Factors Affecting Puget Sound Coho Salmon (<i>Oncorhynchus kisutch</i>) Runs

Abstract

Summer streamflow, apparently affecting survival of zero-age coho salmon (Oncorhynchus kisutch), is shown to be an important determinant of Puget Sound run strength since 1952. Recently, hatchery production has also been a significant factor. Earlier studies indicated a relationship between rearing flows and coho run strength beginning in 1935. The persistence of the correlation between streamflow and run strength for more than 40 yr is noteworthy. Although the mechanism is unclear, survival of hatchery coho may also be positively dependent upon the same environmental conditions that affect stream-reared coho; a depensatory mortality relationship between abundance of hatchery coho and abundance of stream-reared coho is postulated.Key words: coho salmon, survival, run prediction, hatchery contribution