The majority of fishing within the Vatu-I-Ra Seascape is limited to relatively shallow waters of less than 30 metres. This has led to the theory that fish deeper than 30 metres may be naturally protected from fishing, known as a depth refuge effect. This depth refuge effect is difficult to study using conventional methods like Underwater Visual Census, which relies on the use of SCUBA and is therefore limited to relatively shallow depths. Fortunately, researchers from the Marine Ecology Group and Oceans Institute at the University of Western Australia have been utilising a sampling method that is not limited by depth, Baited Remote Underwater Video. Baited Remote Underwater Video systems (commonly known as BRUVs) involve the use a stereo-video system housed within a metal frame and are focused on a bait bag used to attract predatory reef fish (Picture below). The stereo-video component allows for highly accurate length measurements to be made, which can be converted into biomass (the weight of fish).

In 2009 the University of Western Australia teamed up with the Wildlife Conservation Society to assess whether there was a depth refuge effect occurring in the Kubulau qoliqoli. The Goetze et al. 2011 study on depth refuge in Fiji’s reefs was published in the Journal of Coral Reefs and indeed confirmed that the rarer, highly targeted species had been depleted in the shallow waters but not the deep. However, this study was limited to a depth of around 30 metres, begging the question of what is found even deeper? Fortunately, in 2013 a field trip funded by the Waitt Institute, allowed researchers Jordan Goetze and Todd Bond to continue this study across the Vatu-i-Ra Seascape. Baited video systems were deployed at depths of up to 100 metres, where very little is known about the fish assemblages in Fiji. The team recorded rare species like Epinephelus timorensis, which is listed as “data deficient” on the IUCN red list as it is only known from sparse and widely separated localities (Pictured below).

Other species that were recorded in high numbers included, giant trevally, grey reef sharks and long-nosed emperor. Video footage of these species recorded by the BRUVs can be seen in a short highlight clip created by Jordan Goetze.

The next step for the research is to compare this data to the previous study in Kubulau which was limited to 30 metres and determine if this depth refuge effect extends to greater depths. Fishing technology is advancing rapidly, becoming cheaper and more readily available to a broader range of fisherman. Because of this depths which were previously off limits will be at risk of overfishing, highlighting the importance of documenting these deep water fish stocks.

By University of Western Australia PhD Candidate Jordon Goetze