bluuebunny/crossref_metadata_2025 huggingface dataset:
Ontogeny of energetic relationships and potential effects of tissue turnover: a comparative modeling study on lake trout
Authors: He Jixiang , Stewart Donald J
Published: April 2011

Tissue turnover is endogenous energy flow and may play a regulatory role in the metabolic system of an organism. We developed a general growth model addressing potential effect of tissue turnover on energy acquisition and partitioning. We applied the model to estimate energy assimilation of lake trout (Salvelinus namaycush) in Lake Michigan and compared the model with a commonly used complex model. Both models are expansions of the Pütter - von Bertalanffy growth model. The new model suggested a consistent decreasing trend in energy net conversion efficiency (NCE) for somatic growth versus body energy. The complex model suggested that NCE is relatively stable in early ages and decreases slowly in comparison with the pattern suggested by the new model. The new model estimated higher specific assimilation rate and NCE for gonadal growth than for somatic growth of mature fish. The complex model did not distinguish gonadal growth from somatic growth. For a lake trout growing from the start of age-1 to the end of age-10, our new model suggested a total energy assimilation 25% higher than the complex model. The above comparisons support the inference that tissue turnover is an important bioenergetic component. Inclusion of tissue turnover in bioenergetic modeling analyses may be critical for studying the linkages among individual growth, reproduction, and population dynamics.
Bioenergetics and nitrogen balance of the European eel (Anguilla anguilla) fed at high and low ration levels
Authors: Owen S F , Houlihan D F , Rennie M J , van Weerd J H
Published: April 2011

European eel (Anguilla anguilla) were fed either high or low ration levels (1.33 and 0.48% body weight·day1). Eight periods of continuous 24-h respirometry in flow-through conditions were conducted over 70 days to simultaneously examine nitrogen and energy budgets without resorting to the calculation of parameters by difference. Food and oxygen consumption; ammonia, urea, and nitrate-nitrite excretion; and growth production were measured. Nitrogen budgets successfully accounted for 89.6-101.2% of the consumed nitrogen. Energy budgets accounted for 53.4-92.3% of the consumed energy. From the ammonia quotients (AQ), 54.4-57.7% of the available protein was oxidized at high ration, and 59.7-133.5%, at low ration level. To satisfy maintenance requirements, 0.28 mg N·g-1·day-1 was required. At 25°C eels were calculated to have a rate of standard metabolism of 83.3 J·g1·day-1, which is comparable with the range published for other species at this temperature. These data suggest that eels do not have a particularly low metabolic rate, as is commonly assumed in the eel rearing industry, and that the relatively inactive lifestyle associated with the eel masks a metabolic rate in common with other, more active, fish.
Population viability of coho salmon, Oncorhynchus kisutch, in Oregon coastal basins: application of a habitat-based life cycle model
Authors: Nickelson Thomas E , Lawson Peter W
Published: April 2011

To assess extinction risk for Oregon coastal coho salmon, Oncorhynchus kisutch, we developed a life cycle model based on habitat quality of individual stream reaches estimated from survey data. Reach-specific smolt output was a function of spawner abundance, demographic stochasticity, genetic effects, and density- and habitat-driven survival rates. After natural mortality and ocean harvest, spawners returned to their natal reaches. Populations in reaches with poor habitat became extinct during periods of low marine survival. With favorable marine survival, high productivity reaches served as sources for recolonization of lower quality reaches through straying of spawners. Consequently, both population size and distribution expanded and contracted through time. Within a reach, populations lost resilience at low numbers when demographic risk factors became more important than density-dependent compensation. Population viability was modeled for three coastal basins having good, moderate, and poor habitat. With constant habitat conditions, extinction risk in 99 years was negligible in basins with good and moderate habitat and 5-10% in the basin with poor habitat. Reductions in habitat quality up to 60% in 99 years resulted in reduced coho salmon populations in all basins and significantly increased extinction risk in the basin with poor habitat.
Why restriction fragment length polymorphism analysis of mitochondrial DNA failed to resolve sardine (Sardinops) biogeography: insights from mitochondrial DNA cytochrome b sequences
Authors: Grant W Stewart , Clark A -M , Bowen Brian W
Published: April 2011

Restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis of mitochondrial DNA (mtDNA) have generated conflicting hypotheses on the phylogeography of Indian-Pacific clupeid Sardinops. An RFLP analysis of the control region and adjoining segments indicates a phylogenetic affiliation between southern Africa - Australian and Japanese sardines whereas comparisons of an overlapping segment of the control region sequence indicate an affiliation between southern Africa - Australian and Chile-Californian sardines. An analysis of 258 bp of mtDNA cytochrome b in 74 individuals of Sardinops from South Africa, Australia, Chile, California, and Japan revealed 24 haplotypes, resulting in high levels of haplotypic (h) diversity (average h = 0.70), low levels of nucleotide (pi) diversity (average pi = 0.005), and a satisfactory level of divergence (d) for population resolution (dmax = 4.02%). Cluster and parsimony analyses of haplotypic divergences confirmed the existence of three lineages corresponding to southern Africa - Australia, Chile-California, and Japan but failed to confirm a biogeographic connection between Australia and Japan. These results support the model based on control region sequences and highlight potential pitfalls of RFLP analyses of highly polymorphic DNA sequences with numerous homoplaseous transitions. A comparaison of 220 bp of cytochrome b in samples of Sardina and Sardinops produced an average sequence divergence of 23.2% and supports an ancient divergence between Sardina and Sardinops. The three lineages of Indian-Pacific Sardinops may merit subspecies recognition, based on low but significant levels of mtDNA divergence between them and on evidence of separations between these groups on the order of 200 000 - 500 000 years.
Effect of individual variability on estimation of population parameters from length-frequency data
Authors: Wang You-Gan , Ellis Nick
Published: April 2011

