Proximate Composition and Fatty Acid Differences in Hatchery‐Reared and Wild Snake River Sockeye Salmon Overwintering in Nursery Lakes

Abstract

AbstractIn the artificial propagation program for endangered Snake River sockeye salmon Oncorhynchus nerka, a portion of the F1 progeny (produced from spawning captive parents) are retained in the hatchery through maturation and spawning; the remaining progeny are reintroduced to nursery lakes in central Idaho at several life history stages (egg, presmolt, and smolt). In this study, the proximate and fatty acid compositions of sockeye salmon from presmolt releases were analyzed both at planting and at out‐migration to assess their feeding success after overwintering in nursery lakes relative to that of overwintering wild fish. Hatchery‐origin presmolts did not grow significantly over the winter. However, size and length were similar between hatchery‐origin fish and wild out‐migrants. Average percent whole‐body lipid declined significantly in hatchery‐origin sockeye salmon overwinter. Hatchery‐origin out‐migrants also had significantly lower whole‐body lipid than wild counterparts migrating from Redfish Lake, Idaho, over the 6 years examined. The lack of growth and significantly lower body fat content of hatchery‐origin sockeye salmon suggest that the food resources available to both wild and hatchery‐origin presmolts were not utilized equally. There were also significant differences in fatty acid composition between wild and hatchery‐origin out‐migrants. Wild out‐migrants had fatty acid profiles indicative of the zooplankton diet typical of resident sockeye salmon in the lake. In contrast, hatchery‐reared juveniles introduced as presmolts in the fall had fatty acid profiles resembling those associated with hatchery diets and showed no evidence of the fatty acids characteristically observed in zooplankton. After overwintering, hatchery‐origin out‐migrants had fatty acid profiles that were intermediate between those of fish at planting and those of wild fish, reflecting some zooplankton intake during this period. The compromise in lipid quantity and quality for hatchery‐produced presmolts may, in part, explain the large observed reductions in smolt‐to‐adult survival relative to that of naturally produced sockeye salmon.