bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Whole-Lake Base Addition on the Optical Properties of Three Clearwater Acidic Lakes
Authors: Bukaveckas Paul A. , Driscoll Charles T.
Published: April 2011

Data describing changes in the attenuation, absorption, and scattering of photosynthetically active radiation (PAR) were collected over a 5-yr period from three limed lakes and an untreated reference site. Light attenuation rose significantly after liming. Short-term changes in light attenuation were attributed to increased scattering by suspended calcite particles; such changes persisted for fewer than 15 d due to the rapid dissolution of the calcite. Long-term increases in light attenuation corresponded to increases in light absorption, which were attributed to higher concentrations of light-absorbing substances (gelbstoff) as indicated by higher lake dissolved organic carbon (DOC) concentrations. Changes in chlorophyll did not play an important role in regulating light attenuation except during the first summer following liming. Reacidification of one of the three limed lakes was accompanied by a decrease in lake DOC concentrations, followed by a gradual decrease in light attenuation and absorption. Within 3 yr after liming, the chemical and optical characteristics of this site were comparable with the pretreatment period. Results from lake liming experiments are consistent with the hypothesis that changes in the photochemical properties and/or the concentration of light-absorbing organic compounds are important mechanisms by which acidification alters the optical properties of lakes.
Habitat Selection by Stream-Dwelling Predatory Stoneflies
Authors: Peckarsky Barbara L.
Published: April 2011

Patterns of substrate size preference of predatory stoneflies were measured in a western Colorado, USA, stream and associations were examined between substrates and other physical and biological variables. Predatory Megarcys signata (Perlodidae) were found disproportionately on large stones that were not displaced during spring runoff. Predator densities were not consistently correlated with any other physical or biological variables measured. Prey densities were neither correlated with other physical variables nor with their own resource levels, with the exception that shredders were positively correlated with their relatively rare detrital resource. Interestingly, five prey taxa were autocorrelated, indicating that they recolonized, at similar densities, the same stones replaced in the same spots in the stream. Association analysis among the five most abundant taxa of mayfly grazers revealed that stones favorable for one grazer taxon were often favorable for others, but different grazer species rarely occupied distinctly different stones. Patterns observed suggest that predators are persistent enough to avoid negative associations with prey, yet prey taxa are mobile enough to avoid positive associations with predators. Further, habitat selection by predatory stoneflies may have evolved as a response to pressure from their own predators rather than as an adaptation for efficient prey acquisition.
Variation in Prevalence of Nanophyetus salmincola, a Parasite Tag Indicating U.S. Northwest Origin, in Steelhead Trout (Oncorhynchus mykiss) Caught in the Central North Pacific Ocean
Authors: Dalton Timothy J.
Published: April 2011

Infections with the parasite "tag" Nanophyetus salmincola indicated that in 1986 and 1987, steelhead trout (Oncorhynchus mykiss) from the U.S. Northwest (Washington to northern California, including Idaho) were relatively abundant in the central North Pacific Ocean as far west as 165°E, about 5000–5500 km from their area of origin. Infection prevalence (the frequency of the presence of infection) was estimated annually for specimens stratified by 5°-longitude areas. East–west and north–south trends in prevalence occurred in 1986 but not in 1987. Correlation analysis indicated no between-year correlation in the relative magnitude of prevalence in areas sampled in both 1986 and 1987 (r = 0.017). Confidence intervals (90%) for overall annual prevalence in the central North Pacific Ocean steelhead population were 29.9–61.3% (point estimate = 45.4%) for 1986 and 43.3–63.0% (point estimate = 53.2%) for 1987.
Variations in Year-Class Strength of Different Perch (Perca fluviatilis) Populations in the Baltic Sea with Special Reference to Temperature and Pollution
Authors: Böhling Paula , Hudd Richard , Lehtonen Hannu , Karås Peter , Neuman Erik , Thoresson Gunnar
Published: April 2011

Variations in the year-class strength of perch (Perca fluviatilis) were analyzed among 23 populations in Baltic coastal areas distributed between 57 and 66°N using the age distribution in catches. In spite of large differences in abiotic and biotic factors, the variations in year-class strength were similar in 14 of these areas. The similarities could be attributed to large-scale weather variations influencing water temperature. Year-class strength was shown to be correlated with an index based on temperature and day length during the whole first year of life. In two of the nine deviating populations, perch nursery areas are situated in small nearshore freshwaters, where fluctuations in the water level may be more important for recruitment than temperature variations. The other deviating areas were exposed to environmental disturbances, i.e. acidification, oxygen deficits, pulp mill effluents, and thermal discharge, which obviously affected recruitment in a decisive way.
Size-Dependent Ammonium and Phosphate Uptake, and N:P Supply Ratios in an Oligotrophic Lake
Authors: Suttle Curtis A. , Cochlan William P. , Stockner John G.
Published: April 2011

