Use of parasites to clarify residency and migration patterns of Pacific sardine (Sardinops sagax) in the California Current

The views and opinions expressed or implied in this article are those of the author (or authors) and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA. Abstract—Migration patterns of the northern subpopulation of the Pacific sardine (Sardinops sagax) were examined by using parasites as biological tags. This approach has been employed on marine fish species worldwide, but it had not yet been used to investigate the migratory behavior of this ecologically and commercially valuable species in the California Current. In 2005–2008, 14 taxa of parasites were recovered from 1388 Pacific sardine collected between British Columbia, Canada, and Southern California. The results of multivariate analyses indicate significant differences in parasite communities among all size classes of Pacific sardine caught off Vancouver Island, British Columbia, compared with those caught off Washington and Oregon and regions off California. Significant differences in parasite communities also were identified between size classes of Pacific sardine: <210, 210– 219, and ≥220 mm in standard length. Our results support a high degree of residency in all size categories of Pacific sardine off Vancouver Island during the study period, and they indicate that individual sardine behavior is not limited to completing an annual migration between British Columbia or the Pacific Northwest and Southern California. These data indicate that using parasites as biological tags could help clarify annual migration patterns of individual Pacific sardine. The Pacific sardine (Sardinops sagax) is an ecologically important pelagic fish in upwelling systems that transfers energy from lower trophic levels (phytoplankton and zooplankton) to upper trophic predators, including fish, marine mammals, and birds (Cury et al., 2000). The Pacific sardine fishery is also economically important, providing for bait, aquaculture feed, and human consumption (Herrick et al., 2009). In the 1930s and 1940s, the Pacific sardine fishery in the California Current was the largest fishery in the Western Hemisphere (reviewed in Wolf, 1992). The fishery collapsed and was closed off the Pacific Northwest (PNW, Oregon and Washington) in 1947 and off Central California in 1967 (Radovich, 1981). Heavily influenced by ocean conditions, the biomass of the Pacific sardine in the California Current System (CCS) fluctuates widely. After a substantial biomass increase in the late 1980s and 1990s (Hargreaves et al., 1994; Emmett et al., 2005), a purse seine fishery reopened in California, the PNW, and off Vancouver Island in British Columbia, Canada, followed by a formal closure in 2015. Three subpopulations of the Pacific sardine are currently recognized in the CCS (reviewed in Smith, 2005). One spawns in the Gulf of California, one spawns in inshore waters of southern Baja California, Mexico, and a northern subpopulation spawns primarily off Southern and Central California. For the management of Pacific sardine, the governments of both the United States and Canada assume all Pacific sardine of the northern subpopulation belong to one northerly migrating stock (Hill et al.). Pacific sardine have also spawned successfully further north in some years, indicating either a possible separate spawning population