One study found that roughly 4.5 million sea animals are killed as bycatch in longline fishing every year, including roughly 3.3 million sharks, 1 million marlins, 60,000 sea turtles, 75,000 albatross, and 20,000 dolphins and whales.
Even longlines, though, don’t produce the immense bycatch associated with trawling. The most common type of modern shrimp trawler sweeps an area roughly twenty-five to thirty meters wide. The trawl is pulled along the ocean bottom at 4.5 to 6.5 kmh for several hours, sweeping shrimp (and everything else) into the far end of a funnel-shaped net. Trawling, almost always for shrimp, is the marine equivalent of clear-cutting rain forest. Whatever they target, trawlers sweep up fish, sharks, rays, crabs, squid, scallops - typically about a hundred different fish and other species. Virtually all die."