Uncertainty analysis of a fishery under individual transferable quota management: Applied to the fishery for blacklip abalone Haliotis rubra in the Western Zone of Victoria (Australia)

Abstract

A mathematical model was used to examine the effect that uncertainty might have on future best choices for the total allowable catch (TAC) and minimum length. Its outputs are estimates of annual fishing mortality and effort (required to achieve the TAC), catch rate, mean individual weight, exploited density, and population fecundity. Uncertainty about the fixed inputs to the model, and variation in the annual recruitment to the stock, were simulated with a random number generator. Reduction in the minimum length was shown to be associated with the need for less annual effort to achieve the TAC. The variability of the effort was also reduced. The effect of increasing the TAC was to increase the effort and its variability. Lower and more variable population fecundities resulted from increase in the TAC, and also from reduction in the minimum length. When the model included a stock-recruitment relationship, a high TAC with a low minimum length was shown as likely to cause fishery collapse. The probability of collapse was reduced when the magnitude of the TAC was adjusted according to the population fecundity of the previous year. Combinations of adjustable TAC and minimum length were identified which achieved higher although more variable yields, higher and less variable catch rates, and low probabilities of fishery collapse.