bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth, condition, and environmental relationships in Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence and implications for management strategies in the Northwest Atlantic
Authors: Dutil J -D , Castonguay M , Gilbert D , Gascon D
Published: April 2011

Northern Gulf of St. Lawrence Atlantic cod (Gadus morhua) is one of several stocks that collapsed in eastern Canada following a long period of intensive exploitation. Surplus and net production per capita became nil or negative in the mid-1980s so that any level of exploitation would have caused a decline of the stock. This was partly explained by a marked decline in growth production and is consistent with smaller sizes-at-age but also lower condition factor values during the same period. Correlations between size-at-age and temperature were not significant when corrected for autocorrelation, but slopes were always positive, suggesting higher growth rates at higher temperatures. Smaller sizes-at-age in the 1980s were not associated with changes in the fishery or increased fishing mortality, nor were they consistent with the density-dependence hypothesis. Lengths at age 8 decreased by more than 10 cm as the stock decreased 10-fold in abundance. While size-at-age and temperature covary in cod when all stocks are examined, size-temperature relationships are not as clear if the analysis is restricted to cold-water stocks, possibly because of differences in food availability. Biological production varies from year to year and among stocks and should be taken into consideration when managing fisheries in variable or extreme environments.
Crue éclair de juillet 1996 dans la région du Saguenay (Québec). 2. Impacts sur les sédiments et le biote de la baie des Ha! Ha! et du fjord du Saguenay
Authors: Pelletier Émilien , Deflandre Bruno , Nozais Christian , Tita Guglielmo , Desrosiers Gaston , Gagné Jean-Pierre , Mucci Alfonso
Published: April 2011

Several million tons of sediments and various debris were transported to the north arm of the Saguenay Fjord and the Baie des Ha! Ha! following the torrential rains and accompanying flash flood of July 1996 in the Saguenay region (Québec). The flood deposits covered the indigenous sediments and buried the benthic community. The objective of this work is to determine the best chemical and biological indicators of the changes that occurred in the benthic habitat of the fjord. The new sediment layer is poor in organic matter but rich in detrital carbonates and contains low mercury and lead concentrations reflecting the absence of industrial contamination. Ongoing geological processes leading to the re-establishment of steady-state conditions were evidenced by measurements of porosity, redox potential (Eh), and salinity of interstitial waters taken a few weeks and a few months after the events. The meiofauna were severely affected with a massive reduction of the average density of organisms relative to values recorded before the flood, but recolonisation was already in progress 1 year after the flood. Important losses of macrobenthic species were recorded in 1997 relative to 1996. However, the abundance and the diversity of the polycheate taxa were higher in 1997, indicating a recolonisation of the new sediment layer by pioneer species.
Effects of northern pike (Esox lucius) additions on pollutant accumulation and food web structure, as determined by δ13C and δ15N , in a eutrophic and an oligotrophic lake
Authors: Kidd Karen A , Paterson Michael J , Hesslein Raymond H , Muir Derek CG , Hecky Robert E
Published: April 2011

In May 1993 and 1994, northern pike (Esox lucius) were added to eutrophic Lake 227 and oligotrophic Lake 110 at the Experimental Lakes Area in northwestern Ontario. Both lakes were previously dominated by cyprinids, and northern pike additions significantly decreased cyprinid densities in both lakes. Food web relationships were determined pre- and post-manipulation using stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of zooplankton, benthic invertebrates, and fishes. In Lake 110, fathead minnow (Pimephales promelas) shifted from a zooplanktivorous to a zoobenthivorous diet as indicated by a shift in isotopic composition to more depleted δ15N and enriched δ13C values after northern pike additions. It was not possible to direct predator-induced shifts in cyprinid diets in Lake 227. Concentrations of mercury and organochlorines (sum of polychlorinated biphenyls (ΣPCB), dichlorodiphenyltrichloroethane (ΣDDT), and hexachlorocyclohexane (ΣHCH)) in these fish did not change markedly after northern pike introductions despite the shifts in diet for fathead minnow from Lake 110. However, concentrations of all contaminants were lower in biota from eutrophic Lake 227 when compared with Lake 110, which is consistent with previous studies. Our results indicate that nutrient availability, rather than short-term changes in food web structure, determined contaminant concentrations in fish and other biota from these lakes.
Using stable isotopes to monitor watershed influences on aquatic trophodynamics
Authors: Fry Brian
Published: April 2011

Stable C and N isotope measurements of the clam Potamocorbula amurensis were used to help identify watershed-level differences in food webs of San Francisco Bay. Potamocorbula amurensis has become widely distributed in San Francisco Bay since introduction from Asia in1986. Clam samples were collected from both the river-influenced northern arm of San Francisco Bay and the lagoonal southern arm of the Bay during 1990-1991. Carbon isotopic compositions of clams responded primarily to riverine inputs and provided an index of hydrologic mixing across the estuarine system. Nitrogen isotopic compositions of clams were more responsive to watershed nutrient loading, with higher δ15N values found in South Bay, which receives stronger inputs of anthropogenic N. Routine monitoring of animal consumer isotopic compositions could be an effective way to detect long-term watershed-level changes in C and N dynamics important for secondary production in aquatic systems.
Population processes responsible for larger-fish-upstream distribution patterns of Arctic grayling (Thymallus arcticus) in interior Alaskan runoff rivers
Authors: Hughes Nicholas F
Published: April 2011

