Collaborative Research on Dusky Grouper (Epinephelus marginatus): Catches from the Small-Scale Fishery of Copacabana Beach, Rio De Janeiro, Brazil

Abstract

The dusky grouper (Epinephelus marginatus) is a reef fish with high market, cultural and ecological values. Therefore, it is an important species to the food security of small-scale fishers in Brazil and in other coastal regions. Nevertheless, groupers can be susceptible to overfishing because they are large, sedentary and with delayed maturity. The lack of data on fishery catches and on the biology of dusky grouper can be an obstacle for the success of management measures. The main goal of this study was to collect information on dusky grouper catches, morphometry (length and weight) and spawning period (observations of its gonads), through a collaboration with local fishers in the Copacabana Beach (“Posto 6”), southeastern Brazilian coast. Two fishers were trained to measure the total length (TL, in cm), weight (kg), and to observe the gonads (whether mature or not, and with or without visible eggs) of all individuals of dusky grouper caught at Copacabana, from September 2013 to June 2015. During the 21 months of data collection, 800 individuals of dusky grouper were examined by the trained fishers, yielding 793 individuals with both length and weight data. The mean length of dusky grouper caught by fishers (N = 796) was 52.4 cm (standard deviation of 12.4 cm, range from 17-130 cm). Most of the individuals caught ranged between 45 and 65 cm, being thus above both the minimum allowed size in Brazil (47 cm) and above the size at first maturity for this fish according to the literature (range of 35-60 cm for females). Although many individuals were adults, only a few individuals (18 of 800) of dusky grouper had mature gonads. This indicates that large spawning fish may be located at deeper sites or at distant spots, out of the reach of these small-scale fishers. Most dusky groupers were caught by spear fishing, in a single island. The collaboration with local fishers greatly improved the amount of data collected; so, we suggest that this approach should be adopted in future studies. These results show a valuable opportunity to properly manage the dusky grouper population at the southeastern Brazilian coast.