In June, along the shoreline of Mauritania, in northwest Africa, scientists made a gruesome discovery: the carcasses of 230 dolphins, a pilot whale, and 15 endangered hawksbill and leatherback sea turtles.
"Because of the mixture of species found, and the fact that some of them were entangled in sections of fishing nets, it is likely that these animals were killed as bycatch," said Jean-Christophe Vie, deputy coordinator of the World Conservation Union's species program, based in Gland, Switzerland.
Across the world's oceans, large commercial fishing boats haul aboard huge nets and 60-mile (97-kilometer) lines teeming with unwanted creatures—bycatch, sometimes referred to as "bykill" or "dirty fishing."
Bycatch is a mix of young or low-value fishes, seabirds, marine mammals, and sea turtles, often considered worthless and tossed overboard—dead or dying.
The collateral damage amounts to about 30 million tons (about 27 million tonnes) of sea life each year, says marine ecologist Jane Lubchenco of Oregon State University—about one-third the total global catch. Among the worst offenders are shrimp trawlers, who often discard up to 10 pounds of sea life for each pound of shrimp they catch.
"If a hunter is hunting for elk, he's not killing sparrows, eagles, coyotes, and pronghorn," said Elliott Norse, president of Marine Conservation Biology Institute (MCBI) in Redmond, Washington. "That's different in the sea. We fish blindly—and it's an exceedingly wasteful way of doing things."