During the summer months, Arctic grayling (Thymallus arcticus) in Alaskan streams adopt a larger-older-fish-upstream distribution pattern. In this paper, I analyse data from two large interior Alaskan rivers to determine how population processes maintain this size and age gradient. These analyses support the hypothesis that age-phased recruitment and growth-dependent movement are primarily responsible for this distribution pattern. Age-phased recruitment describes the way that the mean age of fish recruiting to a reach increases upstream, from ages 0-1 in the lower river to ages 3-7 in the headwaters. This process begins with the concentration of spawning fish, and the resultant fry, in the lower reaches of the river. Downstream movement during the first year of life further concentrates young fish in the lower river. Over time, the distribution of this cohort broadens steadily as individuals move further upstream, so that fish recruiting to headwater reaches are 3-7 years old. This process contributes to both size and age gradients. Growth-dependent movement magnifies the size gradient by sorting fast-growing fish into the upper river and slow-growing fish into the lower river. This sorting results from the fact that individuals making long-distance upstream movements tend to have grown particularly rapidly that year, while individuals making long-distance downstream movements tend to have grown especially slowly that year. I rejected the hypothesis that age and size gradients are the result of whole-stream gradients in growth or mortality acting on a sedentary population. However, there was some evidence that fish did grow more slowly in the lowest 40 km of one river, although this made only a minor contribution to the size gradient and growth rates were remarkably constant for the next 120 km. There was no suggestion that spatial variation in mortality rate contributes towards the size or age gradient, but natural and sampling variability could have obscured small but significant differences between reaches.
Entrainment, dispersal, and settlement of scallop dredge sediment plumes: field measurements and numerical modelling
Authors: Black Kerry P , Parry Gregory D
Published: April 2011

Entrainment, dispersal, and settlement of sediment plumes generated by scallop dredging were measured with an instrumented towed sled and downstream sensors during a series of experiments conducted in the main scallop grounds in Port Phillip Bay in southeastern Australia. When three 36-ha experimental plots were subjected to closely supervised, intensive dredging by commercial fishers, it was found that dredges suspend a thin layer of sediment (~0.5 cm thick) inducing initial near-bed concentrations of 2-15 kg·m-3 in a billowing turbid plume. At one field site where 30% of seabed sediment was less than 4 phi, concentrations reduced after 30 min to about 2% of the initial value and grain sizes decreased to a predominantly mud-sized sediment with a mean size of 5-6 phi. A numerical model was developed to depict plume transformations and settlement patterns. The model accurately predicted patterns of sedimentation and temporal changes to suspended sediment concentration and grain size distribution in the plume. By explicitly treating local seabed grain size, current, and water column turbulence, the model can be applied to other locations and conditions to examine suspended sediment concentrations and potential sediment-related impacts of scallop dredging.
Multiple dispersal strategies of the invasive quagga mussel (Dreissena bugensis) as revealed by microsatellite analysis
Authors: Wilson A B , Naish K -A , Boulding E G
Published: April 2011

The recent invasion of the Laurentian Great Lakes by Dreissena polymorpha and Dreissena bugensis presents a unique opportunity to study the role of high dispersal ability in the colonization success of invading species. While the dispersal of D. polymorpha has been characterized by several jump dispersal events, census data suggest a more gradual diffusion of D. bugensis from its point of introduction through the lower Great Lakes. In this study, we use six highly polymorphic microsatellite markers to investigate the present-day population genetic structure of D. bugensis in North America in an effort to clarify the role of multiple dispersal strategies in its colonization success. In contrast with survey data, which would suggest a gradual spread ultimately resulting in a pattern fitting a model of isolation-by-distance, the significant allelic and FSTdifferences observed between 18 of 28 population pairs do not correlate with any simple geographic relationship. Deviations from isolation-by-distance are due, in part, to a higher gene flow between disjunct populations than that expected under a normally distributed pattern of dispersal. These results, in combination with recent reports of the quagga mussel outside its established North American range, suggest that boater-mediated jump dispersal of D. bugensis may be contributing to its colonization and spread in North America.
Sperm competition and fertilization success in Atlantic cod (Gadus morhua): effect of sire size and condition factor on gamete quality
Authors: Rakitin Ana , Ferguson Moira M , Trippel Edward A
Published: April 2011

