Bycatch occurs because modern fishing gear is very efficient, often covers an extensive area, and can be highly unselective—it catches not only the target species but many other marine animals as well. Poor fisheries management in certain countries further contributes to the problem. Widespread pirate fishing ignores regulations on net mesh sizes, quotas, permitted fishing areas and other bycatch mitigation measures.
NON-SELECTIVE FISHING GEAR
Fishing gear is largely non-selective—any species can be caught, including non-target species. Longlines, trawling and the use of gillnets are the fishing methods that most commonly result in bycatch. Longlining is a commercial fishing method commonly targeting swordfish, tuna and halibut, where hundreds or thousands of baited hooks hang at intervals along a single fishing line. The hooks (commonly called “J hooks”) cause problems for marine turtles when swallowed, usually resulting in death. Sharks, non-target billfishes and juvenile tunas are often hooked as well.
With trawling, boats drag large nets along the seabed, catching almost everything in their path. They can damage coral reefs and at shallow depths, catch marine turtles. Gillnets are mesh nets that allow fish to pass their heads and gill coverings through a hole in the mesh and then get stuck when they try to back out. They can be several miles long and up to 100 feet deep. Bycatch occurs because the nets also trap everything larger than the net’s mesh, which includes juvenile fish, sharks, seabirds, marine turtles and cetaceans (whales, dolphins, porpoises). The nets are very hard to see, blending in perfectly with the water and difficult for cetaceans to detect by echolocation. Gillnets that are lost at sea are rarely recovered and can continue to capture marine animals for many years.