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100th Basking Shark Tagged this Season

Updated: Apr 1, 2019

The 7m Basking shark was tagged off the Blasket Islands, Co Kerry on Sunday 9 August. This was the 100th shark tagged this season, an astonishing success rate. Prior to this year, only eight tags had been deployed on basking sharks in Ireland, and less than 50 deplyed worldwide.

The tagging study, funded by a Heritage Council Wildlife Grant, aims to determine the movements and migration patterns of basking sharks in Ireland and determine growth rates, longevity and other essential life-history characteristics. The deployment of individually coloured numbered tags have been complimented by two satellite tags. "These two different types of tags compliment each other," explained Project Leader Dr. Simon Berrow. "The satellite tags are set to track the movements of the sharks for up to seven months and will provide high quality data on location and depth during this period. We hope the coloured tags will remain on the sharks for much longer enabling us to get much longer distance recoveries and see if the sharks return to Ireland the following or in future years."

Basking shark head  © E. Johnston

At a recent conference on basking sharks in the Isle of Man, the Irish researchers learnt that less than 50 tags have been deployed on basking sharks throughout the world. This means the Irish tagging project is leading this research.

"Obviously the more tags we deploy the better chance we have of getting a recovery. Already we have eight recoveries from local movements around the tagging sites to over a recovery from Scotland, over 150km away," reported Dr Simon Berrow. "Mariners are requested to look out for tagged sharks which have individually numbered green, yellow and red tags on them. Even if you cannot read the number the colour is very useful as they are specific to a county."

The research team also had another significant breakthrough when they showed that basking shark DNA could be extracted from the slime which coats the sharks body. Tissue samples for genetic analysis are hard to obtain as you require a dead shark or invasive biopsy techniques which do not work well on sharks due to their tough skin. By simple rubbing an oven scourer along the sharks body enough slime can be collected to extract shark DNA. This new technique pens up huge possibilities for shark researchers around the world which is very important as basking sharks exhibit surprisingly low genetic diversity.

The research on basking sharks season has been a resounding success and the team are already looking for funding to continue the work next year

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