The fish assemblage of a Newfoundland estuary: Diel, monthly and annual variation

Twice monthly sampling over two 16 month periods at a shallow site on Newfo undland's cast coast showed the fish assemblage to be dominated by four tax a (Gasterosteus aculeatus, G. wheatlandi, Osmerus mordax, Gadus spp.) that accounted for 96% of the individuals collected. Of the 16479 fish measured, 65% were adults based on the estimated size of first spawning. The fish as semblage was dominated (86%) by species with demersal eggs, several of whic h spawn at the same shallow sites used by juveniles as nursery sites. Coast al spawning and demersal eggs maintain offspring in coastal nursery areas w here survival is thought to be increased. Number of species and number of f ish were both correlated with water temperature being highest from mid-summ er to early autumn and lowest in winter. Temperature, time of spawning, and movements of juveniles and adults facilitated grouping species into five a ssemblages based on seasonal abundance: seasonal periodic species (summer a nd winter), regular species, regular species collected in all seasons excep t winter, and occasional (rare) species. At the diel scale, two consistent species groupings were observed: species that showed no significant differe nce between day and night and species caught primarily at night. Number of night species exceeded day species by a factor of two. No seine-caught spec ies in shallow water exhibited significantly higher catches during the day. Observations by SCUBA divers indicated some species were more abundant dur ing day time at slightly deeper depths. This observation in conjunction wit h day and night seining in shallower water, suggests these species aggregat e in deeper water during day and move to shallow waters at night. (C) 2001 Academic Press.