Researchers deploy new tagging devices to endangered basking sharks off west Cork

Researchers from Trinity College Dublin have begun deploying a new form of tagging device on basking sharks off west Cork in a bid to learn more about the behaviour of the endangered species.

Known as Ireland's gentle giants of the sea – some of which grow to 12 metres in length – the species is the second-largest shark in the world, but its conservation status was changed from vulnerable to endangered two years ago.

Prof Nick Payne and PhD researcher Haley Dolton from Trinity's school of natural sciences have returned from a week on the waves in which they managed to apply tags to four sharks.

These electronic tags accumulate data about the sharks’ behaviour and physiology as they cruise around the coast feeding on plankton; notably on how they respond to temperature variation and how they swim. Other researchers are using satellite tags to track movement of the species in Irish waters.

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“The goal is to learn more about the anatomy and physiology of these ocean giants; information that will guide conservation efforts for an endangered species,” Prof Payne said.

"Sadly, the first phase of the work involved dissecting two dead basking sharks that had washed up on the coastline near Clonakilty within days of one another," he said.

These dissections did, however, allow for detailed examination of the internal anatomy and musculature of these specimens, which helped the researchers learn more about how this species’ physiology allows them to behave the way they do and to cope with environmental variation such as changes in water temperature.

Prof Payne added: “Basking sharks are a difficult species to study because they are not very abundant and they only grace our shores for a brief period each year, from April to August, so I am delighted we were able to learn so much about them this past week. We would rather not have had the opportunity to examine the two sharks that died prematurely before we took to the sea, but these sad events did at least help us learn more about them.”

Continuous risk

While basking shark fisheries no longer operate, the sharks are at continuous risk of death from fishing by-catch and from getting struck by boats, “so the more we know about them – especially their behaviour and physiology – the better chance we have of protecting them”, he said.

One of the sharks died from unknown causes, while the other had a cut to its head and snout, which could have been caused by a collision with a board, Prof Payne noted.

"The amount of data we managed to collect throughout the whole week was phenomenal and beyond what I'd hoped for. We are currently analysing all the results and look forward to sharing our findings with everyone later in the year," Ms Dolton said.

They worked with local marine tourism operator David Edwards of West Cork Charters to observe the free-swimming basking sharks in their natural environment and to deploy the tags. On the final day of their fieldwork, they had the opportunity to observe in close quarters a six-metre female they had tagged the previous day by snorkelling with it.

This research is funded by the Irish Research Council and Science Foundation Ireland.