Why are beaked whales stranding again?

             Cuvier’s beaked whale on Baleshare, North Uist, 10/8/2018 © Sarah Dolman/ WDC

Since early August, a minimum of 38 Cuvier’s beaked whales have stranded, dead, on the coasts of west Scotland. At least 19 have stranded on the Irish coastline. WDC are very pleased that the UK and Irish governments have agreed to conduct an investigation. A further 3 Cuvier’s beaked whales and 9 nothern bottlenose whales (another kind of beaked whale) have stranded dead or alive in Iceland since July.

WDC plan to raise this issue at a forthcoming meeting of ASCOBANS (Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas). We are also discussing necessary actions with scientists involved in each of the countries involved in the strandings.

You may have seen the news stories about a mass stranding of dead Cuvier’s beaked whales along the coast of Ireland. So far, at least six but up to 11 whales from Co Donegal, Mayo, Co Galway and Co Sligo and Scotland’s Western Isles (six individuals found on North Uist, South Uist, Eriskay and Islay), since 3rd August 2018. Why did these strandings happen and what can we do about it?

Great Depths

Cuvier’s beaked whales live in the deep waters off the west coast of the British Isles in the North East Atlantic ocean. We know very little about their distribution or the numbers that live out there.

Cuvier’s beaked whales can dive to great depths, of about 2 miles, and they spend much more time at depth than they do at the surface. Mass strandings of Cuvier’s beaked whales often result from offshore human activities. Most regularly, due to active sonar used by military forces to locate submarines.

Sound travels well in deep water and very loud sounds, like active sonar, may frighten whales to the surface too quickly, leading them to suffer decompression-like symptoms, similar to divers. This can kill them. Some whales strand and others have been found floating dead at sea as a direct result of military activities offshore. There have been no mass strandings of Cuvier’s beaked whales in the Canary Islands, previously a stranding hot spot, since active sonar was banned within 50 nautical miles of the coast in 2004.

All of the individuals that have come ashore in the last 2 weeks (and the two that were found floating dead at sea off Inisboffin in Ireland and Eriskay in Scotland) are severely decomposed. It is much more difficult to determine the cause of their death(s) if the whale’s bodies are in such a poor condition which is frustrating for scientists.

Something appears to be happening offshore that is killing these whales and causing them to come ashore. It is important to find out as much as possible even though their bodies are very decomposed and there are no post-mortem results.

Unusual Mortality Event

It has been 10 years since the last big ‘mass stranding’ (also called an unusual mortality event) in the UK in 2008.  It consisted of 18 Cuvier’s beaked whales, 4 Sowerby’s beaked whales, 5 unidentified beaked whales and 29 pilot whales, that Whale and Dolphin Conservation and others reported here.

Another mass stranding occurred during December 2014 and early January 2015, where five Cuvier’s beaked whales stranded in an advanced state of decomposition along the western coasts of Scotland. During the same period, an additional nine Cuvier’s beaked whales stranded on the western seaboard of Ireland. This was reported by the Scottish Marine Animal Stranding Scheme.

The potential implications of such events and the large number of individuals involved make this a very worrying situation. We do not know how many Cuvier’s beaked whales live out in the North East Atlantic ocean, and we cannot know either how many die but do not wash ashore for us to discover.

The Irish Whale and Dolphin Group and the Scottish Marine Animal Stranding Scheme are doing what they can and we are ready to help them to get to the bottom of these deaths.

Read the full article Why are beaked whales stranding on Irish and Scottish coasts – again? and learn more about WDC here.