The Thresher Shark

Wednesday 7 February: 19.15–20.00

Continuing this evening is the gripping series of wildlife documentaries in which daredevil explorer Monty Halls investigates rare and magnificent beasts of the deep. In tonight’s programme, Monty is on the trail of the elusive thresher shark, an animal that very few divers will ever be lucky enough to see.

To have any chance of encountering a thresher, Monty must travel to the tiny Philippine island of Malapascua, a tropical paradise fringed by coral reefs. The island’s small community were subsistence fishermen until the 1990s, when interest in the threshers brought tourism, and a subsequent revolution in the local economy. The locals – who Monty finds to be warm and friendly – continue to rely on fishing as a source of food and income. Their island lies within the ‘Golden Triangle’, a triangle of rich biodiversity outlined by the coasts of Malaysia, the Philippines and Papua New Guinea, which is home to more species of fish than anywhere else in the world.

On his first dive of the trip, Monty encounters a wonderful array of reef animals including the bizarre frogfish, which has stumpy pectoral fins that allow it to walk along the sea bottom. It boasts the fastest strike of any animal, with the ability to open and close its mouth within six thousandths of a second. Nearby, a huge barrel sponge is covered with sea cucumbers, long white caterpillars that clean parasites from its surface. The thresher, however, remains elusive.

Monty is at pains to point out that a modern method of fishing – dynamite fishing – threatens these fragile coral environments. Without a reef for small life forms to colonise, the foundations of the food chain are destroyed, spelling disaster for all the animals – even majestic predators like the thresher shark. Another environment that is receding fast is the rainforest with which Malapascua was originally covered.

On another of his dives, Monty teams up with local photographer and thresher enthusiast Scott ‘Gutsy’ Tuason. Gutsy has some amazing pictures of threshers, taken at a spot which guarantees some fascinating sights. At a ‘cleaning station’, many different species gather to enjoy the attentions of the cleaner wrasse – small, brightly coloured fish which eat the parasites that gather on the skin of others. It’s a little late for a thresher encounter, however – the sharks prefer low light conditions, so Monty and Gutsy spend the remainder of the day placing a section of artificial reef on the sea floor as part of a regeneration project being carried out by the local people and the dive centre, both of whom rely on the area’s continuing biodiversity.

At four o’clock the next morning, the sun has yet to rise, but Monty and Gutsy are already heading out to sea. The pelagic (open-ocean) thresher shark is easily spooked, and spends most of its time hunting in depths of up to 150m – hence its large eyes. The two divers must remain very still on the ocean floor if they are to catch a glimpse – and before long their diligence is rewarded. From out of the gloom an unmistakeable shape glides into view. Its tail – almost as long as the rest of its body – undulates gently behind it, making its total length up to three metres. Although it’s a big shark, it poses no danger to humans – with its small bite radius and teeth, it eats only small fish, which it stuns with a slap of its huge, strap-like tail. As it drifts closer, this rare and exceptional animal gives the divers a privileged glimpse of a vanishing ecosystem. Some call it the ‘freak’ of the shark world – and it certainly cuts an unusual silhouette as it glides through the water. Yet its grace is undeniable, and Monty and Gutsy are left in awestruck silence as the thresher disappears back into the gloom with a flick of its huge caudal fin.

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