bluuebunny/crossref_metadata_2025 huggingface dataset:
The number of moults in the egg of sealworm, Pseudoterranova decipiens (Nematoda: Ascaridoidea): an ultrastructural study
Authors: Measures Lena N. , Hong Henry
Published: April 2011

The number of moults in the egg of sealworm, Pseudoterranova decipiens (Nematoda: Ascaridoidea), and other ascaridoids is contentious. Transmission electron microscopic analysis of eggs and free-living larvae of sealworm confirmed that only one moult occurs in the egg. The first-stage larval (L1) cuticle on embryos was first observed in eggs incubated at 15 °C in sea water on day 5 after eggs were dissected from the uterus of sealworm obtained from the stomach of grey seals. There was no ecdysis of this L1 cuticle. A second cuticle began to form beneath the L1 cuticle between day 5 and 12. The second-stage larval (L2) cuticle continued to develop and on day 12 the L2 larva hatched enclosed within the cuticle of the first stage. The L1 cuticle appeared to be partially resorbed during development of the L2 cuticle. This study provides the first ultrastructural evidence of the number of moults that occur in eggs of sealworm.
Parasites as biological indicators of stocks of Atlantic cod (Gadus morhua) off Newfoundland, Canada
Authors: Khan R.A. , Tuck C.
Published: April 2011

Atlantic cod (Gadus morhua) were collected from six locations on the continental shelf off Newfoundland, Canada, including one inshore area and examined for parasites from 1981 to 1983. The protozoan Loma branchialis was more prevalent in North Atlantic Fisheries Organization (NAFO) areas 3Pn-4R (Gulf of St. Lawrence) and 2J-3K (Labrador), whereas the acanthocephalan Echinorhynchus gadi was more abundant in the latter than in other locations. Similarly, the prevalence and (or) abundance of the fillet-inhabiting larval nematode Pseudoterranova decipiens and the blood-feeding copepod Lernaeocera branchialis were significantly greater in fish from 3Ps (St. Pierre Bank) and 3Pn-4R than from all adjacent areas. Gastrointestinal ascaridoid nematodes were more abundant in 3M (Flemish Cap) cod than in other localities. No differences in the prevalence and abundance of E. gadi were detected in samples in relation to sex or size class. Paired comparisons of transformed data for the different parasite taxa revealed that there were more significant differences than similarities in cod sampled from adjacent NAFO divisions. These observations based on selected parasites (Loma branchialis, Trypanosoma murmanensis, Myxidium gadi, P. decipiens, gastrointestinal ascaridoid nematodes, E. gadi, and Lernaeocera branchialis) support the view that discrete stocks of cod inhabit the Newfoundland–Labrador continental shelf.
Influence of the transmission of parasites from prey fishes on the composition of the parasite community of a predatory fish
Authors: Valtonen E. Tellervo , Julkunen Markku
Published: April 2011

Helminth parasites and diet of seven freshwater fishes (Lota lota and six common prey species) from the Bothnian Bay, Baltic Sea, were studied monthly or bimonthly during 1978. Twenty-one of the 32 parasites with complex life cycles were shared between Lota lota and its prey fishes and are thus transmissible from prey to predator. Gymnocephalus cernuus and L. lota had the greatest number of shared species (13). Larval and adult cestodes, nematodes, and acanthocephalans could re-establish in the predator, but only one adult trematode was capable of this transition. Infracommunity species diversity was highest in L. lota (eH′ = 3.54), which also had the most species (24), the highest mean number of species and individuals of a given species per fish (6.3 and 62, respectively), and the greatest number of worms in one fish (520). Variety of diet was key in determining exposure to parasite species. However, most specificity finally determined if a given parasite could establish and mature. No ecologically explicable suites of parasites were found in any fish species, except in a few cases where parasites used related intermediate hosts. However, the composition of these suites was not retained in the predator. Unlike in L. lota, important parasites of prey fishes were typically specialists.
Mitochondrial DNA diversity, population structure, and conservation genetics of four native carps within the Yangtze River, China
Authors: Lu G , Li S , Bernatchez L
Published: April 2011

Silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon piceus), bighead carp (Aristichthys nobilis), and black carp(Mylopharyngodon piceus) rank first, second, fourth, and seventh in world fish production. In China, the Yangtze River harbours the most important natural populations of these species. We performed a polymerase chain reaction - restriction fragment length poymorphism analysis on 365 juvenile fish representing three nursery grounds to provide a first assessment of the mitochondrial DNA diversity in these species and test the hypothesis that they are composed of more than one genetic stock. The mitochondrial DNA diversity was high in silver, bighead, and black carp, and much less in grass carp. Analysis of heterogeneity of genotype frequency, fixation indices, intersite molecular variance, and localization indices indicated that juvenile silver, bighead, and black carp from different nursery areas belong to genetically distinct populations. These results suggest that their population structure may be determined by the number of environmental settings that permit closure of their life cycle. They also imply that carp from the Yangtze River cannot be managed as a single unit and that human disturbance through exploitation and habitat modifications, in particular the construction of the Three Gorges Dam, will have differential impacts on fish abundance for different parts of the river.
Scale analyses to estimate somatic growth in sockeye salmon, Oncorhynchus nerka
Authors: Fukuwaka M , Kaeriyama M
Published: April 2011

