Differences in Survival and Physiology between Coho Salmon Reared in Seminatural and Conventional Ponds

Abstract

Abstract Concern that hatchery fish may not transition well upon release into the wild has resulted in research directed at producing fish with more wild characteristics. To explore the possibility of generating more adaptable fish with alternative rearing strategies at a production-level hatchery, we modified an existing dirt-bottomed rearing pond at the Elochoman Hatchery, Washington, into a seminatural rearing pond (SNP) by adding large woody debris and pit-run rock. The pond was stocked with Type-N lower Columbia River coho salmon Oncorhynchus kisutch from three consecutive broods (1995–1997) at densities about 5% of those that are typical for hatchery rearing. Fish were allowed to migrate volitionally from treatment and control ponds (CP) and were sampled weekly to determine size, condition factor (105;th·;thweight/length3), and gill Na+, K+-ATPase enzyme activity. Each group was coded-wire-tagged, and smolt-to-adult survival was estimated. In 2 of the 3 years, fish from the SNP were larger at migrat...