Use of Microsatellites to Determine Population Structure and Migration of Pacific Herring in British Columbia and Adjacent Regions

Abstract

This study assessed genetic population structure of Pacific herring Clupea pallasii in British Columbia and adjacent regions by analyzing microsatellite variation; the utility of microsatellites for stock identification applications was also evaluated. Variation at 14 loci was surveyed in approximately 26,000 Pacific herring from 90 sampling locations. Estimates of the genetic differentiation index F _ST by locus varied between 0.000 and 0.014, and the mean across all loci was 0.003. Four stocks of Pacific herring were defined in British Columbia, and stocks were also identified in southeast Alaska, Washington, and California. In British Columbia, differences in timing of spawning are the main isolating mechanisms among stocks, although geographic isolation of the spawning populations may also have some effect in maintaining the genetic distinctiveness of each stock. The limited genetic differentiation among Pacific herring populations in British Columbia is consistent with among-population straying rates that are sufficient to homogenize allele frequencies over broad areas. Analysis of simulated mixtures from fishery sampling suggested that acceptable estimates of stock composition were achieved by use of the microsatellites. Mixed-stock samples (∼1,700 individuals) were collected during research vessel surveys from 14 locations in British Columbia. Analysis of summer mixed-stock samples from the Strait of Georgia and adjacent waters indicated that resident fish on the west side of the strait were mainly derived from primary-spawning populations (i.e., those that spawned during the primary period in March) that failed to migrate to traditional summer feeding grounds. On the east side of the strait, Pacific herring of mainland inlet origin were found in higher proportions and presumably did not move in appreciable numbers to feeding areas off the west coast of Vancouver Island. In northern British Columbia, fish from northern late-spawning populations dominated fishery samples collected in waters adjacent to the mainland until the end of June; however, by late July, this group had been replaced almost entirely by primary-spawning Pacific herring of British Columbia origin.