Sperm competition experiments were conducted to test the null hypothesis that sperm quality is not affected by male body size in Atlantic cod (Gadus morhua). Genetic markers (allozymes) were used to determine the proportion of larvae sired by pairs of males when their sperm was combined with eggs of a single female simultaneously. Significant differences in fertilization success between males were not explained by differences in body size. Fertilization success was positively associated with male condition factor (K) and with spermatozoa density in each male's semen when equal volumes of semen from each male were used. Male K was positively associated with male fertilization success when the volume of semen used from each male was adjusted to add approximately equal numbers of spermatozoa from each male. The relative fertilization success of males varied depending on which female was the egg donor, suggesting that female "choice" at the gamete level may be occurring in cod.
Ideal free distribution theory as a tool to examine juvenile coho salmon (Oncorhynchus kisutch) habitat choice under different conditions of food abundance and cover
Authors: Giannico Guillermo R , Healey Michael C
Published: April 2011

We investigated the mechanisms affecting habitat choice by juvenile coho salmon (Oncorhynchus kisutch) in relation to the patchy distribution of food and cover. We tested the following hypotheses: (i) the distribution of juvenile coho, both between patches in a pool and between separate pools in a channel, corresponds numerically to the food input rate of those habitat patches as predicted by the "input-matching rule" of ideal free distribution (IFD) and (ii) the addition of instream cover, by increasing visual isolation among competitors, promotes input matching both within and between pools. We conducted our experimental work in artificial channels and we used two different types of cover, instream and overhead. In the absence of cover and with either no differences or relatively small differences in food abundance between patches, the spatial distribution of juvenile coho responded numerically to the input rate of food as predicted by the IFD. However, when differences in food abundance between patches were relatively large or cover was present, fish distributions consistently undermatched food input rate in the rich patch. Coho foraged in open patches away from cover within single pools but preferred pools with cover when choosing between separate pools. Several IFD models were used to examine the observed dispersion patterns.
Changes in isotopic composition of red drum (Sciaenops ocellatus) larvae in response to dietary shifts: potential applications to settlement studies
Authors: Herzka Sharon Z , Holt G Joan
Published: April 2011

The stable isotope composition of larval fish tissues may serve as a chemical tracer of recent settlement due to food web differences among planktonic and demersal habitats. We present the background for the utilization of δ13C and δ15N to trace settlement of red drum (Sciaenops ocellatus), an estuarine-dependent species. The effect of ontogeny and temperature on the relative contribution of growth and metabolic turnover to changes in isotopic composition was examined by simulating dietary shifts in the laboratory. Fractionation was examined as a function of size and the effect of food deprivation was evaluated. Published growth rates were used to estimate the time period within which the isotopic composition of a new food source should be reflected in larval tissues. In response to dietary shifts, larvae exhibited quick changes in δ13C and δ15N in a pattern closely resembling predictions based on growth alone. Fractionation values were about +1 for δ13C and +1.6 for δ15N. There was no effect of 4 days of food deprivation on δ13C and δ15N. Given the fast growth rates reported for newly settled red drum, their isotopic composition should exhibit a shift within 1-2 days and stabilize about 10 days following settlement.
Seasonally shifting limitation of stream periphyton: response of algal populations and assemblage biomass and productivity to variation in light, nutrients, and herbivores
Authors: Rosemond Amy D , Mulholland Patrick J , Brawley Susan H
Published: April 2011

We determined whether there were seasonal changes in the relative importance of consumers and resources in controlling stream periphyton. Our analysis included effects on algal populations and assemblage biomass and productivity. We used factorial experiments in which we manipulated snail densities, irradiance, and streamwater nutrient concentrations during two seasons, fall and spring, and compared responses with previously published summer findings. Periphyton biomass and productivity were much greater when snails were removed and nutrients and light were elevated during all seasons, indicating that all three factors were limiting or nearly limiting throughout the year. However, the relative importance of factors shifted seasonally. Irradiance limited periphyton biomass in summer and fall but not spring. In contrast, nutrients were more limiting in seasons in which light levels were higher: nutrient addition generally resulted in effects of greater magnitude in fall and spring than in summer. Snail growth was stimulated by enhanced irradiance in summer (p = 0.06) and by nutrient addition in fall, indicating resource limitation of both periphyton and snails. However, top-down control of periphyton by snails was also important: snails maintained low biomass assemblages dominated by only a few grazer-resistant species (e.g, basal cells of Stigeoclonium tenue, Chamaesiphon investiens) during all seasons.
Effects of feeding ration on larval swimming speed and responsiveness to predator attacks: implications for cohort survival
Authors: Chick John H , Van Den Avyle Michael J
Published: April 2011

We conducted laboratory experiments to examine the effects of feeding ration on the routine swimming speed of larval striped bass (Morone saxatilis) and their responsiveness to simulated-predator attacks. Striped bass were reared in low (7 prey·L-1), medium (354 prey·L-1), or high (740 prey·L-1) prey treatments from age 4 to 14 days posthatch. Larvae reared in the low-prey treatment had slower routine swimming speeds and shorter reactive distances and were less responsive to simulated-predator attacks. These differences were most pronounced after age 10 and appeared to be an effect of deteriorating larval condition rather than an effect of size. Simulation models were constructed for two potential fish predators, Alosa aestivalis and Pomoxis nigromaculatus, to examine how variation in growth rate, swimming speed, and responsiveness to predator attacks might influence mortality rate. Our simulations predicted that cohort mortality rate would decrease with increasing larval growth rates, even though faster routine swimming speed and growth rate increased encounter rates with predators. The influence of larval growth rate and responsiveness on mortality rate varied between the two predators, but cohorts experiencing no growth always had the greatest mortality rate.
Significance and fate of bacterial production in oligotrophic lakes in British Columbia
Authors: Weisse Thomas , MacIsaac Erland
Published: April 2011