One arm of oligotrophic Sproat Lake was fertilized with weekly additions of inorganic phosphorus and nitrogen (N:P = 50: 1, by atoms). There was a lag of greater than 1 mo before changes in N:P supply ratio were reflected by "relative uptake rates" (RURs) of saturating ammonium and phosphate additions. This supports previous findings that RUR is a sensitive indicator of changes in N:P supply ratio, but suggests that changes in RUR are mediated by changes in composition rather than physiological state of the plankton community. The <3 μm fraction showed a greater demand for phosphate than ammonium compared with larger cells (>3 μm), as indicated by maximum uptake rates for the two nutrients. However, maximum phosphate uptake rates for both size fractions were greater as the result of fertilization. Nonetheless, RURs for both size fractions were consistent with Synechococcus being N limited and diatoms being P limited when the lake was not fertilized. Despite the large increase in nutrient loading, dissolved phosphate turnover times decreased from 10–12 to 5–7 min, indicating increased phosphate demand relative to supply. This study emphasizes that ammonimum and phosphate kinetics data yield valuable information on the nutritional conditions experienced by phytoplankton in lakes.
Calibration of a Gypsum Source for Freshwater Flow Measurements
Authors: Petticrew Ellen L. , Kalff Jacob
Published: April 2011

A method for estimating flow rate in freshwater was refined by calibrating the rate of dissolution of inexpensive and easily made gypsum cylinders at flows of 0–10 cm∙s−1 and at temperatures between 3 and 25 °C. Gypsum flux was linearly related to flow (r2 > 0.94); thus, weight loss combined with the surface area of the gypsum source and exposure period allows an estimate of flux. Temperature-corrected estimates of flow, obtained from calibration equations and observed dissolution of gypsum cylinders, were virtually identical to flow measured with an electromagnetic current meter in five of eight comparisons conducted in a lake and in three rivers; the three other comparisons were within 0.95 cm∙s−1. The calibrations are suitable for inexpensive and quantitative estimates of flow in freshwater within the range of temperature and flow conditions typically encountered. We suggest that the method can be used for comparing flow regimes in virtually any marine or freshwater environment as long as salinity and temperature among water bodies are comparable.
Classification of Fish Assemblages based on Echo Integration Surveys
Authors: Richards Laura J. , Kieser Robert , Mulligan Timothy J. , Candy John R.
Published: April 2011

Echo integration data typically collected during fish biomass surveys have additional utility in species recognition. Our analysis is based on a rockfish (family Scorpaenidae) hydroacoustic survey off the northwest coast of Vancouver Island, British Columbia, Canada. Survey data from 105 echogram sections were divided into two categories on the basis of ocean bottom habitat. One category corresponded to an area of bedrock outcrops and the other to the continental slope adjacent to the shelf break. Hydroacoustic characteristics of the bottom-oriented fish assemblages associated with these habitats could be described by time of day, mean volume density, dispersion, and mean off-bottom distance of the biomass. Nearest-neighbour analysis of these features classified assemblages into habitat categories with up to 97% success. Between-habitat differences in the assemblages were also evident from concurrent experimental fishing. Different rockfish species dominated the assemblages in the two areas. Our results suggest general methods for distinguishing among species groups in hydroacoustic survey data.
Effects of Suspended Sediment on Growth, Respiration, and Excretion of the Soft-Shell Clam (Mya arenaria)
Authors: Grant Jonathan , Thorpe Bruce
Published: April 2011

In long-term exposures for 35 d, soft-shell clams (Mya arenaria) were maintained in a flow-through suspension of intertidal sediment (100–200 mg∙L−1) and in a control treatment of ambient sand-filtered seawater, each with microalgae as a food source. Weekly measurements demonstrated a significant decrease in oxygen consumption and increase in ammonia excretion through time in the turbidity treatment compared with controls. Atomic O:N ratios fell to 14 for exposed clams and remained at 27 for controls, suggesting that exposed clams were utilizing body reserves to meet nutritional needs. Dry tissue weight showed no difference between initial and final values in the presence of suspended sediments, but control animals grew by 43%. In short-term exposures to 0–2000 mg suspended sediments∙L−1, oxygen consumption declined sharply with sediment concentration, suggesting that inhibition of respiration occurred at low values of turbidity. In further short-term observations, the threshold for the production of pseudofeces was 100–119 mg∙L−1. These results suggest that Mya arenaria copes with increased turbidity by reducing its ventilation rate, a response which provides tolerance to intermittent turbidity, but causes starvation during long-term exposure.
Influence of Photoperiod on the Number and Ultrastructure of Gill Chloride Cells of the Atlantic Salmon (Salmo salar) before and during Smoltification
Authors: Lubin Robert T. , Rourke A. W. , Saunders Richard L.
Published: April 2011

Atlantic salmon (Salmo salar) larger than 9 cm held under constant light since October had greater numbers of gill chloride cells in February compared with fish held under simulated natural photoperiod. By April, fish raised under simulated natural photoperiod were able to survive salinity tests, had a threefold increase in Na+/K+ATPase activity, and had increased chloride cell numbers. These increases and salinity tolerance did not occur in fish raised under constant light. Only fish reared under constant light developed apical pits with large and numerous microvilli.
Summertime Bottom Temperatures on the Southeast Shoal of the Grand Bank, and Implications for Exchange Rates
Authors: Loder John W.
Published: April 2011

