Asher, J. M.; Williams, I. D.; Harvey, E. S.

Roving predators reloaded: an investigation of shark and jack populations in shallow (0-30m) and mesophotic depths (30-100m) in the Hawaiian Archipelago

2016

13th International Coral Reef Symposium. 19-24 June 2016

"Coral reef roving predators (sharks, jacks, snappers) are generally believed to be depleted around human population centers. In Hawaii, most of the data to support this conclusion comes from underwater visual censuses of shallow water reef ecosystems (0-30m). However, information on the density and distribution of mobile predators in mesophotic depths (30-100m+) remains sparse. Survey techniques suitable for mesophotic surveys (e.g. technical dive surveys, submersibles) tend to be expensive, logistically challenging, or may only cover a relatively small number of sites per day. A simple, low-cost alternative approach suitable for a wide range of depths is the use of baited remote underwater stereo-video systems (stereo-BRUVs). Between 2012-2014, we deployed stereo-BRUVs to assess roving predator populations around the main Hawaiian Islands (MHI; Maui, Lanai, Molokai, Oahu) and the Northwestern Hawaiian Islands (NWHI; French Frigate Shoals, Lisianski Island/Neva Shoals, Pearl and Hermes Atoll, Midway Atoll), targeting sites previously surveyed by divers (0-30m), along with mesophotic sites (30-100m). Stereo-BRUVs surveys found several species of roving predators are significantly more abundant in mesophotic habitats than in shallow habitats. Although results corroborate diver surveys that roving predators are much more abundant in the remote NWHI than in the populated MHI, the greater depth coverage and diver independent nature of stereo-BRUVs surveys provides much more information and more accurate estimates of relative abundance than was previously available."