We measured bacterial abundance, biomass, production rates, and grazing losses to protozoans in three oligotrophic British Columbia lakes and analyzed bacteria abundance and lake productivity data from 11 other lakes, most fertilized with inorganic nutrients to increase their productivity for juvenile salmon. Bacteria contributed about 24% to the phytoplankton-bacteria carbon biomass in the most ultraoligotrophic lakes, and their relative contribution declined to <11% with increasing lake productivity. At increasingly high nutrient loadings to the lakes, bacteria abundance increased and was closely correlated with phytoplankton biomass and productivity. Heterotrophic nanoflagellate (HNF) abundance was positively correlated with bacterial numbers. Grazing experiments revealed that HNF were the primary pathway for moving bacterial production to higher trophic levels in oligotrophic British Columbia lakes, and predation by the ciliate and rotifer microzooplankton community appeared to exert top-down control over the abundance of HNF and the transfer of carbon from bacteria. The HNF and microzooplankton, in turn, were affected by the abundance of crustacean mesozooplankton, principally copepods in our experiments.
Identification of gender and reproductive maturity in the absence of gonads: muscle tissue levels of sex steroids and vitellogenin in gag (Mycteroperca microlepis)
Authors: Heppell Scott A , Sullivan Craig V
Published: April 2011

Gag (Mycteroperca microlepis) are often landed eviscerated, so their gonads are not available for histological verification of gender and stage of maturity. Information on gender is particularly important for the management of hermaphroditic grouper, where increased mortality through fishing can directly affect sex ratio and therefore the reproductive capacity of the population. Alternative techniques for evaluating fish gender and maturity therefore need to be developed for gag and other grouper. We utilized sensitive immunoassays to measure levels of the sex steroids estradiol-17beta (E2), testosterone (T), and 11-ketotestosterone (11KT) and the egg-yolk precursor vitellogenin (VTG) in gag on a quarterly basis. Plasma and muscle levels of E2, T, and VTG in females were lowest during summer, rising in winter to reach peak values in spring. During winter and spring, plasma and muscle levels of 11KT were significantly higher in males than in adult females or immature fish. Combined measurement of VTG and 11KT in gag muscle proved useful for differentiating between males, adult females, and immature fish between December and April, the period of active gonadal recrudescence. This technique should prove useful in cases where fishery data are primarily collected through port sampling and gonads are not available for analysis.
Distribution of Calanus spp. on and around the Nova Scotia Shelf in April: evidence for an offshore source of Calanus finmarchicus to the central and western regions
Authors: Head Erica JH , Harris Leslie R , Petrie Brian
Published: April 2011

Observations of hydrography and Calanus spp. abundance were made at stations on lines across the central and eastern Scotian Shelf (SS) in April 1995 and 1997 and on additional lines on the western SS and across Cabot Strait (CS) and the Laurentian Channel (LC) in 1997. Calanus finmarchicus was more abundant on the central and western SS than in the east, and Calanus hyperboreus was concentrated in the east and in areas influenced by the Nova Scotia Current. Calanus spp. on the eastern SS probably originated mainly from populations overwintering in the Gulf of St. Lawrence. High abundances of C. finmarchicus occurred at or beyond the shelf break when warm slope water was present, suggesting that they derived from a population overwintering in the deep water south of the SS. In both years, slope water was present in the near-surface layers at shelf stations of the Halifax Line (HL), but in 1997 the degree of intrusion was greater. Calanus finmarchicus abundances were also substantially higher at shelf stations of the HL in 1997, implying contribution from the offshore population to the populations in central and western SS regions. Consistent with the suggested difference in their origins, C. finmarchicus on the western SS belonged primarily to the new year's generation, whereas those on the eastern SS belonged mainly to that of the previous year.
Comparison of parameter estimation methods for detecting climate-induced changes in productivity of Pacific salmon (Oncorhynchusspp.)
Authors: Peterman Randall M , Pyper Brian J , Grout Jeff A
Published: April 2011

