of features that include the arrangement of the testes, length of the cirrus-sac, and sucker-ratio. Its distinctness from other opecoelids from deep-sea fishes is also commented upon.
Philometra margolisi n.sp. (Nematoda: Philometridae) from the gonads of the red grouper, Epinephelus morio (Pisces: Serranidae), in Mexico
Authors: Moravec František , Vidal-Martínez Victor M. , Aguirre-Macedo Leopoldina
Published: April 2011

A new nematode species, Philometra margolisi n.sp., is described from the gonads of the serranid fish Epinephelus morio from Mexico (localities Telchac, Chuburna, Progreso, and Rio Lagartos, Yucatan). It is characterized mainly by long (0.432–0.468 mm) and slender spicules and a simple gubernaculum (length 0.084–0.093 mm) in the male and by body shape and size (length 65–85 mm), arrangement and number of small cephalic papillae (eight papillae in an outer circle and four in an inner one), structure and length (1.07–1.18 mm) of the esophagus, long ovaries, and the presence of a pair of small lateral papilla-like projections on the elongate caudal end in gravid females.
Responses of Lake Pyhäjärvi (southwestern Finland) to variable recruitment of the major planktivorous fish, vendace (Coregonus albula)
Authors: Helminen H , Sarvala J
Published: April 2011

We studied the functional relationships between water quality, phytoplankton, zooplankton, and planktivorous fish (vendace, Coregonus albula) in Lake Pyhäjärvi (southwestern Finland) in 1979-1992. The observed average values of water quality were typical of a mesoeutrophic system: total phosphorus (P) concentration, 16 mg · m-3; chlorophyll a, 5 mg · m-3; and Secchi depth, 3.3 m. The average total biomass of crustacean zooplankton in August was 62 mg carbon (C) · m-3, and large Daphnia spp. (>1.2 mm) were totally missing. The correlation between the late summer (August-September) chlorophyll a concentration and the total P concentration in the lake water was weak. The year-class strength of the vendace in autumn correlated significantly with late summer values of chlorophyll a. The August mean zooplankton biomass was negatively correlated both with the year-class strength of the vendace in autumn and with the August-September values of chlorophyll a, indicating the role of zooplankton as an intermediary in the trophic cascade of vendace feeding through the food web. We suggest that the reduced grazing pressure by zooplankton enabled the observed increase in phytoplankton biomass in years with a strong vendace stock.
Diel activity rhythm of seabass tracked in a natural environment: group effects on swimming patterns and amplitudes
Authors: Anras M-L Bégout , Lagardére J -P , Lafaye J -Y
Published: April 2011

Seabass swimming behavior was investigated in a salt-marsh area located along the Atlantic coast north of La Rochelle, France. Seabass is a natural inhabitant of this coastal zone and is farmed there as well. During its 3rd year, seabass can move about either singly or in small groups. Swimming activity of single fish and fish in a group was studied using an acoustic telemetry recording system. This study demonstrates that swimming activity levels and patterns of this species are modified by a group effect. Single fish were mainly nocturnal and fish in a group adopted a diurnal activity rhythm and lower maximum swimming activity levels.
Determinants of stream life, spawning efficiency, and spawning habitat in pink salmon in the Auke Lake system, Alaska
Authors: Fukushima M , Smoker W W
Published: April 2011

Variation in stream life, spawning efficiency, and spawning habitat among adult pink salmon (Oncorhynchus gorbuscha) in the Auke Lake system, southeastern Alaska, was best explained by stream discharge, stream temperature, and a combination of stream temperature and discharge. We estimated these attributes of female pink salmon spawners in samples of daily cohorts tagged as they entered fresh water and used generalized linear models to analyze variation in the attributes with respect to environmental factors. Spawners varied in stream life (5-11 days), spawning efficiency (30-70% of females in daily entry cohorts retained less than 500 eggs at death), and spawning habitat (30-70% spawned in the lake outlet stream rather than the lake inlet stream). Observed variation of habitat (proportionately more use of the cooler inlet stream early in the spawning season when stream temperatures are warm and development is rapid) would contribute to synchronicity of fry emigration, which is known to be positively correlated with subsequent survival in Auke Lake pink salmon.
Towards a new recruitment paradigm for fish stocks
Authors: Gilbert D J
Published: April 2011

The stock recruitment paradigm involves the hypothesis that recruitment (R) to a fish stock is positively related to the spawning stock biomass (SSB) of the stock, at low SSB. I propose a ``recruitment states'' hypothesis wherein R is independent of SSB but has different mean values during successive periods. Meta-analysis was used to test the null hypothesis that recruitment is a series of random, independent events, against these two alternative hypotheses, for 153 marine spawning bony fish stocks and 31 salmonid stocks. A test statistic for the stock recruitment paradigm, based on estimating derivatives from the first differences of the time series, was not significant for the marine stocks. The null hypothesis was rejected for the salmonid stocks. Recruitment states models significantly fitted time series for the marine stocks. Ricker models also significantly fitted these data, conflicting with the derivatives test result. However, because SSB is dependent on R, lagged by the age at maturity, a period in a low recruitment state would tend to lead to a period of low SSB. Therefore, the significance of the fit to the Ricker model may have been spurious. The recruitment states model best explained the meta-dataset for the marine stocks.
Characteristics and vertical distribution of Atlantic cod (Gadus morhua) eggs in the northern Gulf of St. Lawrence, and the possible effect of cold water temperature on recruitment
Authors: Ouellet P
Published: April 2011

