Genetic Assessment of Surf Smelt Stock Structure in Puget Sound

The surf smelt Hypomesus pretiosus is an abundant and widely distributed forage fish, and an obligate intertidal benthic spawner.  Under the Washington Department of Fish and Wildlife's 1998 Forage Fish Management Plan each documented spawning beach is treated as an independent demographic unit (i.e., stock) for fishery and conservation purposes.  The reproductive independence of these beach-specific stocks, as well as putative summer-only and winter-only Sound-wide stocks, has never been rigorously evaluated.  Bulk sediment samples were collected from spawning beaches throughout Puget Sound, the San Juan archipelago, the Strait of Juan de Fuca, and the southern Strait of Georgia, with nuclear DNA extracted from individual eggs contained therein.  Both summer- and winter-only putative stocks were sampled.  To expand the range of geographic and evolutionary inference of the analysis, genetic material was also collected from adult fish caught near Port Renfrew and Vancouver, BC, as well as in the Bering Sea, AK.  Using microsatellite primers developed for related species, as well a suite of novel primers, seventeen polymorphic microsatellite markers were identified for use in delineating population structure. Alleles per locus ranged from 9 to 54, and heterozygosity exceeded 80% for collections.  Eight of the seventeen markers conformed to Hardy–Weinberg equilibrium, and we suspect null alleles are present at some loci.  Based on F-statistics and principle components analysis, genetics results suggest all Puget Sound samples came from a single, homogenous population.  In addition to having implications for the way that surf smelt fisheries are managed in Puget Sound, this genetic uniformity raises several questions about larval and adult distribution potential and movement patterns, as well as providing evidence for a lack of natal beach homing in this species.