Pacific salmon (Oncorhynchus spp.) populations can experience persistent changes in productivity, possibly due to climatic shifts. Management agencies need to rapidly and reliably detect such changes to avoid costly suboptimal harvests or depletion of stocks. However, given the inherent variability of salmon populations, it is difficult to detect changes quickly, let alone forecast them. We therefore compared three methods of annually updating estimates of stock-recruitment parameters: standard linear regression, Walters' bias-corrected regression, and a Kalman filter. We used Monte Carlo simulations that hypothesized a wide range of future climate-induced changes in the Ricker a parameter of a salmon stock. We then used each parameter estimation method on the simulated stock and recruitment data and set escapement targets and harvest goals accordingly. In these situations with a time-varying true Ricker a parameter, Kalman filter estimation resulted in greater mean cumulative catch than was produced by the standard linear regression approach, Walters' bias correction method, or a fixed harvest rate policy. This benefit of the Kalman filter resulted from its better ability to track changing parameter values, thereby producing escapements closer to the optimal escapement each year. However, errors in implementing desired management actions can significantly reduce benefits from all parameter estimation techniques.
Sources of variability in microcontaminant data for Lake Michigan salmonids: statistical models and implications for trend detection
Authors: Lamon III E Conrad , Stow C A
Published: April 2011

Variability in Lake Michigan salmonid microcontaminant data may arise from differences in contaminant concentrations in the water column, fat content, diet, age, location, and species-specific factors. Polychlorinated biphenyl (PCB) concentrations for salmonids in Lake Michigan have been determined for fish collected from a wide variety of locations and sizes for each of five species. Lake managers and policy makers wishing to evaluate trends in these concentration data must either remove this variability before trend assessment or leave it and settle for less statistical power for identifying the underlying time trend. Classification and regression trees (CART) have proven to be a useful tool for identifying nonlinear patterns of variability in these data and portraying them graphically. We used CART to study patterns of variability in PCB concentrations in five species of Lake Michigan salmonids, using data collected from 1972 to 1994 by both the Michigan and Wisconsin Departments of Natural Resources. For most of the species studied here, length was the major source of variability, followed by location.
A length-based hypothesis for feeding migrations in pelagic fish
Authors: Nøttestad Leif , Giske Jarl , Holst Jens Chr. , Huse Geir
Published: April 2011

We evaluated the costs and benefits of long-distance horizontal migration by pelagic planktivores, Atlantic herring (Clupea harengus), blue whiting (Micromesistius poutassou), mackerel (Scomber scombrus), and capelin (Mallotus villosus) in the Norwegian and Barents seas using a numerical model and tested model predictions against field observations. Specifically, we considered (i) energetic costs as a function of body size, water currents, swimming speed, and distance, (ii) time costs as a function of speed and distance, and (iii) energetic gain in terms of differences in food intake between areas. The model demonstrates how body size restricts large-scale horizontal migration patterns. Model and field results suggest that the extent of migration will increase with increasing body length. The model predicts that long-distance migration costs may exceed energy intake for fish <20 cm, due to increased hydrodynamical drag with decreasing fish size. Field results suggest that migration distance is a function of length, weight, and age. Food abundance and distribution, current speed and direction, and differences in day length at boreal latitudes are believed to be the major driving forces influencing large-scale migration distance, direction, and timing in pelagic planktivores. Northwards latitudinal rather than longitudinal feeding migrations are explained by the improved feeding opportunities with increased day lengths.
Environmental factors associated with a toxic bloom ofMicrocystis aeruginosa
Authors: Jacoby Jean M , Collier Diane C , Welch Eugene B , Hardy F Joan , Crayton Michele
Published: April 2011

Environmental factors associated with the occurrence of toxic cyanobacterial blooms and toxin production were investigated during the summers of 1994 and 1995 in Steilacoom Lake, Washington. A pronounced and prolonged toxic bloom of Microcystis aeruginosa occurred during summer 1994 but not during 1995. Lake characteristics that were associated with the toxic bloom in 1994 were higher total phosphorus, decreased water transparency, high water column stability, high surface water temperature and pH, and decreased lake flushing. Decreased water transparency during 1994 may have been due to significantly lower zooplankton abundance. We hypothesize that this decreased transparency was caused by increased planktivory by higher numbers of coho salmon (Oncorhynchus kisutch) fingerlings during 1994 and (or) inhibition of zooplankton grazing by Microcystis. The success of Microcystis over other cyanobacteria was associated with low nitrogen to phosphorus ratios and low nitrate-nitrogen with sufficient ammonium-nitrogen concentrations. Toxin production (i.e., micrograms of microcystin per gram of plankton biomass) was not constant over the duration of detectable toxicity; hence, no relationship was found between Microcystis abundance and microcystin concentration. However, microcystin concentration was positively correlated with increasing soluble reactive phosphorus concentrations between 1 and 10 µg·L-1, indicating that toxin production may have been limited by phosphorus.
A modelling-based perspective on the past, present, and future polychlorinated biphenyl contamination of the St. Lawrence beluga whale (Delphinapterus leucas) population
Authors: Hickie Brendan E , Kingsley Michael CS , Hodson Peter V , Muir Derek CG , Béland Pierre , Mackay Donald
Published: April 2011

