Abstract
The swimming crab Achelous spinicarpus is commonly captured as a “by catch” of the shrimp fishery. This study evaluated some aspects of the population structure of A. spinicarpus, such as sex-ratio and size classes’ frequency distribution. A shrimp trawler equipped with double-rig nets was used to capture the swimming crabs at Ubatuba and Caraguatatuba areas, northern coast of Sao Paulo state, Brazil. A total of 1,057 individuals were collected in Ubatuba, including 598 males (525 juveniles and 73 adults) and 459 females (379 juveniles and 80 adults, including 15 ovigerous crabs). In Caraguatatuba 5,112 individuals were collected, of which 3,138 males (2,638 juveniles and 500 adults) and 1,974 females (1,746 juveniles and 228 adults, including 29 ovigerous crabs). The sex-ratio favors the number of males in both regions, probably because females have the habit of occupying deeper regions. The size classes’ frequency distribution shows polymodality for both sexes, except for males in Ubatuba. This is the result of some age groups among the juveniles, which migrate to shallower areas, being affected by the fishing activity. Adults have the habit of staying in deeper areas characterized by colder waters.Keywords: Brachyura, sex-ratio, Decapoda, bycatch, size distribution.
Highlights
The decapod crustaceans of the superfamily Portunoidea, popularly known as “swimming crabs”, play a key role in the trophic web of coastal ecosystems, acting as predators of various groups of invertebrates and fishes (Branco and Lunardon-Branco, 2002)
Considering the importance of A. spinicarpus as a component of the assemblage of Portunoidea (Lima et al, 2014) this study aimed to investigate the structure of its population in a region affected by shrimp fishing in the southeast coast of Brazil, evaluating the sex ratio and frequency distribution of individuals in size classes
The sampled regions in this study, both located on the north coast of the state of São Paulo, Brazil, differ in their hydrogeographic characteristics
Summary
The decapod crustaceans of the superfamily Portunoidea, popularly known as “swimming crabs”, play a key role in the trophic web of coastal ecosystems, acting as predators of various groups of invertebrates and fishes (Branco and Lunardon-Branco, 2002). The swimming crab Achelous spinicarpus (Stimpson, 1871) has a wide geographic distribution along the Western Atlantic coast, occurring from North Carolina (United States of America) to Rio Grande do Sul (Brazil) (Melo, 1996). Since this species has no commercial value, it is discarded when captured by fishers. It plays a relevant ecological role in the food web by acting both as a predator and as prey and constituting an important food item for some fish species (Viana et al, 2014; Motta et al, 2016)
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