Abstract

The Stone crab Homalaspis plana supports an important artisanal fishery along the coast of Chile. The objectives of this study were to analyze the trends in crab catches and CPUE between 1991 and 1994 in open access fishing areas of Central Chile and to compare the size and sex composition of the catches for two alternative fishing gears. We explored three different CPUEs, because abundance indicators have not been used before for this fishery. In addition, we compared the CPUE, the crab size distribution, and the sex ratio between open access fishing grounds and Management and Exploitation Areas (private grounds). Stone crab catches decreased between 1991 and 1994 in open access areas. The Stone crab is caught with crab pots and by divers, and no differences in mean crab size were found between fishing gears in El Quisco. The proportion of males caught in crab pots is higher than that caught by divers, and the proportion of ovigerous females was lower in crab pots. The CPUE (catch per trip) also decreased between 1991 and 1994 in open access fishing grounds. We analyzed alternative CPUEs that could be used for crab as well as for other benthic species. We show that the CPUEHours (catch per hour) is affected by the number of species caught, which suggests the importance of taking this factor into account. The CPUETarget (catch per hour corrected by the number of target species) is not affected by the number of species caught (target and/or bycatch) because this estimator considers the time allocation for the main species collected. The latter may be a more appropriate indicator. No differences in CPUE between open access grounds and Management and Exploitation Areas (private grounds) were observed. The size distribution of crabs in open access fishing grounds and in Management and Exploitation Areas was not significantly different; females predominated in both areas (>90%). Previous studies conducted in Management and Exploitation Areas focused on sessile or sedentary species and clearly showed the effect of human activity (removal) on the abundance and size of exploited species, compared with open access zones. The lack of differences in CPUE, crab size, and proportion of sexes between open access zones and Management and Exploitation Areas suggests that mobile species may offer a new challenge to the management tools recently implemented by the Chilean Fisheries Administration.