Between 2014 and 2018, a multidisciplinary team of scientists gathered a treasure trove of images of the Karbonkel trawl grounds. Photographs and video footage show well-known deep-sea fishes, like hake and kingklip in their natural environment, as well as seabed animals about which very little is known.
The five-year Benthic Trawl experiment took place on the South African research vessel Ellen Khuzwayo. The experiment was implemented through a partnership between the South African Deep-Sea Trawling Industry Association, the South African Environmental Observation Network, the Department of Environment, Forestry & Fisheries, the University of Cape Town, the South African National Biodiversity Institute and. The goal of the collaboration is to obtain a scientific understanding of the environmental impacts of hake trawling in South Africa.
In South Africa, hake trawling occurs almost entirely on soft, muddy, sandy or gravelly sediments.
Trawl grounds cover approximately 4.4% of South Africa’s seabed environment. The trawl footprint is ring-fenced; trawling outside the ring-fenced zone requires the completion of an environmental impact assessment.
Even though the size,weight and configuration of trawl gear is strictly regulated, the industry wants to know more about the nature and extent of the impacts of trawl gear on the seabed. The five-year Ellen Khuzwayo experiment was designed to test the extent to which marine life would recover if trawling stopped.
 | A kingklip is pictured on the seabed at a depth of about 300m. Around it are raspberry starfish, Crossaster penicillatus. Kingklip is one of the most highly valued species caught by the deep-sea trawl fishery. The benthic trawl experiment has revealed for the first time that kingklip live in burrows in the sandy seabed. |
| Three species of rattails are caught in trawl nets. This is probably Lucigadus ori. With their bulbous heads and long narrow tails, rattails look a little like helicopters swimming over the seabed. | |
| Monk is a highly valued catch of the deep-sea trawl fishery. The fish is a classic ambush predator – it lies very still in the sand and uses its first dorsal spine as a “fishing rod” to lure its prey close to its cavernous mouth. | |
| These fish are called dragonettes. They are common in the tropics, but this is a deep-water species Paracallionymus costatus. Also visible in this photo are a number of bristle worms. | |
| A deep water hake Merluccius paradoxus swims away from the camera. Stocks of both deep-water hake and shallow water hake (M. capensis) are considered by scientists to be above the level that produces maximum sustainable yield. This means the growth of the stocks is in balance with fishing activity and current catch rates are sustainable. |
To capture these images, a submersible Ski-Monkey camera was mounted on a steel sled and towed behind the research vessel Ellen Kuzwayo. At each deployment, the camera captured 10 minutes of still photographs and 10 minutes of video footage.
Operating a camera nearly half a kilometre under the sea was not without its challenges. It had to be towed sufficiently fast to keep ahead of the plume of dust it raised and, predictably, there were a few failed attempts, with the sled digging into the soft sediment and occasionally rolling over.
The Ski-Monkey towed submersible camera, here deployed at 474.71m, relays an image to the computer laboratory on the Ellen Kuzwayo. This image shows a shoal of deep-sea spiny eels Notocanthus sexspinnis. Many images of these spiny eels were collected – scientists think they were attracted to the camera’s light. Though they look like eels and their common names suggest they are eels, these deep sea fishes are not a member of the eel order (Anguilliformes). Instead, they are members of the order Notacanthiformes.
This image shows evidence of trawling.
An intensive analysis of five years of data gathered by the Ellen Khuzwayo has begun. The scientific team will compare photographs and footage of trawled and untrawled areas. Researchers are focused on the emergent macrofauna – the animals that stick out or sit above the sediment, like sea anemones and sea pens, and the animals that live in the sediment itself, like heart urchins and crabs. They are also looking at the structure of the sediment to see if it is being influenced in any way by repeated trawling.
The scientists’ results will allow them to say definitively what the impacts of trawling are in South Africa.
The benthic trawl experiment is the first of its kind in South Africa but similar experiments have been conducted in other parts of the world. For instance, SADSTIA has participated in a ground-breaking international initiative to determine the global impacts of trawling. This study was published in Proceedings of the National Academy of Sciences. It determined that the impacts of trawling are highly variable: recovery times for ecosystems disturbed by trawling depend on the type of gear used and a range of environmental variables.
The South African trawl fishery for hake is certified as sustainable by the Marine Stewardship Council (MSC) the world’s leading certification and eco-labelling programme for sustainable, wild-caught seafood. Improving knowledge and understanding of the impacts of trawling on the benthic environment is one of the conditions of MSC certification.
Acknowledgement: All images and video were obtained by SAEON staff, Dr Charles von der Meden and Mr Grant van der Heever, using the SAEON towed deep-sea camera, Ski-Monkey III.
