Measuring change in a southern Benguela benthic ecosystem after cessation of trawling

Offshore benthic biodiversity and ecosystem functioning are poorly understood in South Africa. Increasing anthropogenic and climate change pressures on deepsea ecosystems intensifies the urgency for research towards improved... [ view full abstract ]

Offshore benthic biodiversity and ecosystem functioning are poorly understood in South Africa. Increasing anthropogenic and climate change pressures on deepsea ecosystems intensifies the urgency for research towards improved understanding of these habitats. Impacts of demersal trawling have been cited as one of the largest global anthropogenic sources of disturbance to the seabed and its biota. The implications of benthic disturbance resulting from South Africa’s 100+ year-old hake trawl fishery, remains under debate. A previous study in the southern Benguela reported a greater impact on epifauna in heavily trawled areas than infauna however, representative untrawled areas were not available for comparison in this study. Trawling impacts are known to vary with habitat, gear type and trawling practice, necessitating a site specific experimental approach to quantify such impacts. A five-year 'press-and-release' experiment is currently underway that aims to measure changes in a southern Benguela outer shelf ecosystem, after portions of a 6 x 15 nm area were closed to trawl fishing. The baseline survey in 2014 showed that the habitat in the experimental area is largely homogenous, although depth appears to influence biota composition, validating the experimental design implemented. Changes in fish and epifauna are assessed visually using a towed camera, whilst infauna and sediment properties are quantified from grab samples. This experiment showcases an opportunity for long-term, co-operative research through collaborations between industry and scientists.