Wednesday, 15 August 2012

The Big Scary!

One of the world's strangest fish returns each summer to British waters. But in spite of its size, it is shrouded in mystery. basking_sharkbfbbfd

Essentially an industrial-sized mouth with fins, the basking shark isn't one of nature's most attractive creatures. It would take an army of PR gurus some serious brainstorming to develop a way of presenting this cousin of the great white as anything approaching beautiful.

But the basking shark has its own special appeal. For a start, it's big - the second largest fish in the sea (after the whale shark), and by far the largest fish in the North Atlantic. It can weigh more than an African elephant. But a major part of its appeal is that it is one of the least understood large animals on Earth.

Widely distributed in cool temperate waters worldwide, it is a rather uncommon animal except in a few key areas. The western seaboards of Britain and Ireland are particular hotspots. Basking sharks move into our coastal waters in spring and summer, and then disappear for the entire winter. We've no idea where they come from or, for that matter, where they go. But, following a giant fish some 10m long isn't as simple as it sounds.

1,500 teeth that don't bite

The shark's diamond-shaped gaping mouth looked more like the open cargo doors of a military aircraft than the oral cavity of a fish.

Although they have more teeth (around 1,500) than most other sharks, they don't use them for feeding at all. Basking sharks cruise slowly at about two knots with their mouths wide open, capturing tiny planktonic creatures in thousands of filters called gill rakers as the water passes through the gill slits.

The giant feeding-machine passed within a couple of metres of where I floated. Briefly, we made eye contact. Its prehistoric stare was mesmerising, but it was impossible to say if it was inquisitive or uninterested. Shafts of sunlight dappled its greyish-brown flanks. It must have been seven or eight metres long and glided with a smooth, graceful movement that belied its size. All too soon it disappeared into the murk.

A winter's talebasking%20shark

High-tech gadgetry is needed to find out where the sharks overwinter. A collaborative three-year project is using sophisticated Pop-up Archival Transmitting (PAT) tags attached to the sharks' dorsal fins. Programmed to pop up to the surface at intervals of 3, 6, 9 or 12 months and then to beam their location and other critical information to an orbiting satellite. Ten sharks were successfully tagged in UK waters last year and there are plans to tag another 10 this year. Perhaps we are on the verge of solving one of the world's great wildlife mysteries.

The basking shark was given its name by fishermen and other seafarers. They noticed its lethargic movements near the surface and assumed that it must have been sunbathing.

There are reports of individuals reaching 15.2m. The maximum confirmed size is 12.2m, and the most common size range is 3-9m. They possess a high, erect and angular first dorsal fin (up to 2m tall).

They give birth to live young. Gestation is presumed to be 2-3 years, and they produce 2-6 pups (150-170cm long - the largest size at birth of any known shark).


The skin is covered with small denticles, or scales, pointing backwards. Rub your hand down towards the tail and it feels relatively smooth to touch, but rub it the other way and it feels more like sandpaper. It's unique among sharks in being coated with a thick, foul-smelling mucous, though the function of this is unknown - yet another basking-shark mystery.

Its diet is principally small plankton, but includes fish eggs and crustacean larvae, possibly small schooling fish.

Experts estimate that a single basking shark can filter enough seawater to fill a 50m Olympic swimming pool every hour.

The basking shark is distributed through cool temperate waters worldwide; occurs very close to land (even in enclosed bays), but also sometimes offshore; it is noteworthy for its seasonal appearance in known localities and subsequent disappearance. 

Britain is home to one of the largest concentrations of basking sharks anywhere in the world. They can be seen almost anywhere along the west coast and dedicated trips to watch or snorkel with them take place in Cornwall and from the Isle of Man.

Local lore has it that baskers first appear in the waters around the Lizard Peninsula on 10 April, but their precise arrival time seems to depend on the water temperature of the previous winter (any time from mid-April if the previous winter was warm or mid-May if it was cold). They typically arrive in the Porthkerris area first and then move west towards Penzance. They are often very close to shore, and many people snorkel and kayak with them from the various beaches, but they can occur at least 15km offshore, and local dive operators run trips to see them throughout the season. They are usually present until August (though less common at this time).

Basking sharks can also be seen from shore around the Isle of Man, and they occasionally enter harbours along the west coast of the island but are best viewed from a boat. The Basking Shark Society operates daily tours throughout the summer (full-day, half-day or evening, depending on demand) and tour participants are encouraged to join in with the collection and recording of research data. The best time is from mid-May to September, when the sharks are present in force and the weather is at its best.

One of the few things we do know about basking sharks is that they are slow to reproduce. They have a long gestation period (estimated to be between one and three years), probably give birth to no more than half a dozen pups every two to four years and then take as long as 12-20 years to reach maturity.

This low reproductive rate (and therefore low recovery rate) is a major reason why the basking shark is listed as 'endangered' in the North-east Atlantic (and globally 'vulnerable').

The fishing threat

With its large size, slow swimming speed and tendency to feed at the surface, it is highly susceptible to hunting. More than 100,000 have been killed in the northeast Atlantic alone in the past 50 years. Originally they were killed for their meat and for the oil in their jumbo-sized livers (which may account for up to 25 per cent of the total body weight and are probably used in buoyancy control). But now they are being killed for their fins. Demand for shark-fin soup in parts of Asia has increased dramatically since the mid-1980s, and there is now an insatiable market for shark fins of almost any size or type. A large basking shark can yield up to 30kg dry weight of fin worth many thousands of pounds.

Over the years, there have been basking-shark fisheries in many parts of the world, including the Canadian Pacific, California, Ecuador, Peru, Japan, China, Iceland, Norway, France, Spain, Britain and Ireland. It is difficult to generalise, but most basking-shark fisheries have taken hundreds or, typically, about 1,000 individuals every year for a few years before collapsing.

In recent years, the Norwegian fleet has been landing the majority of basking sharks in the North-east Atlantic. Catches have fluctuated widely and declined dramatically after the mid-1970s, with no organised hunt at all in the past four years.

Gaining protection

In the UK, the basking shark has been protected within the 20km limit since April 1998, under Schedule 5 of the 1981 Wildlife and Countryside Act. It is also a priority species under the UK Biodiversity Action Plan. Fishing for basking sharks in European waters can be regulated by the European Commission under the Common Fisheries Policy, and catch limits (based on little or no information about stock size or geographical range) are still set for the Norwegian hunt.

Major progress was made in April 2000 at the CITES (Convention on International Trade in Endangered Species) conference in Kenya. The British Government put forward a proposal for the basking shark to be listed under Appendix II and, though this would not have banned hunting, it would have forced countries trading in basking-shark parts to keep proper records - essential for monitoring the level of threat. Unfortunately, under CITES rules, a two-thirds majority must vote in favour of a proposal for it to pass, and this particular proposal was three votes short.

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