Effects of a spatial closure on highly mobile fish species: an assessment using pelagic stereo-BRUVs

Abstract

The effects of a spatial area closure on pelagic fish assemblages within the Houtman Abrolhos Islands were assessed using mid-water pelagic stereo-BRUVs. The spatial area closure within the Easter group of the Houtman Abrolhos Islands was found to have no significant effect on the species composition and relative abundance of pelagic fish assemblages. The most abundant demersal target species recorded was pink snapper (Chrysophrys auratus) and, individuals measured within the spatial closure were significantly larger than those sampled in the area open to fishing. This spatial area closure is of moderate size (22.3 km2), but the spatial management of highly mobile species may require larger area closures than those for reef-associated species. The monitoring of pelagic species both in large and small spatial area closures is required in order to better understand how mobile species respond to this management strategy. Some species were only recorded in relatively low numbers using pelagic stereo-BRUVs. Moreover, some of the highly mobile pelagic fish species, such as tunas, mackerel and some shark species have proven difficult to measure, as these species were observed furthest from the camera systems. While pelagic stereo-BRUVs are an effective fishery-independent approach to monitor spatial fishing closures, improving the power of replicates by pooling individual deployments, and increasing the attraction rate of pelagic fish to the stereo-cameras, will enhance their performance in future studies.