Temporal and geographic variation in fish communities of lower Cook Inlet,Alaska

Nearshore and shelf fish communities were studied in three areas of lower C ook Inlet, Alaska: the Barren Islands (oceanic and well-mixed waters), Kach emak Bay (mixed oceanic waters with significant freshwater run-off), and Ch isik Island (estuarine waters). Fish were sampled with beach seines (n=413 sets) and midwater trawls (n=39 sets). We found that lon er Cook Inlet supp orted a diverse nearshore fish community of at least 52 species. Fifty of t hese species were caught in Kachemak Bay, 24 at Chisik Island, and 12 at th e Barren Islands. Pacific sand lance dominated Barren Islands and Kachemak Bay nearshore habitats, comprising 99% and 71% of total individuals, respec tively. The nearshore Chisik Island fish community was not dominated by any one species; instead it exhibited higher diversity. These spatial differen ces appeared linked to local oceanographic regimes and sediment influx. Ana lysis of historical data revealed that the nearshore Kachemak Bay fish comm unity changed significantly between 1976 and 1996, showing increased divers ity and abundance in several taxa, notably gadids, salmanids, pleuronectids , and sculpins. Decadal differences appeared to be related to large-scale c limate changes in the North Pacific. Catches of most taxa peaked in May-Aug ust, and were low during other months of the year. Several species were pre sent for only part of the summer. Species composition of seine catches diff ered significantly between consecutive high and low tides, but not between consecutive sets or years. Midwater trawls took 26 species, 14 of which wer e present in Kachemak Bay, 19 near Chisik Island, and 7 at the Barren Islan ds. Community structures in shelf and nearshore waters were similar: divers ity was high and abundance low at Chisik Island, whereas a few abundant spe cies dominated at both Kachemak Bay and the Barren Islands. In addition, th e low fish abundance near Chisik Island appeared to be related to declining seabird numbers at this colony.