From spring to fall, the Southeast Shoal usually has the warmest bottom water on the entire Grand Bank of Newfoundland. Historical hydrographic data indicate that the elevated lower-layer temperatures are derived from the seasonal surface heat input, through vertical exchange across the developing thermocline in combination with the shallow depths of the Shoal. However, in some months, the surface fluxes required by the monthly changes in depth-integrated heat content over the Shoal exceed climatological flux estimates computed using bulk formulae, suggesting that the climatological estimates may be low. The seasonal evolution of the lower-layer temperature provides information on the rates of vertical exchange across the thermocline and horizontal exchange in the lower layer. A seasonal variation in the vertical exchange coefficient, with an approximately inverse relation to the vertical density difference, and significant horizontal exchange in summer are suggested. The associated rates are quantified with a crude axisymmetric model for the lower layer's monthly heat budget.
Introductions as Factors in Diseases of Fish and Aquatic Invertebrates
Authors: Stewart James E.
Published: April 2011

Fish and invertebrates are subject to a wide range of disease agents. Many of their diseases are probably local in origin although a lengthy list of infections were probably imported via the vast array of exotic species which have been transferred to virtually all areas of the world. Since ail living organisms carry a full suite of microorganisms and larger parasites the likelihood of there being pathogens for local species among them is good. Introductions can occur in at least one of three separate ways: (1) intentional introductions for specific purposes, (2) accidental transport of biological agents via massive transfers of ballast waters or (3) through the ornamental or aquatic pet trade. Control measures and information services devised by the International Council for the Exploration of the Sea, the European Inland Fisheries Advisory Commission and the Office International des Epizooties are described.
Ecological and Genetic Effects of Fish Introductions: Synthesis and Recommendations
Authors: Allendorf Fred W.
Published: April 2011

The papers resulting from this symposium review the ecological and genetic effects of fish introductions throughout the world. Purposeful introductions rarely have achieved their objectives. Moreover, both intentional and unintentional introductions usually have been harmful to native fishes and other taxa through predation, competition, hybridization, and the introduction of diseases. We must learn from the past in order to avoid mistakes in the future. Introductions should not be used as a management tool without sufficient prior information and understanding to predict their effects. Introductions are often made or permitted because of the demands of certain interests groups (e.g., anglers or aquaculturists). Education of the public to the potential dangers and costs of such introductions is essential. Cooperation among management agencies is necessary to regulate and control both the purposeful and accidental introductions of fishes.
Differences in acquired and innate resistance among Pacific salmon (Oncorhynchus spp.) against the haemoflagellate Cryptobia salmositica and numbers delivered by the leech vector Piscicola salmositica
Authors: Bower S.M.
Published: April 2011

Susceptible juvenile chinook salmon (Oncorhynchus tshawytscha) were protected from otherwise lethal challenges with the haemoflagellate Cryptobia salmositica by acclimation to an elevated water temperature (20 °C). Following challenge at temperatures advantageous to the haemoflagellate (9–11 °C), surviving fish had plasma with enhanced acquired lytic activity against the parasite. In contrast, most coho salmon (Oncorhynchus kisutch) from a resistant stock survived up to three challenges with C. salmositica, without "immunization" at elevated temperatures. However, they acquired little or no lytic activity against the parasite, which survived in low numbers in some fish. Also, the chinook and coho salmon did not have innate plasma factors that lysed the parasite under in vitro conditions like those demonstrated in other salmonids. Thus, the mechanism(s) that protect the resistant O. kisutch from the pathogenic affects of C. salmositica are different from those identified in other fishes that are resistant to Cryptobia spp. A challenge of 105 flagellates per fish was suggested to be representative of the number of C. salmositica inoculated into a fish by one infected leech vector (Piscicola salmositica).
Proliferative kidney disease and Sphaerospora oncorhynchi in wild-caught salmonids from the Puntledge River system, Vancouver Island, British Columbia
Authors: Kent M.L. , Higgins M. , Whitaker D.J. , Yokoyama H.
Published: April 2011

Proliferative kidney disease (PKD), caused by the PKX myxosporean, was observed in kokanee salmon (non-anadromous sockeye salmon) (Oncorhynchus nerka) and chinook salmon (O. tshawytscha) collected from the Puntledge River, Vancouver Island, British Columbia in July 1993. This is the first report of a natural infection of PKX in either captive or wild sockeye salmon. All 14 underyearling kokanee salmon and the one underyearling chinook salmon exhibited numerous PKX organisms and associated chronic inflammation in the renal interstitium. Thirty-eight percent of sexually mature kokanee salmon collected in the autumn of 1993 from Comox Lake (which drains into the Puntledge River) were infected with Sphaerospora oncorhynchi, Kent, Whitaker and Margolis, 1993 in the renal tubules, while immature cutthroat trout (O. clarki) and coho salmon (O. kisutch) from the same collection did not exhibit myxosporean spores in the kidney. The kidneys of threespine stickleback (Gasterosteus aculeatus) and prickly sculpin (Cottus asper) collected from the Puntledge River during the summer were all infected with a Myxobilatus sp., but no organisms suggestive of PKX or Sphaerospora were observed. This study further supports the hypothesis that PKX is a developmental stage of S. oncorhynchi, which may sporulate only in sexually mature salmonids.
Origins of the Monogenea of selected major taxa of Nearctic freshwater fishes
Authors: Beverley-Burton Mary
Published: April 2011

