Distribution and abundance of small flatfishes and other demersal fishes in a region of diverse sediments and bathymetry off Oregon

Reprinted from Fishery bulletin, Vol. 76 (3), page 629-640.Demersal fishes were sampled at seven stations located inshore of Heceta Bank, on Oregon's continental\ud shelf, over a 2-yr period with a 3-m beam trawl designed to catch small fiatfishes. Two general\ud assemblages of fishes were recognized: a shallow water 74-102 m), sandy-bottom association where\ud Pacific sanddab, Citharichthys sordidus,was numerically the dominant species, and a deeper (148-195\ud m) assemblage, generally on mud, where the slender sole, Lyopsetta exilis, predominated. Rex sole,\ud Glyptocephalus zachirus, was usually the second most common species at all stations. Dover sole,\ud Microstomus pacificus, ranked fourth to sixth by numbers and composed the largest biomass (wet\ud preserved weight) at three stations. Species diversity was lowest at the shallowest station where\ud sediments were well-sorted, fine sands that contained only 0.l'1 organic carbon.\ud The biomass of all fishes captured ranged from 0.9 to 2.4gm - 2 These values are low compared with\ud estimates made by others off Oregon and Washington using commercial-sized otter trawls. presumably\ud because of avoidance of the small beam trawl by large fishes.\ud An analysis of variance of the catches of all fishes combined, of Dover, rex, and slender soles, and of\ud Pacific sanddab revealed few significant effects of sediment, depth or season. Sediment type had a\ud significant effect on the catches of slender sole--largest catches were on a clayey-silt bottom. Catches of\ud sanddab were inversely related to depth of water. Depth-season interactions were significant for all\ud species combined and for rex and Dover soles, numbers were higher at the deepwater stations during\ud winter than summer, indicating seasonal bathymetric movements. Annual variations were marked\ud total catches and catches of most species were larger for unknown reasons during 1968 and 1969 than\ud 1970.\ud Based on length-frequency data, age-group 0 -(50 mm standard length( rex sole were found in high\ud proportions at the deepest stations on the outer edge of the continental shelf. Small sanddab