In early May from 1993 to 1995 the water column in the northern Gulf of St. Lawrence was weakly stratified, with cold water (<2°C) extending from ca. 125 m to the surface. Cod (Gadus morhua) eggs were distributed throughout the water column, but higher densities were observed in the cold intermediate layer. The vertical distribution of cod eggs was determined by egg size and organic (lipids, proteins) composition. Stage I egg density estimates in May 1994 ranged from 25.0 to 26.0 kg · m-3, which is higher than the water density of the upper mixed layer. Between 1980 and 1989, there was a weak positive relationship between the cold intermediate layer temperature anomalies and cod year-class strength (i.e., abundance of 3-year-old cod). However, it is unlikely that low recruitment levels caused by below-average temperature of the cold intermediate layer alone had a major impact on the recent collapse of the northern Gulf stock. Nevertheless, the poor state of the spawning stock (low abundance, poor fish condition, and less buoyant eggs) and harsh late winter and early spring conditions in the northern Gulf can limit the potential for high recruitment and rapid recovery of the northern Gulf cod stock.
Shelter sharing and chemical courtship signals in the lobster, Homarus americanus
Authors: Bushmann P J , Atema J
Published: April 2011

In a 3.7-m Y-maze flume study of social odor-mediated behavior of mature lobsters (Homarus americanus), females preferred male- but not female-occupied shelters over empty shelters: they detected them from a distance and spent much time trying to enter. Males did not show distant detection and preference for female shelters but did spend much time trying to enter female but not male shelters once nearby. Sheltered resident males showed strong aggression toward visiting males but only mild aggression to visiting females; intermolt and premolt females could enter resident male shelters, cohabit for at least 7 h, receive mating attempts, and sometimes mate. Premolt females or females with sperm plugs resisted mating attempts. Visiting females released more than four times and males more than seven times as much urine during a shelter approach compared with an equal time in isolation. Females with or without urine release entered male-occupied shelters successfully, but mating attempts rarely occurred when female urine release was blocked. Female urine block resulted in greatly increased resident male aggression toward her, reaching the same levels elicited by visiting males with or without urine block. The results show that female urine signals reduce male aggression and facilitate mating.
Eutrophication, pollution and fragmentation: effects on parasite communities in roach (Rutilus rutilus) and perch (Perca fluviatilis) in four lakes in central Finland
Authors: Valtonen E T , Holmes J C , Koskivaara M
Published: April 2011

Parasite communities in four study lakes in 1986 reflected the influences of eutrophication, pollution, and habitat fragmentation. Discriminant analyses of communities at the individual host level revealed two major axes. One contrasted communities in a lake affected by chemical pollution from a pulp mill with those from two eutrophic, less polluted lakes. Changes in the density of intermediate hosts, direct effects on ectoparasites, and impaired immune systems were regarded as important mechanisms. The second contrasted communities in an oligotrophic, unpolluted lake with those from the two eutrophic lakes and was more complex, reflecting habitat fragmentation (the absence of glochidia and some digeneans) and pollution or eutrophication, probably mediated by the same mechanisms as above. Changes in some index parasites in Lake Vatia monitored in 1994, following 8 years of reduced pollutant loading, supported our conclusion that parasite faunas in Lake Vatia in 1986 involved the effects of pollution.
Effects of training on respiratory gas exchange, nitrogenous waste excretion, and fuel usage during aerobic swimming in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Lauff R F , Wood C M
Published: April 2011

Fuel utilization during aerobic exercise was determined in juvenile rainbow trout that had previously undergone 2 weeks of continuous aerobic training at 25% of their maximum sustainable speed (Ucrit) and was compared with that in untrained trout. Instantaneous fuel usage was calculated from simultaneous measurements of oxygen consumption ( MO2), carbon dioxide excretion ( MCO2), and nitrogenous waste excretion (MN). Over 58 h of sustained aerobic exercise at 55% of Ucrit, MO2and MCO2remained virtually constant in the trained fish, in contrast to the significant fall over time in untrained fish, but total gas exchange was similar in the two groups. Aerobic respiratory quotient remained constant in the two treatments. MNwas lower in the trained fish, resulting in a much lower (and stable) nitrogen quotient; the nitrogen quotient increased with swimming duration in the untrained fish. Lipid was the major fuel source powering aerobic exercise in both groups. Carbohydrate also played a significant role, whereas protein was of lowest quantitative importance. Training resulted in a decrease in reliance on protein and an increase in reliance on lipid metabolism. The role of protein oxidation in supporting aerobic swimming in fish, which is smaller than commonly believed, is further reduced by training.
Distribution and drift of Atlantic cod (Gadus morhua) eggs and larvae on the northeast Newfoundland Shelf
Authors: Pepin P , Helbig J A
Published: April 2011

