Evaluation of abalone stock enhancement through the release of hatchery-reared seeds

Abstract

The Abu Fishery Cooperative has planted hatchery-reared seed of the abalone Haliotis discus discus since 1981. The number of 15-40-mm seeds planted annually varied from 34000 to 180000 between 1981 and 1992. Catches were sampled on seven to 10 days during each fishing season (29-56 days between July and September) from 1983 to 1992. The numbers of both seeded and wild abalone were recorded per 8-kg shipping basket on each sampling day. The numbers of seeded abalone in the catch were estimated by a two-stage sampling method. Variances were estimated from the data, which were stratified into two periods: the first when divers dived at depths of less than 5 m, and the second during the subsequent period of deeper diving. The values of these variances were substantially lower than the values of variances estimated from unstratified data. Some of the planted abalone reached 90 mm in length 21 months after seeding, and they could not generally be found in the wild stock after the age of 6 years. Recapture rates were estimated to range from 12% to 51% in the 1980-85 year classes that had been fished for their entire lives.