The genetic relationships among 337 northern pike (Esox lucius) collected from the coastal zone of the central Baltic region and the Finnish islands of Aland were analysed using five microsatellite loci. Spatial structure was delineated using both traditional F-statistics and individually based approaches including spatial autocorrelation analysis. Our results indicate that the observed genotypic distribution is incompatible with that of a single, panmictic population. Isolation by distance appears important for shaping the genetic structure of pike in this region resulting in a largely continuous genetic change over the study area. Spatial autocorrelation analysis (Moran's I) of individual pairwise genotypic data show significant positive genetic correlation among pike collected within geographical distances of less than c. 100-150 km (genetic patch size). We suggest that the genetic patch size may be used as a preliminary basis for identifying management units for pike in the Baltic Sea.
A bioenergetics model was developed for Eurasian perch (Perca fluviutilis L.) by revising an existing model for yellow perch and walleye. Data were gathered from field studies and the literature. Besides adjusting the original parameters of the model, effects of season on consumption and metabolic rates were added. The predictive capability of the revised model was high both concerning the levels of growth and its seasonal development in the Baltic coastal waters to which the model was applied. Perch young-of-the-year attained almost maximum consumption and growth except in the highest temperatures experienced. In larger fish, the model estimated consumption to be about 50 per cent of the maximum possible rate.
Population structure, recruitment, mortality, life expectancy, age at maturity, gonad development, fecundity, net reproductive rate and energy storage were studied in a perch population exposed to thermal discharge. The experiment was conducted during 1978-1990 in an artificial enclosure at a nuclear power plant on the Baltic Sea coast. Abundance increased after the plant started operating, although the proportion of larger perch dropped to a low level. Recruitment improved, but adult mortality increased. This effect was accentuated as the fishes matured very early and at a very small size, reducing their ability to support a growing gonad in high winter temperatures. During the spawning period, condition dropped to very low levels accompanied by increased mortality. Surviving fish delayed the next spawning by one or more years and reduced their fecundity. Body condition thus improved in large perch at the end of the study period. Life-time fecundity was reduced, and reproductive performance shifted to younger ages. 1995 The Fisheries Society of the British Isles
Variations in the year-class strength of perch (Perca fluviatilis) were analyzed among 23 populations in Baltic coastal areas distributed between 57 and 66°N using the age distribution in catches. In spite of large differences in abiotic and biotic factors, the variations in year-class strength were similar in 14 of these areas. The similarities could be attributed to large-scale weather variations influencing water temperature. Year-class strength was shown to be correlated with an index based on temperature and day length during the whole first year of life. In two of the nine deviating populations, perch nursery areas are situated in small nearshore freshwaters, where fluctuations in the water level may be more important for recruitment than temperature variations. The other deviating areas were exposed to environmental disturbances, i.e. acidification, oxygen deficits, pulp mill effluents, and thermal discharge, which obviously affected recruitment in a decisive way.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.