We present the results of a study designed to ascertain the importance of variations in transport of cod eggs and larvae on the northeast Newfoundland Shelf. The distribution of cod eggs and larvae is described from a series of ichthyoplankton surveys. The mean and variance in surface currents were estimated from five experiments in which clusters of drogued satellite-tracked drifters were released at the presumed northern limit of the stock's range. These data were used to project the patterns of drift both backward and forward in time and thus the possible sources and destinations of eggs and larvae. Considering the development from the youngest (stage I) to the oldest stages (larvae), we saw a north-to-south and an offshore-to-inshore progression in spatial patterns of spawning and a continuing increase in the overall level of dispersion with increasing age of offspring. The data do not support the hypothesis that coastal or offshore areas represent simple sources or sinks of cod eggs and larvae. Transport plays an important but highly variable role that is coupled to the spawning distribution of adult fish and the availability of suitable conditions or habitats when the young begin to undergo metamorphosis and settle.
An evaluation of techniques for measuring periphyton metabolism in chambers
Authors: Bott T L , Brock J T , Baatrup-Pedersen A , Chambers P A , Dodds W K , Himbeault K T , Lawrence J R , Planas D , Snyder E , Wolfaardt G M
Published: April 2011

Experiments were performed to compare 14C uptake, dissolved O2 and CO2 change, and microelectrode techniques for measuring benthic primary productivity and community metabolism at a site on the South Saskatchewan River, Saskatchewan. The highest estimates of primary productivity were obtained with O2 microelectrodes (two to four times higher than simultaneous estimates from bulk-water dissolved O2 measurements), presumably because measurements are biased toward active communities under optimal conditions for photosynthesis. In daytime experiments lasting ~1.3 and 2.4 h, estimates from 14C uptake were higher than those measured simultaneously from dissolved O2 and CO2 change, suggesting that 14C uptake measured gross primary production (GPP) in these short-term incubations. Differences in experimental water velocity ranging from 0.2 to >6.5 cm · s-1 had less of an effect than chlorophyll a concentration on metabolic rates in diel experiments with rocks taken from a site where velocities were from 5.6 to 7.8 cm · s-1. There was a potential for phosphorus and possibly NH4 limitation of metabolic activity during long-term incubations. Results highlight areas in which further research is needed when using chambers to determine periphyton metabolism.
Role of hyperbenthic crustaceans in the transmission of marine helminth parasites
Authors: Jackson C J , Marcogliese D J , Burt M DB
Published: April 2011

Invertebrates (n = 34<|>813), collected from nine areas in the Northwest Atlantic, were either dissected or enzymatically digested to determine if the animals harboured helminth infections. Six species of endoparasites were found. Mysids were host to the larval nematodes Pseudoterranova decipiens (sealworm), Hysterothylacium aduncum, and Paracuaria adunca, which are found as adults in seals, fish, and birds, respectively, and to the digenean fish parasite Hemiurus levinseni (first record in mysids). Larval Paracuaria adunca and Tetrameres sp., both nematode parasites of birds, and Ascarophis sp., a parasite of fish, were found in amphipods. Some Ascarophis sp. and H. levinsenirecovered from the crustaceans exhibited precocious sexual development. Natural infection rates of helminths in invertebrates are low. Mysids appear to be more important hosts than amphipods for transmission of sealworm to fish.
Effects of fish length and temperature on the timing of peak spawning in capelin (Mallotus villosus)
Authors: Carscadden J , Nakashima B S , Frank K T
Published: April 2011

Some characteristics of Newfoundland capelin (Mallotus villosus) changed during 1991-1994. Peak spawning times were later than most years in the 1980s and fish were smaller. These changes occurred during a period of below-normal sea temperatures. We tested the effects of sea temperatures during maturation and mean size of mature fish on peak spawning times using regression analysis and found significant negative relationships for both independent variables. Results of a stepwise regression showed that fish length and sea temperature during maturation were equally important and together explained about 80% of the spawning time variation. We suggest that maturation and migration are closely linked to seasonal warming and the zooplankton cycle. Given the high spawning mortality of capelin, it seems that this linkage favours maximum gonad production rather than adult survival. Knowledge of spring water temperatures would permit some prediction of capelin spawning time. However, the data series for mean length used in this analysis is not useful for predicting spawning time.
Distribution and abundance of ringed (Phoca hispida) and bearded seals (Erignathus barbatus) in western Hudson Bay
Authors: Lunn N J , Stirling I , Nowicki S N
Published: April 2011

