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Bask in Their Glory; One of the UK’s most elusive summer-time sharks

For most people, the UK doesn’t spring to mind when envisioning a vibrant marine habitat, and yet that’s exactly what it is! British waters house a wonderfully diverse marine ecosystem, supplying the UK with a wealth of opportunity to see an array of creatures. From April through to October, many species migrate through, or to, UK waters as the warmer weather causes massive wide-scale algal blooms, providing a perfect feeding ground to some of the globe’s famously large animals.

Amongst humpback whales, orca, sunfish and the occasional leatherback turtle, 32 species of shark have been recorded in UK waters during the summer months. Most of these species reside far from shore, meaning you won’t meet any whilst paddling in the brisk shallows of the Atlantic. This year, whilst out on a blue shark snorkel trip with MARECO we were also lucky enough to see tuna, dolphins, sunfish and minke whales! However, there is one shark that frequents the coastline and elicits much excitement throughout the year – the world’s second largest shark, the basking shark (Cetorhinus maximus).

Basking shark by Emma Williams

These seasonal visitors, anticipated by many, arrive from May and are thought to leave in October, though there’s no conclusive evidence to say where the UK sharks head to during the colder months. Most recently, an international research team from Queen’s University Belfast and Western University Canada used satellite tags to track the routes of basking sharks travelling off the coast of southern Ireland. Astonishingly, 2 of the sharks travelled to waters in Africa, whilst the other 2 remained in Ireland. Even stranger, the water temperatures in Africa were on average colder than those in Ireland, suggesting this movement wasn’t in search of warmer conditions, and could be down to foraging preferences.

Other electronic tags have tracked the migratory paths of some basking sharks across the Atlantic, arriving off the coast of Brazil and Canada, but their journeys remain a mystery for the most part! The 30th March 2019 saw the earliest ever recording of a basking shark in UK waters, off the coast of Falmouth, attracted by a large algal bloom thanks to an unexpectedly sunny spring weekend. Reaching lengths of up to 10 metres, they are the second largest fish in the sea, beaten by the whale shark, which grows up to an astonishing 18-20 metres. The words “terrifying”, “shocking” and “bus-sized beast” are commonly associated with the basking shark in news headlines across the nation, and although they match the length of Bruce from Jaws, these animals won’t be sinking your fishing vessel anytime soon. These sharks feed by passively swimming close to the surface, mouths agape, filtering the plankton that they flock to the British coastline for.

Though these sharks are massive in size, our knowledge about them remains limited. There is a distinct lack of information about their life histories, as is with most shark species, due to the challenges associated with collecting data from a large migratory fish. Until 2018, it was thought the basking sharks arrived in the UK solely to feed, but scientists from Scottish Natural Heritage and the University of Exeter have uncovered what could look to be courtship behaviours occurring near the Isle of Mull in the Hebrides. Usually solitary animals, they have been seen to engage in behaviours such as parallel swimming, circling one another or following each other nose to tail, which have been associated to courtship, suggesting the sharks are using this area to mate.

Research like this is increasingly important for the status of basking sharks in the UK. Sightings of the species have been decreasing the last few years, even though it was thought that the population was recovering after being heavily fished up until their protection in 1998. Previously hunted for their fins, skin (to produce leather) and liver oil, the species was last assessed in 2018 and is currently at “Endangered” status according to the International Union for Conservation of Nature, and their numbers overall are ever decreasing. In 2019, Science magazine reported that basking sharks are still being illegally landed (404 tons between 2003 and 2017) and sold for their meat in markets within Japan, Hong Kong and the United States. The basking shark is the most heavily protected species in the UK, coming under protection from 4 environmental acts that make it illegal to intentionally kill, injure or harass the species in UK waters, punishable with up to 6 months in prison and a large fine, and another act that make it illegal for EU commercial fishing vessels to fish and land the species.

The Marine Conservation Society currently have the largest basking shark sighting database and believe shark numbers in the UK are increasing - though this could be a result of people reporting their sightings more frequently than ever before due to increased social awareness and engagement toward contributing to science. Either way, getting the public involved in citizen science projects like these assists scientists and simultaneously furthers conservation efforts to protect the species. Whilst the basking shark is a protected species in the UK, spatial protection such as the implementation of Marine Protected Areas (MPAs) should be considered to reduce the risks they face. MPAs restrict fishing activity and commercial routes of vessels to ensure the sharks are less likely to be disturbed, caught as bycatch or injured by boat propellers from the fishing industry and trade of commercial goods. For a migratory species like the basking shark, spatial protection offers temporary heavens and therefore modern dynamic protected areas might serve a better purpose for the protection of the species.

Tourist in water with basking shark

Across the country, wildlife tourism companies do their bit year-round to educate and promote awareness for protecting the natural world and these sharky inhabitants, taking shark-enthusiasts out for a swim with these gentle giants. If you’re ever lucky enough to see one in the wild, let the scientists know! It’s the perfect time to plan some shark spotting trips as we dream of sunnier days by the sea! The more sharks we see, the more we can learn, and most importantly, the more we can do to protect these magnificent animals that visit us along their mystery migration routes.

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"though there’s no conclusive evidence to say where the UK sharks head to during the colder months" - please see Doherty et al. (2017) Long-term satellite tracking reveals variable seasonal migration strategies of basking sharks in the north-east Atlantic - Lucy Hawkes, University of Exeter

Replying to

Hi Lucy, Hope you're well and thanks for flagging! The paper you've linked is one I allude to in that paragraph and the one following. I can see that my use of the word "conclusive" may have been misleading, and rather "inconclusive" or "varied data/evidence about where sharks head to" to make it clear that studies have shown various different migratory routes, as this was the point I was trying to make. Thanks again for taking the time to read the blog, I'll use this as a means to make my words more explicit in future! :) All the best, Connie Chapman, MARECO Researcher

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