夏期ベーリング海に分布するサケ•マス類の生物学的多様性

概要

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Sockeye Oncorhynchus nerka, chum O. keta, and pink salmon O. gorbuscha caught by surface gillnets in the Bering Sea during the summers of 1987 and 1988 were investigated to clarify the ex-tent of the biological variation among individuals of each species. Between fishing dates, chum salmon showed differences in age composition and pink salmon in sex ratio, while sockeye salmon showed none in either category. The mean gonad weight of the three species changed as the dates proceeded, although chum salmon did not exhibit clear modal increases in the gonad weight through the survey period. Diurnal differences in sex ratio and mean gonad weight were only recognized in chum and male pink salmon, respectively. Different ocean age groups of sockeye and chum salmon were observed concomitantly, even in a single short-period catch (2-3 hours in soaking time of the gillnets). The three salmonids showed marked differences in biological variety beyond the specific difference simply predicted from the age variation; the most heterogeneous species was chum, while the least was pink salmon.