We consider estimation of mortality rates and growth parameters from length-frequency data of a fish stock when there is individual variability in the von Bertalanffy growth parameter Linfinity and investigate the possible bias in the estimates when the individual variability is ignored. Three methods are examined: (i) the regression method based on the Beverton and Holt's (1956, Rapp. P.V. Reun. Cons. Int. Explor. Mer, 140: 67-83) equation; (ii) the moment method of Powell (1979, Rapp. P.V. Reun. Int. Explor. Mer, 175: 167-169); and (iii) a generalization of Powell's method that estimates the individual variability to be incorporated into the estimation. It is found that the biases in the estimates from the existing methods are, in general, substantial, even when individual variability in growth is small and recruitment is uniform, and the generalized method performs better in terms of bias but is subject to a larger variation. There is a need to develop robust and flexible methods to deal with individual variability in the analysis of length-frequency data.
Evaluation of side-aspect target strength and pulse width as potential hydroacoustic discriminators of fish species in rivers
Authors: Burwen Deborah L , Fleischman Steven J
Published: April 2011

Split-beam hydroacoustic data were collected on 98 tethered and 10 unrestrained Pacific salmon of known size to evaluate side-aspect target strength and pulse width as species discriminators in rivers. Pulse width was better able to discriminate chinook (Oncorhynchus tshawytscha) from sockeye salmon (Oncorhynchus nerka) than target strength, although its discriminatory power may have arisen from differences in behavior as well as size between species. Standard deviation of -12 dB pulse width was the best univariate size predictor and species discriminator among tethered fish but performed poorly among unrestrained fish at close ranges; mean pulse width at -12 dB performed well among both. Discriminatory power of all variables declined as the number of echoes per fish was reduced. Fish orientation, lateral movement, and spatial position of the fish in the beam affected hydroacoustic measurements. As fish moved more from side to side, and as fish orientation departed from full side aspect, target strength declined monotonically but mean pulse width increased and then declined. We show how some of the confounding effects of fish behavior on hydroacoustic measurements can be removed using corrections based on statistical models.
Influence of changing food web structure on nutrient limitation of phytoplankton in a highly humic lake
Authors: Järvinen Marko , Salonen Kalevi
Published: April 2011

We determined the potential nutrient limitation of summer phytoplankton production using 2 × 2 × 2 factorial design of enrichment bioassays both before and after the introduction of planktivorous whitefish (Coregonus lavaretus) in a polyhumic lake with an abundant population of the large cladoceran Daphnia longispina. After the fish introduction, Daphnia disappeared and was substituted by the rotifer Keratella cochlearis. During the dominance of Daphnia, additions of nutrients had little or no effect on primary production of phytoplankton in short-term (1-day) incubations. However, 5-day incubations suggested that P most likely was the limiting nutrient. After the fish introduction, both 1- and 5-day enrichment bioassays indicated potential N limitation of phytoplankton production. The strong response of phytoplankton production to combined enrichments with P and N also suggested colimitation by P and N, but this was probably forced by the relatively high additions of nutrients. Consistently low primary production after the combined addition of P and glucose suggests that in the presence of a labile organic C source, epilimnetic bacteria were superior to algae in the uptake of P. Our results suggest that changes in the food web structure may determine the limiting nutrient also in a highly humic lake.
Rates of decrease of polychlorinated biphenyl concentrations in five species of Lake Michigan salmonids
Authors: Lamon III E Conrad , Carpenter S R , Stow C A
Published: April 2011

Dynamic linear models (DLM) were used to study time trends in annual average polychlorinated biphenyl (PCB) concentrations in five species of Lake Michigan salmonids using data collected from 1972 to 1994 by both the Michigan Department of Natural Resources and the Wisconsin Department of Natural Resources. DLMs use an adaptive fitting procedure to track changes over time in both the level (mean) of the series and the rate of increase or decline (growth rate), in contrast with other approaches that fit fixed parameters. We used DLMs to provide retrospective time series of estimates of rates of decline in PCB concentrations. Growth parameters indicate that PCB declines have slowed more than first-order models fit in the mid-1980s would predict. Growth parameters for brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) increased only slightly, indicating the most consistency with first-order dynamics. Coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha) showed a pattern of high rates of decline in the early to mid-1980s followed by a period of slower PCB concentration changes. The temporal pattern of rates of decline for lake trout (Salvelinus namaycush) stood apart from the other species, with a growth parameter that increased steadily during the entire period of record.
Linear model analysis of net catch data using the negative binomial distribution
Authors: Power James H , Moser E Barry
Published: April 2011

