Effects of Streamflow and Upwelling on Yield of Wild Coho Salmon (Oncorhynchus kisutch) in Oregon

Abstract

To investigate the dependence of coho salmon (Oncorhynchus kisutch) yield on streamflow and oceanic upwelling, I regressed catch by the Oregon commercial troll fishery from 1942 to 1962 against indices of offshore upwelling the previous spring and measurements of streamflow from five Oregon coastal rivers during the freshwater rearing phase. A highly significant positive relation was found between total streamflows during the freshwater residency of the fish for the five rivers combined and the weight of the annual catch of coho salmon from 1942 to 1962. There was also a significant positive relation between total combined annual (January–December) flows for these rivers and the catch 2 yr later. Conversely, I found no significant relation between the 60 consecutive days of lowest flow during summer and catch 2 yr later. High flows during freshwater rearing probably provide more habitat and better conditions for growth and survival. I also found a significant positive relation between April through June upwelling at two stations and catch of coho salmon the following year from 1947 to 1962. Fifty-six percent of the variation in catch from 1947 to 1962 was explained by the total flows during freshwater residency, 60 consecutive days of lowest flow, plus combined April through June upwelling at both stations. It is suggested that some stocks of coho salmon smolts may move southward or remain in local offshore waters after they enter the ocean to take advantage of the production of invertebrates resulting from upwelling.Key words: streamflow, upwelling, coho salmon, Oregon coast