Declines in the abundance of coral trout ( Plectropomus leopardus) in areas closed to fishing at the Houtman Abrolhos Islands, Western Australia

Abstract

This study aimed to assess temporal trends in the abundance and size of the tropical coral trout, Plectropomus leopardus (Lacepède, 1802), in areas open and closed to fishing at the Houtman Abrolhos Islands. Baited remote underwater stereo-video systems (stereo BRUVs) were used to conduct surveys from 2005 to 2009 from shallow and deep sites across four geographically-separated groups of islands. A total of 1542 P. leopardus were observed from 77% of stereo BRUV deployments with an average abundance of 2.35 ± 0.1 SE per deployment. The lengths of 1238 individuals were measured, with sizes ranging from 118.2 to 727 mm. At commencement of the study in 2005, there were 65% more P. leopardus in areas open vs. closed to fishing. From 2005 to 2009, however, abundances fell by 50% in areas closed to fishing, such that abundances were then similar between areas open and closed to fishing. Relative abundance changed very little in fished locations throughout the course of the study, despite the implementation of fisheries restrictions on other iconic species that may have increased fishing effort on P. leopardus. In areas closed to fishing 12–32% of P. leopardus measured over the five years of the study (average of 25%) were larger than the minimum legal size for retention of 450 mm total length. Much fewer were larger than legal size in areas open to fishing (6–15%, average of 11%). Illegal fishing is considered to be the primary cause of the decline in abundance of P. leopardus inside closed area boundaries.