One Planet News: The Ocean’s Whip-Tailed Predator
The sleek and powerful thresher shark
By Annette J Beveridge
Nature is endlessly fascinating, with each species having its unique traits, but the thresher shark has to be one of the ocean’s most unique and fascinating predators.
Threshers are sleek and powerful sharks and the tail is used as a deadly weapon to stun its prey.
Distinctive Features
Thresher sharks belong to the family Alopiidae. These are one of the easiest sharks to identify with their long, scythe-like caudal (tail) fins, which can make up half their total body length.
Their large eyes are suited to hunting in low-light conditions, and the body is streamlined and perfect for speed and agility.
There are three species:
• Common Thresher (Alopias vulpinus)
• Bigeye Thresher (Alopias superciliosus)
• Pelagic Thresher (Alopias pelagicus)
They vary in size, eye structure and habitat, but all share that signature tail.
Prey includes sardines, mackerel and squid. Schooling fish are herded into a tight ball, and then, the shark strikes using its tail in a lightning-fast whipping motion, stunning or killing multiple fish in just one deadly stroke.
Habitat and Behaviour
These sharks are usually found in open waters but will come close to the coastline, especially juvenile thresher sharks. They prefer deep, pelagic environments and dive down to depths of more than 500 metres. They usually avoid divers and are not known to be particularly aggressive towards humans.
Threshers can grow up to 20 ft (6 metres) in length.
Typically shy and solitary, we do know that some will migrate seasonally with shifting ocean temperatures or to follow prey species.
Reproduction and lifespan
Thresher sharks are ovoviviparous. This is when the female gives birth to live young, and there is a dark side to the reproduction cycle with thresher embryos practising intrauterine cannibalism, where the most developed embryos eat their less-developed siblings in the womb.
This is known as adelphophagy.
Thresher sharks are vulnerable to overfishing as they grow slowly and reach maturity late. Estimated lifespans are thought to be 20-50 years.
Read more: Two new species discovered
Conservation concerns
Thresher sharks are listed as vulnerable on the International Union for Conservation of Nature (IUCN) list. This is because they are often caught as bycatch in longline and drift net fisheries and are sold for the use of their fins or liver oil.
Populations are in decline due to this and due to slow reproduction rates.
To save this shark, there must be a ban on finning, and catch limits. Marine protected areas would help to ensure the survival of this incredible species.