We flew a medium-altitude, systematic, strip-transect survey for ringed (Phoca hispida) and bearded seals (Erignathus barbatus) over western Hudson Bay in early June 1994 and 1995. The mean density (per square kilometre) of ringed seals hauled out on the ice was four times higher in 1995 (1.690) than in 1994 (0.380). The 1994 survey appeared to underestimate seal abundance because it was flown too late. Ringed seals preferred high ice cover habitat (6 + /8 ice) and, within this habitat, favoured cracking ice and large floes. We found no consistent effect of either wind or cloud cover on habitat preference. We estimated a total of 1980 bearded seals and 140<|>880 ringed seals hauled out on the sea ice in June 1995. A recent review of the relationship between ringed seal and polar bear (Ursus maritimus) populations suggests that a visible population of this size should support a population of up to 1300 polar bears, which is in general agreement with the current estimate of 1250-1300 bears in western Hudson Bay.
Effects of a fluctuation in Fraser River discharge of primary production in the central Strait of Georgia, British Columbia, Canada
Authors: Yin K , Harrison P J , Beamish R J
Published: April 2011

High-resolution vertical profiles of salinity, temperature, fluorescence, and nutrients (NO3 and SiO4) were taken along a transect in the central Strait of Georgia, British Columbia. The Fraser River discharge increased rapidly over 4 days and then decreased over the following 3 days (June 16-19, 1991). The thickness and extent of the estuarine plume increased as a response to the increased river discharge. As the estuarine plume flowed seaward, the nutricline (NO3) became shallower and broader, resulting in an increase in NO3 in the euphotic zone. Entrainment of NO3 may explain the increase in NO3 in the surface layer, and the amount of NO3 entrained was estimated to be 5-10 times higher than river-borne NO3. The utilization of entrained nutrients increased Chl a concentrations and primary production to levels comparable with spring bloom values. Our results clearly demonstrated for the first time that entrainment of nutrients and phytoplankton production in the central Strait of Georgia are closely coupled to fluctuations in the Fraser River discharge as the estuarine plume moves seaward. The timing and magnitude of the May-June freshet could control the entrainment of nutrients and thus maintain high primary productivity in late spring - early summer.
A functional classification of the drift: traits that influence invertebrate availability to salmonids
Authors: Rader Russell B
Published: April 2011

Twelve categories/traits were used to classify and rank aquatic invertebrates based on their propensity to drift and importance as a food resource for salmonids. Invertebrate availability was based on their (i) propensity to intentionally drift, (ii) likelihood of being accidentally dislodged by the current, (iii) drift distance, (iv) adult drift, (v) benthic exposure, (vi) body size, and (vii) abundance. This study represents the first attempt to characterize the intentional drift propensity of stream invertebrates. A ranking procedure separated invertebrates into Baetis and three groups decreasing in availability. Predicted ranks were significantly correlated with the actual rank of invertebrates in trout guts taken in three separate studies conducted in the central Rocky Mountains, suggesting that this procedure can effectively rank invertebrates based on their availability as a food resource for salmonids. A cluster analysis separated the 95 taxa into four drift guilds and six availability groups. This study provides criteria for determining when alterations in invertebrate community composition will affect food resources for higher trophic levels by causing a decline in the most available taxa. This research also supports previous findings that floods are important in maintaining invertebrates that represent an important food resource for salmonids.
Bioenergetics of life history strategies and the comparative allometry of reproduction
Authors: McCann Kevin , Shuter Brian
Published: April 2011

Winemiller and Rose (1992, Can. J. Fish. Aquat. Sci. 49: 2196-2218) showed that fish life history data lie on a two-dimensional triangular surface, embedded in the three-dimensional space established by the following biological attributes: (i) age at maturity, (ii) fecundity, and (iii) juvenile survivorship (as measured by the presence/absence of parental care). The vertices of this triangular surface define three endpoint strategies (equilibrium, opportunistic, and periodic) that Winemiller and Rose viewed as boundary strategies for all fish life histories. This paper extends these ideas by showing empirically that (i) the allometric relationship linking peak ovary weight to adult body weight differs across endpoint strategies, (ii) the allometric relationship linking age at 50% maturity to adult body weight is the same across endpoint strategies with the exception of the opportunistic strategy, and (iii) the allometric relationships characteristic of Winemiller-Rose endpoint strategies, plus that of a fourth strategy (composed of the genera Salmo and Onchorynchus), combine to form constraints that bound data on reproductive effort from a sample of species that represent a broad range of fish life history strategies. We offer some hypotheses as to why such constraints might exist.
Temperature, flow, and the migration of adult sockeye salmon (Oncorhynchus nerka) in the Columbia River
Authors: Quinn Thomas P , Hodgson Sayre , Peven Charles
Published: April 2011