Individual- and population-based models are presented that provide quantitative assessments of the accumulation of persistent organic pollutants over the lifetime of the beluga whale (Delphinapterus leucas) and consider all aspects of its life history. The models are used to examine the history of polychlorinated biphenyl (PCB) accumulation by the endangered St. Lawrence beluga population from 1950 to the present and to predict future trends based on likely contaminant loading scenarios. The hypothesis that migrating American eels (Anguilla rostrata) are a significant source of contaminants to the population is examined. The history of PCB exposure via the diet is reconstructed from existing data and from PCB profiles in dated sediment cores. The models adequately describe the effects of age, growth, sex, and reproductive activity on PCB concentrations in the beluga, and results show good agreement with observed concentrations when eels are included as 3% of the annual diet. PCB levels in the population appear to have peaked between 1967 and 1972. The model agrees with recent studies that have shown that PCB concentrations in the population are declining slowly.
Size-dependent winter mortality of age-0 pikeperch (Stizostedion lucioperca) in Pärnu Bay, the Baltic Sea
Authors: Lappalainen Jyrki , Erm Vaike , Kjellman Jakob , Lehtonen Hannu
Published: April 2011

Winter mortality of pikeperch (Stizostedion lucioperca) at age 0 is dependent on size, based on samples collected with trawls during 1961-1994 in Pärnu Bay, Estonia. Mortality increased as mean length of pikeperch in the first autumn decreased. The size-dependent mortality was analysed as correlation between mean lengths at age 0 in autumn and changes in mean lengths between age 1 and age 0. When the varying lengths at age 0 were taken into account, the duration of winter also affected mortality; longer durations of ice cover resulted in less size-dependent winter mortality. Since mean length at age 0 in autumn correlated positively with summer water temperature, winter mortality can be expected to decrease the warmer the summer.
Individual-based genotype analysis in studies of parentage and population assignment: how many loci, how many alleles?
Authors: Bernatchez Louis , Duchesne Pierre
Published: April 2011

We developed multivatiate analytical models to predict the probability of assigning offspring to parental couples as a function of population size, number of loci, and allelic diversity and the relationships between the probability of allocating individuals to their population of origin as a function of number of loci and allelic diversity. The parentage model predicts that the number of loci and number of alleles contribute interactively to increase assignment success. Given sufficient allelic diversity, a relatively low number of loci is required to achieve high allocation success even for relatively large numbers of possible parents. In contrast, the population model predicts an additive contribution of the number of loci and alleles. There appears to be no significant gain in increasing allelic diversity beyond approximately 6-10 alleles per locus in population assignment studies. Such predictive models should contribute to maximizing the returns of population and parentage assignment studies by increasing our understanding of interactions among the various variables affecting allocation success and by allowing the adjustment a priori of the required level of resolution and, consequently, optimizing the costs-benefits ratio in the use of molecular markers.
Egg production rates of Calanus finmarchicus in the western North Atlantic: effect of gonad maturity, female size, chlorophyll concentration, and temperature
Authors: Campbell Robert W , Head Erica JH
Published: April 2011

Egg production rates of Calanus finmarchicus were measured in the Labrador Sea (spring) and on the Scotian Shelf (spring, summer, and autumn), in conjunction with indices of gonad maturity and food availability, female body size, surface layer temperature, and surface nitrate concentrations. Egg production rates were often two to four times higher than any previously reported at similar temperatures. Estimates of egg production rates of populations were most closely related to the proportion of reproductively mature females (as measured by a gonad stage index) and female size. Specifically, the gonad stage index (proportion of females capable of spawning) was correlated with the proportion of females that spawned during 24-h incubations, and female size determined the clutch size (i.e., number of eggs produced). Although there were detectable effects of food and temperature on egg production rates, they were generally weaker than the effect of female gonad maturity. Thus, over the broad spatial and temporal scales of this study, the reproductive (i.e., life history) status of a population was more important in determining its egg production rate than direct external factors (i.e., temperature and food conditions).
Still more spawner-recruitment curves: the hockey stick and its generalizations
Authors: Barrowman Nicholas J , Myers Ransom A
Published: April 2011

Estimation of maximum reproductive rate using spawner-recruitment models involves extrapolating survival for very low spawner abundance. Existing spawner-recruitment curves often lead to biologically unreasonable extrapolations or are unable to model nondecreasing spawner-recruitment data adequately. One alternative is a piecewise linear spawner-recruitment model known as the hockey stick. We compare the fit of the Beverton-Holt with the hockey stick for 246 spawner-recruitment data sets. We show that the Beverton-Holt usually estimates a larger carrying capacity of recruits and a larger maximum reproductive rate than the hockey stick. We propose two families of generalizations of the hockey stick, one with a simple interpretation and one that is more complex but smoother. These generalized hockey sticks are more biologically plausible, less subject to numerical difficulties, and of greater utility in metaanalytic models than the hockey stick.
Thalassiosira baltica (Grunow) Ostenfeld (Bacillariophyta), a new exotic species in the Great Lakes
Authors: Edlund M B , Taylor C M , Schelske C L , Stoermer E F
Published: April 2011

