The fish taxocenes of two typical river systems in Poland and Ontario differed in patterns of species richness, distribution, life history, and ecomorphology. In small streams there were more small nektonic and benthic fishes in Ontario. In Poland where large, nektonic cyprinids dominate, the fishes were larger, longer lived, later maturing, and absolutely and relatively more fecund and had longer reproductive spans, but egg diameters were similar. In Ontario, nester/guarders and brood hiders were common, whereas in Poland all but three species broadcast eggs. Small-stream fishes were small, early maturing, short lived, and sedentary and gave parental care to few, large eggs. Large-river fishes displayed opposite characteristics and often migrated to spawn in habitats suitable for young but not adults. The factor space of a principal components analysis of ecomorphological characteristics corresponded roughly to a longitudinal gradient in fluvial conditions. There was a significantly higher proportion of fishes from Poland in the downstream half of the space, and vice versa. The most prominent differences in taxocene structure generalize to west-central Europe and east-central North America. Evidently, several groups of North American fishes invaded and became adapted to small streams, facilitating speciation. European fishes retained the strategy of seasonal/ontogenetic longitudinal migration. Ancestors to the most diverse groups in North America inhabited both continents; consequently, long-term climatic patterns (glaciation) and/or the influence of lowland ichthyofauna are the most likely causes of the differences.

No abstract

No abstract

This study is based on 18 surveys, 12 in summer, and three each in spring and fall, with bottom trawls over the Scotian Shelf and Bay of Fundy. The data analysis sequence was: temporal and spatial aggregation of trawl sets; estimation of interspecies and intersite distance indices; clustering and ordination of sites and species, and discrimination of site groups using environmental variables. Nine species-groups, and 10 site-groups were defined, and displayed in a two-way table. Depth and temperature were the environmental variables most strongly associated with differences in assemblage structure among site-groups. Changes in assemblage structure from one area to another were distinct but apparently gradual, with no sharp assemblage boundaries. This pattern is expected if species are distributed independently on environmental gradients, rather than if assemblages consist of highly co-evolved, interdependent species. The observed spatial patterns were highly persistent through time. There are regions which are relatively homogeneous with regard to species composition and which can therefore be useful in dealing with bycatch problems. However, this study does not indicate the existence of discrete assemblages which might be appropriate as ecologically based fishery management units.

This study describes and maps demersal fish assemblages for the east coast of North America from Cape Hatteras, North Carolina, to Cape Chidley, Labrador, evaluates evidence for interannual shifts in assemblage distribution, and examines the relationship of the assemblages to accepted biogeographical boundaries. Demersal trawl survey data collected from 1975 to 1994 were analyzed. Visual classification of distribution maps for the 108 most abundant demersal species revealed nine species groups, based on both geography and depth distribution. Eighteen assemblage groups were identified using principal components analysis (PCA) and mapped. Assemblage groups were also identified by cluster analysis. Fish assemblages identified by both methods were spatially coherent. Assemblage distribution patterns were not consistent with accepted biogeographical boundaries. The PCA explained only 56.3% of the variance in distribution of the species, indicating that the assemblages should be interpreted as indeterminate, potentially adaptable entities rather than as rigid ecological constructs. Assemblages were persistent in composition through time but appeared to shift in location. The apparent looseness of the assemblages and their persistence through time in spite of severe impacts from fishing suggest that single-species management approaches may not be entirely inappropriate for the major groundfish species in the study area.