We related the arrival timing of adult sockeye salmon (Oncorhynchus nerka) at a series of dams on the Columbia River (Bonneville, McNary, and Rock Island) and Snake River (Ice Harbor) to the changing flow and temperature regimes over the last several decades. The temperatures experienced by sockeye salmon have increased in the lower but not upper reaches of the system, and the flows experienced by the fish have decreased. The Bonneville-McNary travel rate increased from about 22 to 49 km/day, and sockeye salmon now pass McNary Dam about 11 days earlier than in 1954. Both travel rate and arrival date were correlated with temperature increases and flow decreases at McNary during that period. Sockeye salmon arrival at Rock Island Dam (14 days earlier from 1933 to 1994) was also correlated with temperature and flow there. However, the travel rate between McNary and Rock Island dams did not change from 1955 to 1994, despite a decrease in estimated water velocity from 85 to 23 km/day. Sockeye salmon arrival at Ice Harbor Dam has sometimes been bimodal; the first mode's date has not changed, but annual mean dates have been positively correlated with flow and negatively with temperature.
Differentiation of rainbow trout (Oncorhynchus mykiss) populations in Lake Ontario and the evaluation of the stepwise mutation and infinite allele mutation models using microsatellite variability
Authors: O'Connell Michael , Danzmann Roy G , Cornuet Jean-Marie , Wright Jonathan M , Ferguson Moira M
Published: April 2011

Microsatellites, comprising (GT)\dn6 n tandemly repeated arrays, were isolated from a size-selected genomic library of rainbow trout (Oncorhynchus mykiss) DNA. Primers were designed for five microsatellite loci, four of which were variable. Primers for two of these loci were used in conjunction with primers for three microsatellite loci from a related species, Salmo salar, to investigate patterns of differentiation in freshwater migratory populations of rainbow trout in Lake Ontario. The five loci used revealed high levels of polymorphism with heterozygosity estimates ranging from 0.740 to 0.956. Significant differences in allele frequencies among populations were observed for all loci. Heterozygosity and allele number values, at each locus for each population, were used to test two alternative mutation models, the infinite allele model (IAM) and the stepwise mutation model (SMM). The predictions of the IAM proved to be more accurate for the majority of the data and this model was used to calculate estimates of effective population size.
Nocturnal activity of juvenile Atlantic salmon (Salmo salar) in late summer: evidence of diel activity partitioning
Authors: Gries Gabe , Whalen Kevin G , Juanes Francis , Parrish Donna L
Published: April 2011

Paired day-night underwater counts of juvenile Atlantic salmon (Salmo salar) were completed on tributaries of the West River, Vermont, U.S.A., between 28 August and 10 September 1995. At water temperatures ranging from 13 to 23°C, the relative count of juvenile salmon was greater at night. Nocturnal counts differed for young-of-the-year and post-young-of-the-year (PYOY) salmon, with PYOY exhibiting almost exclusive nocturnal activity. Nocturnal activity in late summer may enable salmon to maintain population densities when space and suitable feeding areas may be limited. Nocturnal activity of juvenile salmon should be considered in studies of habitat use, competition, time budgets, and associated bioenergetic processes.
Effects of habitat complexity and prey abundance on the spatial and temporal distributions of perch (Perca fluviatilis) and pike (Esox lucius)
Authors: Eklöv P
Published: April 2011

Structurally complex environments strongly affect the behaviours and foraging efficiencies of predators and prey. I studied temporal variation in the habitat distribution of perch (Perca fluviatilis) and pike (Esox lucius) in relation to habitat complexity and prey abundance in a lake. The study involved quantitative estimates of different habitat types, estimates of macroinvertebrate prey availability, and distribution and movement patterns of the fish. The numbers of 80-110 mm perch in the littoral zone decreased rapidly in spring, which was a result of either perch moving to the pelagic zone or predation mortality. Predation mortality is the most plausible explanation because piscivorous perch and pike >160 mm aggregated close to these high abundances of 80-110 mm perch, and 80-110 mm perch used only vegetated habitats as a possible protection against predators. Both the biomass and diversity of macroinvertebrates increased with vegetation density, whereas perch abundance was highest in an intermediate vegetation density. Pike size was inversely related to vegetation density as a result of potential cannibalism from the largest pike individuals, which preferred the tree structure habitat. Perch group size decreased with increasing vegetation density, and perch <80 mm always occurred in group sizes larger than three individuals and never occurred in the same groups as perch >160 mm. In contrast, perch >160 mm occurred at decreasing numbers with increasing group size and mainly stayed solitary or in pairs. Perch >160 mm showed no tendencies for homing behaviour and moved actively around the whole lake, whereas pike showed a strong homing behaviour. My study suggests that the structural complexity in the littoral zone can both qualitatively and quantitatively change the interaction between piscivorous predators and their prey.
Genetic variation at microsatellite loci in sturgeon: primer sequence homology inAcipenserandScaphirhynchus
Authors: May B , Krueger C C , Kincaid H L
Published: April 2011