Microfossil analysis of sediment cores collected in 1994 and phytoplankton collected in 1998 from Lake Ontario indicated that the diatom Thalassiosira baltica (Grunow) Ostenfeld was introduced and became established ca. 1988 according to 210Pb date estimates and has remained a predominant component of the phytoplankton since its establishment. Thalassiosira baltica is an exotic species in the Laurentian Great Lakes and is more commonly found in coastal brackish waters in western and northern Europe and only rarely reported from North American coastal waters. The probable vector for introduction of T. baltica was ballast water exchange and the successful establishment attributed to this taxon's euryhalinity tolerance.
Natural mortality rates in tropical tunas: size really does matter
Authors: Hampton John
Published: April 2011

Important size-related variability in natural mortality rates has been revealed in populations of skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares), and bigeye tuna (Thunnus obesus) in the western tropical Pacific Ocean using a new, size-structured tagging model. The tagging data were classified into release groups by size at release, and a growth model was used to predict size at each time at liberty interval. Natural and fishing mortality rates were categorized by broad size-classes and estimated by maximum likelihood. The method incorporates a correction for incomplete mixing of new releases. For each population, the natural mortality rate declined by about an order of magnitude over the initial size-classes. For skipjack and yellowfin tuna, there was also evidence of elevated natural mortality for some of the larger size-classes. Size- or age-related variability in natural mortality is likely to have important implications for tropical tuna stock assessment in the western Pacific.
Detection of QTLs for heading time and photoperiod response in wheat using a doubled-haploid population
Authors: Sourdille P , Snape J W , Cadalen T , Charmet G , Nakata N , Bernard S , Bernard M
Published: April 2011

The genetic basis of heading time in wheat (Triticum aestivum L.) was investigated through the study of flowering under normal autumn sown field conditions as well as photoperiod responses under a controlled environment. Quantitative trait loci (QTLs) for these traits were mapped in a doubled-haploid (DH) population derived from a cross between the wheat cultivars 'Courtot' and 'Chinese Spring'. A molecular marker linkage map of this cross that was previously constructed based on 187 DH lines and 380 markers was used for QTL mapping. The genome was well covered (85%) except for chromosomes 1D and 4D, and a set of anchor loci regularly spaced over the genome (one marker each 15.5 cM) was chosen for marker regression analysis. The presence of a QTL was declared at a significance threshold of alpha = 0.005. The population was grown under field conditions in Clermont-Ferrand, France during two years (1994-1995), in Norwich, U.K. over one year (1998), and also under controlled environments in Norwich. For each trait, between 2 and 4 QTLs were identified with individual effects ranging between 6.3% and 44.4% of the total phenotypic variation. Two QTLs were detected that simultaneously affected heading time and photoperiod response. For heading time, these two QTLs were detected in more than one year. One QTL located on chromosome arm 2BS near the locus Xfbb121-2B, co-segregated with the gene Ppd-B1 known to be involved in photoperiod response. This chromosome region explained a large part of the variation (23.4-44.4% depending on the years or the traits). Another region located on chromosome arm 7BS between the loci Xfbb324-7B and Xfbb53-7B also had a strong effect (7.3-15.3%). This region may correspond to a QTL for earliness per se.Key words: molecular markers, Triticum aestivum, Ppd, Vrn.
Analysis of intragenic recombination atwxin rice: Correlation between the molecular and genetic maps within the locus
Authors: Inukai Tsuyoshi , Sako Aya , Hirano Hiro-Yuki , Sano Yoshio
Published: April 2011

In plant genomes as well as other eukaryotic genomes, meiotic recombination does not occur uniformly. At the level of the gene, high recombination frequencies are often observed within genetic loci in maize, but this feature of intragenic recombination is not seen at the csr1 locus in Arabidopsis. These observations suggest that meiotic recombination in plant genomes varies considerably among species. In the present study we investigated meiotic recombination at the wx locus in rice. The mutation sites of wx mutants induced by ethyl methanesulfonate (EMS) treatment or gamma-ray irradiation and a spontaneous wx mutant were physically characterized, and the genetic distances between those wx mutation sites were estimated by pollen analysis. Based on these results, the recombination frequency at the wx locus in rice was estimated as 27.3 kb/cM, which was about 10 times higher than the average for the genome, suggesting that there was a radically different rate of meiotic recombination for intra- and intergenic regions in the rice genome.Key words: Oryza sativa, wx gene, intragenic recombination.
A comparative study of the structure of the rDNA intergenic spacer ofLens culinarisMedik., and other legume species
Authors: Fernández M , Polanco C , Ruiz M L , Pérez de la Vega M
Published: April 2011

As part of a project on lentil molecular genetics, the sequence of the 18S-25S ribosomal RNA gene intergenic spacer (IGS) of Lens culinaris Medik. was determined. DNA was cloned after polymerase chain reaction (PCR) amplification. The spacer of 2939 bp was composed of nonrepetitive sequences and four tandem arrays of repeated sequences, named A to D. C and D arrays were formed by the repetition of very short consensus sequences. Similarity was found between lentil and other legume species, in particular those of the Vicieae tribe. A transcription initiation site, putative sites of termination and processing, and promoter-enhancer sequences were detected by computer-aided searches. These sites resemble motifs conserved in the IGS sequences of other plant species. The conservation of motifs in the otherwise highly variable plant IGS sequences points to the relevance of these motifs as functional sequences.Key words: legumes, Lens culinaris Medik., lentil, rDNA intergenic spacer, IGS, structure.
Analysis of relationships betweenAegilops tauschiiand the D genome of wheat utilizing microsatellites
Authors: Lelley Tamás , Stachel Maria , Grausgruber Heinrich , Vollmann Johann
Published: April 2011

