Negligible recovery in Chagos holothurians (sea cucumbers)

Abstract

Extensive sampling in 2006 quantified variations in shallow-water holothurian abundance across the Chagos Archipelago, British Indian Ocean Territory, and revealed negative effects of illegal poaching. Median abundance in Diego Garcia, where exploitation is absent, was significantly higher than in three exploited atolls. Repeat surveys undertaken along 64 comparable 100 m × 2 m transects during February 2010 revealed highest median abundance in the Great Chagos Bank, and also significant decline in abundance at Diego Garcia since 2006. Comparison of surveys in 2010 and 2006 with an investigation in 2002 reveals an overall decline in populations of Stichopus chloronotus, Holothuria atra and Holothuria nobilis over 8 years in the exploited atolls of Salomon and Peros Banhos, despite evidence of reduced fishing since 2005/2006 in these and other exploited atolls. A complete census of a large transect, 19 km × 4 m, encircling Salomon atoll, revealed lower total holothurian abundance in 2010 (1661 individuals) than 2006 (2142 individuals). Although information on fishing pressure at different northern islands is not available for 2010, the significant decline in holothurian abundance between 2006 and 2010 observed in Diego Garcia, where poaching is absent, suggests that factors besides fishing also drive populations in Chagos. The designation in April 2010 of Chagos as the world's largest marine protected area may help accelerate recovery of holothurian populations, as has occurred in marine reserves in the Seychelles. However, this requires increased monitoring, control and surveillance capacity.