Population explosion of the burrfish Chilomycterus spinosus spinosus (Diodontidae, Tetraodontiformes) in a eutrophic tropical estuary

Abstract

Guanabara Bay is one of the most ecologically, economically and socially important tropical estuaries in the southwestern Atlantic. Fortnightly samples of the demersal ichthyofauna were obtained from July 2005 to June 2007, by bottom trawling from six stations determined according to the water quality. The net was 7 m long with a 14 m wide mouth and a mesh size of 18 mm. The tows were made at a speed of about 1.5 knots. The most abundant species, occurring in all 48 surveys, was Chilomycterus s. spinosus (14,837 specimens; 61.8 ind/h; 3.85 kg/h). Although commonly captured in Brazilian bays, this species has never been found in such high abundance and wide LT ranges (2.6−35.6 cm). The fish were concentrated in the middle portion of the estuary, which shows their high tolerance to eutrophic conditions, as well as to natural variations in temperature and salinity. In the last quarter of the study, the relative abundance levels rose to 228 ind/h, mostly small specimens of about 8.0 cm LT and 40 g MT, comprising 45% of the total catch. Such a successful recruitment could cause a large shift in species composition in the demersal community, with unpredictable ecological consequences. The population fluctuations of this species coincided with the rainfall pattern; the estuary is used as a nursery area until the fish reach the size at first maturity.