Growth Variation of Coho Salmon Oncorhynchus kisutch in the Western North Pacific

Abstract

Growth variation of coho salmon in the western North Pacific Ocean from 1973 to 1987 was examined on the basis of fork lengths and scale measurements. Average fork lengths of coho salmon sampled by gillnets in July in the area of 44-50°N latitude and 160-180°E longitude showed long-term variations, decreasing from 1975 and increasing from 1983, and also showed strong odd-even year fluctuation. The scale measurements indicated that long-term variations in growth occurred during the freshwater period and during the first year of ocean life. Substantial odd-even year fluctuation in growth occurred only during the second year ocean life. We hypothesize that intraspecific density-dependent growth is an important factor affecting growth during the freshwater stage and interspecific density-dependent growth is important during the second year ocean life, the latter due primarily to the overlap of diet between coho and pink salmon.