Effect of bêche-de-mer fishing on densities and size structure of Holothuria nobilis (Echinodermata: Holothuroidea) populations on the Great Barrier Reef

Abstract

Decreasing catch rates for Holothuria nobilis (black teatfish) on the Great Barrier Reef (GBR) prompted management agencies to close the fishery for this species in October 1999. At the same time, we surveyed densities and size structure of H. nobilis populations in the main area fished on the GBR. Densities of H. nobilis on four reefs protected from fishing (approximately 20 ind. ha–1) were about four times higher than those on 16 reefs open to fishing (approximately 5 ind. ha–1). Each of four other reefs had been divided into an area protected from fishing and an open area. On the largest of these reefs (ca. 28 km long), densities of H. nobilis were nearly five times higher in the protected area compared to the area open to fishing. On three smaller reefs (<11 km long), however, densities were not significantly different between the open and protected area, and were similar to that on reefs completely open to fishing. The average weight of individuals was significantly reduced on fished reefs (1,763 g) compared to closed reefs (2,200 g). Thus, beche-de-mer fishing led to a strong reduction of density and biomass of H. nobilis. The division of smaller reefs into open and closed zones appears not to provide sufficient protection, but reefs that are completely closed to fishing appear to provide some degree of protection. There were some indications that proximity to tourist attractions may enhance the effect of protection.