Basking sharks recover from exploitation of the last Century
23 July 2012, by Marion O'Sullivan
Numbers of basking sharks around Britain's coast seem to be on the increase, say scientists. And not only are there more sharks but they are also living longer, according to the largest study ever carried out.
Basking shark feeding.
Basking sharks were hunted extensively during the 20th century, mainly for their liver oil which was used for industrial lubricants and lamp fuels, but also for other body parts, such as their huge fins, valuable for the Asian shark-fin soup market, and cartilage which was thought to have medicinal properties.
Records show that between 1952 and 2004 more than 81,000 basking sharks were killed in the northeast Atlantic.
Protected by UK legislation since 1998 and more recently by international conservation agreements, basking sharks are now regularly seen in UK waters during the summer.
The research team, from the University of Exeter, the Marine Conservation Society, the Cornwall Wildlife Trust and Wave Action, analysed 20 years' worth of data from public sightings – a total of 11,781 records – and combined them with dedicated boat-based basking shark surveys.
Their analysis shows a rise in the number of sightings from the 1980s and also suggests an increase in the number of older sharks. This is encouraging news as basking sharks are late to mature and breed infrequently, so are slow to recover from over-fishing.
'Our research shows that basking sharks could be recovering from the extensive fishing that took place in the 20th Century,' says Professor Brendan Godley from the University of Exeter.
The team identified three hotspots for sightings, the earliest being off the coast of South West England in April, then the Isle of Man and on to Western Scotland in August. The researchers can't yet tell if there are different groups of sharks in each location or if it is just one group following their main food source, plankton, as it moves northwards during the summer.
'It is notoriously challenging to carry out long-term monitoring of marine wildlife but with the help of many hundreds of volunteers reporting their records, we have made a leap forward,' says Godley.
Very little is known about where the sharks go or how they live once they leave UK waters so the Exeter researchers are involved in a related study to track them using satellite tags.
The study was funded by the Natural Environment Research Council.
Witt MJ, Hardy T, Johnson L, McClellan CM and others (2012) Basking sharks in the northeast Atlantic: spatio-temporal trends from sightings in UK waters. Mar Ecol Prog Ser 459:121-134
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