Comment on the origin(s) of a group of parasites requires an awareness of the paleogeology of the region and historical records – phylogenies of both hosts and their parasites. The paleogeology of the Nearctic Region is described briefly and 11 families of Nearctic freshwater fishes for which phylogenetic information is available are considered: Acipenseridae, Polyodontidae, Catostomidae, Ictaluridae, Fundulidae, Poeciliidae, Cyprinodontidae, Percidae, Centrarchidae, Moronidae, and Percopsidae. A previous hypothesis that the Nearctic ancyrocephalids are of mixed origins is supported and the phenomena of vicariance, dispersal, host-switching, and co-evolution are demonstrated.
Geographical variations in abundance of larval anisakine nematodes in Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the Gulf of St. Lawrence
Authors: Boily France , Marcogliese David J.
Published: April 2011

Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) collected from various sites in the Gulf of St. Lawrence (NAFO divisions 4RST) were examined for larval anisakine nematodes in 1990 and 1992. Sealworm larvae (Pseudoterranova decipiens) were more abundant in southern Gulf (4T) than in northern Gulf (4RS) cod and plaice. The heaviest sealworm infections occurred in fish from St. Georges Bay, Nova Scotia. Abundance of P. decipiens in cod from St. Georges Bay was significantly lower in 1992 than in 1990. Anisakis simplex and Contracaecinea (Contracaecum/Phocascaris spp.) were most abundant in cod from the northern Gulf. American plaice were not heavily infected with A. simplex or Contracaecinea. Geographical and temporal variations in abundance of larval anisakine nematodes in fish may reflect distribution and abundance of the phocid and cetacean definitive hosts and variations in water temperatures.
Parasites as indicators of biological processes, with special reference to sockeye salmon (Oncorhynchus nerka)
Authors: Konovalov S.M.
Published: April 2011

This paper reviews the applicability of parasites as indicators in studying the biology of their hosts, using examples drawn primarily from the extensive research that has been conducted on the sockeye salmon (Oncorhynchus nerka) by scientists of the former Soviet Union and Canada. The data obtained by these researchers has contributed to our knowledge of the feeding and wintering migrations of populations, i.e., local stock complexes, of sockeye and other Pacific salmon. In some local stocks of sockeye salmon, millions of fish carry such biological tags as specific parasites and scale marks that facilitate the study of their seasonal migrations. Parasite indicators are also useful in distinguishing fish of various subpopulations and trophic groups within populations of freshwater species, while an analysis of the parasite fauna of juvenile fish may reveal those fish hosts that inhabited the river in the recent geological past but are now locally extinct. In regulating subpopulations of sockeye salmon, parasites are the effect rather than the cause of mortality. The above examples are evidence of the successful application of parasites for studying biological processes.
Parasites of capelin (Mallotus villosus) in the St. Lawrence estuary and gulf
Authors: Arthur J.R. , Albert E. , Boily F.
Published: April 2011

A survey of the parasites of capelin (Mallotus villosus) caught on the spawning grounds at five localities in the estuary of the St. Lawrence River and the Gulf of St. Lawrence, Canada, was conducted in 1994. From examination of 125 fish, a total of 21 parasite taxa was identified (2 Protista, 3 Monogenea, 4 Digenea, 4 Cestoda, 7 Nematoda, and 1 Acanthocephala). Seven new host records are reported for this fish (Trichodina sp., Brachyphallus crenatus, Bothrimonus sturionis, Ascarophis sp., Pseudoterranova decipiens larva, Spirurida gen.sp. larva, and Echinorhynchus laurentianus). The parasite fauna of capelin is comparatively depauperate. It is characterized by the relative abundance of a few species showing a high level of host specificity (Microsporidium sp., Trichodina sp., Gyrodactyloides andriaschewi, G. petruschewskii, Laminiscus gussevi, and Eubothrium parvum) that mature on or in capelin, several ubiquitous adult digeneans (e.g., B. crenatus, Derogenes various, Hemiurus levinseni, and Lecithaster gibbosus), and a number of species that use capelin as intermediate or transport hosts (e.g., Scolex pleuronectis plerocercoid, Anisakis simplex larva, Contracaecinea gen.sp. larva, and Hysterothylacium aduncum larva).
Competition, predation and environmental factors as structuring forces in freshwater fish communities: Sumari (1971) revisited
Authors: Persson L
Published: April 2011

A study by Sumari (O. Sumari. 1971. Ann. Zool. Fenn. 8: 406-421) of the fish communities in 32 Finnish lakes concluded that the main factors affecting perch (Perca fluviatilis) populations were biotic, of which the competitive interspecific effect of roach (Rutilus rutilus) was the main one analysed. A reanalysis of this data set suggests that abiotic factors such as conductivity and pH are also important in structuring fish communities. It is suggested that abiotic factors affect perch abundance mainly by their effects on other species' performance, particularly roach. The analyses of the whole data set and a subset of this data set consisting of nine lakes having perch only, or perch and piscivores only, also provided evidence that piscivores affect perch biomass. A positive relationship between piscivore biomass and roach biomass suggests that the piscivore-perch-roach interaction may have involved the presence of apparent competition between roach and perch.
The bioavailability of sediment-bound Cd, Co, and Ag to the mussel Mytilus edulis
Authors: Gagnon C , Fisher N S
Published: April 2011