Sampling with nets or trawls remains a common technique for determining the comparative abundances of aquatic organisms, and the objective of such studies is frequently to evaluate relationships among the counts of individuals caught and exogenous variables. Analysis of such data is often done with a general linear model (e.g., ANOVA, ANCOVA, regression), assuming an underlying normal probability distribution. Such analyses are not fully satisfactory because of the symmetry and continuous nature of the assumed normal probability distribution and the high variance to low mean value relationships common to counts of biological populations. The negative binomial is a discrete probability distribution that is recognized as a suitable descriptor of organism count data. We present an approach for undertaking linear model analyses of net catch data that permits estimation of model parameters (including the negative binomial k parameter) and hypothesis testing of both continuous and discrete model effects and their interactions using bootstrap replication. The analysis incorporates adjustment for varying element sizes, such as differences in the amounts of water filtered during sampling.
Interannual variability and species turnover of crustacean zooplankton in Shield lakes
Authors: Arnott Shelley E , Yan Norman D , Magnuson John J , Frost Thomas M
Published: April 2011

We estimated apparent species turnover rates and richness of the zooplankton annually over a 12-year period in eight lakes in south-central Ontario. Although species richness varied little among years (CV = 13%), apparent species turnover rates averaged 16%/year. This apparent turnover varied among years and was influenced by census interval, the number of censuses, the occurrence of rare species, and lake pH. However, Monte Carlo simulations indicated that turnover attributable to sampling error was high. That is, despite high apparent turnover rates, we cannot be certain whether interannual changes in community composition result from immigration and extinction of species because sampling error could largely account for all apparent turnover. Regardless of the source of apparent turnover (sampling or immigrations and extinctions), high turnover rates imply that zooplankton biodiversity can be underestimated in short-term studies because we detect a different assemblage of species every year. Only one third of the total species pool for each lake was detected every year. Annual data underestimated long-term species pools by 33-50%.
Influences of grazing on temporal patterns of algal pigments in suspended and sedimenting algae in a north temperate lake
Authors: Poister David , Armstrong David E , Hurley James P
Published: April 2011

The concentrations of phytoplankton pigments in suspended and settling particles were measured in Trout Lake, Wisconsin, U.S.A., during the 1993 ice-free season. A decrease in water column concentrations of chlorophyll a coincident with an increase in pheophorbide and pheophytin concentrations occurred during a "clear-water" phase in June. The lack of a corresponding decrease in carotenoid pigment concentrations indicated that carotenoid pigments were degraded to a lesser extent than chlorophyll a during this period of heavy grazing pressure. Chlorophyll a, pheophorbide, and pheophytin showed temporal trends in fluxes to sediment traps that were similar for all pigments but did not correspond to trends in water column pigment concentration. Fucoxanthin concentrations and microscopic examination indicated that the sedimentation of large, dense diatoms increased the sedimentation rate of chlorophyll during the clear-water phase. In addition, ungrazed diatoms apparently were the main source of pheophorbide in trap material during the clear-water phase, indicating that pheophorbide should not be used as a surrogate for fecal pellet sedimentation in lakes influenced by the sedimentation of large diatoms.
Decadal changes in growth and recruitment of Pacific halibut (Hippoglossus stenolepis)
Authors: Clark William G , Hare Steven R , Parma Ana M , Sullivan Patrick J , Trumble Robert J
Published: April 2011

Since the climate regime shift of 1976-1977 in the North Pacific, the individual growth of Pacific halibut (Hippoglossus stenolepis) has decreased dramatically in Alaska but not in British Columbia. Recruitment has increased dramatically in both areas. The decrease in age-specific vulnerability to commercial longline gear resulted in a persistent underestimation of incoming recruitment by the age-structured assessment method (CAGEAN) that was used to assess the stock. This problem has been corrected by adding temporal trends in growth and fishery selectivity to the assessment model. The recent sustained high level of recruitment at high levels of spawning biomass has erased the previous appearance of strong density dependence in the stock-recruitment relationship and prompted a reduction in the target full-recruitment harvest rate from 30-35 to 20-25%. The climate regime shift affected a number of other stocks of vertebrates and invertebrates in the North Pacific. While the general oceanographic changes have now been identified, the specific biological mechanisms responsible for the observed changes have not.
Impact of wildfire and clear-cutting in the boreal forest on methyl mercury in zooplankton
Authors: Garcia Edenise , Carignan Richard
Published: April 2011

