A Joint Statement on an unusual mortality event of Cuvier’s beaked whales in Ireland and Scotland

23rd Feb 2015

Cuvier’s beaked whales (Ziphius cavirostris) are native to both British and Irish waters where they occur in deep waters, typically greater than 50 km offshore. They are protected by a range of national and EU legislation and International agreements. Over a 45 day period between 11 December 2014 and 30 January 2015, a total of 15 Cuvier’s beaked whales stranded along the western seaboard of Ireland (n = 9) and Scotland (n = 6). Analysis of 24 years of stranding data indicates a long-term average of 2.8 whales per annum. During December 2014, 10 whales were found stranded in Scotland and Ireland. The probability of 10 strandings occurring by chance (based on the 24 year mean) in a given year is 0.1 %.[1] Therefore, we consider this to be an unusual mortality event.

During a typical year, 20 % of strandings of Cuvier’s beaked whales occur during December in Scotland and Ireland. During 2014 however, 80 % of strandings occurred during December. It was the highest monthly total ever recorded in the region, and the highest annual total since 2008.[2] In 2008, another unusual mortality event occurred involving several deep diving species, including Cuvier’s and Sowerby’s beaked whales and long-finned pilot whale. Fifty six animals stranded over the course of seven months but the cause of this event remains undetermined.[2] The recent event is distinct however in that it involved just a single species and over a short period of time. The recent strandings occurred firstly in the northwest of Ireland and the Outer Hebrides. Thereafter they were recorded throughout the western seaboard of Ireland and Scotland. The carcases which stranded in December 2014 were in a less advanced state of decomposition than those discovered in January 2015. This scenario is consistent with a mortality event that was both spatially and temporally discrete.

It was not possible to determine the cause of death for any of the Cuvier’s beaked whale carcasses that stranded in Ireland or Scotland from December 2014 to January 2015. This was due to a lack of a post-mortem scheme in Ireland, and the advanced state of decomposition of those carcases that stranded in Scotland. It is well documented that Cuvier’s beaked whales are one of the most sensitive species to acoustic disturbance. There are many case studies from the Atlantic and Pacific Oceans and Mediterranean Sea where mass-strandings of this species were linked to exercises using military sonar.[3,4,5] Furthermore, a controlled exposure experiment has demonstrated prolonged reactions by some beaked whale species to navy sonar.[6] Approximately one half of all known mass-strandings of this species have been linked to sonar or seismic surveys.[7]

In the media the recent mortality event was anecdotally linked to military activities to the west of Scotland during December 2014 and January 2015. However a lack of data on military presence, use of active sonar or indeed other sources of anthropogenic sounds prevents an independent and conclusive assessment. Attributing any anthropogenic activity as being causal to mortality events requires baseline acoustic data on such activities.

Stranded whales that are detected and reported represent a small proportion of those that actually die at sea. A carcass has to make landfall, be discovered and finally be reported in order to be registered as a stranding. The likelihood of this occurring is low, particularly along the Irish and Scottish western seaboard where the coastline is long and remote. Therefore the estimates and figures presented here should be considered highly conservative.


  • In the case of previous mass standings the link with anthropogenic activities was not established until a full and open investigation had been completed to explore all possible causes.[8] We call for a similar exercise drawing together data on major underwater noise sources which may have been in use, such as military or scientific sonar, seismic surveys, use of explosives.
  • We urge that an underwater noise register is established in both the UK and Ireland, including data from all sources of intense noise to the greatest extent possible, to generate baseline data for use in, inter alia, future investigations of unusual mortality events.
  • Unusual mortality caused by or exacerbated by anthropogenic activities may be mitigated if action is taken immediately to curtail the sound. A long-term forum comprising a panel of experts should be established to identify and oversee response to future unusual mortality events as they unfold.  
  • A post-mortem programme needs to be established in Ireland to determine the causes of death of cetaceans.
  • With regard to the Precautionary Principle, if activities thought to have a potentially negative impact on cetaceans, which are fully protected under national and EU law, are to be carried out within the EEZ, the relevant governments should be informed and mitigation measures in place to reduce any impacts.

Finally, we commend the provision of funds already in place for the stranding networks in UK and Irish waters. We hope that these long-term studies continue to receive the necessary support given that they are invaluable for conservation and for reporting to forums as part of our commitments to international agreements such as ASCOBANS*. We also welcome plans by the JNCC to instigate a noise register. We hope that the actual occurrence of impulsive noise can be collated on a temporal or spatial scale relevant to investigating future unusual mortality events. Establishing a comparable system in Ireland will be essential to establishing likely causation and devising effective mitigation in any future cases of unusual mortality events throughout this region.


Yours Sincerely,


Conor Ryan (Hebridean Whale and Dolphin Trust)

Mick O’Connell (Irish Whale and Dolphin Group)

Sarah Dolman (Whale and Dolphin Conservation)

Mark Simmonds (Humane Society International)