Shark surprises surfer in Cornwall

23 September 2009

On 23^rd September, surfer Rory Mason saw what he thought was a whale or dolphin in the surf at The Towans, Hayle, on the north coast of Cornwall. He was instinctively rather shocked to find it was a shark, but was relieved when he found that the gills were not moving and it was, in fact, dead. The shark, a mature male, was reported to the Cornwall Wildlife Trust Marine Strandings Network (MSN) and was identified as  a common thresher shark (Alopias vulpinus), a species which poses no real threat to humans apart from potential injury from its whip-like tail.

The MSN called out one of its trained volunteers, Dave Jarvis, who measured the fish at approximately 3.65 metres (around 12 feet). Given its length, it was thought to be over 5 years old, although they can live to around 20 years. It was very fresh with no external signs of boat strike, net entanglement or injury. Regrettably, none of the organisations researching sharks had funding available for a post-mortem examination, but samples were taken for DNA analysis.

The thresher shark is one of only three members of the Alopiidae family, along with the Bigeye Thresher (A. superciliosus) and the Pelagic Thresher (A. pelagicus). The MSN records all stranded marine life in Cornwall but has only two previous records of dead thresher sharks in the county: a 1.37 metre big-eye thresher shark found dead on the strandline in 2001 and a 5 metre long common thresher shark which was found entangled in lobster pot ropes 6 miles off shore in 2007.

In November of 2007, a 4.9m common thresher was caught by fishermen 3.5 miles south of the Runnel Stone, off Land's End. It weighed 510 kg and was one of heaviest recorded in the world. It was sold at Newlyn fish market.

This is one of only a handful of sharks that can maintain its body temperature above that of the surrounding water and it is one of the fastest swimming sharks found in British waters. It is easily recognised by its long tail, which is about the same length as its body and may be used to stun prey such as herring, bluefish, butterfish or mackerel.

These fish are slow to mature and produce so few young - between two and four annually - that they have difficulty in replacing losses from their population. Their main threat is from fishing and bycatch in nets or ropes.  As we have only a small population around our coasts, mainly in the central and western Channel, this makes them very vulnerable. In some parts of the world, demand for shark fins, mainly for shark fin soup, leads to the inhumane practice of 'finning', where the fins are removed from the shark, often while it is still alive. The sharks may then be thrown overboard to die, either from suffocation because they can no longer swim, or from being eaten by other sharks or animals. This horrific practice is carried out in UK waters, where legislation to protect sharks is weak, despite the fact that a third of European shark species are considered under threat by the World Conservation Union (IUCN).

Reports from divers of stranded marine animals in Cornwall are welcomed by the Marine Strandings Network and calls to their 24 hour Hotline – 0845 201 2626 - can be made on any day of the year. Examination of the bodies is helping to form legislation to protect marine species such as sharks, cetaceans and seals and provides a strong indicator of the health of our seas.