More female sperm whales being found off Irish coast

A new study on sperm whales off the coast of Ireland has found females and their calves are swimming in higher latitudes than before.

The presence of the whales at higher latitudes is most likely linked to climate change, according to the study's lead scientist Seán O'Callaghan.

Mr O'Callaghan is a PhD candidate at the Marine and Freshwater Research Centre in Atlantic Technological University in Galway.

He has been following and documenting the activity of the deep-diving whales from their traditional breeding grounds near the Azores in the middle of the Atlantic, to where male sperm whales traditionally feed in Norway.

Earlier this week, he recorded a large sperm whale on the continental shelf off Co Mayo, where the canyons are closest to the coast.

Next month, he will join a research ship from the Strait of Gibraltar which will follow the huge creatures to Ireland.

Once hunted for their oil, Norwegians ran a number of whaling stations on the coast of Ireland, sperm whales are the largest of the toothed whales and are under-researched in Irish waters, Mr O’Callaghan said.

Sperm whales traditionally separate as they mature.

In the north Atlantic, male whales move to higher latitudes as far as Svalbard at the 80th parallel, while females and young whales typically remain around lower latitudes below the 40th and 45th parallel, near the Azores, Madeira and the Canary Islands.

Irish waters represent a midpoint for this species’ spatial segregation in the north east Atlantic.

Historically, only male whales were found off Ireland, with just one "stray" female recorded in Irish waters in 1910 by commercial whalers.

"It appears that the population structure for sperm whales off Ireland began to change over the past decade from a primarily male-based population to now include females, as indicated by stranding and sighting records," Mr O’Callaghan said.

Between 1995 and 2023, ten female sperm whales have been stranded around the coast of Ireland.

Eight of the whales have been stranded since 2013 and there was at least one stranding per year between 2019 and 2023.

Four of the strandings have occurred in Donegal, indicating the presence of female whales along the continental shelf of the region.

Two females were stranded within a day of each other and in 2013, Mr O’'Callaghan photographed a stranding on Bá Bhreandáin, Co Kerry of a large female.

Sperm whale calves and juveniles were also sighted in Irish waters in 2001, 2004, and 2010 in the Rockall Trough, along the Porcupine Bank and Goban Spur.

The research shows female and young sperm whales off Ireland have increased over the past decade.

"Historically we should only have males in our waters as they forage off of our canyons or move between the southern nursery grounds and high latitude foraging grounds when they're adults," Mr O'Callaghan said.

Marine heatwaves have increasingly become a concerning issue for the world's oceans, given that they permeate into deepwater habitats and may affect depths down to 200m, while the duration of their effects also increases with depth.

Irish waters have cooled since reaching a peak in 2007 and still remain 0.4C warmer this century when compared to the last century.

The recent cooling has been linked to a weakening of the Atlantic Meridional Overturning Circulation/
The influence of the Atlantic Niño/Niña events likely plays a role in the dynamics of predator and prey distributions.

"So, it remains to be seen how offshore Irish waters alter as the effects of climate change become clearer in the years ahead, but the apparent increasing presence of female sperm whales is a signal of widespread habitat change for the species and other top predator communities," Mr O’Callaghan said.