IMPLICATIONS OF INTERFERENCE AMONG FISHING VESSELS AND THE IDEAL FREEDISTRIBUTION TO THE INTERPRETATION OF CPUE

Despite recognized biases, catch per unit effort (CPUE) statistics rem ain widely used for the estimation of fish abundance. Previous workers have shown that CPUE can be a misleading index of abundance due to fi sh behavior, the nominal effort units used, and increases through time in efficiency of fishing (catchability). We examine the theoretical i mplications of a different factor, interactions among fishing vessels, for the relationship between abundance and CPUE. Our model simulates a fishery that occurs in several adjacent fishing grounds. The spatial distribution of catch and effort is based on a simplification of the Baranov catch equation, the relationship between fishing efficiency an d local fishing effort (interference), and the assumptions of the idea l free distribution. Our results indicate that (i) even low levels of interference among fishing vessels can cause a breakdown in the correl ation between CPUE and local abundance and (ii) the influence of inter ference on this relationship is dependent on the correlation of abunda nces among adjacent areas. Our model suggests an alternative index of abundance, based on the proportion of fishing effort on a ground, that would be appropriate for cases where interference occurs among fishin g gear.