Using baited remote underwater videos (BRUVs) to characterize chondrichthyan communities in a global biodiversity hotspot

Abstract

Threatened chondrichthyan diversity is high in developing countries where scarce resources, limited data, and minimal stakeholder support often render conservation efforts challenging. As such, data on many species, including many evolutionarily distinct endemics, is poor in these countries and their conservation status and habitat needs remain uncertain. Here, we used baited remote underwater videos (BRUVs; n = 419) conducted at 167 sites over two years to assess the frequency of occurrence (FO), relative abundance, diversity, and structure of chondrichthyan assemblages in one of the world’s chondrichthyan biodiversity and endemism hotspots, South Africa. We compared chondrichthyan assemblages across three habitat types, and between unprotected and protected areas (a small marine protected area [MPA] and a larger, seasonal whale sanctuary). Although in total we observed 18 chondrichthyan species (11 families), over half of all observations were of just two species from the same family of mesopredatory endemic catsharks; only 8.8% were larger shark species. These mesopredatory species do not appear to be threatened, but some skates and larger shark species, including some endemics, were much rarer. Overall chondrichthyan FO was high (81% of all BRUVs); FO was higher in kelp (100% of BRUVS) and reef (93%) sites than at sites in sandy habitat (63%), which had a distinct chondrichthyan community. Independent of habitat, the chondrichthyan community did not relate strongly to protection. Because sites with kelp and reef habitat were rare in the whale sanctuary, this protected area had a lower chondrichthyan FO (67% of BRUVs) than either unprotected sites (81%) or those in the small MPA (98%), as well as having lower chondrichthyan relative abundance and species richness. Our study provides evidence of the importance of distinct habitat types to different chondrichthyan species, and suggests that even small MPAs can protect critical habitats, such that they may provide safe refuge for endemic species as anthropogenic pressures increase.

Sandbar shark aggregation in the central Mediterranean Sea and potential effects of tourism

“…Owing to their non‐extractive and non‐invasive characteristics, BUV systems are particularly good in studies focused on elusive, shy, and predator species, such as sharks (e.g. Espinoza et al, 2014; Juhel et al, 2018; Osgood, McCord & Baum, 2019). The benthic BUV system consisted of two GoPro Hero3 cameras placed in a sealed chamber and fixed on a cross‐shape steel structure.…”

“…Each deployment lasted 65–70 min to allow for 1 hr of footage after the BUV reached the bottom. Three simultaneous BUV deployments at a time (average lag time of deployment ~15 min) were randomly located at least 150 m apart from each other (Ellis & DeMartini, 1995; Osgood et al, 2019), with a minimum of 24 hr between repeated sampling at the same site within the study area.…”

Evaluating the evidence for ecological effectiveness of South Africa’s marine protected areas

“…Since then, numerous studies have described the biodiversity or biodiversity features that are currently protected by various MPAs (e.g. Bennett and Attwood 1993;Attwood et al 1997;Hanekom et al 1997;Götz 2005;Sink et al 2005;Mann et al 2006;Celliers et al 2007;Götz et al 2009aGötz et al , 2009bOlbers et al 2009;Hanekom 2011;Currie et al 2012;Floros et al 2012;Solano-Fernandes et al 2012;Venter and Mann 2012;De Vos et al 2014, 2015Roberson et al 2015;Attwood et al 2016;Heyns et al 2016;Tucker et al 2017;Joshua et al 2018;Osgood et al 2019;Purdon et al 2020). Some studies, especially of 'iconic' marine species that are listed as Threatened or Protected in South Africa (RSA 2017), further describe how species utilise the MPAs (e.g.…”

“…Hockey and Bosman 1994). In addition, some MPAs fail to improve the abundance of particular groups of species simply because the location lacks suitable habitat for those species, even though the habitat might be present in nearby unprotected areas, as was the case for reef fishes at De Hoop (Heyns-Veale et al 2019) and chondrichthyans at Walker Bay Whale Sanctuary (Osgood et al 2019). Götz et al (2013) developed a framework to assess the ecological benefits of MPAs, which is of relevance to the protection of linefishes and other harvested species.…”

Comparing the efficiency of paper-based and electronic data capture during face-to-face interviews

“…Remote data collection by electronic mechanisms is now widely used across scientific disciplines. For example, video or still cameras and other sensor systems can be positioned at fixed terrestrial locations or access points such as boat ramps or hiking trails to monitor recreational activity levels across a 24-hr day [ 5 , 7 – 11 ] while waterproof systems can be used to monitor a suite of species or habitats [ 4 , 12 ] as well as vessel activity [ 13 ]. Unmanned aerial vehicles have applications for many projects including monitoring of specific activities, species, and habitats [ 14 – 16 ].…”