Critically Endangered
Scalloped hammerhead
Sphyrna lewini
Scalloped hammerhead is a shark or ray in the family Sphyrnidae (order Carcharhiniformes) — Sphyrna lewini, recorded as Critically Endangered.
Appearance
Scalloped hammerhead sharks are typically uniform grey, grayish brown, bronze, or olive with a white underside for countershading.
Typically, males measure 1.5 to 1.8 m (4.9 to 5.9 ft) and weigh about 29 kg (64 lb) when they attain sexual maturity, whereas the larger females measure 2.5 m (8.2 ft) and weigh about 36.2 kg (80 lb) at sexual maturity.
Range and habitat
The scalloped hammerhead is a coastal pelagic species. It occurs over continental and insular shelves and in nearby deeper water. It is found in warm temperate and tropical waters, worldwide from 46°N to 36°S. It can be found down to depths over 500 m (1,600 ft), but is most often found above 25 m (82 ft).
Marine reserves have been implemented in many areas to allow the sharks to recover. It is very important to place these reserves over areas that sharks use as breeding grounds and nurseries, so they have somewhere to raise their pups.
Pins are Wikidata “endemic to” fields. Orange dots, when present, are GBIF occurrence tiles — survey bias included.
Diet
There is no difference in what male and female sharks eat, but larger sharks are noted to eat larger prey than smaller, juvenile hammerheads. Juveniles typically feed on inshore fish, while adults feed on inshore fish as well as larger organisms that live in deeper waters.
Specifically, this shark feeds primarily on bony fish such as sardines, mackerel, and herring, and occasionally they feed on cephalopods such as squid, octopus, and cuttlefish, and crustaceans such as lobsters, shrimps, and crabs. Hammerheads located in the Indo-West Pacific have been observed to prey on sea snakes.
In crisis
As of 2019, the scalloped hammerhead has been categorized as Critically Endangered by the IUCN Red List. The IUCN cites overfishing as the main cause for the drop in population numbers. Scalloped hammerheads return to their birthplace to have their own pups. The pups will then spend their first years of life in these coastal nursery areas where they are safe from predators and have less competition for feeding before they venture into the open ocean.
Bycatch has also greatly reduced these species because they often migrate in large groups. The mortality rate of the sharks that are caught is almost always 90% of the individuals.
Scalloped hammerhead is Critically Endangered on this catalog because that is the IUCN category stored on Wikidata. Confirm the official criteria and any later count on iucnredlist.org.
Sources
Written for this catalog from the English Wikipedia article on Scalloped hammerhead, Wikidata item Q873701. Family and order context is original field-guide writing about the group, not a copied assessment of this one species. Wikipedia text is CC BY-SA. Not an IUCN assessment. Counts, when quoted, can change — confirm them on the recovery programme and on iucnredlist.org.