The relationships between individual growth and scale pattern were examined for juvenile sockeye salmon (Oncorhynchus nerka) marked with passive integrated transponder (PIT) tags to assess the usefulness of scale analyses for estimating somatic growth. The relationship between absolute somatic growth and increment of scale radius was linear. The relationship between increment of scale radius and number of circuli was also linear. Path analysis showed that the number of circuli was directly correlated with absolute growth. A negative path coefficient (-0.200) between absolute growth and number of circuli indicated that circulus spacing was positively correlated with somatic growth. The relationship between circulus spacing and absolute growth was linear (circulus spacing ( µm) = 0.528 times absolute growth (mm) - 9.57). Results indicate that somatic growth affects circulus spacing directly. Circulus spacing was useful for comparing mean growth from the above equation, while back-calculation was useful for estimating individual growth.
Analysis of harvest strategies for red king crab, Paralithodes camtschaticus, in Bristol Bay, Alaska
Authors: Zheng J , Murphy M C , Kruse G H
Published: April 2011

A modifiable harvest rate constrained by a minimum spawning abundance (threshold) is currently used to set the annual harvest level for Bristol Bay red king crab, Paralithodes camtschaticus. A length-based simulation model was constructed to evaluate effects of recruitment, natural mortality, and handling mortality on this harvest strategy. Evaluation criteria included mean yield, stability of yield, harvest opportunity, and stability of spawning stock. Optimal mature male harvest rates were strongly negatively related to handling mortality. For any given harvest rate, handling mortality is a key factor influencing optimal thresholds. The current harvest strategy produces a high mean yield and low variability in yield under low handling mortality scenarios, but the population is at high risk of collapse with a high handling mortality. Given uncertainties of recruitment, natural mortality, and handling mortality estimates, we recommend reducing mature male harvest rate from 20 to 15% and maximum legal male harvest rate cap from 60 to 50%. If handling mortality rate is greater than 30%, then we recommend increasing the threshold from 6600 to 11<|>000 metric tons of effective spawning biomass. Our recommended harvest strategy produces a mean yield similar to the current harvest strategy and safeguards against recruitment overfishing.
An examination of the PCB: lipid relationship among individual fish
Authors: Stow C A , Jackson L J , Amrhein J F
Published: April 2011

We examined data from 1984 to 1994 for five species of Lake Michigan salmonids to explore the relationship between total PCB concentration and percent lipid. When we compared mean species lipid and PCB values, we found a strong linear correlation. When we compared values among individuals, we found modest positive PCB:lipid associations in brown trout (Salmo trutta), chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), and rainbow trout (Oncorhynchus mykiss) collected during spawning, but positive associations were not apparent among nonspawning individuals. Lake trout (Salvelinus namaycush) exhibited no discernible PCB:lipid relationship. Our results are not incompatible with previous observations that contaminants are differentially partitioned into lipids within a fish, but these results do suggest that lipids are not a major factor influencing contaminant uptake.
Egg production rates of Calanus finmarchicus in the Northwest Atlantic (Labrador Sea)
Authors: Cabal J , Harris L R , Head EJH
Published: April 2011

Egg production rates and population characteristics of Calanus finmarchicus were examined in the Labrador Sea during the spring of 1994. Several experiments were conducted in order to compare egg production rates and clutch size using different types of container and in the presence and absence of food. In one series of experiments, individual females were incubated either in petri dishes or in polycarbonate bottles (80 mL) in filtered seawater. In these experiments, clutch sizes and egg production rates were not significantly different. In a second series of experiments, groups of 20 females were placed in containers under three sets of conditions: in the presence of food and with a screen to separate copepods from their eggs (FSCREEN), in the presence of food without a screen (FOOD), and in filtered seawater without a screen (FSW). Average egg production rates of female C. finmarchicus were significantly higher in the FSCREEN treatments than in either of the other two. In these experiments, egg production rates were not obviously related to ingestion rates, and these in vitro observations together with observations of in situ conditions suggest that stored reserves may have been used to fuel, or supplement, reproduction in C. finmarchicus in this area.
The relationship between prey selectivity and growth and survival in a larval fish
Authors: Mayer C M , Wahl D H
Published: April 2011

We examined prey preference, growth, and survival of small larval (8-10 mm total length (TL)), large larval (11-17 mm TL), and early juvenile (>18 mm TL) walleye (Stizostedion vitreum) in laboratory aquaria and field mesocosms using multiple prey assemblages that included cladoceran, copepod, and rotifer prey of varied sizes. Both prey taxa and size affected prey preference during the larval period. All sizes of walleye avoided rotifer and nauplii prey. Small and large larvae selected for intermediate-sized (0.4-0.9 mm) cladoceran prey and selected against large prey (>0.9 mm) of both taxa. Although neither capture efficiency nor handling time differed between prey taxa, larvae oriented more frequently towards cladoceran prey suggesting that they were more visible than copepods to these small fish. Larval walleye that were fed exclusively cladoceran prey survived better than fish that were fed other prey. Early juveniles selected primarily on the basis of prey size, choosing large copepods and cladocerans. Prey taxa did not affect early juvenile growth or survival. Prey taxa and prey size interacted with predator size to influence selectivity and its effect on growth and survival. Consequently, these factors must be considered in combination when examining the importance of foraging decisions in young fish.
Use of spectral analysis to estimate short-term periodicities in growth rates of brook troutSalvelinus frontinalis
Authors: Hosn W Aboul , Dutilleul P , Boisclair D
Published: April 2011

