After being boosted by the recent heat wave, massive amounts of zooplankton is now attracting record numbers of basking sharks into British and Irish waters.

Last year, 26 basking sharks were reported from the most southerly headland of Cornwall during a 10 week long period. This year, 900 sightings have been recorded since the beginning of June.

“Last year we had a really poor year because of the weather. But even though temperatures have obviously picked up, we never expected to see the sharks in such large numbers,” saysTom Hardy of Cornwall Wildlife Trust, coordinator of the south-west basking shark project.

Record breaking numbers of basking sharks are being reported from the other side of Irish Sea as well. In June alone, the Irish Whale and Dolphin Group reports having seen no less than 248 basking sharks.

“In a three-day period we tagged more than 100 sharks in just one bay in north
Donegal,” says Simon Berrow of the Irish Whale and Dolphin Group. “You only ever see five or six of these creatures on the surface, which doesn’t reflect what’s going on under the water.”

From the Isle of Man, 400 sightings have been reported since early May.

‘”We saw a lot more in May than is usual and after a couple of quiet weeks sightings are picking up again,” said Fiona Gell, marine wildlife officer for the Isle of Man government.

Very little is known about the basking sharks, but the Irish Whale and Dolphin Group is currently carrying out a pioneering tagging project in hope of furthering our understanding of these basking giants. Simultaneously, the 47 wildlife trusts found across the UK, the Isle of Man and Alderney are working to identify basking shark hotspots.

Scientists tagging sharks off the Irish coast have tagged a surprisingly high number of Basking sharks this year: 50 specimens in just three days.

“I would normally expect to be lucky if we tagged 50 in a whole year,” said Dr Simon Berrow of the Irish Whale and Dolphin Group.

Basking SharkA record

Together with National Parks and Wildlife Service conservation ranger Emmett Johnston, Dr Berrow set out earlier this week to tag sharks off Donegal, as part of a project funded by the Heritage Council.

“In two hours last Monday we tagged 23 sharks, and we found 19 the following day – four of which had been tagged the day before,” Dr Berrow said. By the third day, they had tagged their 50^th basking shark.

Basking sharks were once a significant source of income for Irish whalers and the coastal towns of Galway and Waterford did for instance have street lights lit with basking shark oil as early as the 18^th century.

The importance of Basking sharks in Irish culture is evident in the number of names and monikers give to these peculiar creatures. In Irish, this “monster with sails” is known under the names Liabhán chor gréine (Great fish of the sun), Liop an dá (unwieldy beast with two finns) and Liabhán mór (great leviathan) – just to mention a few. The epithets “Fish of the sun” and “Sunfish” both pertains to its fondness of swimming just under the surface.

In the mid-1970s the Irish stopped their whaling, but the problems weren’t over for these sharks since they frequently ended up as by-catch in drift nets; a fishing method now outlawed in Irish waters. In addition to this, Norwegian whalers continued to hunt for shark off the Irish coast until 1986.

The Basking shark (Cetorhinus maximus) is listed as Vulnerable on the IUCN Red List of Threatened Species, and is a protected species in Great Britain but not in Ireland. However, the European Union has just placed a moratorium on fishing for Basking sharks in these waters.

If you spot a Basking shark in Irish waters, the Irish Whale and Dolphin Group would very much like to know any details about the sighting. You can find more information at www.baskingshark.ie.

Want to know more about Basking sharks and where they head when the Northern Seas become too cold for comfort? Check out our earlier blog post on Sharks of the Caribbean.

Basking sharks have surprised researchers by leaving the cold waters of the north Atlantic during fall and head down to Bahamas and the Caribbean.

“While commonly sighted in surface waters during summer and autumn months, the disappearance of basking sharks during winter has been a great source of debate ever since an article in 1954 suggested that they hibernate on the ocean floor during this time,” said Gregory Skomal of Massachusetts Marine Fisheries. “Some 50 years later, we have helped to solve the mystery while completely re-defining the known distribution of this species.”

Basking Shark

Basking sharks are notoriously difficult to study for several reasons. They feed exclusively on plankton which means you can’t catch them using traditional rod-and-reel methods and they disappear down to deep waters for extended periods of time. During the part of the year when they do stay close to the surface, they are only found in cool waters teaming with plankton where the underwater visibility is close to zilch.

This situation has led to a lot of speculation about their life style and where they actually spend the winters. Despite being the second largest fish in the world, the basking shark is remarkably elusive and mysterious.

What finally solved the puzzle was the aid of new satellite-based tagging technology and a novel geolocation system which made it possible to track the basking whales as they commenced their annual migration. Data sent out from the tags unveiled that basking sharks migrates to warm tropical waters in fall. Their migrations have been able to go undetected until know since the sharks travel at depths of 200 to 1,000 meters and sometimes remain at those depths for weeks or even months at a time.

Skomal said he and his fellow researchers were absolutely surprised when they first received a signal from the tagged sharks coming from the tropical waters of the western Atlantic, since virtually everyone assumed basking sharks to be cool-water dwellers found in temperate regions only.

This new breakthrough show just how little we still know about even the largest marine animals inhabiting the world’s oceans. The basking shark can reach a length of 10 metres and weigh up to seven metric tons, yet it has managed to spend every summer in the Caribbean without anyone noticing it.

You can find more information in the report published on May 7 in Current Biology.