The discovery of oceanic migratory movements by basking sharks is not new. For instance in 2007/08 the Manx Basking Shark Watch group, working with Save Our Seas Foundation, tagged a creature off the Isle of Man that crossed the Atlantic from east to west.
However, new findings refute the view held by some marine biologists that basking sharks stick to cool, temperate waters throughout the year. Rather, it would appear that they like to switch to more tropical zones.
Last year a team headed by Greg Skomal, of Massachusetts Division of Marine Fisheries, tagged 25 basking sharks off southern New England. Of these, during winter six migrated to the Caribbean, while a further two ventured even further south, crossing the Equator to end up off northern South American coasts. Swim depths were generally between 200m and 1000m.
The tags worked by recording depths, water temperatures and light levels, from which a “novel geolocation technique” allowed positions in the ocean to be calculated. The tags would release from the creatures at a set time, rising to the surface to relay data via satellite.
“When in these [southern] areas, basking sharks descended to mesopelagic depths and in some cases remained there for weeks to months at a time,” the team reported in the US-based Current Biology magazine and online source.
“Our results demonstrate that tropical waters are not a barrier to migratory connectivity for basking shark populations and highlight the need for global conservation efforts throughout the species range.”
Historically basking sharks have been hunted for their large livers – a six-tonne animal can yield a two-tonne liver – and nowadays fins for lucrative Asian markets.
They are protected in the UK and some other countries, but remain vulnerable in many parts of the world, despite a CITES Appendix II listing established in 2002 and which restricts international trade in basking shark products.
The global population is estimated at about 10,000, some 80 per cent down on the population calculated to have prevailed around 50 years ago.
Meanwhile the Isle of Man plays host this summer to a three-day international conference, Basking Sharks: A Global Perspective. It is organised by Manx Wildlife Trust’s active Basking Shark Watch group and Save Our Seas Foundation.
At Erin Arts Centre from 3-6 August, delegates will hear speakers from the UK, Ireland, France, the USA, Canada, South Africa, New Zealand and Seychelles tackle all aspects of basking sharks’ biology, habitats, population movements and conservation requirements.
The possibility of establishing new photo-identification and DNA-profiling schemes to examine breeding patterns between migratory groups will be discussed.
*Manx Wildlife Trust voluntary marine officer Jackie Hall, who set up Manx Basking Shark Watch in 2004, has been included in The Independent on Sunday’s Happy List 2009 – a celebration of people as good examples of how to make Britain a “more caring and contented place” in which to live.
Amongst the list’s better known names are naturalist Sir David Attenborough, actor Sir Ian McKellen, survival specialist Ray Mears, children's author Jacqueline Wilson, England football team manager Fabio Capello, and comedian Peter Kay.
The newspaper canvassed a number of organisations, including The Wildlife Trusts, for a volunteers representative. Hall was selected as “a fine representative of those people and the work they do”.
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