Bycatch deaths are believed to be among the main causes of the drastic decline of Pacific leatherback turtles
, whose numbers have reduced by 90% since 1980 to as low as 2500 females in the eastern Pacific Ocean. While there are uncertainties about the precise, relative contribution of bycatch to global marine turtle declines, it is beyond any doubt that turtles cannot sustain current bycatch rates. Global longline fisheries, for example, caught more than 250,000 endangered loggerhead turtles and critically endangered leatherback turtles in 2000.
With over 300,000 small whales, dolphins and porpoises dying each year from entanglement in many types of fishing gear, bycatch is causing one death every 2 minutes and is the single-largest cause of mortality for small cetaceans. While large whales can usually break free, entanglement can nevertheless cause debilitating injuries and eventual death.
Bycatch reduction may make the critical difference in the fight to save 9 of the 15 cetacean species or populations classified as endangered or critically endangered. These include New Zealand’s Māui dolphins
, Mexico’s vaquita
, North America’s North Atlantic right whale
, Asia's Irrawaddy dolphin
, Europe’s harbour porpoise, and South America’s franciscana dolphin.
Many seabird species are victims of bycatch, particularly albatrosses
, petrels, shearwaters, and penguins
. Around 300,000 seabirds drown each year after diving for bait set on longlines and becoming hooked. Such deaths threaten many species, including 18 species of albatross, with extinction. Tens of thousands more seabirds die in drift nets, trawls nets, and gillnets. Seabirds also die after hitting trawl warps (the rope that attaches the net to the boat) often while feeding on fish offal discharged from on-board fish processing.
Bycatch accounts for about half of global shark catches. Longlines are mostly responsible, but bycatch in nets is also important. In the Pacific Ocean alone, 3.3 million sharks are caught each year as bycatch on longlines. Indeed, in terms of numbers, sharks are the most significant bycatch species in the world’s major high seas fisheries. They are also particularly vulnerable to over-fishing due to their relatively slow reproductive rate, with several species showing recent drastic declines.