Population trends of remote invertebrate resources in a Marine reserve: Trochus and holothurians at Ashmore Reef

Abstract

Marine protected areas (MPAs) have a high capacity to protect fish and invertebrate resources, given adequate surveillance and enforcement. Ashmore Reef National Nature Reserve (Ashmore Reef) was closed to commercial fishing and harvesting of invertebrates such as trochus (Trochus niloticus) and holothurians in 1983. We evaluate population trends in trochus and holothurians during eight years of monitoring, focusing largely on the differences between their populations before and after a lapse of surveillance. The trochus population increased in density from 1998 to 2005, followed by a slight decline in all surveyed habitats in 2006. This decline followed approximately five consecutive months without surveillance. Amongst populations of 18 species of holothurians, densities declined in five, and remained relatively stable in the others. Densities of commercially valuable holothurians (primarily Holothuria whitmaei and H. fuscogilva) were too low to allow the detection of trends. Continuous enforcement of the fishing closure is important to ensure successful conservation of Ashmore Reef, as are standardized monitoring techniques to enable temporal trends to be detected with confidence.