Enhancement of red abalone Haliotis rufescens stocks at San Miguel Island: Reassessing a success story

Abstract

Outplanting of hatchery-reared juvenile abalone has received much attention as a strategy for enhancement of depleted natural stocks. Most outplants attempted to date appear to have been unsuccessful. However, based on genetic analyses of a population sample taken in 1992, it has recently been suggested that a 1979 outplanting of red abalone Haliotis rufescens, on the south side of San Miguel Island (California, USA), was successful and probably sustained the fishery there through the 1980s. We resampled the San Miguel population in 1999 and found no genetic signature of the outplants. Allelic frequencies in our 1999 sample closely resemble those observed in a pre-outplant 1979 southern California sample and two 1999 northern California populations. All genotypic frequencies were in Hardy-Weinberg expected proportions. We also assessed mtDNA diversity at San Miguel and found it not to differ from that of 2 robust northern California populations of H. rufescens. Our results suggest that either the composition of the San Miguel abalone population changed rapidly between 1992 and 1999, or the genetic anomalies attributed to hatchery source for the 1992 sample were due to sample degradation or other laboratory artifacts. Since we lack samples from the 1992 collections, we cannot directly test which explanation is valid. However, several lines of reasoning call into question the earlier conclusion of outplant success.