MIGRATION OF PACIFIC SARDINE (SARDINOPS SAGAX) OFF THE WEST COAST OF UNITED STATES IN 2003-2005

The Pacific sardine, Sardinops sagax (Jenyns, 1842), is distributed along the West Coast of North America from Baja California to British Columbia and supports a relatively large fishery off Oregon and Washington (Pacific Northwest, PNW). Based on four trawl surveys in July 2003, March and July 2004, and March 2005 off Oregon and Washington (42 degrees N-48 degrees N, 124 degrees W-128 degrees W), we estimate overall and size-specific annual population migration rates in 2003-2005 from the PNW to California and a minimum migratory biomass from California to the PNW. The difference in biomass of potential migrants (fish >= 200 mm) between July and March cruises was used to estimate the annual total and length-specific Pacific sardine migration rates in 2003-2005. An estimated 54% (CV = 0.12) of the total biomass of Pacific sardines, 42% (CV = 0.29) of 200 mm fish, 44% (CV = 0.25) of 210 mm fish, and close to 100% of > 210-mm fish moved from the PNW to California annually in 2003-2005. At least 16,000 mt (CV = 0.42) moved from California to the PNW in the summer of 2004. These results indicate that Pacific sardine populations off California and the PNW are not isolated stocks. The estimated annual migration rates can be incorporated into stock assessment models and be used to enhance understanding the stock structure off the PNW and California.