Marine sediments, long thought to be a final repository of toxic contaminants in marine ecosystems, may also serve as a source of toxic contaminants for marine food chains. The influence of physical and chemical properties of oxidized sediments on the bioavailability of metals from sediments to marine filter-feeding invertebrates is largely unknown. We examined the relative importance of specific sedimentary components that may affect the uptake of Cd, Co, and Ag by the mussel Mytilus edulis. Iron and manganese oxides, montmorillonite clay, silica, and natural sediment particles were radiolabeled with 109Cd,57Co, and 110mAg; some particles were also coated with marine fulvic acids to simulate the influence of organic coating on metal bioavailability. Mussels were fed radiolabeled particles and then allowed to depurate by feeding on nonradioactive particles, following a pulse-chase protocol developed to determine assimilation efficiencies of ingested metals. Metals were absorbed by mussels from all sediment particles, but metals associated with organic-coated particles were generally absorbed to a greater extent than metals associated with uncoated particles; absorption efficiencies were as high as 34% (for Co from organic-coated silica particles). Desorption experiments with radiolabeled particles at pH 5 were performed in parallel to simulate the behavior of food-bound metals in the acidic gut of bivalves. High correlations (r > 0.97) between the amount of metal desorbed under these conditions and the assimilation efficiency for metal bound to particles were noted among organic-coated particles but not uncoated particles (r < 0.6). Differences between coated and uncoated particles were principally due to differences in gut transit times of the ingested particles. These results suggest that suspended sediment particles may be a source of metals for suspension-feeding animals, but the relationship between metal partitioning to sediments and biological availability is not obvious, because organic coatings and the acidic gut environment influence metal absorption in mussels.
Accumulation and elimination of cyanobacterial hepatotoxins by the freshwater clam Anodonta grandis simpsoniana
Authors: Prepas E E , Kotak B G , Campbell L M , Evans J C , Hrudey S E , Holmes C FB
Published: April 2011

Freshwater clams (Anodonta grandis simpsoniana) exposed to 51-55 µg · L-1 of dissolved microcystin-LR (MC-LR) in the laboratory for 3 days did not accumulate MC-LR equivalents (MC-LReq). However, clams placed in three eutrophic lakes with phytoplankton containing MC-LR (concentrations from below detection to 8.3 µg · L-1 cellular toxin) for 12-28 days accumulated the toxin (24 ± 7 to 527 ± 330 ng · g-1 MC-LReq; mean ± SE). The relative MC-LReq concentrations in clams reflected MC-LR concentrations in lake phytoplankton, but individual variation was high. In individual clams exposed for 24 days, the average MC-LReq concentration was usually greater in the visceral mass than in gills and muscle, but average toxin concentrations in the three tissues were similar (587, 310, and 364 ng · g dry weight-1). In clams removed from the lake and placed in toxin-free water, MC-LReq concentrations in tissues declined rapidly for 6 days (by 69-88%) but remained relatively stable for the remaining 15 days. Analysis of clam tissues appears to be a more sensitive MC-LR indicator than analysis of phytoplankton. Accumulation of potent cyanobacterial toxins by this clam warrants further study as many are consumed by muskrats (Ondatra zibethicus), which in turn are consumed by terrestrial predators.
Influence of trophic role and life-cycle duration on timing and magnitude of benthic macroinvertebrate response to whole-lake enrichment
Authors: Clarke K D , Knoechel R , Ryan P M
Published: April 2011

Phosphorus and nitrogen additions over a 3-year period (1991-1993) significantly increased the abundance of most benthic macroinvertebrate taxa collected on artificial substrates in a small oligotrophic lake in insular Newfoundland relative to a nearby control lake. The speed and magnitude of response was related to both the trophic role and the life-cycle duration of the taxa. This created a response continuum with small, fast-growing herbivores such as sphaeriid clams and gastropods demonstrating more pronounced and more rapid abundance responses than longer lived detritivores such as Ephemeroptera, which, in turn, had quicker responses than long-lived predators. These observations support the hypothesis that these benthic communities are controlled by bottom-up resource processes during the initial years of enrichment and provide the basis for expecting future enhancement of benthivorous salmonid populations in the fertilized lake.
Production of Fraser River sockeye salmon (Oncorhynchus nerka) in relation to decadal-scale changes in the climate and the ocean
Authors: Beamish R J , Neville C-E M , Cass A J
Published: April 2011

The abundance of Fraser River sockeye salmon (Oncorhynchus nerka) stocks was low in the 1960s, increased to high levels in the 1980s, and possibly entered a period of low abundance in recent years. The abundance changes of the combined stocks can be separated into productivity regimes that correspond to changes in climate trends. The most distinct change occurred when there was a major change in the climate over the Pacific Ocean in the winter of 1976-1977. The existence of natural shifts in abundance trends means that the high returns that occur during periods of high productivity would not be expected to occur during the low-productivity periods. The response of Fraser River sockeye to climate changes may be a specific example of a more general response by a number of species of fishes in the Pacific and perhaps in other oceans. Because the shift from one regime to the other occurred quickly in the 1970s, future shifts could also occur quickly. It is necessary to detect natural shifts in productivity when attempting to manage fishing impacts to ensure that economic expectations are sound and that overfishing does not occur.
Intraspecific genetic structure of white sucker (Catostomus commersoni) in northeastern North America as revealed by mitochondrial DNA polymorphism
Authors: Lafontaine P , Dodson J J
Published: April 2011

