We live of the ocean. We use it for food, we transport huge amounts of cargo across it, and every summer we head for the warm seas to dive, surf and fish. Therefore it’s important for us to know how healthy our ocean is.
Conventional methods mostly required we take large amounts of fish out and start counting them. The large problems with these were: everything we caught died. We got excellent measurements from them: we knew how big they grew at what life-stages; we knew how many were pregnant at what time of the year; we know how many species were around in the areas we caught. But all these methods were very destructive.
Then we developed methods whereby we dove down there and see things for our own eyes. Dive surveys became the conservation friendly survey method. However, divers could only go out in ideal weather situations, depth was limited to a maximum of 30 meters, and we found out that we were getting skewed results. The mere presence of the divers down there scared away some fish, while others were more curious and came from far around to investigate. We weren’t getting the right picture. Enter the Baited Remote Underwater Video (BRUV).
First developed in Australia in the mid-2000s, BRUVs were [developed] as a non-destructive, non-extractive alternative to look at the fish community structure under a whole host of environmental conditions. The principle of the BRUV is simple: an underwater camera and a canister with bait are attached to a metal structure, which in turn is attached to a long rope with a buoy. With the camera rolling, the metal structure is dropped at a pre-determined location, and after a while (usually 30-60 minutes), the BRUV rig is retrieved, the video downloaded, and the footage analysed.
The BRUV has shown to be more useful than dive surveys, as the rig can be deployed in practically any situation, on any substratum, and the depth is limited only to the camera’s specifications and adding illumination. Only recently researcher used BRUVs to compare shallow sea life to life in the deep sea.
Bait is used to attract fish species to the camera, otherwise the method would mostly rely on the fish swimming by by chance. While sardines (Sardinops sagax) are usually used as bait, different research groups have experimented with various types of other bait, with various degrees of success. Interestingly, often species that don’t feed on fish, and thus would not be interested in the bait, are seen. It is suspected that these species approach the BRUV rig due to the activity that’s going on around the bait canister, not necessarily because of the bait itself.
While normal BRUV rigs employ a single camera to view the passing underwater life, by attaching a second camera it is possible to get a 3D view of the fish. With specialised technology it is possible to get accurate measurements of the fish that swim by.
BRUV research has allowed us to compare the species diversity amongst various substrata (reef sites vs sand sites) and depths. Continuously monitoring a specific area allows us to explore seasonal variation in species diversity. In addition to analysing the diversity and abundance of species, exploring the underwater video allows for some amazing behavioural footage. We’ve seen beautiful footage of catshark species interacting with octopus, their favourite prey, and Red Roman fiercely attacking other species, defending their ‘turf’.
BRUVs has also shown to be a useful tool for conservation. Showing people a glimpse of life underwater, how a healthy sea is supposed to look like, and - for people not able to dive down and see for themselves - a glimpse of the beauty that can been seen often just a dozen meters from the shore. The future holds a lot for BRUVs as researchers find more wide-ranging possibilities of using underwater cameras.
about the author
Born in South Africa and raised in The Netherlands, Ralph Watson has a research background in genetics and marine biology, and is currently looking at the ecology of two catshark species endemic to Southern Africa. Ralph has been working with BRUVs for his Master’s in 2012, and again for his PhD since 2015. Currently he’s using BRUVs to assess the catshark population structure around Mossel Bay, South Africa.
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