Age and growth of the blacknose shark, Carcharhinus acronotus (Poey, 1860) off the northeastern Brazilian Coast

Abstract

From August 1994 to January 1999 and July 2004 to December 2007, 369 blacknose sharks, Carcharhinus acronotus (Poey, 1860), (43.5–146 cm in total length, TL) were collected from gillnets and surveys (longline) carried out on the continental shelf off the state of Pernambuco, Brazil (07°15′45″S and 09°28′18″S). Vertebral sections from 131 males (43.5–124 cm TL) and 146 females (46–146 cm TL) were analyzed. The index of average percentage of error ( IAPE) estimated from two readings ranged from 1.61 to 4.83 (mean: 6.66%) in the vertebrae of specimens between 0 and 15 years of age. The monthly marginal increment ( MIR) ratio revealed a tendency toward band pair deposition between autumn and winter, whereas the monthly distribution of growth band pair classes revealed that the first band pair appears on the vertebrae of newborns (ages 0+) about 6 months after birth (by June). This deposition pattern was found in specimens with one, two and three band pairs on the vertebrae (1+ and 2+, respectively), thereby confirming annual band pair completion in winter. Growth parameters were derived using the von Bertalanffy model ( VBGM), VBGM b (modified by length at birth: L 0), the Richards, Gompertz and Schnute models. No significant differences in growth rates were detected between the two sampling periods (1994–1999 and 2004–2008). Models with multiple inflection points, particularly the Richards model, best represented growth for the species, which was evidenced by the lowest Akaike information criterion value. There were no differences in growth between sexes. Growth parameters estimated for both sexes were L ∞ = 129.34 cm (SE = 1.35), k = 0.24 (SE = 0.009) and m = 1.34 with the Richards model. The “average” model was determined by averaging L ∞ between the models with substantial statistical support that were considered the most plausible (Richards and Gompertz). Thus, a consensual L ∞ = 130.69 cm, estimated by multi-model inference, was employed to minimize the effects of sample size and selectivity. Males and females mature at 6 years of age and the largest specimen in the catches was 15 years of age (132 cm TL). Local fishing exploitation using gillnets caught only juveniles, whereas the longlines used for the surveys caught subadult and adult specimens. C. acronotus is a relatively fast-growing species inhabiting shallow coastal waters throughout its lifespan, which is a pattern to be taken into account in the years to come for the management of coastal exploitation targeting valuable teleosts.