Pelagic gillnets

Target

A wide variety of pelagic species (those that spend most of their lives in the mid-water, with little contact with the seabed), including salmon and herring.

How they work

Pelagic gillnets or 'set nets' are fine-filament nets that are kept at or below the surface by numerous floats and weights and held in position by anchors. If a fish's head goes through the net but its body can't follow, it is 'gilled' or entangled in the netting when it tries to get out. Gillnets are used either alone or in large numbers placed in a row. Drifting gillnets or driftnets float freely with the current or with the boat to which they are attached, usually across the path of migrating fish schools.

Advantages

When set correctly and with the right mesh size, gillnets can be highly size selective: small fish can swim right through the net while larger fish will not get their heads stuck.

Problems

Poorly set gillnets or a bad choice of mesh size can result in higher levels of bycatch. Gillnets are associated with bycatch of marine mammals. Acoustic deterrents or 'pingers' attached to fishing nets may discourage some marine mammals from swimming too close and getting caught; however, trials of these have shown very mixed results for effectiveness, depending on the fishing area and the mammal species. Driftnets are associated with a high level of bycatch - large-scale pelagic driftnets are banned by a UN resolution. Lost or abandoned nets continue to entangle marine creatures - known as ghost netting.