Widespread decline in the abundance of sea cucumber assemblages in atolls of the protected Rowley Shoals, northwestern Australia

The Rowley Shoals, off northwestern Australia, are renowned as a biodiversity hotspot. This remote system comprises three atolls, Clerke, Imperieuse and Mermaid, which in recent years have been increasingly targeted by illegal fishing, a pressure rising across the Indo-Pacific. The objective of this study was to quantify recent changes in sea cucumber assemblages across the Rowley Shoals. We surveyed nine sea cucumber species at monitoring sites in 2018 and 2023 to assess changes in their abundance. Total assemblage densities declined significantly across all atolls and habitats. Documented seizures of illegally harvested holothurians by the Australian Fisheries Management Authority over this period suggest that illegal fishing pressure likely contributed to the observed declines. Notably, IUCN-listed species Holothuria whitmaei and Actinopyga miliaris declined severely, raising concerns about their recovery potential. These findings provide the first quantitative evidence of widespread declines within this protected reef system and bring renewed attention to its conservation.