We compared the effects of forest logging and wildfire on methyl mercury (MeHg) concentrations in bulk zooplankton collected in 38 oligotrophic lakes located in the boreal forest. Mean MeHg concentrations were slightly but significantly higher (P < 0.01) in zooplankton collected in lakes with recently logged watersheds (135 ng·g dry weight-1) than in lakes with recently burned (97 ng·g dry weight-1) or undisturbed watersheds (112 ng·g dry weight-1). MeHg levels in zooplankton collected in burned and reference lakes were not significantly different. Multiple regression including all the lakes showed that four variables (dissolved organic carbon, pH, dissolved oxygen, and immature zooplankton biomass) explained 43% of the variability in MeHg levels in bulk zooplankton. Regressions calculated for each group of lakes explained less (reference lakes) or more of the variability in MeHg (logged and burned lakes) than the general model did. Dissolved organic carbon was the only variable common to all models, which indicates the importance of watershed processes in the transfer of humic matter bound Hg to lakes. However, variables related to methylation rate, such as pH, sulfate concentrations, and average dissolved oxygen in lake water, also explained part of the variation in MeHg concentrations in zooplankton.
Increase of heart rate without elevation of cardiac output in adult Atlantic salmon (Salmo salar) exposed to acidic water and aluminium
Authors: Brodeur Julie C , Ytrestøyl Trine , Finstad Bengt , McKinley R Scott
Published: April 2011

Adult Atlantic salmon (Salmo salar) were exposed for 48 h to water from acidified (pH 5.2) Fossbekk River (Norway), with and without 94 µg aluminium (Al)/L added as AlCl3, and to water from circumneutral (pH 6.7) Ims River (Norway) (controls). Cardiac output, heart rate, and stroke volume were monitored throughout the exposure period with Doppler flow probes placed around the ventral aorta of the fish. Fish exposed to Fossbekk River water without added Al showed few physiological disturbances. When 94 µg Al/L was added to Fossbekk River water, most of the fish died before the end of the 48-h exposure period, and a large elevation in heart rate was observed together with a decrease in plasma chloride concentrations and an increase in haematocrit, plasma glucose and plasma cortisol levels. Cardiac output was maintained at basal levels during the first 24 h of exposure because the tachycardia was accompanied by a concomitant reduction of stroke volume. Signs of arrhythmia appeared after 32 h of exposure and were associated with a further decrease in stroke volume that caused cardiac output to decrease below basal levels. The incapacity of the tachycardia to elevate cardiac output and the subsequent death of the fish suggest that this response to low pH and Al is more of a maladaptation reaction than a compensatory or adaptative reaction.
Light and diel vertical migration: spectral sensitivity and light avoidance by Mysis relicta
Authors: Gal Gideon , Loew Ellis R , Rudstam Lars G , Mohammadian Ali M
Published: April 2011

Ambient light levels determine the extent of diel vertical migration of many species including mysid shrimps. Light levels perceived by an organism depend on the intensity of light at the surface, the extinction of light through the water, and the sensitivity of the organism's light receptors. Each of these processes has spectral characteristics that should be taken into account when measuring perceived light levels. We used microspectrophotometry to determine that Mysis relicta has a single pigment with the characteristics of rhodopsin based on vitamin A1 and a peak sensitivity of 520 nm. Similar to the use of the lux (scaled to human vision), we give ambient light levels scaled to the mysid's visual spectrum in mylux units. Mysid distributions were observed with acoustics around two artificial light sources in Cayuga Lake, New York. Mysids avoided light levels of 3.4 × 10-7 to 2.1 × 10-6 mylux. Similar light levels limited their vertical distributions during the night in Lake Ontario and during the day in Cayuga Lake. Of standard light sensors available, lux meters are more appropriate than photosynthetically active radiation meters for determining light levels perceived by mysids.
Larval fishes of a Middle Atlantic Bight estuary: assemblage structure and temporal stability
Authors: Witting David A , Able Kenneth W , Fahay Michael P
Published: April 2011

We collected weekly, quantitative ichthyoplankton samples over 6 years (1989-1994, 1309 samples) to identify temporal scales of variability in the abundance and occurrence of larval fish assemblages near Little Egg Inlet in southern New Jersey, U.S.A. We collected species that spawn in the estuary (30%), both the estuary and continental shelf (35%), continental shelf (25%), and the Sargasso Sea (10%). The following analyses suggest an annually repeated seasonal progression of species assemblages: (i) the rank abundance of the 20 dominant species did not change significantly from year to year, (ii) variation in the density of the dominant species was primarily explained by intraannual rather than interannual variation, and (iii) multivariate analysis of the assemblage matrix identified five seasonal assemblages that occurred during all six years. We found that the timing and duration of each of these seasonal groups were correlated with two characteristics of the annual temperature cycle, magnitude (higher or lower temperature) and trajectory (increasing vs decreasing temperature). We suggest that the repeated occurrence of larval fish assemblages in temperate estuaries along the U.S. coast may, in part, be driven by local environmental processes.
Patterns of covariation in survival rates of British Columbian and Alaskan sockeye salmon (Oncorhynchus nerka) stocks
Authors: Peterman Randall M , Pyper Brian J , Lapointe Michael F , Adkison Milo D , Walters Carl J
Published: April 2011