Eleven tri- and tetra-meric motif microsatellite loci were identified in a lake sturgeon genomic library and were tested against the six North American species of Acipenser (lake sturgeon, A. fulvescens; shortnose sturgeon, A. brevirostrum; white sturgeon, A. transmontanus; green sturgeon, A. medirostris; Atlantic sturgeon, A. oxyrhynchus oxyrhynchus; gulf sturgeon, A. o. desotoi) and the two species of Scaphirhynchus (pallid sturgeon, S. albus; shovelnose sturgeon, S. platorhynchus) using four to six individuals of each species. Eight loci were amplified equally well in all eight species, and the remaining three loci were amplified in two, four, and seven species, respectively. Of the eight loci that worked in all species, one was monomorphic in all species, while the other seven were polymorphic in three to eight species. Single repeat differences in these tri- and tetra-meric repeat motifs can be readily scored on 4% Metaphor agarose gels stained with ethidium bromide. In addition, dosage for those loci exhibiting four gene doses can also be readily scored with this technique. These loci provide a much needed group of genetic markers, detectable with non-invasive sampling (blood, barbel, or fin), that should work well in threatened and endangered species of sturgeon worldwide.
In situ evaluation of options for chemical treatment of hepatotoxic cyanobacterial blooms
Authors: Lam A K-Y , Prepas E E
Published: April 2011

Closed-bottom limnocorrals were placed in a hardwater lake in central Alberta to compare the effect of two alternative approaches to chemical removal of toxic phytoplankton blooms. Reglone A, which lyses phytoplankton cells, and lime-alum, which precipitates intact phytoplankton cells out of the water column were both effective in removing phytoplankton from the water column. Our results were consistent with laboratory studies in that treatment with Reglone A removed phytoplankton (primarily cyanobacteria) blooms with a concomitant increase in dissolved microcystin (exo-MCYST) and phosphorus concentrations in the surrounding water whereas lime-alum treatment did not. Maximum exo-MCYST concentrations in the water phase of the lime-alum treated limnocorrals were 32-fold lower than those recorded in the Reglone-treated limnocorrals. Treatment with lime alone caused a sharp rise in pH (to >10), and the observed increase in exo-MCYST was likely due to pH shock. Exo-MCYST concentration in the Reglone-treated enclosures remained high for the duration of the experiment (>5 days). As microcystin did not partition onto lake sediments in laboratory studies, our limnocorrals results were probably a good indication of microcystin dynamics in lakes. Thus, the use of chemicals such as lime-alum that precipitate out intact phytoplankton cells lessens the potential health risk where microcystins are present.
Bioenergetics of Arctic cod (Boreogadus saida) at low temperatures
Authors: Hop H , Tonn W M , Welch H E
Published: April 2011

The Arctic cod (Boreogadus saida), a key component of the marine food web of Canadian high Arctic waters, occurs at temperatures close to or below zero. We established a complete energy budget for this Arctic fish, based on laboratory measurements of consumption (C), growth (G), respiration (R), egestion (F), and excretion (U) at about 0°C. An average (N = 3) energy budget for individual juvenile Arctic cod fed live Arctic zooplankton was 100C = 50G + 24R + 9SDA + 3F + 6U + 8Z, where SDA is specific dynamic action (derived from previously published studies) and Z included activity and unaccounted energy. Eight determinations of total energy budgets for fish fed to satiation accounted for 72-104% of the energy consumed. Maximum daily rations and growth rates were dependent on fish size and the energy content of prey. Although maximum daily rations were similar for small fish fed different prey, diets of Calanus copepods (high energy content) resulted in faster growth rates than diets of Themisto amphipods or capelin (Mallotus villosus) fillets. Both consumption and respiration rates were low at temperatures close to 0°C. The net result was slow growth rates, although the assimilation efficiency was about 80%. Because of slow growth of individuals, the relatively high annual production of Arctic cod mainly reflects their large standing biomass.
Allometry of diet selectivity in juvenile Atlantic salmon (Salmo salar)
Authors: Keeley E R , Grant JWA
Published: April 2011

Juvenile salmonids in streams typically feed on larger invertebrates than the average size available in the drift. Our objective was to describe the allometry of this size-selective foraging in juvenile Atlantic salmon, Salmo salar of Catamaran Brook, New Brunswick. We compared paired samples of the stomach contents of 46 salmon (age 0 + to 2 + ; fork length 2.9-14.5 cm) with drift samples collected from their feeding territories. Juvenile salmon fed opportunistically on all major types of invertebrates in the drift, except for water mites (Hydracarina). However, newly emerged salmon fed on smaller prey than the average available in the drift, primarily chironomid larvae, whereas salmon larger than 4.6 cm fed on larger prey than average, primarily dipteran adults and pupae. Larger salmon ate larger prey. Minimum prey length in stomachs was well predicted by gill raker spacing, but mean prey width was only one third of the optimal size and maximum prey width was much less than mouth width. The allometry of prey size appeared to be related primarily to an increase in size-selective foraging with increasing body size, rather than to morphological constraints. Juvenile Atlantic salmon in our study ate smaller prey than similar-sized salmonids in other studies.
Gonadotropin-releasing hormone analogue (GnRH-A) induces multiple ovulations of high-quality eggs in a cold-water, batch-spawning teleost, the yellowtail flounder (Pleuronectes ferrugineus)
Authors: Larsson DGJ , Mylonas C C , Zohar Y , Crim L W
Published: April 2011