We used spectral analysis to investigate the periodic components of relative growth rates (on a mass and length basis) in two groups of six\b young-of-the-year brook trout (Salvelinus fontinalis). Fish were measured every 2 days for 25 days according to a repeated measures design in time. The predominant frequency components were estimated at the end of a stepwise procedure involving the analysis of the multifrequential periodogram. We found mainly two superimposed periodic components that resulted in short rhythms; these had a period of about 5 and 10 days for the growth rate in mass and of about 4 and 6 days for the growth rate in length (R2= 91% for mass and 90% for length, both including an autocorrelation term). Repeatability of rhythms was assessed by ANOVA of the finite Fourier transform, which showed that the two groups of fish reared under the same experimental conditions exhibited growth rhythms that were not significantly different from each other. On that basis, we present a harmonic model which predicts short-term variation in growth rate of brook trout in mass (R2pred= 0.73, with an autocorrelation term) and in length (R2pred= 0.72).
Periphyton assemblages as indicators of recovery in acidified Canadian Shield lakes
Authors: Vinebrooke R D , Graham M D
Published: April 2011

Periphyton is very responsive to abiotic changes within recovering acidified shield lakes. We conducted a survey of acidified shield lakes to assess epilithic periphyton assemblages as indicators of natural recovery. Canonical correspondence and regression analyses both showed that dissolved inorganic carbon (DIC) was the best predictor of taxonomic composition, biomass accrual, and species richness in lakes of low alkalinity. Dissolved organic carbon (DOC) was also a significant predictor of taxonomic composition, and biomass accrual (desmids, filamentous green algae, and total). Constrained indicator species analysis identified Actinotaenium cucurbita, Cylindrocystis brebissonii, Eunotia bactriana, Fragilaria acidobiontica, Homoeothrix juliana, Tetmemorus laevis, and Zygogonium ericetorum as indicators of high-acidity (pH <5.0), clearwater lakes with low (<0.3 mg/L) DIC concentrations. Achnanthes minutissima, Cymbella microcephala, and Gomphonema acuminatum were indicative of low-acidity (pH >5.6) lakes with higher DIC concentrations (>0.6 mg/L) and positive buffering capacities. Our findings suggest that periphyton in recovering acidified shield lakes are stimulated by increasing DIC and DOC concentrations. Increases in DIC availability might enhance recolonization by diatoms in clearwater lakes, while increases in DOC concentrations may favour desmids and filamentous zygnematacean taxa, especially in naturally acidic brown-water lakes.
Spatial and temporal variation in the diet of double-crested cormorants (Phalacrocorax auritus) breeding on the lower Great Lakes in the early 1990s
Authors: Neuman J , Pearl D L , Ewins P J , Black R , Weseloh D V , Pike M , Karwowski K
Published: April 2011

We sampled 1573 pellets and 560 boli regurgitated at double-crested cormorant (Phalacrocorax auritus) colonies on the three lower Laurentian Great Lakes (Lake Ontario, Lake Huron, and Lake Erie) during the breeding season in 1992 and 1994. This constitutes the first extensive study of cormorant diet in this region. We found significant spatial and temporal heterogeneity in diet among colonies within a lake. Differences in diet among colonies were usually consistent with knowledge of changes in fish behaviour during the cormorant breeding season, differences in the surrounding bathymetry among breeding colonies, and the proximity of colonies to the preferred habitat of prey species. Our results indicate that temporal and spatial variation, as well as the technique for diet determination, are very important factors that must be considered when assessing the effects of double-crested cormorant predation on fisheries.
Genetic relationships among subpopulations of the American lobster (Homarus americanus) as revealed by random amplified polymorphic DNA
Authors: Harding G C , Kenchington E L , Bird C J , Pezzack D S , Landry D C
Published: April 2011

Random amplified polymorphic DNA (RAPD) profiles were used in a preliminary investigation of the genetic relationships among American lobsters (Homarus americanus) from the ecologically disparate and geographically separate regions of the southern Gulf of St. Lawrence, a bay off southwestern Nova Scotia, and a deep-sea canyon off Georges Bank. Phenotypic analyses of the RAPD bands showed no significant difference between samples caught at these three geographic locations. Lobsters from the Gulf of Maine, collected inshore from Lobster Bay, Nova Scotia, and offshore from Georges Bank, were genetically the most similar (D = 0.002), whereas Gulf of St. Lawrence lobsters were about three times as genetically distant from these two subpopulations (D = 0.005-0.006). However, FSTvalues at each RAPD band ranged from <0.000 to 0.073, indicating that lobsters at these three locations are not genetically isolated. The number of migrants needed to account for this observed level of genetic differentiation could be as few as five animals in each generation. The present findings should not have been surprising given the enormous potential for larval dispersal, the wide ranging movements of adult lobsters within each region, and the level of anthropogenic interference through both displacement of larvae and adults over the past century in the name of conservation, particularly adults released into the Gulf of Maine.
Differences in sexual maturity and fall emigration between diploid and triploid brook trout (Salvelinus fontinalis) in an Adirondack lake
Authors: Warrillow J A , Josephson D C , Youngs W D , Krueger C C
Published: April 2011

