Idade, crescimento e análise demográfica do cação-flamengo Carcharhinus acronotus na plataforma continental de Pernambuco,Brasil

Abstract

Between 1994 and 2008, 369 blacknose sharks, Carcharhinus acronotus (43,5-146 cm total length, TL) were collected from gill nets and surveys carried out on Pernambuco’s continental shelf, Brazil (07° 15’ 45’’ S and 09° 28’ 18’’ S). Vertebral sections of 109 males (43,5-124 cm TL) and 141 females (46-146 cm TL) were analyzed; the index of average percentage of error (IAPE) ranged from 1:17 to 13:33% (mean 6,13%) in vertebrae displaying between 0 to 15 growth rings (GR). The marginal increment relative analysis (MIR) was not conclusive showing only a tendency of ring deposition between autumn and winter months. Significant differences were not found between the individual length (TL, cm) and the vertebra radius (VR, mm). Growth parameters were derived using von Bertalanffy function (VBGF a), von Bertalanffy modified (VBGF b), Gompertz and Schnute models. The von Bertalanffy growth model was that which best represented growth for the species. Parameters estimated for both sexes were: k = 0.12, t0 = -3.66, L¥= 142.06 cm. Male and female maturity was reached at 105 cm TL, presenting about 5 growth rings (GR's). The largest specimen whose age was observed had 15 growth rings (132 cm TL). Adults were only caught in longlines. Mortality was estimated from the biological information of the species according literarature. Mortality values obtained were: M = 0,275; Z = 0,709 (gillnets), 0,31 (longline); F = 0,43 (gillnets) 0,04 (longline) Z0 = 0,06 and Z' = 0,349. The Exploitation rates calculated for gillnets were 0,61 and 0,130 respectively. Considering a scenario of equilibrium, the population would increase by approximately 8,3% per 8,5 years (R0 = 1,971; G = 8,43; r = 0,080). However, taking into account the current level of exploitation, the population appears to be over-exploited, decreasing 13,6% in 8,3 years (R0 = 0,3; G = 8,3; r = -0,041).