In the “Pinger Use on Gillnets Instruction & Background Information

Gillnet fishing is only one of many different types of fisheries that have by-catch. Gillnets are made of either multi-filament twine or monofilament nylon, woven into netting designed to lock behind the gills of fish. Gillnets come in all sizes and range from the large pelagic driftnets that can reach lengths of 50-60km down to small coastal nets less than 30m (Northridge 1991, Richards 1994). However, regardless of size, gillnets sometimes catch animals that were not the target species of the fishery including other fish, turtles, birds, and marine mammals.

Marine mammals, especially dolphins and porpoises, are particularly susceptible to being caught in gillnets. When the flippers, dorsal fins, tails, or heads of these animals become entangled underwater in the webbing of a gillnet, the animal will soon drown because they cannot swim backwards to dislodge from the net. It is estimated that many tens of thousands of marine mammals, most of them dolphins and porpoises, are caught and killed in passive fishing gear (e.g. gillnets and fish traps) world-wide (Northridge 1991, Perrin et al. 1994).

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