Stock Composition of Chinook Salmon in California Recreational Ocean Fisheries Inferred from Genetic Analysis

Chinook salmon is a valuable species for commercial and recreational fisheries in North America. Together with several rockfish species, it constitutes the most important target for marine recreational fisheries along the California Coast. During the last 30 years, a general decline of southern salmon stocks has been noticed, resulting in the recent complete closure of the fishery off of California. A better understanding of the temporal and spatial distribution of stocks in the ocean are critical for fishery management, for a better understanding of natural fluctuations of populations, and for protection of endangered stocks. Knowledge of salmon stock distribution in the ocean has come mainly from the use of coded wire tags (CWT). While CWTs contain exact information about the river and date of release, they are mostly deployed on hatchery fish and their recovery rates are low. Today, a variety of naturally occurring genetic markers allow assignment of ocean-caught salmon (wild or hatchery populations) to their stock of origin. We used 96 single nucleotide polymorphisms (SNPs) to assign fish caught in California recreational ocean fisheries over a five years period (1998 to 2002) to 21 potential reporting units from Alaska, British Columbia, Washington, Oregon, and California. A total of 10,273 samples were processed. The individuals were assigned to 16 out of the 21 potential reporting units. Almost all (97%) of the fish were assigned to stocks from rivers in California, with 3% assigned to rivers in Oregon and Washington and no fish assigned to either Canadian or Alaskan reporting units. In addition 0.1% of fish were assigned as Coho salmon. The Central Valley fall run reporting unit dominated the fishery across fishing zones (79 - 95 %) and years (86 - 92 %). Most of the reporting units showed a distribution according to distance from their estuary, with highest proportions found in the vicinity of the estuary and decreasing with distance from natal rivers. We did not find large variance in reporting unit proportions between years sampled, however, within a year significant temporal changes in the fishery composition were observed.