Subsistence and recreational mussel (Perna perna) collecting in KwaZulu-Natal, South Africa: fishing mortality and precautionary management

Abstract

Both recreational and subsistence collectors utilise Perna perna in KwaZulu-Natal. The former collect 200–2501 of mussels annually from about 110 km of rocky shore and the latter 12–501 from 3 km of rocky shore. Recreational collectors are subject to a daily bag limit of 50 mussels and so select larger mussels than subsistence collectors. In central KwaZulu-Natal, there were 700–800 mussels of the size range selected by recreational collectors per running metre of rocky shore and, at Kosi Bay, 1400–1500 mussels in the subsistence size range per running metre. This excludes stretches of rocky shore in both areas where mussels are virtually absent. Parametric bootstrapping was used to estimate variance in fishing mortality from variances in input parameters (including catch). Fishing mortality at two recreational zones was 0.6 (95% confidence interval: 0.58–0.62) and 0.46 (0.45–0.47) and at two rocky points at Kosi Bay where subsistence collectors target mussels, 0.42 (0.410.44) and 0.27 (0.26–0.28). Decision tables are provided of target fishing mortalities for three levels of risk of exceeding fishing mortality at maximum sustainable yield for each fishery vs three assumptions about the variability in catch estimates. One recreational zone requires a substantial reduction in effort to reduce fishing mortality to the target No change in subsistence collecting at Kosi Bay is required, but the limited access policy should be maintained.