Why Are Great Hammerheads Critically Endangered? Threats

What the IUCN assessment says

The IUCN Red List has listed the great hammerhead as Critically Endangered, the highest threat category before extinction in the wild, since an assessment published in 2019. It had been listed as Data Deficient in 2000 and Endangered in 2007.

The assessment looked at changes over three generations. For great hammerheads, one generation lasts about 24 years, so three generations cover roughly 71–74 years. Using catch-rate and survey data from the Atlantic and Indian Oceans, the experts calculated a median global decline of about 51–62%, with the highest probability falling in the category of more than 80%. Because many regions have no data but heavy fishing, they took a precautionary approach and concluded that the decline is most likely greater than 80%, which meets the Critically Endangered threshold.

The population trend is listed as decreasing. The Atlantic population is thought to have declined by more than 50% and the Indo-Pacific population by more than 80% over three generations.

Fishing and the fin trade

Great hammerheads are caught in fisheries throughout the tropics, on longlines, in gillnets and purse seines, and sometimes by trawls. Some fisheries target them, but many are caught incidentally while fishers are after tuna, swordfish or other sharks. Their meat is rarely eaten, but the fins are highly valued. Hammerhead fins are considered among the best for shark fin soup, and together the great, scalloped and smooth hammerheads made up about 4% of the shark fins imported into Hong Kong in 2014. Skin, liver oil and remains may also be used.

Catches are hard to track. Few fisheries record great hammerheads separately from other hammerheads, and many catches in small-scale or remote fisheries go unreported. That makes it difficult to set safe limits, and it is one reason the IUCN took a cautious view. The global scale of the problem is described in How many sharks are killed each year?

Why so many hooked hammerheads die

Even when a great hammerhead is not wanted, it often does not survive being caught. Hammerheads fight hard and tire quickly, and the Florida Museum describes them as among the more physiologically fragile sharks. Studies summarized by the IUCN estimate that about 56% of great hammerheads are already dead when US bottom longlines are hauled in, and about 31% on demersal longlines off Western Australia.

Sharks that are released alive may still die later from exhaustion or injury. For the closely related scalloped hammerhead, deaths after release from purse seine nets have been reported as high as 100%. Large great hammerheads are also killed in the shark nets set to protect swimming beaches in South Africa and Australia. Off KwaZulu-Natal in South Africa, catch rates of great hammerheads in these nets fell by about 6.5% a year between 1978 and 2003.

Slow breeding makes recovery hard

Great hammerheads live long and reproduce slowly. Females mature at roughly 5.5–8 years old and 2.1–3 m (6.9–9.8 ft) long, are pregnant for about 11 months, and breed only once every two years. Litters usually hold 6–42 pups. The oldest aged sharks were 39–44 years old.

These traits mean a great hammerhead population can grow by at most about 7% a year, even under ideal conditions. When fishing kills more than that, numbers fall steadily, and a population that has been cut by 80% may need decades to rebuild once fishing pressure is reduced.

Where declines have been steepest

The picture varies by region:

• Indian Ocean: steep declines, shown most clearly by the KwaZulu-Natal beach net records. Fishing pressure across the tropical Indian Ocean has risen sharply in recent decades.
• Mediterranean Sea: a study of historical records from the northwest Mediterranean found that hammerheads declined faster than any other large shark with enough data, disappearing from coastal waters after 1963; they are now very rare.
• West Africa: intense and poorly monitored fishing is thought to have caused steep declines.
• Northwest Atlantic and Gulf of Mexico: the population was overfished from the 1980s, but survey catch rates have increased since US management measures began around 2005, a sign of possible slow recovery.
• Pacific: data are scarce, and trends are largely unknown.

How great hammerheads are protected

Protection has increased since 2010, but it is uneven:

• ICCAT, the commission that manages Atlantic tuna fisheries, has banned keeping, landing and selling hammerheads in its fisheries since 2010, with limited exceptions for local consumption in developing countries.
• Mediterranean: since 2012, the General Fisheries Commission for the Mediterranean has required great hammerheads to be released.
• CITES: listed on Appendix II in 2013, so international trade in fins and other products needs permits showing they come from legal and sustainable fisheries.
• Migratory species: listed on Appendix II of the Convention on Migratory Species in 2014.
• United States: Florida protects great hammerheads in state waters, and since 2024 keeping them has been banned in US Caribbean waters. In 2022, NOAA Fisheries decided that a petition to list the species under the US Endangered Species Act did not justify a full review. Sharks in Florida are covered in sharks in Florida.
• Finning bans: the US, the EU and many other countries require sharks to be landed with fins attached, although such bans do not limit how many sharks are caught.

What would help great hammerheads recover

The IUCN assessment recommends banning the retention and landing of great hammerheads for as long as the species is Critically Endangered or Endangered. Other priorities are reducing bycatch, handling and releasing caught sharks quickly and safely, and improving catch records, so that hammerheads are reported by species rather than lumped together.

Protecting the places where great hammerheads gather also matters. Tagged sharks return year after year to sites such as Bimini in the Bahamas and Jupiter in Florida, mostly between October and March. These predictable hotspots make the sharks easier to protect and support dive tourism, which gives local communities a reason to value live hammerheads. Despite their fearsome looks, they pose little risk to people, as explained in Are hammerhead sharks dangerous?