Baited remote underwater video system (BRUVs) survey of chondrichthyan diversity in False Bay, South Africa

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

“…False Bay contains a considerable diversity of chondrichthyans (22 sharks, 14 batoids and one chimera) as recorded from landings of various fisheries (Best et al, 2013) and baited remote underwater video systems (De Vos et al, 2015c). Chondrichthyans used to constitute a minor component of the catch or were caught as bycatch; however, with new markets for sharks and rays emerging, they have become a primary target of the demersal shark longline fishery.…”

“…The role of chondrichtyans as top (or highorder) predators suggests that they influence the structure of marine food webs, which makes them suitable as indicators of ecosystem health and functioning. The relative abundance, diversity and seasonal distribution of this group have recently been described for False Bay (De Vos et al, 2015c), providing a baseline for future monitoring of ecosystem effects of continued exploitation and other environmental drivers.…”

Low abundance of sharks and rays in baited remote underwater video surveys in the Arabian Gulf

“…Only 29.4% of elasmobranch species known from fisheries-dependent surveys to occur in Arabian Gulf waters were recorded using BRUVS 17 , 24 , 25 . Other surveys along the Great Barrier Reef in Australia, Indonesia, and South Africa also recorded less than 50% of known elasmobranch diversity 15 , 26 , 27 . This low diversity in BRUVS could be due to several factors including the behavior of animals in the presence of bait, or environmental variables such as depth gradients or habitats surveyed 15 , 26 .…”

“…Other surveys along the Great Barrier Reef in Australia, Indonesia, and South Africa also recorded less than 50% of known elasmobranch diversity 15 , 26 , 27 . This low diversity in BRUVS could be due to several factors including the behavior of animals in the presence of bait, or environmental variables such as depth gradients or habitats surveyed 15 , 26 . Firstly, our BRUVS recorded during the day and some elasmobranch species exhibit diel changes in behavior and activity 28 , 29 .…”

“…The relationship between soak time and the number of species of elasmobranchs, sharks, and rays observed was evaluated by plotting a species cumulative curve against each 50-hour soak time interval. Finally, the CPUE was graphically compared to published estimates obtained using similar BRUVS approaches in terms of camera orientation (vertical to substrate), number of cameras (one at a time), bait type (pilchards or sardines), soak time (at least 60 mins), and video metrics used (MaxN), from different regions around the world 6 , 12 , 15 , 16 , 20 , 21 , 26 , 27 , 33 . Where more than one study has been conducted in the same region (i.e., Northwest Australia and Indonesia), the average of all published estimates was depicted 21 .…”