Sustained delivery systems for a gonadotropin-releasing hormone analogue (GnRH-A) were used for the first time in a cold-ocean teleost for inducing multiple ovulations. Intramuscular implants of 75-224 µg/kg GnRH-A ((D-Ala6,Pro9-NHEt)LHRH) were administered to female yellowtail flounder (Pleuronectes ferrugineus) either as a cholesterol pellet or as biodegradable microspheres. Females implanted with GnRH-A ovulated 3-4 weeks earlier than controls, producing multiple batches of high-quality eggs (average rates of fertilization 66-68% and hatching 55-60%); control fish eggs had significantly lower fertilization (39%) and hatching rates (25%). GnRH-A treatment doubled the egg production, synchronized the females, and shortened the interovulatory periods. The proportion of round, clear, and floating eggs lacking a perivitelline space before fertilization was an indicator of the fertilization (r2 = 0.60) and hatching (r2 = 0.56) success. Moreover, egg collections of less than 10 mL varied greatly in quality, whereas larger batches, generally promoted by GnRH-A, consisted of relatively high-quality eggs. GnRH-A treated fish had increased plasma levels of estradiol-17 beta 4 days after implantation. A model for prediction of the time between hormone treatment and first spawning (T; days) was developed using the initial follicle diameter (D; µm) as the only predictor (T = 365(D - 380)-0.82; r2 = 0.91).
Spatial and temporal distributions of smallmouth bass (Micropterus dolomieu) nests in Lake Opeongo, Ontario
Authors: Rejwan C , Shuter B J , Ridgway M S , Collins N C
Published: April 2011

Smallmouth bass (Micropterus dolomieu) nests were patchily distributed within the littoral zone of Lake Opeongo at two spatial scales (1 km and 100 m shoreline segments). Nest locations were recorded by snorkelling along 155 and 6.3 km of littoral zone over 4 and 11 years, respectively. The degree of patchiness was greater and occurred more consistently at the 1-km than at the 100-m spatial scale. However, the degree of patchiness was not significantly affected by 200% differences in spawning population size, implying that competitive interactions did not strongly influence nest locations over the study period. High-density nesting areas remained stationary between years at the 1-km and 100-m scales. This suggests that habitat variables having stationary spatial characteristics, influence nest site choice. Since the locations of nest patches are less stationary and less consistent among 100-m than among 1-km scale sites, influential habitat variables at the 100-m scale are either less important to the locations of nests or less stationary from year-to-year in their effects on nest distributions. If stationary nest patches are typical of spawning smallmouth bass in lakes, permanent protection of known patch locations could enhance their reproductive success.
Hybridization between Atlantic salmon (Salmo salar) and brown trout (S. trutta) in a restored section of the River Dälalven, Sweden
Authors: Jansson H , Öst T
Published: April 2011

Enzyme electrophoresis revealed a significant increase of Atlantic salmon (Salmo salar) times brown trout (S. trutta) hybrids among ascending spawners in the River Dalälven. The hybrid frequency increased from 0.1% in 1989 to 3.1% in 1995. Electrophoresis also showed a high hybrid frequency (41.5%) among parr from a river section restored for natural reproduction in 1989. Restriction fragment analysis of a species-specific region of the mitochondrial cytochrome b gene showed unidirectional hybridization as all hybrids had brown trout mitochondrial DNA genotypes. The increased incidence of hybrids was evidently a result of natural spawning in the restored river section. Massive stockings of hatchery-reared fish and environmental constraint have forced Atlantic salmon and brown trout to common spawning grounds leading to a high level of hybridization. The unidirectional hybridization may be explained by the involvement of sexually mature Atlantic salmon parr acting as sneakers.
Utility of escapement time series data for monitoring the response of salmon populations to habitat alteration
Authors: Korman J , Higgins P S
Published: April 2011

We provide a quantitative examination of the utility of escapement data for monitoring changes in salmonid populations caused by habitat alterations. We used Monte Carlo simulations to determine the precision, duration of monitoring, and the effect size required to achieve acceptable statistical inferences based on before-after (BA) and before-after-control-impact (BACI) comparisons. There was generally less than a 50% chance of detecting a population response unless the population change was large (more than a twofold increase) or the post-treatment monitoring period long (>10 years). Statistical power was improved by increasing the precision of escapement estimates, but the extent of improvement was dependent on the magnitude of population response to treatment, the duration of monitoring, and the extent of natural variability in abundance. BACI comparisons generally had a 10-15% lower probability of detecting a population change than BA comparisons unless the degree of covariation in survival rates between control and treatment stocks was very strong. Autocorrelation in error, simulating patterns of high and low survival rates over time, generally reduced power by 5-15%. Our results identify the conditions where escapement information can be used to make reliable inferences on salmonid population changes and provides a means for evaluating alternative monitoring designs.
Changes in population structure, growth, and biomass of cisco (Coregonus artedi) during hypolimnetic oxygenation of a deep, eutrophic lake, Amisk Lake, Alberta
Authors: Aku PMK , Tonn W M
Published: April 2011

