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Basking Shark Distribution
The Basking Shark has a circumglobal distribution although it appears to be separated into a number of regional populations with limited genetic exchange. In the East Atlantic it is known from Russia and northern Norway, Iceland, the British Isles, all through the Mediterranean Sea and as far south as Senegal. The species is also found in Namibia and South Africa. In the Northwest Atlantic it is found from Canada to the northern Gulf of Mexico and in the Southwest Atlantic it is known from southern Brazil to southern Argentina and the Falkland Islands. In the West Pacific it can be found in south Australia and New Zealand, further north in Japan, the Korean Peninsula, Taiwan and China. In the Northeast Pacific It is known from the Gulf of Alaska to the Gulf of California, including the Aleutian Islands and further out, the Hawaiian Islands. In the Southeast Pacific it can be found from Ecuador to southern Chile.
A coastal to oceanic species, the Basking Shark is normally encountered at or near the surface but has been recorded as deep as 1264m. It is known to venture inshore to shallow bays, almost to the surf line, and is regularly sighted from land at certain times of the year. Records from the open ocean are rarer but aerial surveys and pelagic driftnet catches show that it is found in oceanic basins. The majority of records from the United Kingdom, Japan and Newfoundland are from water 8–14°C in temperature, although most records from New England are in water from 11–24°C with most of these over 16°C. It seems to prefer ocean fronts where different masses of water meet and where plankton may flourish. These areas include headlands, islands and bays with strong tidal flow.
Where do Basking Sharks go during winter?
Commonly observed during summer months, Basking Sharks are only rarely seen during the winter. It was previously thought that Basking Sharks hibernated during winter due to a number of circumstantial pieces of evidence, mainly their disappearance during the colder months and that the liver weights of fishery-caught Basking Sharks was much less in the spring than in the autumn, indicating a cessation of feeding. This was supported by reports that the sharks shed their gillrakers over the winter and so were presumably incapable of feeding.
Recent studies have disproved the hibernation theory, instead showing that Basking Sharks are in fact very active throughout the winter. Using satellite tags it was determined that in the winter months, rather than spending time near the surface, Basking Sharks spend more time in deeper water, at up to 900m, feeding on deep-water plankton communities. The research also showed Basking Sharks continue to move thousands of kilometres during the winter months, actively tracking plankton blooms in order to feed.
Research also found that rather than losing the gillrakers in one moult, shedding and re-growing new gillrakers is an on-going process over the winter months.
Recent satellite tagging studies are highlighting movements never before documented for Basking Sharks. Gore et al. (2008) tagged a shark off the Isle of Man which promptly headed straight for Newfoundland, demonstrating the first trans-Atlantic migration recorded by a Basking Shark. The intrepid shark also reached a record depth (for Basking Sharks) of 1264 metres. On the other side of the Atlantic, Skomal et al. (2009) tagged a Basking Shark off New England which then headed south, crossing the equator into Southern Hemisphere waters where it spent time at depths of between 800-1000m – the first proven trans-equatorial migration for the species.
Overall, satellite tagging is showing that Basking Sharks are considerably more wide-ranging than previously thought, and raises important questions regarding the population size and genetic mixing of Basking Sharks both in the Atlantic and further afield. These studies are also highlighting the need for global, rather than regional, protection for this species.
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