Genetic Structure of Chum Salmon (Oncorhynchus Keta) Populations in the Lower Columbia River: Are Chum Salmon in Cascade Tributaries Remnant Populations?
Prior to the 1950's, the lower Columbia River drainage supported a run of over a million chum salmon composed of at least 16 populations. By the late 1950's, over-fishing and habitat destruction had decreased the run to as little as a few hundred fish. With the exception of Grays River in the coastal region of the Columbia River and an aggregation of chum salmon spawning in creeks and the mainstem near Bonneville Dam in the Columbia Gorge region, most populations were considered extinct. However, over the years, WDFW biologists detected chum salmon spawning in tributaries originating in the Cascade Range: the Cowlitz, Lewis, and Washougal rivers. Further, chum salmon in the Cowlitz River appeared to have summer and fall run-timings. To assess whether Cascade spawners were strays from Grays River and Gorge regions or remnants of former populations, chum salmon from the Coastal, Cascade and Gorge regions were characterized genetically at 17 microsatellite loci. With the exception of Washougal River chum salmon, which grouped strongly with the Gorge genetic group, significant heterogeneity in genotype distributions were detected between regions and genotype distributions overlapped among collections within regions. In a neighbor-joining consensus tree, regional groups occupied branches with over 77% bootstrap support. In assignment tests, over 63% of individuals were correctly assigned back to region of origin although an average of 29% assigned to river of origin. Genetic distinction of Cascade region chum salmon was similar to distinction of Coastal and Gorge chum salmon and the Cascade region chum salmon had twice the number of private regional alleles. Further, the Cowlitz River supports the only summer chum salmon run in the Columbia River drainage. We propose that chum salmon in the Cascade region are remnants of original populations. We attribute the strong divergence between regional groups to diverse ecological conditions in each region, which promoted regional genetic adaptation and to genetic drift experienced in small populations.
- Research Organization:
- Bonneville Power Administration (BPA), Portland, OR (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- CR-113766
- OSTI ID:
- 948106
- Report Number(s):
- P109823; R&D Project: 200871000; TRN: US200907%%79
- Country of Publication:
- United States
- Language:
- English
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