Microsatellite DNA Data Indicate Distinct Native Populations of Kokanee, Oncorhynchus nerka, Persist in the Lake Sammamish Basin, Washington

Abstract

Large-scale introductions of resident and anadromous salmonids from exogenous sources and urbanization have led to major changes in, and concern for the fate of, indigenous fish populations of the Lake Sammamish/Lake Washington Basin. Specifically, introductions of kokanee (the resident form of Oncorhynchus nerka) from the Lake Whatcom Hatchery and sockeye (the anadromous form of O. nerka) from Baker Lake have caused uncertainty about the ancestry of the kokanee that currently spawn in the basin. We used nine microsatellite loci to investigate the inter-relationships of kokanee populations that spawn in streams in the Sammamish sub-basin, sockeye salmon populations that share spawning areas with the kokanee, Lake Whatcom Hatchery kokanee and Baker Lake sockeye, and an outgroup, Meadow Creek kokanee, from Lake Kootenay which drains into the upper Columbia River. We observed high levels of genetic variation (5–49 alleles per locus). Explicit tests of population sub-division revealed that collections from most spawning aggregations differed from each other. Observed allele frequency distributions strongly suggest that natural spawning kokanee in the basin are not descended from recent Lake Whatcom stock introductions. We found no compelling evidence to suggest that the kokanee sampled from spawning areas within the Lake Sammamish sub-basin have resulted from, or been altered substantially by, past introductions of non-native kokanee or sockeye.