MEPS 190:37-51 (1999)  -  doi:10.3354/meps190037

ABSTRACT: Juveniles and small adults of at least 75 species of demersal fishes were identified in trawl catches from the nearshore waters of Kodiak Island, Alaska, in August 1991 and 1992. We derived several indices to characterize community structure at each site, identified key environmental gradients along which community structure was organized, and identified those species whose abundances varied most strongly along these gradients. We related species richness, species diversity, and total catch per unit effort to environmental variables observed at each site. Species richness and diversity were highly variable among sites, but decreased significantly with salinity and were significantly higher on heterogeneous sediments. Standardized catch per unit effort for all species combined differed significantly among 5 geographic areas and was significantly higher on sediments with a high sand and/or mud content. Indices of species composition for each sampling site were obtained as the scores of ordination axes based on non-metric multidimensional scaling of Bray-Curtis dissimilarities between sites. The indices summarized different aspects of community composition and were associated with different species groups. The first and major index was primarily related to the depth-temperature gradient and contrasted a shallow, warm water species group with a deep, cold water group. Non-linear depth effects on most indices suggest relatively rapid changes in species composition in shallow water (0 to 50 m), and more gradual changes in the lower part of the depth range. While the depth-temperature gradient was the most important gradient along which species composition was structured, sediment composition and geographic area accounted for a significant proportion of the variance of each of the indices. While species composition changed most strongly along the depth-temperature gradient, species richness, diversity, and total abundance were not related to depth or temperature, suggesting that species composition changed independently of the overall abundance and of species richness and diverstity.

KEY WORDS: Community structure · Demersal fish · Depth · Kodiak Island, Nearshore zone · Non-metric multidimensional scaling · Sediment composition