High levels of emigration coincident with maturity and spawning have been reported from brook trout (Salvelinus fontinalis) populations in Adirondack lakes. These lakes typically had few spawning areas and required stocking to maintain populations. We compared diploid and triploid brook trout to identify differences in gonadal development and emigration. Age 1 + and 2 + diploid and triploid brook trout held in captivity were examined internally for gonadal development. More diploid trout were mature than triploid fish (p < 0.01). Of triploid brook trout that matured, all were males. Yearling diploid and triploid brook trout were also stocked into a lake that had an outlet but no spawning areas. During the fall spawning season, only mature yearling triploid males, diploid males, and diploid females were caught in an outlet trap. No triploid females were caught. A greater proportion of diploids emigrated than triploids (p < 0.01). Triploidy in females arrested emigration by preventing sexual maturation. Triploid male brook trout should not be stocked because they can pose a reproductive risk to wild brook trout downstream from lakes. Stocking triploid females could reducefall emigration and thus reduce the loss of catchable brook trout from Adirondack lakes with outlets and little spawning habitat.
Riverine salmonid egg burial depths: review of published data and implications for scour studies
Authors: DeVries P
Published: April 2011

Published data on salmon, trout, and charr egg burial depths are highly variable and inconsistent. Primary sources of variation include elevation datum and portion of the egg pocket referenced to; differences in spawning behavior and the number, thickness, and location of egg pockets; relationships between egg depth, fish species, and corresponding size of female and spawning substrate and velocity characteristics; sampling method; presence of excavation barriers; redd superimposition; and scour and fill by hydraulic and other mechanical processes. Such sources of variability in the reported data have important implications for studies of scouring processes in salmonid spawning areas that require accurate identification of egg burial depths for predicting and preventing potential scour impacts. Cumulative measurement error and unexplained variation may amount to 5-20 cm or more in published values. The most relevant data for scour impact assessments are depths from the original stream bed elevation down to the top of the main egg pocket. Frequency distribution data are needed for determining probabilities and cumulative levels of scour impacts and for managing genetic diversity as well as population size. Preliminary depth threshold criteria are proposed for use now, pending further research.
Factors controlling the timing of the spring bloom in the Strait of Georgia estuary, British Columbia, Canada
Authors: Yin K , Harrison P J , Goldblatt R H , St.John M A , Beamish R J
Published: April 2011

We present a conceptual model to illustrate how wind events and the annual migration and grazing of the dominant copepod Neocalanus plumchrus interact and affect the development of the spring bloom. The model was supported by observations made during 1988, 1992, and 1993. For example, in 1992, an El Niño year, the annual freshet of the Fraser River and probably the spring bloom started 1 month earlier. The bloom was interrupted by a wind event in late March. A few days later, its full recovery was interrupted by the peak in zooplankton grazing, and ambient ammonium concentrations increased. In contrast, in 1988, the annual freshet started later (mid-April), and winds remained strong throughout the same period, hindering the development of the spring bloom. The spring bloom was further suppressed by large numbers of zooplankton during April, resulting in a prolonged spring bloom. These observations indicate that interannual variations in winds and the timing of the annual freshet determine the timing and duration of the spring bloom, which in turn, determine the matching of phytoplankton to zooplankton in the Strait of Georgia. The matching or mismatching bears significant implications for food availability for juvenile fish.
Quantification of historic lake trout (Salvelinus namaycush) spawning aggregations in Lake Michigan
Authors: Dawson K A , Eshenroder R L , Holey M E , Ward C
Published: April 2011

We used commercial catch reports to determine site-specific characteristics of lake trout (Salvelinus namaycush) spawning aggregations in Michigan's and Wisconsin's waters of Lake Michigan before reproduction ceased in the 1950s. One hundred sites where annual catches exceeded 25 kg/year were identified. Two thirds of the catch was made in offshore waters and nearly half was made in the northeast sector of the lake. Catch was a better descriptor of the size of spawning aggregations than catch per unit effort (CPUE). CPUEs were not significantly different among onshore, offshore, and southern deepwater reefs. Spawning activity as measured by CPUE had peaked by the week beginning 29 October at all locations. Spawning aggregations were strongly clustered in the northeast section of the lake where Devonian rocks were subject to brecciation, i.e., fracturing and recementing following slumping. Areas zoned as refuges in the current lake trout rehabilitation plan account for 36% of the historical catch targeted at spawning aggregations. We recommend a refocusing of rehabilitation efforts in northern waters from sites where historical catches were modest to sites that produced the largest catches of lake trout aggregated for spawning.
Population-specific aggregations of steelhead trout (Oncorhynchus mykiss) in the North Pacific Ocean
Authors: McKinnell S , Pella J J , Dahlberg M L
Published: April 2011

