Idade, crescimento e biologia reprodutiva da Raia-viola Rhinobatos percellens (Walbaum, 1792) capturada pelo arrasto de praia em Caiçara do Norte/RN

Abstract

Caiçara do Norte (05º 04‘S and 36º 03’W) is considered one of the biggest marine fish producer in the Rio Grande do Norte State where beach seine captures shrimp. Rhinobatos percellens is the third most abundant species found in the by-catch. From June 2003 to May 2011, 714 beach seine hauls were closely monitored with the objective of analyzing the population structure of R. percellens. A total of 712 individuals were collected, including 303 females (42.56%) and 409 males (57.44%). The sexual proportion was significantly different of the expected ratio of 1:1 (1.0: 0.74 to male; p < 0.01). Female total length (TL) varied from 14.8 to 69.4 cm (mean=36.4 cm) and male from 14.5 to 57.5 cm (mean=34.5 cm). Although the females presented maximum length 17.2% higher than male, there was no significant difference (p = 0.11) in length by sex. Age and growth studies from annual rings allowed the age structure of the population to be known. Female ages ranged between 0-10 years and male between 0-6 years, however growth did not differ between sexes. The length at maturity of female was 44.3 cm and 43.2 for male, which corresponded to 2.9 and 2.8 years respectively. All life phases were included in the sample being represented by 36.65% of young-of-the-year, 44.52% of juveniles and 18.82% of adults. It was possible to assess that the recruitment to fisheries begins at age zero and a majority of juveniles are withdrawn through exploitation. Results reveal that the species is highly vulnerable and has low resilience according to the analysis of ecological risk of elasmobranchs caught by beach seine. Summing up, if the species is not able to develop a fast compensatory response to the fishing pressure, it may follow the same fate as its congener R. horkelii, from southern Brazil which is currently categorized as critically as endangered.