Yield‐ and egg‐per‐recruitanalyses for the new zealand rock lobster, jasus edwardsii

Abstract

The effects of different values of the instantaneous natural (M) and fishing (F) mortality rates and the minimum legal size on the yield‐ and egg‐per‐recruit of Jasus edwardsii were estimated for 10 areas around New Zealand. At the current assumed value for M of 0.10, the yield‐per‐recruit of females was insensitive to changes in F or the minimum legal size, whereas the yield‐per‐recruit of males was maximised at relatively low levels of F and large values for the minimum legal size. Egg‐per‐recruit (EPR) values varied considerably among areas. The weighted average exploited EPR as a percentage of the unfished EPR for the North and South Islands combined was 27%, and it is not clear if current levels of egg production are sufficient to sustain the population. At the current minimum legal size, a large reduction in F below the current estimated value is required to increase EPR values substantially. Increasing minimum legal size at the current level of F would result in modest increases in EPR. The goals of maximising yield‐ and egg‐per‐recruit do not conflict, provided fishing mortality is not reduced below about 0.4. © Crown copyright 1989.