The distribution of North American hatchery-origin steelhead (Oncorhynchus mykiss) in the North Pacific Ocean varied by age and hatchery location. Columbia River steelhead were more abundant south of the Aleutian Islands at an earlier age than steelhead from the Georgia Basin (Georgia Strait, Puget Sound, and waters connecting with the open Pacific). Between 1984 and 1989, there were eight independent and coincident recoveries of coded-wire-tagged steelhead, where individuals released from hatcheries as juveniles at similar times and locations were recovered together on the high seas up to 3 years later. A statistical test was developed to determine whether these coincident recoveries should be expected if individual steelhead within populations travelled in the North Pacific in an uncoordinated manner. The overall test suggested that some tagged steelhead populations travelled together in a significantly (P < 0.05) coordinated manner on the high seas.
A genetic test of metapopulation structure in Atlantic salmon (Salmo salar) using microsatellites
Authors: Fontaine P -M , Dodson J J , Bernatchez L , Slettan A
Published: April 2011

The principal objective of this study was to describe the pattern of genetic exchange and isolation of Atlantic salmon (Salmo salar) populations among geographical regions of the province of Quebec, Canada. Seven riverine populations, associated with three putative regional metapopulations (North Shore, Gaspé Peninsula, and Ungava), were analyzed using microsatellites. Our results did not support the putative metapopulation structure. Significant heterogeneity in allelic frequency was observed among most rivers independently of their location or group subdivision. Interpopulation genetic variance ( symbol fST) indicates less heterogeneity among rivers than chi2analysis and was mainly associated with the geographical distance of the most isolated rivers, the Natashquan and the Koksoak. Even with low genetic variance among populations, the overall significant allelic heterogeneity among rivers strongly suggests that each population, whether separated by thousands or tens of kilometres, should be considered and managed as a specific stock.
Intrastrain and interstrain variability in biotransformation enzyme activities of rainbow trout (Oncorhynchus mykiss)
Authors: Koponen Kari , Ritola Ossi , Huuskonen Sirpa , Linder Dan , Monostory Katalin , Lindström-Seppä Pirjo
Published: April 2011

We assessed the intrastrain and interstrain variability of cytochrome P450 enzyme activities and conjugation reactions of different rainbow trout (Oncorhynchus mykiss) strains. The study protocol was divided into two parts: in two separate experiments, monooxygenase (7-ethoxyresorufin O-deethylase, EROD) and conjugation (glutathione S-transferase, GST; UDP-glucuronosyl transferase, UDPGT) enzyme activities were measured from liver and kidney samples of commonly used rainbow trout breeds. In the preliminary study, the differences in the basal biotransformation enzyme activities were detected in two separately cultivated rainbow trout strains. Results indicated significant intrastrain (UDPGT, GST) and interstrain (EROD) differences in biotransformation enzyme activities. In the experimental study, corresponding enzyme activities were measured from three different rainbow trout strains exposed to beta -naphthoflavone (BNF), a polycyclic aromatic hydrocarbon (PAH) type model compound.The results revealed significant interstrain differences, especially in hepatic EROD and GST\b activities. However, UDPGT activities in the liver, as well as the measured monooxygenase and conjugation activities in the kidney, showed no notable variance between strains.The present work addresses intrastrain differences between hatcheries and highlights the need for intercalibration of rainbow trout strains used in experimental studies in aquatic toxicology.
Habitat, benthic prey, and distribution of juvenile lake sturgeon (Acipenser fulvescens) in northern Ontario rivers
Authors: Chiasson Wayne B , Noakes David LG , Beamish F William H.
Published: April 2011

The spatial and temporal distribution and relative abundance of juvenile lake sturgeon (Acipenser fulvescens) and benthic macroinvertebrates were examined in the Mattagami and Groundhog rivers, tributaries of the Moose River in northern Ontario, Canada. Relative density and diversity of the benthic fauna were low, the most common taxa being Ablabesmyia sp. (Diptera) and Hexagenia sp. (Ephemeroptera). Benthic organisms were most abundant in substrate dominated by sand and clay. An appreciable portion of the riverbed was strewn with wood chips and was particularly depauperate of macrobenthos. Lake sturgeon foraged exclusively on the benthos, especially taxa of Ephemeroptera, Diptera, and Trichoptera. Hexagenia was the only prey species in greater density in sturgeon stomachs than in the benthos. The largest concentration of juvenile lake sturgeon was found adjacent to substrate dominated by sand and clay. Gillnet catches of lake sturgeon suggest that they are more active at night, which may enhance their foraging success. In these northern rivers, the trophic status of juvenile lake sturgeon is marginalized by an impoverished food supply, in part the consequence of habitat loss resulting from anthropogenic activities.
Quantitative inferences of past hypolimnetic anoxia in south-central Ontario lakes using fossil midges (Diptera: Chironomidae)
Authors: Quinlan Roberto , Smol John P , Hall Roland I
Published: April 2011

