Estimating the abundance of abalone ( Haliotis spp.) stocks—examples from Victoria and southern New Zealand

A survey method appropriate for the estimation of the relative abundance of disaggregate substocks is described using examples from abalone fisheries of Victoria (Australia) and southern New Zealand. The method, based on the collection rates of research divers from timed searches, can produce precise estimates of relative abundance over large spatial scales. For Victoria stocks of abalone, both seasonal and annual variation in the relative abundance of abalone was demonstrated. Seasonal differences in abundance may be attributed to incentive-driven effort applied to the Victorian fishery and the aggregative behaviour of abalone. Stocks of abalone from southern New Zealand are distributed over large spatial scales and are subject to conditions of extreme exposure. Nonetheless, preliminary surveys established that future surveys would have high power to detect a change in the relative abundance of abalone. The survey method, successfully applied to spatially heterogeneous stocks in Victoria and southern New Zealand, has the potential to improve the robustness of stock assessments of abalone fisheries and other accessible disaggregate fish species.