Comparison of Midsummer Survival and Growth of Age-0 Hatchery Coho Salmon Held in Pools and Riffles

Habitat use studies have shown that juvenile coho salmon Oncorhynchus kisutch select pools over riffles. However, stream alterations have caused pool habitat to be lost or degraded throughout the Pacific Northwest. This study compared the growth and survival of age-0 coho salmon in riffles and pools in four streams in the South Umpqua River basin, Oregon. Hatchery coho salmon were stocked in block-netted riffles and pools. At the end of the study, the fish were recovered in order to measure their growth and survival in each habitat type. The survival of coho salmon was significantly higher (P < 0.01) in pools (67%) than in riffles (27%). This variation in survival was related primarily to water depth. The growth of coho salmon did not differ significantly (P > 0.05) between pools and riffles. The condition factor of the coho salmon was significantly (P < 0.05) lower at the end of the experiment but did not differ between fish in pools and riffles (P > 0.05). The results of this study suggest that land management activities that reduce pool habitat may also reduce juvenile coho salmon survival or rearing capacity in small streams.