We used a multi-stock comparison to identify spatial and temporal characteristics of environmentally driven sources of variability across four decades in the productivity of 29 sockeye salmon (Oncorhynchus nerka) stocks from British Columbia (B.C.) and Alaska. We examined patterns of covariation among indices of survival rate (residuals from the best-fit stock-recruitment curve) and found positive covariation among Fraser River sockeye stocks (southern B.C.) and, to a greater extent, among Bristol Bay stocks (western Alaska) but no evidence of covariation between these two regions or with stocks of other regions in B.C. and Alaska. This indicates that important environmental processes affecting variation in sockeye survival rate from spawners to recruits operate at regional spatial scales, rather than at the larger, ocean-basin scale. The observed covariation in survival rates of Bristol Bay stocks appears to be due to a combination of both freshwater and, to a greater degree, marine processes. Bristol Bay sockeye stocks showed a dramatic and persistent increase in survival rates coinciding with the abrupt changes in the North Pacific environment in the mid-1970s; however, there was little evidence of a similar response for Fraser River stocks.
Accumulation of Cd by a freshwater mussel (Pyganodon grandis) is reduced in the presence of Cu, Zn, Pb, and Ni
Authors: Stewart A R
Published: April 2011

The effects of a metal mixture on Cd bioavailability and uptake in the freshwater mussel Pyganodon grandis (formerly Anodonta grandis grandis) were investigated in a limnocorral experiment in a Precambrian Shield lake during the summer of 1992. Differences in the partitioning of Cd in water, sediment, and mussels were identified between limnocorrals treated with Cd alone or with Cd and a mixture of metals (Cu, Zn, Pb, and Ni) at three concentration levels. Loss of Cd from the water column was slower in treatments with the metal mixture (22- to 34-day half-life) than in the treatment with Cd alone (11-day half-life). Despite the higher concentrations of Cd in the water column in treatments with the mixture of metals, the mussels accumulated proportionally less Cd as the metal concentrations increased. These relationships were observed in mussels exposed for 40 days ([Cd] <4.4 µg·L-1) and 80 days ([Cd] = 4-14 µg·L-1). The uncoupling of the effects of the metal mixture on Cd bioavailability and uptake suggests that laboratory studies may be appropriate for characterizing metal uptake in mussels exposed to mixtures of metals under nonequilibrium conditions. The significant deviation in the behavior of Cd in the presence of the metal mixture emphasizes the need to further investigate regulatory approaches that focus on individual contaminants.
Influence of nitrogen to phosphorus supply ratios and physicochemical conditions on cyanobacteria and phytoplankton species composition in the Experimental Lakes Area, Canada
Authors: Levine S N , Schindler D W
Published: April 2011

To test the hypothesis that N:P supply ratios influence phytoplankton species composition, and particularly that cyanobacteria are favored by a low ratio, mesocosms at one pelagic and two littoral sites within the Experimental Lakes Area, Ontario, were fertilized for 10-12 weeks with similar amounts of P but different amounts of N. Total N:P supply (LN:LP) ratios (fertilizer plus natural inputs) ranged from 8:1 to 50:1. Nitrogen deficiency was detected in all mesocosms with LN:LP ratios <17:1, but N2-fixing Anabaena gained dominance only in the low-N:P pelagic mesocosms, and only in late summer. Cryptophytes and (or) chlorophytes dominated littoral mesocosms at all N:P ratios, while Pseudoanabaena catenata, a nonheterocystous cyanobacterium, was the late-summer dominant in pelagic mesocosms with LN:LP ratios >17:1. Canonical correlation analysis related cyanobacterial dominance to high P and low CO2 availability. Low light intensities and low N:P ratios also favored heterocystous (but not nonheterocystous) cyanobacteria. Total phytoplankton biomass and productivity increased with LN:LP ratio, while periphyton growth was maximal at low N:P ratios. Nitrogen limitation of phytoplankton may encourage blooms of N2 fixers or drive productivity down to the sediment surface where N is more available.
Accumulation and recycling of PCBs and PAHs in artificially eutrophied Lake 227
Authors: Jeremiason Jeff D , Eisenreich Steven J , Paterson Michael J
Published: April 2011

The influence of lake trophic status on the cycling and burial of polychlorinated biphenyls (PCB's) and polycyclic aromatic hydrocarbons (PAH's) was examined in Lake 227 (L227), an artificially eutrophied lake in the Experimental Lakes Area, northwestern Ontario, Canada. Sedimentary accumulation of PCB's, PAH's, and organic carbon (OC) was determined pre- and post-eutrophication in L227 and compared with accumulation in other regional lakes. Mass and OC accumulation increased an average of 1.4 and 2.0 times, respectively, since nutrient addition began in June 1969. ΣPCB and ΣPAH sediment accumulation rates and profiles in L227 were similar to those in Lake Superior and other proximate and midlatitude lakes unimpacted by point sources. Eutrophication did not increase contaminant accumulation. In general, individual PAH accumulation rates declined following eutrophication, which coincided with similar signals elsewhere. Perylene declined markedly (4 times) since eutrophication as a result of decreased in situ formation. An increase in OC accumulation did not enhance contaminant accumulation in L227 because phytoplankton community structure shifted to species characterized by lower bioaccumulation factors, and water column recycling rates were high. Accumulation rates of mass, OC, PCB's, and PAH's, when compared with ice-free settling fluxes in 1993 and 1994, exhibited similar recycling ratios in eutrophic L227 and oligotrophic L110 due to the efficient preservation of organic matter in sediments.
Modeling sources of variation for growth and predatory demand of Lake Erie walleye (Stizostedion vitreum), 1986-1995
Authors: Kershner Mark W , Schael Denise M , Knight Roger L , Stein Roy A , Marschall Elizabeth A
Published: April 2011

