Purse seines are used in the open ocean to target dense schools of single-species pelagic (midwater) fish like tuna and mackerel.
Purse-seine fishing in open water is generally considered to be an efficient form of fishing. It has no contact with the seabed and can have low levels of bycatch (accidental catch of unwanted species).
MSC certified fisheries using purse seines must ensure that they leave enough fish in the ocean to reproduce. This can be achieved by targeting schools of adult fish and using a mesh size large enough to allow smaller fish to swim free.
Purse seines can also be used to catch fish congregating around fish aggregating devices (FADs). This fishing method can result in higher levels of bycatch, making it harder for these fisheries to achieve MSC certification.
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Pelagic trawls are cone-shaped nets that are towed along behind one or two boats. They are designed to target fish in the mid and surface water.