Cod and other species of fish larvae, and nauplii and copepodite copepods, were sampled in the western Irish Sea in April/May 1988 and 1989. The diet of cod larvae was determined by gut analysis, and consisted almost entirely of copepods. The daily energy requirements of 3 sizes of cod larvae were determined from modified forms of published energetic models, and used to estimate numbers of copepods eaten per larva per day. The volume of water searched by larvae is modelled as a power function of larvae length. Modelling predictions indicate that cod larvae of < 5 mm length require high densities of copepod nauplii as they can search only small volumes of water. Larger larvae, 2 7.5 mm length, consume large numbers of copepodites and so require high densities of copepods to avoid depletion of the food resource. Observed copepod densities were sufficient for the energy requirements of the cod larvae populations at the densities observed in the western Irish Sea. However, when all species of larvae are considered, the model predicts that competition for food is likely to occur among larger larvae at observed copepod densities.
The abundance of Profilicollis botulus was monitored in eider ducks for 3 years. No significant difference in P. botulus abundance was found between eiders taken alive and those collected dead from the shore line, or between adult males and adult females. Adult male eiders had a seasonal pattern of infection. Incubating female eiders lost their infection in almost all cases, suggesting that a seasonal pattern of infection must also occur in these birds. Eiders in their first winter had P. botulus abundances which were approximately 10 times that of adult eiders, but by the following summer the abundance had declined to that found in adults. Data are compared with previous studies undertaken on the Ythan estuary. Captive eiders were used to determine the developmental rate of female P. botulus and the percentage of administered cystacanths which established in the intestine. There was no evidence to suggest that male and female P. botulus have different life-spans.
Eastern mosquitofish (Gambusia holbrooki) having inbreeding coefficients of 0, 0.125, and 0.25 were exposed to a salinity stress of 14.34 parts per thousand (ppt) for 96 h, and their survival times were determined. Statistical models were fitted to the failure-time data to assess differences between the survival functions based on inbreeding coefficient, family, and genotype of the fish. Predicted median survival times were determined for inbreeding classes, families within inbreeding classes, classes based on number of heterozygous loci, and genotypes at single loci. Family significantly affected survival of individuals in all analyses, regardless of the inbreeding coefficient of the individual. The inbreeding coefficient of an individual did not statistically affect survival. The number of heterozygous loci per individual significantly affected survival time but only when family as well as number of heterozygous loci per individual were included as independent variables in the analysis. Genotypes of two loci, m-isocitrate dehydrogenase A and glucose phosphate isomerase B, also significantly affected survival. Our study demonstrates that family can account for a greater proportion of the variance in survival under environmental stress than either inbreeding coefficient or number of heterozygous loci. Family effects, in addition to inbreeding, should be considered in conservation management plans.Résumé : On a exposé la gambusie (Gambusia holbrooki) possédant des coefficients de consanguinité de 0, 0,125 et 0,25 pendant 96 h à un milieu dont la salinité était de 14,34 ppt, puis on a déterminé son temps de survie. On a appliqué des modèles statistiques aux données échec-temps en vue d'évaluer les différences entre les fonctions de survie basées sur le coefficient de consanguinité, la famille et le génotype du poisson. On a déterminé la valeur médiane des temps de survie prévus pour les classes de consanguinité, les familles à l'intérieur de ces classes, les classes basées sur le nombre de locus hétérozygotes et les génotypes à des locus seuls. Dans toutes les analyses, la famille influait de façon significative sur la survie des individus, indépendamment du coefficient de consanguinité de l'individu. Le coefficient de consanguinité d'un individu n'influait pas statistiquement sur la survie. Le nombre de locus hétérozygotes par individu influait beaucoup sur le temps de survie, mais seulement lorsque la famille ainsi que le nombre de locus hétérozygotes par individu était inclus comme variables indépendantes dans l'analyse. Les génotypes de deux locus, la m-isocitrate-déshydrogénase A et la glucose-phosphate-isomérase B, influaient aussi considérablement sur la survie. Notre étude montre que la famille permet d'expliquer une plus grande proportion de la variance dans la survie en présence d'un stress environnemental, que le coefficient de consanguinité ou le nombre de locus hétérozygotes. En plus des effets de la consanguinité, il y aurait lieu de tenir compte des effets de la famille lors de l'élaboration de plans...
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