The ability to infer long-term changes in hypolimnetic oxygen levels is important for ecological studies of eutrophication and the impacts of climatic change on freshwater lakes. We examined the distributions of fossil midge (Diptera: Chironomidae) assemblages in the surface sediments of 54 south-central Ontario lakes and, using canonical correspondence analysis (CCA), determined if fossil chironomid assemblages could be used to reconstruct levels of hypolimnetic anoxia in thermally stratifying Laurentian Shield lakes. Anoxia was expressed as the anoxic factor (AF), which represents the days per season that a sediment area equal to a lake's surface area is overlain by anoxic water. Forward selection in CCA showed that AF, maximum depth, [SO4], [Na], and watershed area all explained significant portions of species variation. A weighted-averaging regression and calibration model of the chironomid-anoxia relationship was developed which suggests that it is possible to infer AF from fossil chironomid assemblages ( (r2appar ) = 0.70, bootstrapped RMSE = 6.5 days/summer). Quantitative reconstruction of past changes in anoxia using fossil Chironomidae should provide a new and useful tool for paleoecological assessments of lake ecosystems.
Long-term retention and detection of oxytetracycline marks applied to hatchery-reared larval striped bass, Morone saxatilis
Authors: Reinert Thomas R , Wallin Julie , Griffin Mary C , Conroy Michael J , Van Den Avyle Michael J
Published: April 2011

Hatchery-reared larval striped bass, Morone saxatilis, destined for stocking in the Savannah River, Georgia, were immersed in oxytetracycline (OTC) to mark bony structures for later identification. Approximately 170 000 of these fish were raised to larger sizes and tagged with micromagnetic coded-wire tags (CWT). Recaptures of OTC-marked (OTC only) and marked and tagged (OTC and CWT) fish allowed us to determine retention of the OTC mark in otoliths to 3 years of age and to evaluate reader ability to detect those marks. The estimated retention rate was 80.2% for the first year, with no detectable change in additional years. Detection of OTC was age independent and estimated at 72.6% when one otolith was examined versus 92.5% when both otoliths were examined. Only 74.2% (retention x detection) of recaptures in this study would have been correctly identified as stocked fish if OTC alone was used as the marking method.
Fate of 60Co and 134Cs added to the hypolimnion of a Canadian Shield lake: accumulation in biota
Authors: Bird G A , Schwartz W J , Motycka M
Published: April 2011

The addition of 60Co and 134Cs to the anaerobic hypolimnion of a thermally stratified Canadian Shield lake in summer initially isolated the exposure of biota to only zooplankton that undergo vertical migration into this region of the lake. Once the radionuclides became mixed throughout the water column with autumn turnover, other biota were exposed to the radionuclides. In general, 60Co concentrations in biota were low because of the rapid loss to the sediments. Exceptions were for initial 60Co concentrations in filter-feeders (cladocerans and clams) during autumn turnover. Concentrations of 134Cs were higher in biota the following spring and summer, reflecting the tendency of 134Cs to remain in the water column. Concentrations of 134Cs still continued to increase in forage fish 1 year following the radionuclide addition. The addition of radionuclides to the hypolimnion resulted in higher concentrations in forage fish than when added to the epilimnion. Radionuclide concentrations in biota varied with taxon and were greatest in periphyton. This study demonstrates that radionuclides that may enter the bottom waters of a lake as a result of nuclear fuel waste disposal will be available to biota and result in a radiation dose to aquatic biota and to humans via the water-fish-human pathway.
Marine reserves: patterns of adult movement of the coral trout (Plectropomus leopardus (Serranidae))
Authors: Zeller Dirk C , Russ Garry R
Published: April 2011

Movements of Plectropomus leopardus (Serranidae), a major fisheries species, across marine reserve boundaries were investigated on the Great Barrier Reef, Australia. Mark-release-recapture and ultrasonic telemetry were used to assess movements. Mark-release-recapture used hook and line as the method of capture and underwater visual census (UVC) as the "recapture" tool. Catch rates were significantly higher in zones closed to fishing, despite UVC indicating no significant differences in density between closed and open zones. Of 183 fish marked with numerical freeze brands, 93 estimates of movements of branded fish were obtained. No branded fish was recorded to cross the reserve boundaries during the 2-month study, probably due to the initial decision to allocate capture effort evenly across the study area, rather than concentrating it on reserve boundaries. Fish carrying ultrasonic transmitters, and having home ranges straddling reserve boundaries, crossed boundaries on average 15.3 times ·month-1. The mean distance moved by freeze branded specimens between capture and recapture was significantly larger in areas closed to fishing than in those open to fishing. However, mean distance moved per day determined by ultrasonic telemetry did not differ between areas closed and open to fishing. This study suggests low flux rates of adult P. leopardus across marine reserve boundaries.
Brown trout (Salmo trutta) habitat use and life history in Swedish streams: possible effects of biotic interactions
Authors: Näslund Ingemar , Degerman Erik , Nordwall Fredrik
Published: April 2011

To test if habitat use and life history of stream-dwelling brown trout (Salmo trutta) differed between allopatric and sympatric situations, we compared three streams with differing fish communities and used data from a large national database containing electrofishing results from Swedish streams. In the three-creek study, allopatric brown trout used all habitats and shifted from nursery areas in riffles to pool habitats, where adult growth and survival were higher. Mainly females shifted habitat and this was undertaken after age 1. Sympatric brown trout under intense pressure from other fish species remained in the riffles throughout their life cycle. Under moderate pressure from other species, larger brown trout used slow-flowing habitats. Early growth was more rapid in sympatry. Sympatric brown trout also had a lower adult to juvenile growth ratio and lower adult survival and matured earlier than allopatric brown trout. The data from the nationwide database showed that frequency of occurrence and abundance of brown trout were negatively associated with the number of coexisting fish species. It was also verified that the habitat shifts between riffles and pools were more common and possibly more beneficial in terms of growth and survival in allopatry. In addition the existence of differences in juvenile growth between allopatric and sympatric populations was verified.
Influence of beaver ponds on the phosphorus concentration of stream water
Authors: Klotz R L
Published: April 2011

