Seabed experiment enters its third year

For the third year in a row, a team of scientists on board the South African research ship, Ellen Khuzwayo, is surveying an experimental area on the west coast fishing grounds of “Karbonkel”. The team is using a submersible camera and a benthic grab to closely examine the state of the seabed in three lanes that have been closed to fishing, and two lanes in between them where trawling is allowed.

The no-trawl lanes on Karbonkel have been closed to trawling since January 2014 as a result of a successful collaboration between SADSTIA, the Department of Agriculture, Forestry and Fisheries (DAFF) and a number of universities and marine research agencies. These include the University of Cape Town (UCT), the South African Environmental Observation Network (SAEON) and the South African National Biodiversity Institute (SANBI).

Deep-sea skippers have voluntarily avoided trawling in the three no-trawl lanes since the first survey of the seabed was conducted from the Ellen Khuzwayo in 2014. On that cruise, the seabed was closely filmed and photographed to record its state prior to the closure of the lanes to trawling. This year’s survey aims to examine the state of the same trawl lanes two years after their closure.

“We’re doing exactly what we did last year, we’re filming in each of the trawl lanes,” explained Chief Scientist, Colin Attwood, Associate Professor at the University of Cape Town prior to his departure on Ellen Khuzwayo. “There’s been no trawling in three of these lanes for two years and if there has been any recovery, we might pick it up – but it’s probably too soon.”

The seabed surveys will continue from Ellen Khuzwayo in 2017 and 2018 and it is hoped that after five years scientists will be able to describe at least some of the impacts that trawling has on the seabed.

SADSTIA Secretary, Johann Augustyn, says that in spite of the fact that about 25 percent of the world’s wild fish catch is caught with trawl gear, trawling gets a bad rap:

“Some people believe that trawling turns the seabed into a desert, but in South Africa, hake trawling occurs almost entirely on soft, muddy, sandy or gravelly sediments and the size and weight of trawl gear is strictly regulated. Even though we believe the negative impacts of trawling are often vastly exaggerated, SADSTIA and its members want to better understand the impacts that trawling has on the ecosystem – and the time it takes for the seabed to recover after it has been trawled,” he said.

In addition to video footage, the scientific team will analyse samples of mud and sand taken by a benthic grab all along the trawl lanes. This will help them to determine whether there are any changes in the macrofauna – small marine animals, including snails, worms, clams and other thumbnail-sized creatures that live and feed in the sediments on the sea floor.

The Ellen Khuzwayo is due to return to Cape Town on Tuesday 2 February and SADSTIA looks forward to releasing the latest set of photographs of deep-sea fish and other organisms as soon as they become available.