Age and growth of the dusky grouper, Epinephelus marginatus (Lowe, 1834) (Pisces: Epinephelidae), off Southeast Brazil

Abstract

The dusky grouper, Epinephelus marginatus (Lowe, 1834), is a commercially-important demersal fish in Southeast Brazil, inhabiting rocky and sandy substrates of the outer shelf and upper continental slope. Age, growth and natural mortality were studied by means of the scale-reading in 135 specimens of both sexes, with total length ranging from 11.5 to 70.5 cm, in the period from June, 1999 through May, 2000. The scale was found to grow on an alometric proportion with fish length after the equation S = 0.0199 L0.958 (r = 0.979; P<0.01), there being an annual periodicity in age ring formation, which takes place every year in March on NovemberDecember. Back-calculated mean total lengths ranged from 15.2 cm (age group I) to 68.5 cm (age group XIV). The growth equation in length (cm) is Lt = 101.1 [1 – e – 0.075 ( t + 2.2) ] which was represented as weight (kg) by Wt = 22.6 [1 – e – 0.075 ( t + 2.2 ]3.221 obtained through the weight/length regression equation ln W = - 11.76 + 3.221 ln L (r = 0.995; P<0.01). The annual natural mortality coefficient was estimated as M = 0.204. The dusky grouper has a low growth coefficient (K = 0.075) and a high a high longevity age at the fishery (tmax = 37.7 years), with values of M/K = 2.72 and coefficient of growth performance, φ = 2.881, biological features that are typical of fifth trophic-level carnivorous fishes.