A study of five beaver ponds in central New York State showed that the ponds differed in how they influenced streamwater P concentration. Processes in three of the ponds increased soluble reactive P (SRP) of the stream water during warmer months, and also dramatically increased SRP in one of these ponds (Black Warrior) during an extended period of ice cover. The remaining two ponds were consistent in reducing SRP in stream water at all times of the year. Total soluble P trends essentially followed those of SRP at each of the ponds, while total P differed from SRP at four of the sites. Microbial respiration created anaerobic conditions within the pond sediments which influenced biogeochemical cycling of P. Anaerobic conditions and H2S production occurred at Black Warrior pond during the extended winter ice cover, resulting in SRP release. My results showed that elevated levels of P may occur for only short distances downstream of ponds before equilibrium processes reduce the concentration.
Anaerobic capacity and swim performance of juvenile salmonids
Authors: McDonald D G , McFarlane W J , Milligan C L
Published: April 2011

This study describes the development of procedures for the assessment of anaerobic capacity and swim performance in juvenile Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis). Three exercise tests, with exhaustion as an end point, were evaluated: a fixed-duration, high-intensity exercise; a fixed-velocity exercise; and an incremental-velocity exercise. Muscle (or whole body) lactate, phosphocreatine (PCr), and ATP were used to calculate, in ATP equivalents, the anaerobic energy expenditure (AEE, in µM ·g-1or µmoles) and to document the recovery from exhaustion. AEE was maximal in the first of these tests and submaximal in the second. Recovery was characterized by rapid restoration of PCr, slower recovery of ATP and lactate, and even slower recovery of glycogen. Mathematical expressions were developed to express the rates of recovery and thereby permit intra- and inter-species comparisons. Body size was the most important determinant of performance. Anaerobic capacity (AEE in the fixed duration test), sprint duration at fixed velocity, and maximum swimming speed scaled as length L4to L5, L4to L5, and L1.3, respectively. Each of these tests are effective measures for evaluating intra- and inter-specific differences in anaerobic capacity and swimming performance providing correction is made for the large scaling coefficients.
Effects of temperature and chronic hypoxia on survivorship of the zebra mussel (Dreissena polymorpha) and Asian clam (Corbicula fluminea)
Authors: Johnson Paul D , McMahon Robert F
Published: April 2011

We examined the effects of four levels of chronic hypoxic stress at three temperatures on the survivorship of Dreissena polymorpha and Corbicula fluminea to assess the efficacy of O2 deprivation as a macrofouling control treatment and examine if critical hypoxia limits support reported distribution patterns. At 25°C, the hypoxia tolerance was examined at Po2 = 7.9, 11.9, 15.9, 23.8, and 31.8 Torr (1 Torr = 133.322 Pa) or 5, 7.5, 10, 15, and 20% of full air O2 saturation (Po2 = 159 Torr). At 15°C, the hypoxia tolerance to 7.9, 11.9, and 15.9 Torr was tested and at 7.9 Torr for 5°C treatments. For both species, Po2 and temperature influenced survivorship dramatically with increasing survivorship at higher Po2 and decreasing temperatures. At 25°C, C. fluminea experienced mortality at 7.9, 11.9, and 15.9 Torr, with LT50 values of 144, 216, and 216 h, respectively, versus 288, 384, and 480 h for the 15°C exposures. Dreissena polymorpha treatments had LT50 values of 120, 216, and 216 h at 25°C for the 7.9-, 11.9-, and 15.9-Torr treatments versus 26% mortality after 600 h and 28% mortality after 720 h at 15°C. The 7.9-Torr treatments at 5°C had LT50 values of 480 h for C. fluminea and 1056 h for D. polymorpha. This study showed that both species displayed broad seasonal variation in hypoxia tolerance and that hypoxia limits may be used to assess infestation risk.
The impact of global positioning systems and plotters on fishing power in the northern prawn fishery, Australia
Authors: Robins Carolyn M , Wang You-Gan , Die David
Published: April 2011

The impact of global positioning systems (GPS) and plotter systems on the relative fishing power of the northern prawn fishery fleet on tiger prawns (Penaeus esculentus Haswell, 1879, and P. semisulcatus de Haan, 1850) was investigated from commercial catch data. A generalized linear model was used to account for differences in fishing power between boats and changes in prawn abundance. It was found that boats that used a GPS alone had 4% greater fishing power than boats without a GPS. The addition of a plotter raised the power by 7% over boats without the equipment. For each year between the first to third that a fisher has been working with plotters, there is an additional 2 or 3% increase. It appears that when all boats have a GPS and plotter for at least 3 years, the fishing power of the fleet will increase by 12%. Management controls have reduced the efficiency of each boat and lowered the number of days available to fish, but this may not have been sufficient to counteract the increases. Further limits will be needed to maintain the desired levels of mortality.
Simple dynamics underlie sockeye salmon (Oncorhynchus nerka) cycles
Authors: Myers Ransom A , Mertz Gordon , Bridson Jessica M , Bradford Michael J
Published: April 2011

