Thresher Shark

Thresher Shark
    • Scientific name: Alopias vulpinus
    • Also known as: Common Thresher Shark, Fox Shark
    • Size: Over 30ft (although half of this length is the tail), and 1250lbs.
    • UK minimum size: All UK shark species have a default minimum weight of 40lbs/18kg (shore) and 50lbs/23kg (boat).
    • UK shore caught record: N/a
    • IUCN Status: VU (Vulnerable)
    • Distribution: Migratory species which (although rare) can be found in UK waters in the summer months. Generally stays far offshore over deeper water.
    • Feeds on: Pelagic shoaling fish such as mackerel and herring, and will also eat squid.
    • Description: Powerfully built shark with squat, powerful body. Colour is grey, on the back and flanks, sometimes with tinges of blue and purple, with white underside. Head is fairly broad and eyes are small for a shark species. Dorsal fin is small but pectoral fins are large and broad. Mouth is fairly small and full of small but very sharp teeth. Upper part of narrow, tapering tail fin is massively extended, making up around half of the bodylength.
    • Additional notes: There are actually three species of thresher shark: the common thresher, the pelagic thresher (Alopias pelagicus) and the bigeye thresher (Alopias superciliosus). Only the common thresher is found in UK waters and all of this article refers to this species.
Thresher sharks are a predatory shark that is found all around the world in tropical, sub-tropical and temperate waters. Like the porbeagle shark they can retain heat generated by their muscles, meaning they can tolerate a wide range of water temperatures. Thresher sharks usually live far out at sea and do not come close to land. They are pelagic and live within the top several hundred metres of water, even if they are in an ocean which is considerably deeper than this. Thresher sharks usually come to British waters in the summer when the seas are at their warmest. Thresher sharks are not exactly common in the UK, but several are confirmed as being seen each year.
Pacific Thresher Shark

A small thresher shark caught on a boat in the pacific.

The most striking aspect of the thresher shark is its tail, which makes up around half of its overall length. Thresher sharks hunt in small packs and use their tail to herd and round up their prey of small, shoaling fish such as mackerel, herring and sardines. They will also use their tail to swipe out at small fish and injure and incapacitate them. Thresher shark will also feed on larger fish such as hake and cod, and also take squid. There are unconfirmed reports that thresher shark have been known to use their long tails to attack seabirds which have settled on the surface of the water, but as yet no one has been able to provide footage or any other form of solid evidence to prove that thresher sharks feed in this way. In their natural environment thresher sharks are not aggressive and generally move away from divers who approach them, or any other kind of human interaction. There have been no confirmed reports of human deaths due to thresher sharks, and only a handful of attacks – all of which were due to the thresher shark being provoked.

Attacks on Humans and Commercial and Sport Fishing

Thresher sharks are hunted both commercially and by sport anglers. They have a wide range of commercial uses – the flesh is highly prized to eat, the skin can be made into leather, the fins used for shark fin soup and the oil from the liver is also valuable. They are caught on long-lines and in static nets, while a small number may be harpooned. They are also killed when they get tangled in nets designed to catch other species. Anglers on big-game fishing charter boats also target thresher sharks, mostly in the Pacific Ocean. The thresher shark is said to be one of the hardest fighting fish in the world meaning that the heaviest gear has to be used. The all-time world-wide confirmed record for a rod and line caught thresher shark is 767lb 3oz. The thresher was caught off Cape Brett, northern New Zealand, in 1983.

However, notable thresher sharks have been caught in British waters. The current record is a thresher of 323lb which was caught by Mr. S. Mills off the coast of Portsmouth in 1982. Larger thresher sharks have been caught, but in these conservation-minded times anglers have released the fish rather than killed them to claim a record. For example a thresher shark estimated at 550lb was caught one mile off the coast of the Isle of Wight in 2013, but it was released back into the sea and not retained to claim the record. Similarly two thresher sharks weighing in excess of 250lb were caught within days of each other off the Welsh coast in summer 2015, and again returned to the sea alive, as was a 368lb thresher shark caught off the coast of Cornwall in August 2016.

Biggest Thresher Shark Ever – Caught in British Waters

The largest thresher shark ever recorded was caught in British waters. In 2007 a commercial fishing vessel captained by Roger Nowell was trawling for squid off the coast of Cornwall and caught a 1250lb thresher shark in its nets. Including its tail the shark was 32ft in length. Although alive when hauled on board the shark was retained by the crew of the vessel and sold at a local fish market, although the owners of the fish market refused to say how much the shark sold for or who bought it. The thresher shark smashed the record for the largest commercially caught thresher shark, which was previously a 953lb specimen, caught off the coast of Hawaii.

Thresher Shark Hooked

Commercial and sport fishing are both responsible for reducing thresher shark numbers. Left, a thresher shark hooked on a commercial long line and right, a thresher shark foul-hooked through the tail by an anglers lure. Thresher shark are often hooked in this way due to the way in which they lash their prey with their tail.

Unfortunately the combined fishing of both commercial vessels and recreational anglers has meant that thresher shark numbers have been badly hit, collapsing in some areas. This species is now classed as Vulnerable by the IUCN (International Union for the Conservation of Nature). The American government has limited fishing for thresher sharks and in some areas, such as off the coast of California, numbers of thresher sharks are thought to be climbing. However, measures such as this will need to be adopted everywhere where threshers are present to prevent numbers sliding any further.

Thresher Shark getting Tagged

Due to the endangered status of thresher sharks there are a number of conservation projects going on around the world aimed at tracking and protecting thresher numbers. Here a thresher shark is tagged during the 2009 Shark Survey off of the Channel Islands. The object in the shark’s mouth is a pump which pumps seawater over the gills so the shark can breathe while it is being tagged.

Myths about Thresher Sharks

There are a number of myths associated with the thresher shark. Although (as discussed above) it does use its tail to strike and stun prey many inaccurate reports and myths have developed over the years which have greatly exaggerated the destructive power of thresher shark’s tail. A thresher shark will thrash its tail around to defend itself when caught and brought onto a boat, and divers have been injured by thresher shark’s tails. However, a thresher shark is not capable of decapitating a human being with its tail nor is it capable of breaking people’s backs. Another widely believed myth from the 1800s was that thresher sharks worked together with swordfish to attack and kill large whales. It was believed that thresher sharks would herd the whales into a group and then slit open the bellies of the whales with their tails. While this was going on the swordfish would attack the whales and stab them with their swords. It is unknown how this belief originates and there is no evidence to suggest that this – or anything like it – ever took place.

The ancient Greek philosopher Aristotle believed that the thresher shark was extremely intelligent and could outwit fishermen and avoid nets and traps. This led to him naming the thresher shark the alopex which means fox (due to the fact the shark was clever like a fox). This explains the thresher shark’s alternative name of fox shark, and its official scientific name of Alopias vulpinus is based on the Latin word for fox. Again, there is no scientific evidence to back up this belief about the high intelligence of the thresher shark and they do not seem to be any more intelligent than any other shark species.

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