The first satellite tags ever deployed on basking sharks in Ireland were successfully attached this week. Two Wildlife Computers MK10 Archival tags were deployed on basking sharks under the shadow of Slea Head, Co Kerry. The tags are attached at the base of the sharks dorsal fin and will record location, water temperature and depth for the next 215 days (7 months). After this period the tag will detach from the shark, float to the surface and relay the data back to shore via the ARGOS satellite system. The track of the shark is reconstructed based on the timing of the setting of the sun and sea-surface temperature.
Dr Mauvis Gore from Save Our Seas, who is collaborating on this project, recently tracked a basking shark from the Isle of Man to Newfoundland a distance of 9589km in 82 days. Where will these Irish sharks get to in 215 days ?
Over the last two weeks the tagging team have travelled from North Donegal to West Cork searching for basking sharks suitable for satellite tracking. Hundreds of km of the Irish coastline have been searched with the hope of encountering some large sharks which will allow the tagging vessel to approach for tagging purposes. Leader of the project Dr. Simon Berrow said: "I had almost given up hope, we have seen a number of sharks but they were often quite small only 5m or less and just sank in the water when the research vessel approached." Out of the blue, a call from Nick Massett in Ventry on the Dingle Peninsular in West Kerry alerted the tagging team to the presence of sharks off Slea Head. It was somewhat surprising as the weather was not great - the fresh winds and large swell were not usually great conditions for observing basking sharks on the surface. With the assistance of Nick who directed the vessel from a high vantage point on the headland, the team finally approached a group of four sharks feeding very close to the shore. "They were large and so intent on feeding that they hardly noticed our 6m Rigid Inflatable Boat approaching them," continued Dr. Berrow. "The first attempt to attach a satellite tag failed when the tagging pole bent as the tag's anchor was pushed into the shark. Fortunately a colleague from the Isle of Man had made me a pole similar to the ones they used. As we rushed to grab this pole, I was fearing the shark would react to the tagging attempt and dive but amazingly it was completely unfazed and continued to feed away at the surface." The second attempt went very smooth and the tag quickly deployed just below the dorsal fin, again the shark seemed not to notice and continued feeding away on the surface. A second tag was soon deployed and after many anxious weeks the research team drew a sigh of relief as the two basking sharks lazily swam off, towing the tag beside them.
The tags may detach at any time due to drag or from rubbing off other sharks. The ARGOS satellite system is now scanning the North Atlantic for these tags and as each day passes with no signal more information on the movements, behaviour and migration of Irish basking sharks is obtained. "We now face an anxious wait to see how long these tags will remain on the shark," says Dr Simon Berrow, "but this is a much more satisfying wait than the wait to deploy them !"
The team also tried to obtain tissue samples for genetic analysis and obtained images for photo-identification. This tagging has been supported and filmed by Crossing-the-Line films as part of a programme commissioned by RTE called Wild Journeys (www.ctlfilms.com) This work is also supported by the Galway-Mayo Institute of Technology (www.gmit.ie) who also sponsored one of the satellite tags. This tagging was carried out as part of the Irish Basking Shark Survey sponsored by a Heritage Council Wildlife Grant 2009.