The influence of environmental factors on the abundance of swimming crabs (Brachyura, Portunidae) in a tropical estuary, northeastern Brazil

Abstract

Swimming crabs (family Portunidae) were collected in Santa Cruz Canal, Brazil from March 2009 through February 2010 using a beach seine and fishing line. The purpose of this study was to characterize the abundance of portunid crab species and to analyse the influence of environmental factors on the catches per unit effort (CPUE) values of Callinectes danae Smith, 1869 in the canal. The catches included five species: C. danae (the most abundant species), Callinectes marginatus (A. Milne-Edwards, 1861), Callinectes exasperatus (Gerstaecker, 1856), Charybdis hellerii (A. Milne-Edwards, 1867) and Callinectes bocourti A. Milne-Edwards, 1879. The species could be assigned to groups according to their abundance and the values of catches were higher during the dry period. The influences of water temperature, tide height, lunar illumination, salinity, precipitation and season were tested, although the average CPUE (μ) of C. danae for the beach seine and line methods was influenced only by tide height (T) and by salinity (S), according to the model: μ seine = exp ( 3 . 4921 − 1 . 3584 T ) and μ line = exp ( 0 . 055589 S ) . Within the ranges of the environmental variables included in the study, a tide height of 0.1 m was found to optimize the CPUE of the beach seine (28.68 Ind/h per m2). Furthermore, the CPUE using the line was optimized as the salinity level increased, with a capture rate of 05.92 Ind/h.