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to study the influence of Pleistocene glaciations on the intraspecific genetic structure and distribution of the white sucker (Catostomus commersoni) in northeastern North America. A total of 312 white sucker from 13 populations, including a population of dwarf ecotypes (Catostomus commersoni utawana), were analysed. An average of 93 fragments per individual and 40 haplotypes were generated by nine restriction endonucleases. Four discrete clades were identified but the majority of the genotypes found (70%) were not associated with any of the clades. The phylogenetic continuity and the geographic admixture of some of the few clades identified are associated with the extensive distribution of the species south of the ice sheets during Pleistocene glaciation events. Hierarchical analysis of the variability in mtDNA revealed a significant regional subdivision to the northwest and southeast of the St. Lawrence drainage system and significant structure at the population level. As the dwarf form exhibited a haplotype identical to that found among normal forms, we tentatively conclude sympatric divergence as the most likely origin of the dwarf and normal ecotypes sampled in the Adirondacks.
Solar ultraviolet radiation dependent decrease of particle light absorption and pigments in lake phytoplankton
Authors: Maske H , Latasa M
Published: April 2011

The ultraviolet (UV) spectral component of daylight on a clear day at mid-latitudes can significantly reduce phytoplankton pigments within a daylight period. Phytoplankton samples from Redberry Lake, Saskatchewan, dominated by cyanobacteria were incubated in quartz bottles under optical long band-pass filters (cutoff wavelength 420-305 nm) in daylight in June. After incubation, samples were filtered, and in vivo particle light absorption (380-700 nm) and pigment concentrations were measured. Solar ultraviolet-B irradiance (UV-B; 280-320 nm) was measured radiometrically. On sunny days the samples that were exposed to daylight UV light showed a relative decrease in particle absorption and pigment concentration after the incubation compared with samples exposed only to visible daylight. No such decrease was observed during an overcast day. The UV-B data did not show a clear relation with the degree of pigment reduction, suggesting that other environmental factors or the state of adaptation partially controlled the pigment decrease of phytoplankton under UV-B exposure. Neither specific spectral components of the absorption spectrum nor specific pigments were more easily degraded than others by solar UV light, although the ratio of zeaxanthin to chlorophyll a probably increased in cyanobacteria as a result of UV exposure.
Physiological responses of natural plankton communities to ultraviolet-B radiation in Redberry Lake (Saskatchewan, Canada)
Authors: Ferreyra G A , Demers S , del Giorgio P A , Chanut J -P
Published: April 2011

Damaging effects of ultraviolet radiation on the aquatic biota, related to anthropogenic modifications in the ozone layer, have been extensively described. However, most of the research has focused on marine environments, and information about the effects of ultraviolet radiation on saline prairie lakes of Canada is lacking. To test the deleterious effects of ultraviolet-B (UV-B) radiation on the planktonic community, two exposure experiments were performed in Redberry Lake, Saskatchewan. The responses of primary productivity, phytoplankton chlorophyll a and size, bacterial changes, and the electron transport system to natural UV-B fluxes reaching the surface of the lake were studied. No clear effects of UV-B on phytoplankton carbon assimilation and chlorophyll a were observed. However, significant responses were found for the two phytoplankton size fractions studied (0.7-2 and >2 µm), which were more related to the experimental conditions than to UV-B effects. Bacteria presented a clear decrease in cell number under the highest UV-B doses, whereas the opposite was observed for the electron transport system activity.
Effects of measurement error on catch-effort estimation
Authors: Gould W R , Stefanski L A , Pollock K H
Published: April 2011

We have investigated the consequences of using imprecise catch and effort estimates in closed-population catch-effort analyses using traditional regression techniques and maximum likelihood to estimate the catchability coefficient and population size parameters. Our simulation study involved adding known amounts of measurement error to error-free catch and effort data to determine the effects of using such estimates of catch and effort rather than the true, and in many cases unknown, quantities. Our results suggest that naive estimation using estimates of catch and effort as true values may bias estimates of population size and the catchability coefficient. In most cases, the effects of measurement error in catch and effort were to inflate the parameter estimates, the magnitude of inflation being dependent on the size of the measurement error variance. Maximum likelihood estimation proved to be the estimation procedure most robust to the errors in measurement, but still displayed the need for correction of the measurement-error-induced bias. A recently developed simulation-extrapolation method of inference (J.R. Cook and L.A. Stefanski. 1994. J. Am. Stat. Assoc. 89: 1314-1328) is suggested as a possible means for making bias adjustments.
Changes to the deepwater benthos of eastern Lake Erie since the invasion of Dreissena: 1979-1993
Authors: Dermott Ronald , Kerec Dave
Published: April 2011

