Reproduction and population structure ofAchelous spinimanus(Crustacea: Portunoidea) in the northern coast of Sao Paulo, Brazil, and influence of environmental factors

We studied the reproduction and population structure of a population ofAchelous spinimanusin the region of Ubatuba, Brazil. We collected them monthly, in 2000, in eight sites of different depths (5 to 40 m). The size at the onset of sexual maturity was estimated by the carapace width and the population structure was analyzed based on the size frequency distribution. In total, we collected 402 individuals: 28 juveniles, 105 males and 269 females. In 2000,A. spinimanusreproduced continuously and had a single peak in September-October. This timing contrasts with what has been observed in other populations and may be a local strategy to decrease the interspecific competition with other swimming crabs. The individuals ofA. spinimanusfrom Ubatuba in 2000 were smaller (16.8-93.5 mm) than those from Fortaleza Bay (near Ubatuba) in 1988-1989 (19.0-97.3 mm). We suggest that intense trawling pressure may have contributed to a reduction in the size of individuals.