Gentle Giants - Basking Sharks Natural World

In the summer months there is always someone that lets ‘that’ movie get the better of them, reporting supposed sightings of Great Whites off the Devon coastline and sparking off a media feeding frenzy. But although those fins gliding through the distant water do indeed belong to sharks, they belong to one of the ocean’s ultimate gentle giants.

Harmless and docile, Basking Sharks are the largest fish in British waters, which always makes them very exciting to spot. Weighing in at 7 tonnes (the same as two elephants), they can reach up to 11 metres in length, with fins 2 metres high. One of only three plankton-feeding species of shark, they cruise the oceans in search of their microscopic prey, slowly moving through the water and sometimes congregating in groups of 100 or more.

Looming out of the blue, mouth agape, the Basking Shark is surely one of the most awe-inspiring sights in the entire animal kingdom. With their enormous mouths wide open, they can process 1,800,000 litres of sea water every hour, the equivalent to half an Olympic-sized swimming pool.Rare and elusive, very little is known about the life of the Basking Shark, partly because of the difficulty in studying an animal which spends most of its life under water out of sight, and partly because like many of our most magnificent sea creatures, it is under threat.

In the recent past Basking Sharks were hunted mercilessly for their highly valuable fins, which go to the shark fin trade causing rapid crashes in their population. Historically the meat has been used for human consumption fresh or dried salted, the liver (very large and rich in oil, formerly used as a vitamin A source, for tanning leather, and for lamp oil) is extracted for its high squalene content, the hide for leather, and the rest of the carcass for fishmeal. Despite current protection measures, the global decline in numbers does not appear to have been reversed: the IUCN Redlist classifies Basking Sharks as endangered, with numbers decreasing. More than 80,000 basking sharks were slaughtered in the north-east Atlantic in the 20th century, and numbers are thought to have declined by 95% or more from historic levels.

Basking sharks are the largest fish in British waters, which always makes them very exciting to spot

But here in Devon we are lucky enough to be host to these harmless creatures each summer as they reappear to feed on plankton, encouraged by the rise in the surface temperature of the sea.

Catch them on camera!

Breaching (or jumping clear of the water) is relatively common behaviour, which watchers are also often lucky enough to see. This gives researchers (and members of the public) the opportunity to take photographs of the sharks, many of which display significant and recognisable identification markings. These can be natural markings (such as changes in pigmentation) or acquired markings (like scars), which are unique to individual animals and normally spotted on the dorsal fin or tail fin.

Photo-identification is a powerful non-invasive way to study live sharks in their natural environment. The European Basking Shark Photo ID Project is a way that the public can help to keep track of these sharks around the British Isles and abroad. The project aims to catalogue images sent in by water users, coastal path walkers, beach users, sailors, researchers – in fact anyone who spots a Basking Shark and happens to have a camera handy. By submitting a good, clear image of the dorsal fin or tail that you may have taken over the summer, you can help the ongoing conservation project (see www.baskingsharks.org). As matches are made, so are inferences about geographic movements over different timescales providing valuable information about migrations, population structure and feeding behaviour. It can then be used in developing conservation and management measures for the shark.

The Marine Conservation Society (MCS) has been recording Basking Shark sightings since 1987, and has since received information on over 15,000. The MCS now holds the UK’s largest database on Basking Shark distribution and behaviour, and is contributing to wider studies to determine the factors that affect their seasonal appearance in UK waters. No more than a few hundred Basking Sharks remain to visit UK waters.

Protect and preseve

But ironically conservation also comes with its problems. Today, one of the critical issues facing Basking Sharks is disturbance and harassment by water users; in the excitement of observing these magnificent creatures, there are often reports of sharks being struck by boats or jet-skis, as well as being disturbed by swimmers.

The Shark Trust and National Marine Aquarium in Plymouth have joined forces to present a ‘Code of Conduct’ that aims to protect Basking Sharks from seafarers and others who are keen to follow up the often well-publicised sightings.

Dr David Gibson, Managing Director of National Marine Aquarium, is totally supportive of the code: “You don’t need to get up close to these magnificent animals to appreciate their beauty. At this time of year, the Hoe makes an excellent vantage point if you have a pair of binoculars and a bit of patience. Despite their size, we still know very little about this enigmatic and secretive animal. We hope that by working with the Shark Trust we will gain important insights into this fascinating species. We support this Code as all sea animals, especially those in our native waters, deserve the utmost protection.”

As well as information on the species the Basking Shark , the Code of Conduct contains a poster for water users which aims to ensure safe interaction between human and shark – safe for both humans and sharks! Whilst Basking Sharks are not normally referred to as dangerous, their sheer size and potential power makes them creatures to be treated with respect and caution, and their depleting numbers means that it is Devon’s responsibility as annual hosts to these magnificent visitors to protect and preserve them as best as we can. The Basking Shark Code of Conduct can be found at www.national-aquarium.co.uk.

BASKING SHARK FACTS

• Slow-growing, they are late to reach sexual maturity (at 12-20 years) and produce few young (bearing five or six pups for a gestation of one to three years)• They find their dinner by smelling and tasting smells in the water• Their gill slits have big brushes called gill rakers in them covered in mucous to trap their food• The stomach is about the same size as a bath and full of half-digested shrimps• When the sharks rub against one another, they leave a fishy-smelling oily slick in the water• Shark skin is very rough and scratchy because it is covered in millions of scales like tiny teeth. In the past it was made into leather for non-slip boot soles• The biggest Basking Shark recorded was 13.72m long• Their brains are very small for such big animals. The main part of the brain is about the same size and shape as a hotdog. The most important bit of their brain is two long thin stalks, which work out the smell and taste of what is in their mouth

Tell us about your basking shark sightings! You can comment below or upload your photos.