Scotland’s basking sharks
Tagged basking sharks off the Scottish coast have given scientists a greater understanding of these species behaviour in UK waters.
Basking sharks (Cetorhinus maximus) are the world’s second largest fish species, which feed on some of the smallest species in the ocean (zooplankton). They are found throughout the oceans and can undertake huge migrations, for which the purpose is unknown. Large groups of basking sharks seasonally gather in the shallower, coastal waters in the Atlantic, Pacific and Indian Oceans for feeding and possibly reproduction. One of the most popular, seasonal gathering areas in UK coastal waters is off the west coast of Scotland, in the Sea of Hebrides.
Scientists working for the Scottish Natural Heritage (SNH) and the University of Exeter, tagged 61 basking sharks between 2012 and 2014 in the Sea of Hebrides. They discovered that during the summer months (July to end of September) the tagged basking sharks mainly remained in the shallow coastal waters, characterised by rocky seabed and low to medium tidal currents. Some of the basking sharks travelled out to the Irish and Celtic Sea but within these months generally returned to the Sea of Hebrides. At the beginning of autumn (October/November), there was a general southerly migration of the basking sharks, with some being recorded as far as Madeira and the Canary Islands, although most basking sharks remained in the north-east Atlantic, Celtic Sea or the Bay of Biscay. As the tagging programme occurred over several years, the scientists were also able to observe the return of many of the basking sharks every year to the same areas within the Sea of Hebrides.
The tags used by the scientists to track the basking sharks
Several behaviours (breaching, toe-to-tail following) have been suggested to be part of a courtship rituals in basking sharks. This behaviour was observed within the ‘hotspots’ identified by the tagged sharks movement. Although no mating was seen, it suggests that areas off the west coast of Scotland could also be potentially important breeding grounds for basking sharks.
The research presented within this paper was important to highlight the difficulty of protecting species that have large migrational patterns, but also highlight that static protected areas can protect important feeding grounds, that are revisited annually by a individuals. Whilst in shallower, coastal waters, basking sharks remained closer to the surface, potentially increasing their chances of colliding with vessels. The basking shark ‘hot spots’ were mainly identified within a proposed Scottish Marine Protected Area (MPA) (Sea of Hebrides) and adds to the evidence that this MPA should be approved by the government.
Witt, M.J., Doherty, P.D., Godley, B.J. Graham, R.T. Hawkes, L.A. & Henderson, S.M. 2016. Basking shark satellite tagging project: insights into basking shark (Cetorhinus maximus) movement, distribution and behaviour using satellite telemetry. Final Report. Scottish Natural Heritage Commissioned Report No. 908 and references within the report.
BBC. Tags give insight into basking shark behaviour. Online: http://www.bbc.co.uk/news/uk-scotland-highlands-islands-35380327
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