THE CHILEAN ARTISANAL STONE CRAB (HOMALASPIS-PLANA) FISHERY - CATCH TRENDS IN OPEN ACCESS ZONES AND THE EFFECT OF MANAGEMENT AREAS IN CENTRAL CHILE

The Stone crab Homalaspis plana supports an important artisanal fisher y along the coast of Chile. The objectives of this study were to analy ze 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 compositionof the catches for two alternative fishing gears. We explor ed three different CPUEs, because abundance indicators have not been u sed before for this fishery. In addition, we compared the CPUE, the cr ab size distribution, and the sex ratio between open access fishing gr ounds and Management and Exploitation Areas (private grounds). Stone c rab catches decreased between 1991 and 1991 in open access areas. ?he 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 p roportion of males caught in crab pots is higher than that caught by d ivers, and the proportion of ovigerous females was lower in crab pots. The CPUE (catch per trip) also decreased between 1991 and 1994 in ope n access fishing grounds. We analyzed alternative CPUEs that could be used for crab as well as for other benthic species. We show that the C PUEHours (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 bycatc h) because this estimator considers the time allocation for the main s pecies collected. The latter may be a more appropriate indicator. No d ifferences in CPUE between open access grounds and Management and Expl oitation Areas (private grounds) were observed. The size distribution of crabs in open access fishing grounds and in Management and Exploita tion Areas was nor significantly different; females predominated in bo th areas (>90%). Previous studies conducted in Management and Exploita tion Areas focused on sessile or sedentary species and clearly showed the effect of human activity (removal) on the abundance and size of ex ploited species, compared with open access zones. The lack of differen ces in CPUE, crab size, and proportion of sexes between open access zo nes and Management and Exploitation Areas suggests that mobile species may offer a new challenge to the management tools recently implemente d by the Chilean Fisheries Administration.