PRECISION OF EXPLOITATION-RATE ESTIMATES IN THE TASMANIAN ROCK-LOBSTER FISHERY BASED ON CHANGE-IN-RATIO TECHNIQUES

Determination of exploitation rate is considered important for both st ock assessment and establishment of fishery reference points. From 199 2 to 1996, a project was undertaken to evaluate the change-in-ratio te chnique for estimating exploitation rates for male lobsters off southe rn Tasmania. Confidence limits of exploitation rate estimates were det ermined by bootstrap analysis. This showed wide confidence intervals a round the estimates for the fishing years from 1992-93 to 1994-95. Boo tstrap analysis was used to determine the appropriate sample size (num ber of pot-lifts) for improved precision in exploitation rate estimate s for the 1995-96 fishing year. Results from field estimates confirm t he expected decrease in confidence intervals. The level of exploitatio n had an inverse relationship to the precision of exploitation rate es timates. Relationships can be determined between the level of exploita tion in the fishery and the degree of precision achievable for a set n umber of pot-lifts. Thus, sampling programmes can be designed to minim ize cost and provide the degree of precision required for management s trategies.