A whale found washed up on Arranmore has been traced back to a sighting off a tiny Portuguese island almost two decades ago.
Marine experts say the details they have been able to garner from the animal demonstrate the value of collaboration between countries.
The deceased male sperm whale was discovered by a woman out walking on Arranmore Island recently.
She reported it to the Irish Whale and Dolphin Group which in turn got in touch with Seán O’Callaghan, a volunteer with the Stranding Network group and a PhD candidate with the Marine and Freshwater Research Centre at Atlantic Technological University.
Mr O’Callaghan travelled from Killarney to examine the carcass. He took detailed images as well as various biological samples and measurements.
While he was not able to ascertain a cause of death due to the animal’s advanced state of decomposition, his investigations did lead him some 2,300 kilometres from the whale’s final resting place.
He sent his findings to Lisa Steiner of Whale Watch Azores who was able to check the unique markings on the tail against images held on her photo-identification catalogue. Ms Steiner came up with a match that confirmed the whale was last seen off Faial Island in the Portuguese region in 2004.
Seán O’Callaghan said very little is known about the movements of the male sperm whale. The Arranmore discovery was only the second in history linking Ireland to the traditional breeding ground in the Azores.
The other was a stranding in 1997, again along Ireland’s west coast.
“It was unfortunate that he died but it did give us a rare insight into how this deep diving whale species uses our waters,” he said.
Strandings Officer with the Irish Whale and Dolphin Group, Stephanie Levesque, said that while ultimately tragic, the whale’s journey demonstrated the value of stranding and sighting schemes and the importance of collaboration.
Ms Levesque said, “Unfortunately we don’t have a post mortem scheme in Ireland at the moment so we weren’t able to ascertain a cause of death.
“In a case like this all you can do is encourage people to take detailed photos and sometimes from those you can see net marks or maybe propeller marks. In this case, due to the stage of decomposition, there was not much we could do.
“But what the case does highlight is the importance of reporting strandings and sightings. Some countries keep a catalogue of whales and dolphins so they can be tracked in terms of their age and whether they have calves.
With some you can trace it back to who their grandparents were.
“From engaging with our colleagues in the Azores Seán and Lisa were able to ascertain that this whale was last sighted in 2004 over 2,000 kilometres from Arranmore.
“From the information Seán has collated Whale Watch Azores will now be able to update their catalogue. Sperm whales are particularly difficult to track so it’s great that we have been able to make this match.
“It’s sad but it’s also very interesting,” Ms Levesque added.
Whale and dolphin strandings have become more and more common on Ireland’s shores. In August 2020 seven whales died after washing up in Rossnowlagh.
Stephanie Levesque said they received record numbers of reports from members of the public during the pandemic period.
“Last year was down on 2021 but then 2021 was an outlier year when we had 96 reports of strandings. We don’t know why there were so many, perhaps because there were so many people on our beaches during the pandemic.”
Seán O’Callaghan added that a lot of what is known about male sperm whales comes from strandings. But the advance of technology has made tracking them easier.
“There was an increase in acoustic surveys off Ireland over the past decade that really gave us an understanding of where the whales are offshore. ObSERVE Acoustic was a critical project to build up our knowledge for species in offshore waters.”
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