The Basking Shark

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The Basking Shark

February 17, 2014 - 18:52
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First scientifically described by Gunnerus in 1765 from a specimen in Norway, there is an earlier published reference to the shark in 1739 in Ireland.

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Unlike the scientific findings that there are now recognized several different species of killer whale (orca) there is only one distinct species of basking shark, despite their wide ranging distribution. Along with the whale shark and megamouth shark, the basking shark is one of only three sharks which are known to filter-feed. But unlike the whale shark and megamouth shark, which are also known to use ‘suction’ to aid their feeding, the basking shark only feeds by swimming and allowing the water to pass through its gills which trap the zooplankton, small fish and fish eggs.

Life of a basking shark

Little is known about the life of this massive shark, other than that it was born to travel. Whilst we know that some of the larger whales travel thousands of miles between their breeding grounds and birthing bays, basking sharks are similarly adept and have been electronically tracked to cover massive distances also. Their common name derives from their habit of ‘sunning’ themselves on the surface with their backs and fins clear of the water.

One female in particular had been tagged off the west coast of Scotland and proceeded to travel into the Mediterranean during the winter months where it is thought that they have their pups. That spring, the shark travelled around the United Kingdom, went north to Iceland and travelled south past Greenland, the east coast of the United States and the signal was finally lost somewhere off Cuba!

They are distributed widely throughout the world and are recorded on the eastern United States from Newfoundland to Florida and Cuba; from Alaska to Mexico along the western flanks of North America; from Ecuador to Chile; Argentina and the Falklands; South Africa; Southern Australia and Tasmania; north and south New Zealand; around Japan, China and Korea and from the Canaries, right through most of the Mediterranean, all around the United Kingdom and Ireland, around Scandinavia to the White Sea and onwards to Iceland and Greenland.

Travelling at around two to three knots, they feed at the surface, or just below, and are usually spotted by the tell-tail signs of their pointed snout out of the water as well as their large triangular dorsal fin and tail fin, making three distinct surface contacts all at the same time. They are also known to feed in the various zooplankton levels found off the continental shelf and are thought to migrate between deep water and the surface to take advantage of various migrating plankton populations.

Hotspots

Scottish Natural Heritage have discovered that there are a few ‘hot-spots’ on the west coast of Scotland with shoals of over 50-100 basking sharks in each group including the Isle of Coll and an offshore group of rocky mounts called Hyskeir found near the Isle of Canna. Further research has discovered that there is a deep trench that runs between the Outer Hebrides and mainland west Scotland, and this undersea highway is being used by all manner of marine mammals, too, such as sperm whales. A recent electronic triggering survey has indicated that over 900 basking sharks tripped the trigger as they moved north past Hyskeir.

These figures are quite phenomenal, and it is now reckoned that there are more basking sharks found in Scottish waters than any other place on the planet. It is also widely understood that if we look back at historical records of where the sharks used to be hunted for their livers, these should also indicate other hotspots, such as Cornwall, the Isle of Man and Ballyshannon in Ireland.

Hunted

Once hunted extensively for the oil from their livers, the most famous fishery was at Achill, County Mayo when the fishery caught over 9,000 individuals between 1950 and 1964. Unfortunately, the last targeted fishing for these sharks was done by the Norwegians in 2006, but they had been catching around 4,000 sharks each year prior to this. When prices dropped worldwide for the liver oil, the fishermen more than made up the loss by selling the fins with prices at around US$1000 to $2400 per fish caught. You can see why their plight is of international importance.

Thankfully there is now no active fishery in European, American or Australasian waters, although Norwegians are still allowed to land them as bycatch. New Zealand still allows finning and basking sharks are sometimes caught as bycatch over the hoki spawning grounds. These fins are sold under licence.

Absent from British waters from November through to March or April (depending on the water temperature and subsequent zooplankton bloom), it was widely thought that they all migrate beyond the continental shelf, however on a deep dive off Fort William in Loch Linnhe on the west coast of Scotland, my dive buddy and I received one of those life defining frights when we came face to face with a simply massive basking shark, which seemed to be resting at a depth of 42m (140ft)—until we startled it...

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Originally published

on page 80

X-Ray Mag #59

February 17, 2014 - 21:00
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