Population structure of the swimming crab Achelous spinicarpus (Crustacea, Portunoidea) in São Paulo northern coast, Brazil

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 São 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. ResumoO siri candeia, Achelous spinicarpus, é comumente capturado como "by catch" da pesca camaroeira. Este estudo avaliou alguns aspectos de sua estrutura populacional, como razão sexual e distribuição de frequência em classes de tamanho. Para coletar os siris, foi utilizado um barco de pesca camaroeiro equipado com redes "double rig" nas áreas de Ubatuba e Caraguatatuba, litoral norte do estado de São Paulo, Brasil. Um total de 1.057 indivíduos foi coletado em Ubatuba, incluindo 598 machos (525 juvenis e 73 adultos) e 459 fêmeas (379 juvenis e 80 adultas, incluindo 15 ovígeras). Em Caraguatatuba, 5.112 indivíduos foram coletados, dos quais 3.138 machos (2.638 juvenis e 500 adultos) e 1.974 fêmeas (1.746 juvenis e 228 adultas, incluindo 29 ovígeras). A razão sexual favoreceu o número de machos em ambas as áreas, provavelmente devido ao hábito de as fêmeas ocuparem regiões mais profundas. A distribuição de frequência em classes de tamanho apresentou polimodalidade para ambos os sexos, exceto para machos em Ubatuba. Isso é resultado de alguns grupos etários entre os juvenis, os quais migram para áreas mais rasas, sendo afetados pela atividade pesqueira. Os adultos permanecem em áreas mais profundas, caracterizadas por águas frias. Population structure of the swimming crab Achelous spinicarpus (Crustacea, Portunoidea) in São Paulo northern coast, Brazil Palavras

Unveiling the dynamics of the spider crab Libinia ferreirae, through reproductive and population characteristics on the south-eastern coast of Brazil

“…Similarly, there was no sexual dimorphism found for Achelous spinimanus (Latreille, 1819) in Macaé, on the coast of Rio de Janeiro (Andrade et al ., 2017) and A. spinicarpus (Stimpson, 1871) in the region of Ubatuba and Caraguatatuba (Silva et al ., 2017), with all these studies showing female-biased sex ratios. In addition, some authors have pointed out that trawling (as used in the present study) is the most reliable collection method for characterizing population aspects (Able et al ., 1999).…”

“…The identification of juvenile specimens based on the abdominal condition (sealed or not) has been widely used for Portunoidea (e.g. Taissoun, 1969; Williams, 1974; Silva et al ., 2017; Sousa et al ., 2019) and is useful for the representatives of the superfamily Majoidea. Four demographic groups were used in the analyses: juvenile males and females (J), adult males (AM), non-ovigerous adult females (AF) and ovigerous females (OF).…”