Improved indices of catch rate in the fishery for blacklip abalone, Haliotis rubra, in New South Wales, Australia

There was a non-linear relationship between daily catch and effort within the NSW abalone fishery between 1983 and 1995. Larger catches were collected at a faster rate than small catches. To account for this, a generalized linear model was fitted which described the observed effort as a function of catch and several other standardizing variables. This model provided indices of catch rate that were significantly different from those derived from a more traditional analysis of CPUE which does not account for the non-linear relationship between catch and effort. Changes in indices of catch rate from the analysis of catch and effort were associated with major management changes, including increases in the minimum length limit and the introduction of individual quotas. Increases in catch rate between 1992 and 1995 were not associated with changes in management, and suggest that densities and abundance of abalone on the NSW coast may have increased. This interpretation is strengthened when catch rates are considered in conjunction with independent surveys of abundance. Calculation of standardized indices of catch rate that acknowledge the non-linear relationship between catch and effort, and their interpretation in conjunction with other information, is likely to improve the potential of catch rate as an indicator of change within the NSW abalone fishery. (C) 1998 Elsevier Science B.V. All rights reserved.