Human threats to sharks and rays

The primary threat

Overfishing and bycatch

Of about 1,200 known species of sharks, rays, and chimaeras, 391 were assessed as threatened with extinction in the 2021 global reassessment for the IUCN Red List, and overfishing affects every one of them. Overfishing, where fish are removed from a population faster than they can replace themselves, has already led to the probable global extinction of three shark and ray species.

Estimates of the global shark catch, counting bycatch and discards, range from about 1.4 to 1.7 million metric tons (1.5 to 1.9 million US tons) a year. Although some sharks are targeted, most are caught incidentally in fisheries for other species, such as gillnet and longline fisheries for tuna. In the open ocean, the abundance of oceanic sharks and rays fell by 71% between 1970 and 2018, while relative fishing pressure rose 18-fold between 1970 and 2014.

Ocean pollution

Pollutants typically bioaccumulate, building up in a shark's body faster than it can excrete them, and sharks take in still more from their prey. Toxic chemicals and heavy metals such as mercury are now routinely found in sharks and rays, yet research on what these pollutants do to the sharks themselves is still at an early stage.

On a population level, pollution is likely to have a minor but chronic effect, and it is getting worse. Plankton-feeding sharks and rays, such as manta rays and whale sharks, are particularly vulnerable to plastic pollution and oil spills.

Climate change

Most sharks and rays are cold-blooded, so the temperature of the water sets the pace of their digestion, growth, and reproduction. Warm-water species are being recorded farther toward the poles, some tropical waters may become too warm for some species, and expanding low-oxygen zones can squeeze open-ocean sharks such as blue sharks toward the surface, where they may be easier for fisheries to catch.

Habitat loss

Mangroves, seagrass meadows, and rivers give young sharks and rays food and shelter, and many species also depend on reefs. Between 20 and 35% of the world's mangrove area has been lost since about 1980, and dams and flow controls have reduced sawfishes' access to the river nurseries their young depend on. Bottom trawling, the largest human source of physical disturbance to the marine environment, can also damage the corals and sponges to which some species attach their eggs.

Tourism

More than a million people a year join tours to dive or snorkel with sharks and rays, in more than 40 countries. Compared with overfishing, habitat loss, pollution, and climate change, tourism has had minimal impact on shark populations, and well-run tourism can help fund protection.

Unmanaged feeding, crowding, and boat traffic can still injure animals and disturb the feeding areas and cleaning stations (reef sites where small fish remove parasites) they depend on.