Cetacean Bycatch Facts
The scientific classification for the world's 80 or so species of whales, dolphins and porpoises.
Bycatch: The industry term for the inadvertent capture of non-target species in fishing gear. Besides cetaceans and other marine mammals, sea turtles, seabirds and non-commercial fish species also are regularly caught and killed unintentionally as bycatch.
World Wildlife Fund convened a summit of the world's leading cetacean experts in January 2002 in Annapolis, Md., which was attended by 25 scientists from six continents. The group reached consensus that the single biggest threat facing cetaceans worldwide is death as bycatch in fishing gear.
- More whales, dolphins and porpoises die every year by getting entangled in fishing gear than from any other cause. Researchers at Duke University and the University of St. Andrews in Scotland estimate a global annual average of nearly 308,000 deaths per year - or nearly 1,000 per day.
- For comparison, an average of 21,470 whales were killed annually in the 20th century around Antarctica (where most commercial whaling occurred), causing severe declines of nearly all populations of large whales. A global moratorium on commercial whaling went into effect in 1986, a major step toward alleviating this threat. On the other hand, the cetacean bycatch threat continues unabated in much of the world.
- Fishing gear that poses the biggest danger to cetaceans includes: gillnets, set nets, trammel nets, seines, trawling nets and longlines. Because of their low cost and widespread use, gillnets are responsible for a very high proportion of global cetacean bycatch. Experts agree that wherever there are gillnets, there is cetacean bycatch.
- When caught in fishing gear, small whales, dolphins and porpoises often die because they aren't strong enough to break free and come to the surface to breathe. Large whales can usually break free, but may continue to tow some of the gear for long periods, causing debilitating injuries and even slow death. Fishing line, for example, can coil around an animal's head or lodge in its baleen, interfering with feeding.
- Several cetaceans are on the verge of extinction because of bycatch:
- Vaquitas, the world's smallest porpoises, are disappearing because they are being trapped and drowned inadvertently in gillnets set for mackerels, sharks, rays and other species. WWF and other experts estimate that only about 500 vaquitas - found only in the Gulf of California - may remain in the wild.
- There are probably fewer than 100 Maui's dolphins left in New Zealand's waters due to high rates of entanglement in set nets and pair trawlers.
- Irrawaddy dolphins in the Philippines, down to fewer than 70 individuals, will soon disappear if nothing is done to keep them from drowning in lift nets.
- In some cases, relatively simple and inexpensive alterations of fishing methods and gear are all that is needed. This includes attaching acoustic alarms, or "pingers," to fishing nets to alert cetaceans to the presence of fishing gear or perhaps annoy them into swimming away. Pingers have significantly reduced harbor porpoise mortality in gillnet fisheries in the Gulf of Maine and may work for other species as well. Weights at the top of fishing nets that allow small cetaceans to swim over the nets to freedom also have been found to work in some fisheries. Setting nets in deeper water, an inexpensive and simple strategy, can also help to reduce bycatch in some cases.
- In cases where whales and dolphins migrate in and out of fishing areas, fisheries can be closed temporarily when the animals arrive and reopened when they leave. These measures are often unpopular with fishermen and can be difficult to enforce. However, if information on patterns of bycatch and movement of animals is significant and the closure area is large enough and time period long enough, this can be a viable mitigation option.
- In the U.S., in fisheries where bycatch levels are high enough to pose a threat to cetacean populations, the Marine Mammal Protection Act requires the development of a strategy to reduce bycatch. These plans must be developed by a team with representatives from every group with a stake in the problem: fishermen, scientists, fisheries managers and environmental groups, who must work together to find solutions. The cooperation of fishermen is essential in tackling any entanglement situation. Some of these teams have come up with highly effective solutions.
- In the Gulf of Maine, bycatch of harbor porpoise in gillnets was so severe that there was a movement to put them on the Endangered Species List. A combination of approaches, including use of pingers, temporary fisheries closures and placement of observers on fishing boats, reduced mortality by around 77 percent in just the first year of implementation in 1999.