Genetic diversity of sockeye salmon of Cook Inlet, Alaska, and its application to management of populations affected by the Exxon Valdez oil spill

Genetic data from sockeye salmon Oncorhynchus nerka were collected from all major systems in upper Cook Inlet, Alaska, that produce sockeye salmon, in cluding the Kenai River drainage, a major system that was affected by the E xxon Valdez oil spill. The products of 29 enzymes encoded by 67 protein-enc oding loci resolved by allozyme analysis revealed a substantial amount of g enetic diversity among populations distributed both within and among major drainages. The data support a model of population structure based on the nu rsery lake. A gene diversity analysis estimated that 0.4% of the total vari ability was attributable to the effect of sampling at different sites withi n nursery lakes, compared with 7.5% among nursery lakes within regions and 2.9% among regions. This diversity probably arises from isolation and genet ic drift within nursery lakes and the tendency of sockeye salmon to home wi th great fidelity. Sockeye salmon from these drainages are commercially har vested in mixed-stock aggregations in upper Cook Inlet. Mixed-stock analyse s using maximum likelihood methods with data from 27 loci were performed to estimate the proportion of source populations in upper Cook Inlet fisherie s. Simulations indicated that six regional groups (Kenai River, Susitna and Yentna rivers, West Cook Inlet, Kasilof River, Northeast Cook Inlet, and K nik Arm) could be identified in mixtures at a level of precision and accura cy useful for fishery management. Samples from fisheries were analyzed both in-season (within 48 h) and postseason. Samples taken from within the rive rs were also analyzed to evaluate the baseline and to estimate the contribu tions of individual spawning populations to the larger river systems.