The deepwater benthic community in Lake Erie was resampled in 1993, using the same sites and methods as used in a 1979 survey (before establishment of Dreissena bugensis). This exotic mussel was present at all 13 sites in 1993 (shells >2 mm long, averaged 3240 cdot m-2) and formed over 91% of the benthic biomass beyond 30 m depth. Total dry biomass (shell-free) increased from 1.58 g cdot m-2 in 1979 to 11.93 g cdot m-2 in 1993. The burrowing amphipod Diporeia hoyi declined from 38 to 1.8% of the total benthic biomass from 1979 to 1993, and its density declined from 1840 cdot m-2 in 1979 to 220 cdot m-2 in 1993. Diporeia hoyi was common at all sites in 1979, but absent at eight sites and common at only two sites in 1993. Likewise, reductions in native clams (Pisidium spp.) (from 330 to 80 cdot m-2) may be due to competition with mussels for freshly settling algae. No significant reduction was measured for oligochaetes or chironomids. Excluding Dreissena, the total macro- and meio-fauna increased from 20<|>100 to 48<|>400 organisms cdot m-2, but total biomass decreased from 1.58 to 0.98 g cdot m-2. The meiofauna (small nematodes, ostracods, and harpacticoids) increased in density, perhaps benefiting from the deposited pseudofeces of the mussels.
A model for estimating meal frequency and meal size from stomach data with an application to Atlantic cod (Gadus morhua) feeding on capelin (Mallotus villosus)
Authors: Magnússon K G , Aspelund T
Published: April 2011

The feeding of a predator on prey that occurs in schools is modelled as a stochastic process involving two random variables: (i) the number of schools that the predator finds per unit time and (ii) the number of prey items captured in each encounter. The number of encounters is governed by a Poisson process and the number of prey items can be either a Poisson random variable or more generally a negative binomial. The principal parameters in the model can be interpreted as the average meal frequency and the average meal size. This model is applied to Atlantic cod (Gadus morhua) feeding on capelin (Mallotus villosus). Cod stomachs from six length-groups were sampled off eastern Iceland and the number of capelin in individual stomachs recorded. The parameters in the stochastic feeding model are estimated by the method of maximum likelihood using the observed frequency distribution of capelin numbers in cod stomachs. The data fit the model well where the meal size is modelled by a negative binomial distribution, but less successfully where the meal size has a Poisson distribution. Finally, using the estimates of average meal frequency and average meal size the average and the standard deviation of consumption rate are calculated.
Reproductive timing and use of redd sites by lake-spawning brook trout (Salvelinus fontinalis)
Authors: Blanchfield P J , Ridgway M S
Published: April 2011

We provide a detailed description of a salmonine mating system based on daily observations of tagged individuals in a lake-spawning population of brook trout (Salvelinus fontinalis) throughout two breeding seasons. Actual spawning occurred over a period of ~50 d. Over 90% of spawning males were present soon after spawning commenced and outnumbered females for the duration of the spawning period. The amount of time males and females remained on the spawning grounds increased with body size; however, males were present over a longer period than females of equivalent size. A distinct seasonal peak in spawning activity (~15 d) accounted for 58 and 84% (1994 and 1995) of all reproduction and was coincident with a decline in water temperature below 11°C and increased rainfall. Selection of redd sites by female brook trout was determined by groundwater flow which was significantly greater than at nonspawning sites. A preference for certain redd sites was observed, with 50% of spawnings occurring at 11 sites. The construction of multiple redds and duration in spawning activity by females increased with body size. Extensive reuse of redd sites and rapid replacement of females during removal experiments indicate that redd sites are a limiting resource.
Origin of relation between K and Linf and synthesis of relations among life history parameters
Authors: Jensen A L
Published: April 2011

Four patterns occur in growth and mortality parameters across species of fish. Three of these relations, Mxm = 1.65, M = 1.50K, and L(xm) = 0.66Linf where M is natural mortality, xm is age at maturity, L(xm) is length at maturity, and Linf is asymptotic length, were previously shown to result from optimization of the age at maturity. In this study the fourth relation, that between asymptotic size and the growth coefficient, Linf = CK-h, was obtained from a bioenergetic growth equation. A numerical value of h = 0.33 was predicted, and this agrees with the observed value. The relation between the growth coefficient K and size Linf results from the limited amount of assimilated food that must be used both for growth and body functions, and the body functions are a function of body size. The four Beverton and Holt invariants, together with the net reproductive rate, relate many life history parameters to a metabolic parameter and mortality.
Larval parameters determining preschooling juvenile production of Pacific saury (Cololabis saira) in the northwestern Pacific
Authors: Watanabe Y , Oozeki Y , Kitagawa D
Published: April 2011

Production of larvae in the hatching size-class of Pacific saury (Cololabis saira) was highest in autumn 1990-1994, implying that spawning activity was highest in this season. Growth and mortality rates were stable in the winter-spawned cohorts in Kuroshio waters (south of Honshu); variable rates were found in the autumn- and spring-spawned cohorts in the mixed water region to the northeast. Although no particular period of high mortality was detected through the larval and juvenile stages, overall percent survival through the larval and juvenile stages differed by an order of magnitude among seasons. Production of 40-mm preschooling juveniles was determined by larval production in the smallest size-class in the winter cohort, but by overall percent survival through the larval and juvenile stages in the spring and autumn cohorts. Over the last 44 yr, percentage of winter-spawned cohorts in commercial catches was stable, compared with large interannual variations of autumn- and spring-spawned cohorts. These observations were assumed to stem from stable juvenile production in winter and variable production in autumn and spring, suggesting the possibility of recruitment forecasts of seasonally spawned cohorts of saury based on preschooling juvenile production estimates in the northwestern Pacific.
Sex-specific temperature distribution of American plaice (Hippoglossoides platessoides) and its relation to age and abundance
Authors: Swain D P
Published: April 2011