A variety of mechanisms have been proposed to explain the renowned British Columbia sockeye salmon (Oncorhynchus nerka) cycles, most of which invoke between-brood interactions (delayed density dependence) or depensatory harvest practices. We examine the dynamics of the Ricker model with realistic parameter values and suggest that the cycles could result from a stable mode excited by stochastic forcing. The previously proposed mechanisms are not required to generate cyclic patterns, although they could play a role in reinforcing cycles. Our results suggest that relaxing harvest rates will increase yields and decrease variability in sockeye abundances.
Turnover of polychlorinated biphenyls in an oligotrophic and a eutrophic lake in relation to internal lake processes and atmospheric fallout
Authors: Larsson Per , Okla Lennart , Cronberg Gertrud
Published: April 2011

The atmospheric deposition of PCB within the catchment areas of an oligotrophic lake and a eutrophic lake in southern Sweden resulted in a flow of about 1 mg PCB ·m-2·year-1to the lakes. The sedimentation of the pollutants in the lakes (measured by sediment traps) was 110 and 52 mg PCB ·m-2·year-1for the oligotrophic and eutrophic lake, respectively. The concentration of pollutants in plankton (separated in fractions of >>150, 45-150, and 10-45 µm) was lower than that found in the sedimenting material. This indicated that the degradation of lipid and organic carbon was higher than the release of persistent pollutants from settling particles. Higher concentrations of PCB were recorded in the phytoplankton of the oligotrophic than of the eutrophic lake and attributed to higher lipid content. The higher lipid content and the higher pollutant amounts found in the primary producers suggest a mechanism that leads to zooplankton and fish displaying high pollutant concentrations in oligotrophic ecosystems. No biomagnification for phytoplankton to zooplankton was detected. The results indicate that the major part of the persistent pollutants cycling in the lakes is due to internal lake processes.
Predicting the identity and impact of future biological invaders: a priority for aquatic resource management
Authors: Ricciardi Anthony , Rasmussen Joseph B
Published: April 2011

The identification and risk assessment of potential biological invaders would provide valuable criteria for the allocation of resources toward the detection and control of invasion threats. Yet, freshwater biologists have made few attempts at predicting potential invaders, apparently because such efforts are perceived to be costly and futile. We describe some simple, low-cost empirical approaches that would facilitate prediction and demonstrate their use in identifying high-risk species from an important donor region: the Ponto-Caspian (Black, Caspian, and Azov seas) basin. This region is the source of several freshwater organisms already invading North America, including the zebra mussel (Dreissena polymorpha), quagga mussel (Dreissena bugensis), ruffe (Gymnocephalus cernuus), and round goby (Neogobius melanostomus). Based on a thorough literature review, we identify 17 additional Ponto-Caspian animals that have recent invasion histories and are likely to be transported overseas in ship ballast water; moreover, their broad salinity tolerance could allow them to survive an incomplete ballast-water exchange. These results suggest that, unless current vectors are more effectively controlled, the Great Lakes - St. Lawrence River system and other North American inland waterways will continue to receive and be impacted by invasive Eurasian species.
Partitioning the influence of physical processes on the estimation of ichthyoplankton mortality rates. II. Application to simulated and field data
Authors: Helbig J A , Pepin P
Published: April 2011

Helbig and Pepin (1998. Can. J. Fish. Aquat. Sci. 55: 2189-2205) developed a theory partitioning the bias and variance of a number of population and mortality measures in terms of the space and time scales of natural variability of the underlying current and plankton fields. This study verifies that theory through a series of numerical simulations and by comparing predicted variances in estimated fluxes with those observed in an earlier field study. In the simulations, errors in estimated mortality rates were clearly dominated by errors in estimated fluxes due to transport, and estimates of variance and bias were all in good agreement with theoretical predictions. For the field data, the theory predicted a distribution of values slightly lower than that observed, but of the correct order. That the model performed well for both simulated and field data suggests that it can be applied in practice with reasonable confidence. We also briefly explore the role of the model in survey design and analysis for ichthyoplankton studies in which transport might be important.
Sperm motility patterns of Atlantic cod (Gadus morhua) in relation to salinity: effects of ovarian fluid and egg presence
Authors: Litvak Matthew K , Trippel Edward A
Published: April 2011

A significantly greater proportion of Atlantic cod (Gadus morhua) sperm were motile in the presence of ovarian fluid and egg compared with seawater. Sperm mean and maximum swimming speeds were also significantly greater in the presence of ovarian fluid and egg compared with seawater. However, there was no significant difference in path linearity among treatments. We also examined the interaction between maternal stimuli (egg and ovarian fluid), time sperm spent in seawater prior to exposure to each stimulus, and salinity on proportion of motile sperm and their swimming behaviours. Proportion of motile sperm decreased significantly with a decrease in salinity in the presence of both maternal stimuli. Proportion of motile sperm also decreased with time spent in seawater prior to exposure to ovarian fluid but not to an egg. Both mean and maximum swimming speeds were maintained in the salinity range of 20-30 ppt and only declined significantly at lower salinities (15 and 17.5 ppt). Mean and maximum swimming speeds decreased with time spent in seawater. This study demonstrates the importance of maternal factors when examining sperm swimming behaviour and highlights the significance of maternal-paternal gametic interactions in understanding fertilization success.