Alarming rise in stranded deepwater whales on Irish and Scottish coasts

Irish and British marine scientists are seriously concerned about a spike in strandings of the protected deepwater Cuvier’s beaked whale along the west Irish and Scottish coasts.

A total of 15 Cuvier’s beaked whales were stranded on coasts between mid-December 2014 and the end of January this year – far higher than the average of just under three per year – with nine of them on this Atlantic seaboard.

Some 80 per cent of the entire year’s recorded strandings of this species occurred in December, the scientists note – describing it as an “unusual mortality event” involving a single species over a short time.

They have called for an investigation into major underwater noise sources which may have been deployed at the time, such as military or scientific sonar, seismic surveys and explosives.

Cuvier’s beaked whales, normally found over 50km offshore, are very sensitive to acoustic disturbance. They are protected under national and EU legislation and Irish waters have been a declared whale and dolphin sanctuary since June 1991.

A number of previous case studies in the Atlantic, Pacific and Mediterranean have linked mass-strandings of this whale type to military exercises at sea using sonar. About half of all known mass-strandings of this species have been linked to sonar or seismic surveys.

Affected whales become disoriented and lose the ability to eat, often starving to death, which means mortality at sea could be much higher.

Scientists from the Irish Whale and Dolphin Group (IWDG), Hebridean Whale and Dolphin Trust, and the British-based Whale and Dolphin Conservation, and Humane Society International say it is not possible to determine the cause of death in this instance, because there is no postmortem scheme in Ireland and due to the decomposed state of those found in Scotland.

They refer to “anecdotal” media reports of military activity to the west of Scotland during December and January, but note that lack of data on military presence and use of active sonar or other sources of human-influenced sound prevents an “independent and conclusive assessment”.

Under the UN Law of the Sea Convention, military vessels from other states have the right of innocent passage through the Irish exclusive economic area, and diplomatic clearance is only required within the 20km (12 mile) limit.

The Naval Service said it had no knowledge of any unusual activity in these waters during that period.

The Department of Energy said there had been no seismic surveys by the petroleum exploration industry in the Irish offshore area since mid-October 2014. It pointed out such surveys must comply with National Parks and Wildlife Service guidance on managing risk to marine mammals from man-made sound sources and suitably qualified marine mammal observers must be on board.

Marine scientists, including Conor Ryan of the Hebridean Whale and Dolphin Trust, Mick O'Connell of the IWDG, Sarah Dolman of Whale and Dolphin Conservation and Mark Simmonds of Humane Society International, have called for an underwater noise register to be established in both Britain and Ireland to generate baseline data for use in future investigations into unusual mortality events.

They said governments should be informed and mitigation measures put in place if activities with a potentially negative impact on whales and dolphins are to be conducted within exclusive economic zones.

They also call for a postmortem programme for whales in Ireland. Dr Simon Berrow, IWDG co-ordinator, said a postmortem could identify death caused by acoustic trauma if the stranded mammal was identified in time.

He said a recent rise in common dolphin mortalities on this coast was probably associated with pelagic fishing, due to markings identified on the mammals examined.