Big BRUVer Watching Sharks
Updated: Apr 27
Baited Remote Underwater Video (BRUV) is a relatively new technique which can be used to observe marine life. The method involves submerging cameras mounted on a steel frame onto the ocean floor and attracting predatory fish, like sharks, to the recording equipment using bait, which is concealed in a bag or cage connected to the frame. The footage can be very valuable for scientific research and is also just seriously cool to watch!
BRUV studies are especially powerful because once the footage is taken, data can be extracted from the video after the fact, so multiple different research questions can be asked from the same field work. For example, the video can be used to count sharks and estimate their abundance, or it can be used to observe the competitive behaviour of sharks around a resource, or it can be used to assess how many different species live in one area (known as the "species composition", or it can be used to evaluate the health of the habitat or to identify individual animals based on distinctive scarring or pigmentation patterns.
For instance, a recent study conducted in Maluku, Indonesia, used BRUV footage to identify individual blacktip reef sharks (Carcharhinus melanopterus). The researchers placed tuna in a bait bag to attract the sharks and then recorded whoever showed up to the party using two 12 megapixel cameras. These sharks have distinctive black and white pigmentation patterns on their pectoral fins and tail (known as the "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. Therefore, images of individual sharks' pigmentations patterns which were captured in BRUV footage could then be used to identify if the shark was seen again. The researchers identified a total of 21 different blacktips, which they recorded repeatedly at the site which was (aptly) named Blacktip Point (Mukharror et al, 2019).
This research group were also able to assess the distribution of the blacktip reef sharks based upon differences in the habitat. The video was recorded at several different locations with contrasting topography and coral cover, and they also measured water temperature, salinity, acidity, current and water visibility, and assessed the quality of corals at each study site. They compared the numbers of sharks seen at different habitats to investigate how the physical environment was related to shark abundance- basically which areas do they like, which do they not like and why?
They found that the occurrence of blacktip reef sharks were influenced by both the quality of the water and by the health of the coral reef. They concluded that sighting sharks was related to the current and water salinity; sharks were not seen on the footage in areas with very strong currents or when waters were especially salty. Comparatively, blacktip reef sharks were videoed in high numbers when waters were relatively warm ( 29°C), relatively less saline (38 – 40 ppt), with good visibility (10 m), moderate currents and with neutral acidity (pH 7). Whatsmore, they also found that the sharks preferred sites with significant coral cover and were less commonly seen in areas where corals were sparse or unhealthy (Sentosa et al, 2020).
These findings are particularly important because they imply that blacktip reef sharks may be impacted by future climate change. Changes in acidity and increasing temperatures may directly affect the blacktip reef sharks and mean they become less abundant in the area. Whatsmore, acidification and higher temperature may indirectly affect the sharks because they cause coral bleaching and a retraction in reef cover. Therefore, we may see an associated constriction in the range of blacktip reef sharks in the near future, if climate change continues to advance as it is predicted to.
If you are interested in BRUV research, you can follow @globalfinprint on twitter.
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.
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.