Catch per unit effort (CPUE) is widely used as an index of abundance in the assessment of abalone fisheries even though it has often been considered unreliable. This is because, it is susceptible to hyperstability and influenced by factors other than stock abundance such as increased fishing efficiency, market demand for particular product, weather, diver habits, and putative rotation of fishing grounds. These factors introduce uncertainty to the use of CPUE as an index of relative stock abundance, with some of these factors causing hyperdepletion of the index. In the western and southern zones (WZ and SZ) of South Australia, commercial fishers recently suggested that declining CPUE in 2014 was attributed to a fishing season with poor weather, and in particular higher than average swell, rather than to declines in stock abundance. To evaluate the effect of weather on CPUE in the SZ and WZ daily, logbook catch and effort data were linked with swell and wind observations. Analysis demonstrates that, although the observations of extrinsic factors were correct, fishers avoided diving on days with unsuitable weather conditions. Consequently, the observed decrease in CPUE is not likely to have been affected by weather-related hyperdepletion, and therefore managers should not rule out interpreting recent declines in CPUE as reflecting decreases in stock abundance. This highlights the independence of CPUE to the effects of the extrinsic factors evaluated and challenges some of the reasoning provided for it not being a reliable index of abundance. Further exploration of the effects of other factors that may affect CPUE, as well as the link between this index and fishery-independent estimates of abundance, are needed to determine the weighting it should receive in the stock assessment process.
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Vol. 35 • No. 3