Pioneering stereo-BRUV for long-term monitoring in Africa

The stereo-BRUV camera system is set up onboard Honkeneii, SAEON’s research platform. (Picture courtesy of the SAEON Elwandle Node). View larger version Large numbers of sparids flock to the bait canister, with the stereo-BRUV cameras mounted on the frame in the background. (Picture courtesy of Steve Benjamin) View larger version Using the newly acquired capstan winch on Honkeneii, a stereo-BRUV rig is retrieved from the ocean floor where the cameras are left to record fish populations for a one-hour period. (Picture courtesy of Steve Benjamin) View larger version A cheeky pyjama catshark (Poroderma africanum) takes a nibble at the stereo-BRUV rig. (Picture courtesy of Steve Benjamin) View a larger version

Centuries of extraction from our oceans have left us, the human race, in a somewhat precarious position.

With booming populations and decreases in food availability, the need for a wake-up call has never been more evident. South Africa’s fisheries have seen a steady decline in catch rates since the 1950s, for both the recreational and commercial sectors, and fisheries management appears to lurch from one crisis to another.

For the effective management of resources and conservation of biodiversity, reliable population data are essential. In among the doom and gloom there are glimmers of hope emerging from new and innovative ways to protect, monitor and manage the crumbling resources.

Historically, subtidal habitats have been complicated to survey effectively and, as a result, much of the management has been based on inadequate data. Recent methodological advances that allow accurate habitat mapping and remote video sampling over broad depth ranges, have begun to alleviate these shortfalls by providing comprehensive and standardised data.

Over the last decade, baited remote underwater stereo-video (stereo-BRUV) emerged as one of the most efficient and comprehensive ways to survey reef fish populations.

Marine protected areas

Marine protected areas (MPAs) are at the forefront of an ecosystem-based approach to fisheries management and are gaining recognition as appropriate tools to conserve resources and biodiversity. South Africa’s MPA network consists of some 23 parks, and there are plans to expand this network to ensure all of South Africa’s coastal and offshore habitats are sufficiently protected.

The bastion in the network is the Tsitsikamma National Park. Proclaimed in 1964, Tsitsikamma is approaching its 50^th anniversary and is the oldest and one of the largest (323 km²) no-take MPAs in Africa. It is thus the ideal location to see what fish communities on subtidal reefs are meant to look like.

This relatively pristine study site saw the first application of stereo-BRUV technology in African waters by researchers from SAEON’s Elwandle Node, of which I was fortunate to be one.

The SAEON Elwandle Node’s Tsitsikamma Research Project is in its seventh year, with sampling taking place bi-annually to incorporate both summer and winter. The project involves a host of research methods including plankton sampling, biomarker techniques, controlled angling, fish and invertebrate trapping, SCUBA diving surveys and collections, and a variety of underwater video techniques.

Stereo-BRUV

The year 2013 saw the introduction of the stereo-BRUV technique to South Africa, a method developed by Prof. Euan Harvey’s team from the University of Western Australia. The method makes use of two cameras carefully mounted on a stainless steel frame to allow stereo-vision of the fish community.

To ensure sufficient fish are seen, bait (crushed pilchard) is used to attract them into the camera’s field of view. While essentially still a baited remote underwater video (BRUV) system, the stereo-BRUV amplifies the data output, as fish size and the visible area can be accurately estimated from the stereo-images with specialised software.

As with all remote underwater video techniques, stereo-BRUV removes biases caused by the selectivity and destructiveness of the various fishing techniques, and the intrusive effect of SCUBA diver presence on the fish community. By being able to analyse the size structure of fish populations, researchers can use stereo-BRUVs to evaluate fish stocks, their population dynamics and calculate biomasses, without the need to trawl the oceans and remove hoards of fish.

As a new MSc candidate, my research involves optimising stereo-BRUV for use in South Africa’s temperate continental shelf waters by testing different types of bait, light sources and an examination into the effects of observer bias on the reliability of the abundance and size data.

The first field trip

The February 2013 field trip was a great success, and solidified the collaboration between the SAEON Elwandle Node and the University of Western Australia. With four stereo-BRUV systems available to the Tsitsikamma Research Project in February 2013 (cameras and housings on loan from the Australian collaborators), more samples and more comprehensive data were collected as compared to all conventional sampling techniques deployed previously in the park.

In addition, the stereo-BRUVs allowed us to sample at greater depths, a weakness of many monitoring methods, such as SCUBA surveys. The field trip also included evaluating biomass to allow for trophic modelling, evaluating abundance correction factors through angling and essentially examining the effectiveness of MPAs.

Although still in its infant stages, the project is gaining momentum and attention from researchers and managers around the country. Judging from the success of the method on the international research stage, and the experience and confidence gained through the international collaboration and the first field trip, stereo-BRUV is set to open and conquer new frontiers in subtidal research in South Africa, and hopefully contribute to the future sustainable management of reef fish resources.