IWDG tag basking sharks off North Donegal

31st Jul 2008 The IWDG tagged a further 6 basking sharks off Donegal last week as part of a new study of their movements.

Following on from our earlier success in West Kerry in June, the IWDG spent three days last week looking for basking sharks around Inishtrahull off the Northern tip of the Inishowen peninsula. As basking shark sightings become scarce elsewhere in Irish waters, local IWDG members Des Mills and Emmet Johnston were still regularly reporting large numbers around the island of Inishtrahull and in the sound between the island and Malin Head, Co. Donegal.

The IWDG are involved in an RTE funded film on migration being produced by Crossing the Line Films. The film will feature the migrations of both basking sharks and whales. We are working with Mauvis Gore of the University of Edinburgh who successfully tracked basking sharks from the Isle of Man to Newfoundland last year: a distance of 9,500km. Crossing the Line Films and the Galway-Mayo Institute of Technology are funding two satellite tags which we hoped to deploy this year.

The film and tagging crew met for three days in Culdaff on the Inishowen Peninsula from 24-26 July. Local NPWS Conservation Ranger Emmett Johnston had been keeping a close eye on basking shark sightings in the area through his local network. Emmett also organised boats and other logistics to enable the maximum amount of time to be spent on the water looking for sharks. Each day two boats searched for surface feeding sharks.

A small 4m shark was observed close to Inishtrahull on Thursday lunchtime, but was considered too small to attach a satellite tag too, but was tagged with an individually numbered, red coloured tag. These tags are attached to the shark below the dorsal fin with a long pole.

Feeding Basking shark©Jeremy Stafford-Deitsch

The weather on the following day was poor in the morning but was forcast to improve in the afternoon. At 2pm the 11m angling boat Gemini and a 5.4m RIB left Culdaff in search of sharks. None were found around Inishtrahull, but at 5pm as the tide started ebbing, sharks started appearing on the surface in the deep channel between Malin Head and Inishtrahull. At least 6 sharks could be seen feeding along the tide line. A number of attempts to deploy satellite tags was attempted but the sharks were small and quite scittish, avoiding close contact with the RIB (the tagging vessel). After a number of attempts it was decided to call it a day.

The following morning the sea was very calm and four hours was spent trying to locate sharks but to no avail. After Mauvis had left to travel to Belfast airport, the tagging team continued to wait for sharks and after 7 hours sharks started to appear in the same sound as the previous day. In about 30 minutes five more coloured tags had been deployed on sharks ranging from 4.5 to 6.5m in length. Only the snapping of the pole brough the tagging effort to a close and a tired but happy tagging team finally headed back to port.

This brings the total number of tags deployed by the IWDG this summer to eight. Many more sharks will need to be tagged before any recoveries could be expected but the IWDG are building up valuable experience and creating a "shark team" for future research work.

The IWDG would like to thank Cepa Giblin of Crossing the Line Films for their interest and support of basking sharks and GMIT for agreeing to fund a second tag, Emmett Johnson, NPWS for his continued drive and logistical support, Mauvis Gore for spending three days in the middle of her busy summer season in North Donegal and Des Mills, IWDG for boat cover and his immense local knowledge.

Dr Simon Berrow

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