A record number of beaked whales washed up on Irish shores this month in a mystery mass whale death event that saw bodies strewn as far away as Iceland and Scotland.
The Irish Whale and Dolphin Group reports that at least 16 Cuvier beaked whales were found on western coastlines between August 3 and August 22.
Over the same period at least 13 of the whales washed ashore in Scotland, while two were found in Iceland.
Five whales washed up in just one week earlier this month.
IWDG Strandings Officer Mick O’Connell noted in a statement that “nothing on this scale has been recorded for this species in Ireland before”.
Research suggests that only a small number of dead animals actually wash ashore, so the death toll may be “significantly higher”, according to O’Connell.
The cause of death is still unknown as the animals were all found in very poor condition.
But they seem to have all died at around the same time.
This rules out potential causes such as disease or plastic ingestion, and the species’ behaviour and distribution means they are unlikely to come into contact with large-scale fisheries.
Smaller mass death events were recorded over longer periods in late 2014 and 2015 in what O’Connell called a ‘worrying’ trend.
Normally only up to three of these whales are stranded each year.
Cuvier’s beaked whales (Ziphius cavirostris) are thought to be the deepest-diving whale.
Although fairly common, they are rarely seen alive.
They live offshore in deep water where they often dive for 20-40 minutes in undersea canyons near the edge of the continental shelf.
One animal was even tracked in a dive down 2,992 metres, holding its breath for over two hours.
O’Connell noted that beaked whales are vulnerable to loud man-made underwater noise, such as low-mid frequency naval sonar and some acoustic surveys used to examine the sea floor.
“Mass strandings of beaked whales coincidental with naval exercises have been recorded in Greece, the Canaries and the Bahamas,” he added.
However, the Irish navy does not use these types of sonar.