Given the variable nature of the Lake Erie ecosystem, we investigated biotic and abiotic sources of variation for walleye (Stizostedion vitreum) growth, consumption, and population-wide predatory demand. We determined how temperature, population structure, and age-specific consumption influenced walleye growth and consumption during 1986-1995. For each year, we used individual-based bioenergetics modeling to compare growth and consumption by walleye in Lake Erie's western or central basin with those of walleye moving seasonally between basins. Population structure strongly affected walleye growth and consumption but had little influence on interbasin growth rate comparisons. Based on water temperature alone, growth and consumption by western basin walleye were generally lower than for central basin or migratory populations and were more limited by summer water temperatures. In simulations combining effects of population structure, temperature, and age-specific consumption, migratory walleye grew most rapidly, taking advantage of temperature-related growth peaks in both basins. Estimates of walleye predatory demand declined with population size from 1988 through 1995. With natural feedbacks, predatory demand interacts with prey production, limiting walleye reproductive potential when prey availability is low. However, immediate impact on predatory inertia is limited, complicating our ability to predict how predatory demand and prey availability interact in Lake Erie.
Trophic position and individual feeding histories of fish from Lake Okeechobee, Florida
Authors: Fry Brian , Mumford Patricia L , Tam Franklin , Fox Don D , Warren Gary L , Havens Karl E , Steinman Alan D
Published: April 2011

We used C and N stable isotope measurements to identify trophic position and feeding histories of fish from Lake Okeechobee, one of the largest lakes in North America. When δ15N values were used to estimate trophic levels, analyses of about 500 individual fish collected in two seasons at five sites showed that trophic level varied from 2 (herbivore) to 4.3 (second-level carnivore) among the 29 fish species examined. Lower trophic levels predominated among small fish caught at a littoral marsh site, and highest trophic levels were found among larger offshore fish. Marsh fish showed about three times the C isotope variation than did offshore fish, consistent with the wider array of foods in the marsh versus offshore food web. In addition to these community-level results, there were often unexpected large isotopic differences between individuals in almost all fish species examined, suggesting large differences in individual feeding behavior. Isotopic analyses indicate long-term differences in feeding among individuals, in addition to the short-term differences often observed in stomach content studies. Long-term individual variation in fish foraging may be important in understanding variation in other biochemical parameters measured in fish, such as Hg or PCB contents.
Spawning behaviour of Atlantic cod, Gadus morhua: evidence of mate competition and mate choice in a broadcast spawner
Authors: Hutchings Jeffrey A , Bishop Todd D , McGregor-Shaw Carolyn R
Published: April 2011

We quantified individual differences in Atlantic cod, Gadus morhua, reproductive behaviour at a field-reported spawning density under experimental conditions. Marked individuals (nine females, seven males) were observed twice daily and videotaped continuously for 9 weeks at ambient photoperiod and temperature in a large tank (60 m3). Agonistic interactions appeared to maintain a size-based dominance hierarchy among males. Multiple paternity per spawning bout, revealed by microsatellite DNA analysis, suggested a link between dominance and fertilization success. Interactions between sexes were dominated by the circling of females by males. Predicated by vertical separation from males, and after descending to the bottom, a motionless female would be circled up to 17 times, often by one male per circling bout but by several males throughout the spawning period. Although circling frequency increased with male dominance and male body size, initiation and termination of this behaviour appeared to be under female control. Circling provides opportunities for males to gain individual access to reproductive females and for females to assess the quality of potential mates. Our evidence for nonrandom mate choice and for male-male competition and display has implications for Atlantic cod mating systems and effects of fishing on their reproductive success.
Estimation of fishing and natural mortalities from tag experiments with exact or grouped times at liberty
Authors: Xiao Yongshun , Stevens John D , West Grant J
Published: April 2011

A simple probabilistic model that incorporates fishing mortality, natural mortality, tag shedding, and differing reporting rates is developed, a likelihood function for estimating its parameters is derived, and a set of tagging data on newborn school shark, Galeorhinus galeus, is analysed to estimate their instantaneous natural and fishing mortalities. For a truncated tagging experimental period of 92 days, the instantaneous rate of natural mortality of newborn school sharks was estimated at 9.0427 × 10-3 (±2.4553 × 10-2)·day-1 or 3.3028 (±8.9680)·year-1 and is equal to a survival rate (from natural death only) of e-0.0090427 = 99.10%·day-1 or e-3.3028 = 3.68%·year-1. From this estimate and its corresponding estimates of catchability coefficients, we also calculated their instantaneous rate of fishing mortality in the study area from longlines, gill-nets, or both, and their survival rate, all as a function of time. This work extends previous work by incorporating fish tag shedding rates and reporting rates and by giving a detailed derivation of the likelihood function.
Effects of tidal currents on Pacific salmon migration: results from a fine-resolution coastal model
Authors: Bourque Marie-Claude , LeBlond Paul H , Cummins Patrick F
Published: April 2011

