The overfishing of sharks happens because of the huge demand—mainly for shark fins—and a lack of management to ensure shark fisheries are sustainable. Some species, such as spiny dogfish and porbeagle, are targeted primarily for their meat.
The oceanic whitetip, porbeagle and three hammerhead species are some of the shark species of concern for WWF, where the impact of trade is contributing to declines in populations. Millions of these sharks continue to be fished annually to supply the persistent demand for their fins and meat. Controls on fishing are woefully insufficient. As a result, the oceanic whitetip, porbeagle, and the smooth hammerhead are classified as vulnerable by the IUCN, while scalloped and great hammerhead sharks are classified as endangered.
Threats to pelagic sharks
Overfishing is the overwhelming threat, with open ocean longlines using hundreds if not thousands of hooks each catching the greatest volume of sharks globally. While these fisheries may be primarily targeting tuna and billfishes such as marlin, the sharks caught are an important source of income, particularly their fins. Tuna purse-seiners also catch sharks, although these have a better chance of being released alive, while gill nets are an ecological disaster, catching almost anything in their path, including whales, dolphins, turtles and sharks.
While the oceans are vast, there are few refuges from industrial fishing, and some pelagic species, such as the oceanic whitetip have suffered massive population losses due to their inability to reproduce more quickly. Seventeen out of the 39 pelagic shark species are threatened with extinction.
Threats to reef sharks
As with most shark species, overfishing is by far the biggest threat to most larger reef sharks, while damage to reef and other key habitats is also having an impact. The clearance of mangroves has a negative impact on species whose young use these as nursery grounds. The loss of living coral reefs due to sedimentation and fertilizer run-off from farmland, and climate change, will often reduce the amount of prey for sharks. Many kinds of food fishes that humans like to eat inhabit reefs, and so reefs are targeted by fishers, using types of fishing that also catch sharks.
Some 25% of all the 494 sharks and rays inhabiting coastal continental shelves, which includes all reef sharks, are threatened with extinction. There may be many more as the conservation status of 35% is not yet known.
Threats to rays
In the ray's marine realm, overfishing is the largest threat. Some of the most valuable fins in the shark fin trade are from shark-like rays, such as sawfishes and large guitarfishes, while the meat of many species of rays and skate are also eaten in coastal communities.
Five out of the seven families of elasmobranch most threatened with extinction are rays.