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This means it is important that fish stocks are exploited in a sustainable way. Sustainable exploitation means that we can continue to harvest the same number of fish from the seas over years to come, without fish numbers and marine biodiversity decreasing.
My research at the School of Ocean Sciences at Bangor University makes a contribution to the sustainable management of our marine resources.
Later, the attractions of marine biology grew, especially the opportunities for joining offshore research cruises and expeditions.
The seabed is home to a large biodiversity, as many species of crabs, shrimps, starfish, worms and clams live on the seabed. Welsh seas are also home to soft corals and sponges. These seabed invertebrates are the main source of food for many fish species.
Most fishermen catching fish and shellfish – such as cod, plaice, scallops and prawns – are using heavy nets, which are towed over the seabed and are known as “bottom trawls”.
These trawls have chains, teeth and steel wires on the bottom to stir the fish and shellfish off the seabed and into the net. As the nets are towed over the seabed, they damage and kill about half of the biodiversity on the seabed.
As the trawls kill the food source, fish that live in frequently-fished areas may have less to eat.
We’ve used the Bangor University research vessel Prince Madog to study the growth of the flatfish plaice in the eastern Irish Sea. We’ve caught, measured and weighed thousands of fish and found that plaice in frequently-trawled areas grow slower.
Bottom trawl fisheries may therefore have a double effect on fish – firstly fish are caught and removed from the sea, and secondly the fish that are not caught have less to eat and grow slower.
Slower growth of fish means smaller fish, and this means that fisheries using bottom trawls catch a smaller amount of fish.
The negative effects of bottom trawls could be reduced when fishers switch to gears that do not affect kill fish food – such as gill nets or long-lines – but it may not be possible to efficiently catch all fish species with such gears.
Alternatively, managers of fisheries could minimise the area of the seabed fished by creating trawl lanes that are fished at a high frequency, while leaving the remaining seabed un-fished.
This research provides the science needed to manage Welsh natural resources in a sustainable and profitable way, and could lead to a higher fishing yield at a lower cost to biodiversity.
To contact Jan please email firstname.lastname@example.org.
This article first appeared in the Western Mail‘s Health Wales supplement on the 9th January 2012, as part of the Welsh Crucible series of research profiles.