Once a mysterious, alien world, the advancement of modern technology has allowed us to learn ever more about life at the bottom of the oceans. One such wonder technology is known as Baited Remote Underwater Video or BRUV for short. BRUVs allow us to actually watch sharks and other marine life through a video stream, without ever having to set foot in the water. The footage can be very valuable for scientific research and is also just seriously cool to watch! So how do BRUVs work? What can they teach us?
What is a BRUV?
BRUVs are a relatively new technique; developed in recent years to remotely observe marine life. The method involves lowering cameras which are mounted onto a steel frame onto the ocean floor to video predatory fish. Sharks are attracted to the recording equipment with bait, which is concealed in a bag or cage connected to the frame (Harvey et al, 2012).
BRUV studies are especially powerful because once the footage is taken, and the video safely downloaded, it can be watched again and again. This means that multiple different research questions can be asked from one trip to collect data (Harvey et al, 2012).
As the recording equipment does not require any human intervention, BRUVs are also less invasive compared to some other sampling methods. This means we can observe sharks in a some-what natural way. It also allows us to observe sharks which live in especially challenging habitats, or to spot sharks which are often quite elusive (Harvey et al, 2012).
BRUV Surveys Can Be Used to Monitor Shark Abundance
BRUVs can also be used to assess shark abundance. Because it is common for many species to live and hunt in groups, they often show up to BRUVs in numbers. This means we can count how many sharks we see over a certain period of time (this is known as "Catch per Unit Effort" or CPUE for short). By comparing the CPUE in different places, we can determine which areas have more sharks than others (Clarke et al, 2012).
This is very helpful for conservationists trying to determine where sharks have been depleted and where their populations remain stable. If we repeatedly sample in the same place over several years, BRUVs can also allow us to monitor whether the populations are still declining (Clarke et al, 2012).
BRUVs Allow Us To Study Shark Biodiversity
BRUVs are especially handy for studying the biodiversity of a particular area. By watching which species show up to feed at the BRUV, scientists can learn about the structure of the ecosystem and assess how different species interact in the community. This is known as the "species assemblage" (Clarke et al, 2012).
For example, a BRUV study in the Indian Ocean found that 11 different species of sharks were living in the area. This included whitetip reef sharks (Triaenodon obesus), silvertips (Carcharhinus albimarginatus), grey reefers (C. amblyrhynchos), Galapagos sharks (C. galapagensis), silkies (C. falciformis), sicklefin lemon sharks (Negaprion acutidens), tiger sharks (Galeocerdo cuvier), zebra sharks (Stegostoma fasciatum), tawny nurse sharks (Nebrius ferrugineus) and scalloped hammerheads (Sphyrna lewini) (Clarke et al, 2012).
This information can be used to identify areas of high shark biodiversity, which can be important for conservation (Harvey et al, 2012).
BRUVing Can be Used to ID Individual Sharks
BRUV surveys can be used to study the behaviour and movement ecology of individual sharks. For instance, a recent study conducted in Maluku, Indonesia, used BRUV footage to identify individual blacktip reef sharks (Carcharhinus melanopterus) (Mukharror et al, 2019).
These sharks have distinctive black and white pigmentation patterns on their pectoral fins and tail (aka "caudal; fin"), which are unique to each shark... much in the same way that iris colouration in the eye is unique to each human being (Mukharror et al, 2019).
Therefore, images of individual sharks' pigmentations patterns which are captured in BRUV footage can then be used to identify if a particular shark is seen again. This can be used to study shark behaviour and their movement ecology (Mukharror et al, 2019).
BRUVs Can Show Us Which Habitats Sharks Prefer
BRUVs can also be used to study the distribution of sharks. Another research group in Morotai recorded at several different locations with contrasting topography and coral cover. Their BRUV also included several instruments which could measure water temperature, salinity, acidity, current and water visibility. When watching the footage back, the scientists were able to count how many sharks they saw and also assess the quality of the habitat at each sampling site, to determine how the physical environment was related to shark abundance... Basically asking which areas do they like, which do they not like and why? (Sentosa et al, 2020).
They noticed that sharks were not seen on the footage in areas with very strong currents or when waters were especially salty. Yet sharks were abundant in warmer waters, with good water quality and healthy coral cover (Sentosa et al, 2020).
This information is vital because it gives us some idea how sharks might respond if their habitat were altered - as is predicted to happen with impeding climate change (Sentosa et al, 2020).
We've already learned so much from BRUVs, but as the technology continues to improve, who knows what marvels we might capture on video... No matter what BRUV footage can teach us, at the very least the footage is always absolutely beautiful!
If you are interested in BRUV research and would like to check out some of these videos yourself, you can follow @globalfinprint on twitter.
References
Brooks EJ, Sloman KA, Sims DW & Danylchuk AJ (2011). Validating the use of baited remote underwater video surveys for assessing the diversity, distribution and abundance of sharks in the Bahamas. Endangered Species Research, 13, 231-243. Access online.
Clarke C, Leaa J & Ormond R (2012). Comparative abundance of reef sharks in the Western Indian Ocean. Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia. Access Online.
Harvey ES, McLean D, Frusher S, Haywood MDE, Newman SJ, Williams A (2012). The use of BRUVs as a tool for assessing marine fisheries and ecosystems: a review of the hurdles and potential. The University of Western Australia 2011 National Workshop Report. Access Online.
Mukharror DA, Susiloningtyas D, Handayani T & Pridina N (2019). Blacktip reefshark (Carcharhinus melanopterus) individual’s identification in Morotai waters using its fin’s natural markings. International Conference on Science and Applied Science (ICSAS) Conference Proceedings, 2202, 020085, https://doi.org/10.1063/1.5141698. Access online.
Sentosa WB, Nurruhwati I, Apriliani IM & Khan AMA (2020). Distribution of blacktip reef sharks (Carcharinus melanopterus) based on habitat characteristics by the baited remote underwater video (BRUV) method in Morotai waters of North Maluku. Asian Journal of Fisheries and Aquatic Research, 7:3, 34-50. Access online.
By Sophie A. Maycock for SharkSpeak
the underwater footage is fantastic.