Response Of predators to Protection and Enhancement
Funded by the European Maritime and Fisheries Fund (£187,545), ROPE focuses on how mobile species of commercial importance (e.g. brown crab, Cancer pagurus, and European seabass, Dicentrarchus labrax) interact with an offshore longline mussel farm using acoustic telemetry. The University of Plymouth have been monitoring the effects of a new offshore mussel farm in Lyme Bay on the surrounding ecosystem, since the beginning of its development in 2013. The farm, owned by Offshore Shellfish Ltd., is located between three and six miles offshore in Lyme Bay, South Devon. Once completed, the development will be the largest of its type in European waters, covering a total area of 15.4 km², and producing up to 10,000 tonnes of native blue mussels, Mytilus edulis, per year.
Our underwater monitoring surveys have shown that the farm which exists as a living reef structure has increased the number of predators in the area. The vertically hanging rope droppers act like Fish Aggregation Devices (FADs) and large shoals of Atlantic horse mackerel (Trachurus trachurus) are frequently seen swimming around and feeding on the ropes. Larger predatory fish including European bass (Dicentrarchus labrax) and grey mullet (Chelon labrosus) have also been observed around the rope droppers. Underneath the ropes, commercially important brown crab (Cancer pagurus) feed on the mussel clumps that fall to the seabed and there is a wide diversity of other species attaching to the ropes.
Our research in Lyme Bay over the past ten years, has approached this management at the site level, to support both conservation of marine biodiversity and socioeconomic growth; an approach which has recently been adopted and promoted by the Government’s 25 year plan. However, there is still research needed to evaluate whether MPAs and offshore aquaculture contribute to commercial fisheries through the process of spill-over. Within the mussel farm, we know that crabs, lobsters and predatory fish utilise the site for food and shelter, due to the habitat enhancement that the rope droppers, screw anchors and fallen mussel clumps provide. However, we do not know how these predators move around the farm or how long they remain resident compared to the surrounding area and the nearby MPA.
Does co-locating shellfish aquaculture in close proximity to MPAs have synergistic benefits for replenishing fished populations and supporting sustainable fisheries? Answers to this bigger question could have important implications in conservation policy, marine spatial planning and the blue economy. To understand animal movements in and around the mussel farm and between the mussel farm and the MPA, we plan to track multiple species including sea bass, brown crab, lobsters (Homarus gammarus) and crayfish (Palinurus elephas). Acoustic tags will be used to track these crustaceans and fish for up to two years. The tags emit a unique ping which can then be recorded and monitored by static receivers placed around the farm and the MPA boundary.
This project presents a unique and exciting opportunity to look at the effects of habitat enhancement resulting from offshore aquaculture development. Very little is known about the ecological consequences of offshore aquaculture, despite calls for a move towards offshore development and a recent emphasis on Blue Growth in the UK, with aquaculture listed as one of the major development sectors. This study will support the evaluation of offshore aquaculture in sustainable management of the ocean as recommended by UN Sustainable Development Goal 14 and addresses a number of the Marine Management Organisation and Defra evidence requirements.
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