Diver behaviour and its influence on assessments of a quota-managed abalone fishery

摘要

During 1998, we initiated an on-board observer program to gain a better understanding of spatial and temporal patterns of catch and effort in the blacklip abalone fishery of Victoria, Australia. Although average catch per unit effort (CPUE) for thisfishery has been increasing, there has also been significant spatial contraction of the fishing grounds away from reefs of low productivity as a consequence of quota introduction during 1988 to 1989. It is this shift away from.reefs of low productivityrather than an increase in abalone abundance that is responsible for the trend in CPUE. From our on-board observations, divers do not operate in an area if they believe that they will not meet their daily catch expectations; they have a relatively high catch rate threshold for deciding when to shift to another reef. Catch rates per bag of abalone are several times higher than the daily reported CPUE rates, but vary substantially. We conclude that the incentive to maintain high catch rate thresholds forcessation of fishing has led to patterns of rotation of effort at the reef scale that tend to mitigate against high rates of exploitation. This has provided an effective tier of fine-scale self-governance below that controlled by management regulations.However, contemporary changes in the fishery, such as reductions in the number of divers who own access entitlements and their levels of experience, may lead to reduced catch rate thresholds and unfavorable patterns of fishing behavior. There is also a tendency for divers who have recently entered the fishery to concentrate their effort on shallower reefs for reasons of health and safety. Although there is no evidence to date that the over-all status of Victorian abalone stocks has been compromised by these changes, managers need to be aware that regulations affect diver behavior and that it is the divers not the resource that is managed. Our studies reinforce the importance of identifying and promoting behaviors among divers that are desirable in terms of sustainable production within the context of contemporary management strategies.