Optimising harvest strategies in a multi-species bivalve fishery

Optimising harvests from fishery resources requires appropriate data. In this study, fishery-independent survey and size-at-first maturity (L₅₀) data were used to assess the suitability of current minimum legal sizes (MLS) and total allowable commercial catches (TACC) in the South Australian, mixed-species, mud-cockle (Katelysia spp.) fishery. Estimates of L₅₀ suggested the MLS was conservative in one fishing zone (Coffin Bay), but appropriate elsewhere. Harvestable-biomass estimates (HB) demonstrated that TACCs were excessive in the Port River (41% of HB), suitable in Coffin Bay (10% of HB) and precautionary in the West Coast (1.5%of HB) fishing zones. Consequently, the MLS was decreased by 5 mm shell length in Coffin Bay and the TACCs for the Port River (reduced by 80%) and West Coast (increased by 40%) amended. This study demonstrated that harvest strategies in mixed-species fisheries can be optimised by explicitly considering data on species composition, abundance and population biology.