The smooth hammerhead is a large species of hammerhead shark, the second largest after the great hammerhead (Sphyrna mokarran). They’re usually about 3 meters long. The largest specimen ever found was 5 meters long.
It’s found in most of the world’s temperate and tropical seas, but unlike other hammerheads, the smooth hammerhead prefers slightly cooler waters. In the summer large schools migrate towards the poles to find more temperate waters.
Their name comes from the shape of their cephalofoil (their hammer). Most hammerheads have indentations at the front part of their hammer, but Sphyrna zygaena doesn’t, hence their name “smooth” hammerhead.
Sphyrna Zygaena is viviparous. Females become sexually mature when they’re about 250-300 cm long. Babies are born no longer than 60 cm after a gestation period of 11 months. The average litter size is 35
They can weigh up to 400 kg and their lifespan is estimated to be about 20 years.
Smooth hammerheads are highly migratory and can be found both inshore and offshore. They’re mostly found between 1-140 meters deep. Their main preys are smaller sharks, rays, and skates, but will eat anything they can catch. Stingrays seem to be a common prey item, as stingray barbs are often found inside smooth hammerheads’ mouths. In one case, 95 barbs were found in a single individual. Their predators are larger sharks, especially when still young, and killer whales.
Their migrations are notorious for their school size. Schools of over a hundred juveniles have been observed.
Due to their size, they’re potentially dangerous to humans, but there are very few confirmed cases of attacks on people as they’re often mistaken for other hammerhead species.
Often caught as bycatch in tuna fisheries, their meat is consumed and their fins are highly-valued in the shark fin market due to their high number of fin rays. They’re also used in traditional Chinese medicine and as a source of cartilage and fishmeal.
They are a vulnerable species according to the IUCN and are listed in CITES Appendix II, which makes it illegal to export it without a permit. They’re protected by some nations such as the United States and Brazil. They have declined in abundance by 89% since 1986. The main threats to their survival are their high by-catch mortality and targeted fisheries for their valuable fins.
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