Research Document - 2000/172

Structure of Yelloweye Rockfish (Sebastes ruberrimus) Populations in British Columbia

By Yamanaka, K.L., Withler, R.E., Miller, K.M.

Abstract

Genetic analyses of 2520 yelloweye rockfish at 13 microsatellite loci were conducted in 1999-2000. Twenty-five samples were collected at nine sites from northwestern Vancouver Island (49.50 N 127.5 W) to southeast Alaska (57.18 N 136.07 W) and included Bowie Seamount (53.30 N and 135.60 W). Allelic diversity and observed heterozygosity levels at microsatellite loci were high, indicating that effective population size was large. Pairwise tests of allele frequencies between samples did not refute the hypothesis that all samples were drawn from a single panmictic population. Although the genetic data provides evidence of a single 'unit stock' among yelloweye rockfish in this study, the age composition data indicate that demographic factors vary on a much smaller spatial scale. The low level of genetic differentiation among yelloweye rockfish is likely the result of larval dispersal by ocean currents. However, adult yelloweye rockfish are resident over specific rocky habitats and move little. Hence the combination of biological characteristics (longevity and sedentary behavior) and fishery harvests, have caused detectable changes in yelloweye rockfish population parameters. The general north to south cline of increasing total mortality estimates highlights the influence of fishing on local population structure. Heavily fished populations are characterized by a truncation of the age distribution as older individuals are removed by fishing and not replenished rapidly by adult immigration or population growth. The use of management units for yelloweye rockfish, which are geographically smaller than the single panmictic population detected, seems prudent.

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