Experiments with a numerical model of salmon homing migration show that tidal currents can significantly affect return timing of sockeye salmon (Oncorhynchus nerka) off the northern coast of British Columbia. The numerical model combines results from a fine-resolution hydrodynamic model of the waters off northern British Columbia with an individual-based model of salmon migration. Results suggest that coastal tidal currents affect the return timing by causing the number of returning salmon to vary at a cycle corresponding to the dominant tidal period of 12.4 h. Such variations are associated with a patchiness that develops in the spatial distribution of simulated salmon. These features occur as the salmon swim through an oscillating tidal current that exhibits relatively sharp gradients in amplitude. The results may be of use to the design of sampling strategies where aliasing problems may occur.
An advection–diffusion–reaction model for the estimation of fish movement parameters from tagging data, with application to skipjack tuna (Katsuwonus pelamis)
Authors: Sibert John R , Hampton John , Fournier David A , Bills Peter J
Published: April 2011

The mobility of fish populations is often ignored in population dynamics models. However, in many cases (with tunas being a prime example), movement and spatial heterogeneity may be striking features of the fish populations and their exploitation. We describe a general quantitative framework to estimate movement and mortality of fish populations from tagging data. Movement is represented by an advection-diffusion process, which is the population equivalent of individual movement based on a biased random walk. Finite difference approximations for solving the partial differential equation are provided. The model is parameterized by assuming that movement parameters are homogeneous within specified geographical regions and seasons, that fishing mortality is proportional to fishing effort, and that natural mortality is constant over area and time. All model parameters are estimated simultaneously by maximum likelihood. The method is illustrated by application to skipjack tuna (Katsuwonus pelamis) in the western Pacific Ocean. Skipjack movement is shown to be highly variable at both seasonal and interannual time scales. Comparison with the results of a spatially aggregated analysis of the same data reveals that the spatial model provides a much better fit to the data and, unlike the spatially aggregated model, enables estimation of the natural mortality rate free of the effects of movement within the model domain.
Population decline of the Japanese sardine, Sardinops melanostictus, in relation to sea surface temperature in the Kuroshio Extension
Authors: Noto Masayuki , Yasuda Ichiro
Published: April 2011

The relationship between the population size of the Japanese sardine, Sardinops melanostictus, and sea surface temperature (SST) from 1979 to 1994 was studied. Significant positive correlations were found between the natural mortality coefficient during the period from the postlarval stage to age 1 and winter-spring SST in the Kuroshio Extension and its southern recirculation area (30-35°N, 145-180°E). That is, higher (lower) SST over the possible migration route corresponded to higher (lower) mortality rate. This result is consistent with the high mortality and low population size for the high-SST period of the 1950's and 1960's and the population increase during the low-SST period of the 1970's and 1980's due to a decrease in mortality. The population decline after 1988 possibly occurred as a result of the abrupt increase in SST since 1988 in the Kuroshio Extension region and suggests a close relationship between interdecadal climate-ocean variability and sardine population size. This may also explain the relationship between biomass size and distribution area.
Growth modelling in accordance with daily water temperature in European grayling (Thymallus thymallusL.)
Authors: Mallet J P , Charles S , Persat H , Auger P
Published: April 2011

The model of von Bertalanffy has been and is still widely used to model fish growth, mainly because of its good description of annual growth over the whole life span. However, it does not take into account a seasonal variability in growth rate, an important phenomenon that appears quite well correlated with water temperature fluctuations in temperate climates. In the present study, we demonstrated that it was possible to model such variations by including daily water temperature in the von Bertalanffy growth formula owing to the correlation between the growth coefficient k and water temperature. The model we chose to describe such a correlation includes parameters with obvious biological significance and is mathematically well structured, which allowed an extensive use of our growth model. Hence, we use our new model to describe annual variability in the growth of European grayling (Thymallus thymallus L.) in a river section where water temperature could rise up to the thermal tolerance limit for this species, inducing reduced growth rates and severe mortality events. Finally, we were able to explain the growth rate variability from one year to the next by interannual water temperature fluctuations.
Organic matter and pigments in surface sediments: possible mechanisms of their horizontal distributions in a stratified lake
Authors: Ostrovsky I , Yacobi Y Z
Published: April 2011

The analysis of spatial changes of organic matter and pigments (chlorophyll a, chlorophyll b, bacteriochlorophyll e, and phaeophytin a) in the uppermost bottom sediments was used to distinguish between sources of settled material in Lake Kinneret (Israel) during thermal stratification. The proportion of phytobenthic chlorophyll a decreased relatively to total chlorophyll a down to zero at 17 m. Bacteriochlorophyll e, derived from Chlorobium phaeobacteroides, was the most abundant pigment below the thermocline. Organic matter content in the sand-free sediment fraction and chlorophyll a to organic matter ratio were the lowest in the bottom area most extensively affected by shoaling internal seiches and where resuspension occurred. The proportion of resuspended matter sharply decreased with bottom depth in the hypolimnion. The importance of degraded materials of planktonic origin apparently increased towards the lake center. These distribution patterns could be achieved by dispersion of the rapidly sinking resuspended particles with fast metalimnetic jets and by focusing of the lighter planktonic particles by water motions in the turbulent benthic boundary layer. Our study showed that analysis of distribution of freshly settled organic components on the bottom may be a useful tool for understanding particle transport mechanisms in lakes.
Relative importance of water and food as cadmium sources to the predatory insect Sialis velata (Megaloptera)
Authors: Roy Isabelle , Hare Landis
Published: April 2011

