THE BASKING SHARK FILE
This picture is one of the latest - such sightings are the most sought-after in the UK, says Paul Naylor
Basking sharks are named after those surface cruising habits that appear so idyllic, but energy budget calculations show that they work hard for a living. Unless the water is rich in plankton, they can use more energy swimming through the water than they obtain in return for their feeding efforts.
Basking sharks produce fully formed youngsters that are already up to 2m long at birth, after a pregnancy of more than 2 years. They can take up to 20 years to reach breeding age and this, coupled with their low rate of reproduction, makes them prone to over-exploitation.
THAT'S A LIVER!
Aside from the tropical whale shark, the basking shark is the world's biggest fish. It can reach up to 10m in length and weigh 7 tonnes. The shark's gigantic liver can make up a quarter of its weight and is extremely rich in oil. It therefore contributes valuable buoyancy because, like other sharks, it has no swimbladder.
PRICE ON ITS BACK
Basking sharks are legally protected in British waters and some other areas, but vulnerable elsewhere. Exploitation is driven by huge demand for large shark fins, with a single fin worth many thousands of pounds. The Shark Trust (www.sharktrust.org) provides advice on how you can help these creatures and watch them in safety (yours and the sharks').
Basking sharks come into British coastal waters to feed in the summer, travelling alone or in groups of up to 60 individuals. Popular places to see them are Cornwall, the Isle of Man and the Western Isles of Scotland. Where the sharks spend the winter is a mystery however; do they go to warmer regions or move into deeper water?
ALL MOUTH & RAKERS
Although a relative of the great white, the basking shark poses no danger to man, and feeds on plankton. By swimming with its mouth wide open, it can filter 2000cu m of seawater per hour, equivalent to the contents of four big swimming pools! Its gill-rakers (filtering gear) are often shed for winter and regrown in spring, whichsuggests that hibernation occurs.