Although most hypolimnetic oxygenation studies are designed to enhance cold-water fish populations, production-related responses have rarely been evaluated. We examined changes in density, biomass, and growth rate of cisco (Coregonus artedi) in Amisk Lake during 1989-1991, when one of the basins received hypolimnetic oxygenation, and in the nearby, untreated Baptiste Lake during 1990-1991. Variations in monthly density and biomass estimated using hydroacoustics suggested that as summer progressed, cisco in Amisk Lake responded behaviorally to hypolimnetic oxygenation by migrating from the hypoxic reference basin into the treated basin where oxygen concentrations remained high; by summer's end, the treated basin supported a density and biomass of fish that were twice as great as in the reference. Whole-lake fish density increased almost fivefold and biomass tripled in Amisk Lake during treatment, but there were no parallel changes in Baptiste Lake, where the hypolimnion remained anoxic each summer. Growth rate and condition of cisco in Amisk Lake decreased during treatment compared with pretreatment data, suggesting a density-dependent relationship with biomass; no coincident change in growth rate occurred in Baptiste Lake. These results suggest that hypolimnetic oxygenation can be an effective technique to enhance cold-water fish production, especially if combined with other management practices, such as regulated fish exploitation.
Vertical distribution of the chloromonad flagellate Heterosigma carterae in columns: implications for bloom development
Authors: Hershberger P K , Rensel J E , Matter A L , Taub F B
Published: April 2011

Blooms of the marine flagellate Heterosigma carterae have been associated with catastrophic fish kills at mariculture facilities around the world. The precise cause(s) of the sudden appearance and disappearance of Heterosigma surface blooms has not been completely described or understood. Environmental data from prior studies of blooms indicate the presence of vertical stratification of the water column that is often induced by freshwater runoff. We report the relatively rapid concentration of Heterosigma cells at the surface of tubes shortly after the addition of distilled water to the surface. This phenomenon of cell concentration in surface waters may partially explain the sudden appearance of Heterosigma cells near the surface and subsequent disappearance when vertical stratification is lost due to turbulence or mixing. The results may lead to bloom mitigation techniques for net pen aquaculture.
Reducing flows in the Nechako River (British Columbia, Canada): potential response of the macrophyte community
Authors: French T D , Chambers P A
Published: April 2011

Approximately 50% of the Nechako River's flow was permanently diverted into another watershed in the early 1950s. Up to 50% of the remaining flow may be diverted in the future. To give insight as to how future and past flow reductions will/have affect(ed) macrophyte abundance, we first developed equations relating average summer channel speed to cross-sectional biomass and bottom cover from data collected at 26 sites. The average summer channel speed at each site was then estimated assuming flows (at Fort Fraser) of 408 m3 ·s-1 (natural), 165 m3 ·s-1 (1952-1990 average), and two future scenarios: 120 and 60 m3 · s-1. We then used these estimates in our equations to compute abundance under the various flow regimes. Our models suggest that flow has little influence on macrophyte abundance in two fast-flowing reaches, which together account for 50% of the river's length. In contrast, the diversion was predicted to have increased biomass and cover by, on average, 66 g ·m-2 and 15%, respectively, in a slow-flowing reach accounting for 20% of the river's length. Biomass and cover in this reach could increase by an additional 65 g ·m-2 (or 240 g · m-2) and 9% (or 29%) if flows are reduced to 120 m3 ·s-1 (or 60 m3 · s-1).
The community dynamics of epiphytic midge larvae across the pelagic–littoral interface: do animals respond to changes in the abiotic environment?
Authors: Cardinale B J , Burton T M , Brady V J
Published: April 2011

In some littoral systems, abiotic heterogeneity results from the edge of vegetation towards the shore as macrophytes gradually impede mixing between pelagic and littoral water. During the summer of 1994, we investigated whether such abiotic heterogeneity influenced epiphytic midge larvae (Diptera:Chironomidae) inhabiting a stand of Scirpus americanus in Saginaw Bay, Lake Huron. After macrophytes became well established, gradients in six parameters of water quality (turbidity, alkalinity, pH, dissolved oxygen, conductivity, and chloride) formed horizontally from the macrophyte edge towards the shore. In outer portions of the stand where physico-chemical properties were influenced by the influx of pelagic surface waves, chironomid abundance increased to 1076 larvae · stem-1. Diversity (H prime ) in these areas remained constant over the summer with grazing and filter-feeding taxa equally represented. Further into the macrophyte bed where water quality indicated highly reduced mixing, midge abundance never exceeded 27 individuals · stem-1 and larval biomass was reduced 2-4 fold. Loss of filter-feeding taxa resulted in a dramatic decline in diversity in these areas after formation of the abiotic gradients. This study suggests that pelagic-littoral water exchange may result in environmental heterogeneity that directly or indirectly influences epiphytic invertebrate community structure and function.