I examined variation in the temperature distribution of American plaice (Hippoglossoides platessoides) in the southern Gulf of St. Lawrence using data from bottom trawl surveys conducted each September since 1971. Plaice tended to select cold temperatures relative to those available. Temperature distribution was unrelated to age over the range 3-12+ years. Females tended to occupy warmer water than males, although the extent of this difference between the sexes varied among years. Annual variation in plaice temperature distribution was positively correlated with variation in the temperatures available. After accounting for annual variation in available temperatures, female temperature distribution was density independent but males tended to occupy colder water at higher levels of abundance. The median temperature occupied by both sexes tended to be warmer at higher levels of abundance of Atlantic cod (Gadus morhua), a competitor of plaice. The difference between the sexes in temperature distribution increased as cod abundance decreased or as plaice abundance increased (depending on the measure of temperature distribution used). The observed difference between the sexes in temperature distribution and its density dependence may reflect differences in foraging rate associated with differences between the sexes in the fitness benefits of growth.
Changes in the planktonic food web of a new experimental reservoir
Authors: Paterson M J , Findlay D , Beaty K , Findlay W , Schindler E U , Stainton M , McCullough G
Published: April 2011

Changes in plankton community structure were examined in an experimental reservoir (Lake 979) before and after impoundment. The role of allochthonous organic matter in planktonic food webs is unclear, and reservoir creation can be viewed as an extreme manipulation of terrestrial organic matter inputs. After impoundment of Lake 979, concentrations of phosphorus, nitrogen, and dissolved organic carbon increased as a result of decomposition of flooded terrestrial organic matter. In the first year of impoundment, mean bacterial biomass increased 10 times , and individual bacterial cell volumes increased 2 times over pre-flooding averages. Phytoplankton production and biomass decreased to approximately 25% of pre-flooding levels. Zooplankton biomass and production by Cladocera increased 10 times , and zooplankton community composition changed from dominance by small-sized Bosmina longirostris to dominance by large Daphnia rosea. In the first year of impoundment, production by Cladocera usually exceeded phytoplankton14C productivity, suggesting that the main pathway of carbon flow to secondary producers shifted from an autochthonous to an allochthonous base derived from flooded terrestrial vegetation. In the second year of flooding, bacterial biomass decreased and phytoplankton biomass was higher than in the two previous years of study.
Summer growth patterns of northern Dolly Varden (Salvelinus malma) smolts from the Prudhoe Bay region of Alaska
Authors: Fechhelm R G , Bryan J D , Griffiths W B , Martin L R
Published: April 2011

Summer length growth patterns of northern Dolly Varden (Salvelinus malma) smolts from the Sagavanirktok River, northern Alaska, were analyzed for the years 1985-1994 and found to be sigmoidal, indicating slow rates of growth in early and late summer with the most rapid growth occurring in midseason. Nonlinear logistic regression functions of mean cohort length against date provided a reasonable fit of the data for all years except for 1991, accounting for more than 94% (r2 values ranged from 0.95 to 0.99) of the variation in mean daily length in any given year. Slow growth in early summer is in direct contrast with the growth patterns reported for juvenile broad whitefish (Coregonus nasus) and Arctic cisco (C. autumnalis) which inhabit the Sagavanirktok River and estuary. Some possible explanations for the observed Dolly Varden growth patterns include migration, dispersal, prey availability, water quality, and stock mixing.
Carotenoid pigment profiles distinguish anadromous and nonanadromous brown trout (Salmo trutta)
Authors: Youngson A F , Mitchell A I , Noack P T , Laird L M
Published: April 2011

Carotenoid pigment profiles were determined in muscle tissue extracts of anadromous and nonanadromous brown trout (Salmo trutta). In nonanadromous fish, zeaxanthin, lutein, astaxanthin, canthaxanthin, and two unidentified pigments were detected in some or all individuals. In anadromous fish, only astaxanthin and lutein were detected. On the basis of carotenoid pigment profiles, it was possible to distinguish the anadromous and nonanadromous individuals examined in this study with complete accuracy.
A recruitment index and population model for spiny lobster (Panulirus argus) using catch and effort data
Authors: Medley Paul AH , Ninnes Christopher H
Published: April 2011

Using only catch numbers and effort data, we developed a recruitment index that exploits underlying seasonal changes in lobster size frequencies in the Turks and Caicos Islands' spiny lobster (Panulirus argus) fishery. The recruitment index was successfully used to model the lobster population dynamics. An empirical bootstrap method to simulate observation errors suggests that the models are robust enough to form the basis of a management plan. A tentative stock-recruitment relationship between estimates of the spawning stock and recruitment has been identified that can be used to guide escapement levels from the fishery. If correct, the stock-recruitment relationship indicates that the lobster population is largely self-recruiting.