A key aspect of modeling contaminant uptake by animals is knowledge of the route taken by the contaminant to enter the animal. To determine the relative importance of food and water as Cd sources for benthic insects, we measured Cd accumulation by the predatory alderfly Sialis velata (Megaloptera) from either water alone or from chironomid prey (Cryptochironomus sp.). We determined that Cd uptake from prey was far more important than that from water. Chironomid prey fed to S. velata also appeared to take up the bulk of their Cd from food (meiobenthic organisms). The efficiency with which Cd was assimilated by the predator from its prey is high (50%) and comparable with values reported for several other insects. In the predator, Cd taken up from food was largely stored in gut tissues (as is the case for insect larvae in nature), whereas a greater proportion of the metal taken up from water was stored in other animal parts.
Floating, switching, or nonswitching as different behaviours when Arctic char (Salvelinus alpinus) are visiting two feeding tanks
Authors: Brännäs Eva , Eriksson Torleif
Published: April 2011

The following questions were addressed. Will individual Arctic char (Salvelinus alpinus) differ in their visiting strategies when given a choice between two feeding tanks? If so, will the choice of strategy depend on individual characteristics (size) and will it affect their success (growth)? Further, will their allocation of visits to the two feeding tanks correspond to the food ratio? The passages between the nonfeeding tank and the two equally rich feeding tanks were recorded for four separate groups during a 3-week period. In an additional study, a single group was continuously monitored for 5 months using the same setup, but the feed ratio between the two feeding tanks was changed. Certain individuals in both studies consistently visited the same feeding tank (nonswitchers) and these were the most successful ones in terms of growth rate. Other individuals either kept visiting both tanks (switchers) or spent most of their time in the nonfeeding tank (floaters). These behaviours were applied by individuals that had a lower growth rate and are therefore likely to have lower competitive ability or feeding motivation. No significant difference in initial weight between the behavioural categories was found in either of the two studies. In the four-group study, the proportion of visits into the two feeding tanks matched the food ratio among the switchers only and the distribution of the groups failed to match the food ratio. In the single-group study, the group distributed according to the food ratio (ideal free distribution) if they were given sufficient time to learn the quality of the patches. A change in the relative food ratio caused the switchers and floaters to alter their visiting behaviour, always favouring the more profitable tank, whereas the nonswitchers continued to visit the same tank.
Fecundity and duration of egg incubation for multiparous female snow crabs (Chionoecetes opilio) in the fjord of Bonne Bay, Newfoundland
Authors: Comeau Michel , Starr Michel , Conan Gérard Y , Robichaud Guy , Therriault Jean-Claude
Published: April 2011

Multiparous female snow crabs (Chionoecetes opilio) were collected by trap and Nephrops trawl in the fjord of Bonne Bay, Newfoundland, between April 1988 and August 1992 to study the fecundity and embryonic development. A relationship was established between the color of the egg mass and embryonic development. Fecundity was positively correlated with carapace width. A female of 67 mm carapace width can produce up to about 54 000 eggs. Egg mortality over the incubation period could reach 21%, being greater in larger females. Based on the bimodal distributions of embryonic developmental stages observed in the study, the female reproductive cycle was determined as 2 years and females probably only hatch two broods in their lifetime. Eggs hatch mainly in May and June.
Spawning season influences on commercial catch rates: computer simulations and Plectropomus leopardus, a case in point1
Authors: Fulton Elizabeth , Kault David , Mapstone Bruce , Sheaves Marcus
Published: April 2011

Spatial and temporal closures of sections of the marine environment are proposed frequently as fishery management devices, particularly when specific areas, such as spawning aggregations, can be identified. The ultimate effectiveness of spawning area closures is unknown, as spawning-related determinants of catch rate have not been studied. A simulation model, based on existing biological and fisher information, was constructed to examine the most important determinants of the spawning season catch rates using the protogynous aggregative spawner Plectropomus leopardus (Family Serranidae, Subfamily Epinephelinae) as a test case. Model output indicated that spawning season catches rose as long as catchability of spawners was equal to or greater than that of nonspawners. Greatest increases in catch were produced by fish moving from habitats inaccessible to fishers into regularly fished locations during migrations to spawning aggregations. Elevated catches were not simply dependent on the targeting of aggregations by fishers. Small-scale spatial closures around spawning aggregation sites would not be sufficient to protect the spawning stock of fish such as P. leopardus, but larger scale closures during the spawning season may be useful even when fishers are not targeting spawning aggregations.