Sixty Aegilops tauschii accessions and 60 European hexaploid wheat varieties were analyzed with 14 wheat microsatellite (WMS) primer sets to (i) study the phylogeny of Ae. tauschii, (ii) search for a specific genotype of Ae. tauschii most closely related to the D genome of hexaploid wheat, and (iii) narrow down the presumed birthplace of the latter. An average of 6.5 and 4.0 alleles per locus was detected in Ae. tauschii and in wheat, respectively. The highest genetic diversity of Ae. tauschii was found in Transcaucasia and southeast of the Caspian Sea. Distribution of the 87 alleles (without null alleles) found in Aegilops did not allow differentiation of the species into the two subspecies strangulata and tauschii. Excluding null alleles, 41 alleles occurred parallel in wheat and in Aegilops. Data obtained in this study supports the view of the D genome of hexaploid wheat being a composite of several sources but does not support subsp. strangulata as the possible major source of the D genome. The highest number of region-specific alleles (three) in Ae. tauschii occurring also in the D genome of wheat, and therefore most indicative for its evolution was found in present-day Georgia, where subsp. strangulata is not endemic.Key words: Triticum aestivum, Aegilops tauschii, genetic distance, center of origin, evolution.
An anchored AFLP- and retrotransposon-based map of diploidAvena
Authors: Yu Gong-Xin , Wise Roger P
Published: April 2011

A saturated genetic map of diploid oat was constructed based on a recombinant inbred (RI) population developed from a cross between Avena strigosa (Cereal Introduction, C.I. 3815) and A. wiestii (C.I. 1994). This 513-locus map includes 372 AFLP (amplified fragment length polymorphism) and 78 S-SAP (sequence-specific-amplification polymorphism) markers, 6 crown-rust resistance loci, 8 resistance-gene analogs (RGAs), one morphological marker, one RAPD (random amplified polymorphic DNA) marker, and is anchored by 45 grass-genome RFLP (restriction fragment length polymorphism) markers. This new A. strigosa × A. wiestii RI map is colinear with a diploid Avena map from an A. atlantica × A. hirtula F2population. However, some linkage blocks were rearranged as compared to the RFLP map derived from the progenitor A. strigosa × A. wiestii F2population. Mapping of Bare-1-like sequences via sequence-specific AFLP indicated that related retrotransposons had considerable heterogeneity and widespread distribution in the diploid Avena genome. Novel amplified fragments detected in the RI population suggested that some of these retrotransposon-like sequences are active in diploid Avena. Three markers closely linked to the Pca crown-rust resistance cluster were identified via AFLP-based bulk-segregant analysis. The derived STS (sequence-tagged-site) marker, Agx4, cosegregates with Pc85, the gene that provides resistance specificity to crown-rust isolate 202 at the end of the cluster. This framework map will be useful in gene cloning, genetic mapping of qualitative genes, and positioning QTL (quantitative trait loci) of agricultural importance.Key words: AFLP, Bare-1 retrotransposon, sequence-specific-amplification polymorphism (S-SAP), resistance-gene analog, crown-rust resistance, Pca, Gramineae, grass anchor probe.
Identification of AFLP markers on the satellite region of chromosome 1BS in wheat
Authors: Zhang Hangning , Nasuda Shuhei , Endo Takashi R
Published: April 2011

The satellite region on the short arm of chromosome 1B in wheat (Triticum aestivum L., 2n = 6x = 42) carries many agronomically important genes; i.e., genes conferring fungal disease resistance, seed storage proteins, and fertility restoration. To find molecular markers located on the satellite region, we applied the fluorescent AFLP (amplified fragment length polymorphism) technique to aneuploids and deletion stocks of the cultivar T. aestivum 'Chinese Spring'. Out of 6017 fragments amplified with 80 primer combinations in normal 'Chinese Spring', 24 were assigned to 1BS. Twelve of them clustered within a small region of the satellite known to be rich in RFLP (restriction fragment length polymorphism) markers. AFLPs in 1BS and in the whole genome were calculated between 'Chinese Spring' and T. spelta var. duhamelianum. The polymorphism rates in the satellite region (58.3%) and in the 1BS arm (45.8%) were much higher than the average rate for the whole genome (10.7%). Seven of the 12 AFLP markers in the satellite region were revealed to be specific to 'Chinese Spring' and could potentially be useful for genetic mapping in a segregation population of 'Chinese Spring' × T. spelta.Key words: AFLP, wheat, deletion mapping, 1BS satellite.