Noisy Oceans: Military Sonar

Article by Dave Wall, Conservation Officer with the IWDG

Between August and September 2018 more than 70 dead Cuvier’s and Sowerby’s beaked whales and Northern Bottlenose whales, washed ashore on the Atlantic coasts of Ireland and Scotland. All of the animals were in an advanced state of decomposition, indicating they had died offshore and spent a considerable time drifting at sea before being washed ashore. Alarm bells went off with both the IWDG and UK strandings recording programmes as this mortality rate was far higher than the average strandings rate of less than 10 animals per annum for the Ireland and the UK combined.

August 2020 again saw mass strandings or nearshore sightings of 29 Northern Bottlenose whales and Sowerby’s beaked whales in Ireland, Scotland, the Faroe Islands and the Netherlands.  This included the live stranding and subsequent death of seven Northern bottlenose whales in Donegal Bay. A further mass mortality of 27 beaked whales and 29 long-finned pilot whales was recorded in in Ireland and Scotland in 2008 and another, of 15 Cuvier’s beaked whales, in December / January 2014/15.

What could be causing these mass mortalities? In 2020 no post-mortems were conducted on the seven whales which died in Donegal Bay due to a lack of funding and resources. In the other events the advanced state of decomposition of the animals meant that a definitive cause of mortality could not be established. However, investigations by UK and Irish researchers have indicated military sonar to be a strong suspect due to the mortalities occurring over short time spans and in relatively discrete areas.

Cuvier’s beaked whale

So how likely is it that military sonar could be causing these mass mortalities of beaked whales? Well, we have known for decades that military sonar, specifically mid frequency active sonar (in the range of 1–10 kHz), has been linked to the mass strandings of beaked whales in the Mediterranean, Caribbean and Canary Islands. The ability to dive deep for long periods in beaked whales is linked to physiological changes in their bodies, including a very slow heart rate. It is thought that the noise from military active sonar frightens deep diving beaked whales, causing their heart rate to increase and results in the animals suffering the bends (where air bubbles form in the whale’s blood and tissues) and ultimately leading to their death.

While the Irish Naval Service does not possess or use military active sonar, our waters are frequented by vessels from other navies which do possess such technology. Twice every year a flotilla of NATO warships gathers off the west coast of Scotland, to the north of Ireland, for the Joint Warrior naval exercises. The environmental risk assessment for these exercises bans the use of military active sonar within the 50 m contour due to the risk of exposure to human divers. However, no such grace is proffered to whales, dolphins or porpoises in one of the most biodiverse regions for cetaceans in UK or Irish waters. Source levels of up to 211 db are permitted and may be exceeded in some instances, and such noise exposure may last for up to 8 hours a day for the 11 days of each exercise.

Outside of these known training exercises, we know little or nothing about the use of active military sonar within the Irish Whale and Dolphin Sanctuary (which extends 200 nm off our shores). Foreign naval vessels are not required to notify the Irish government of their activities within the Irish EEZ once they are beyond our 12 nm limit. So how can we find out to what extent military active sonar is being used in the Irish Whale and Dolphin Sanctuary? One way of monitoring its use is via static acoustic monitoring (SAM) which can detect and record active sonar. We know that active sonar use has already been detected during some SAM monitoring projects and existing recording data sets for Irish waters could be checked for active sonar detections. SAM arrays permanently mounted to the seabed as part of marine monitoring observatories could certainly broaden our knowledge of active sonar use in the Irish EEZ and perhaps link detections to subsequent mass stranding events.

So why should we be concerned at these mortalities? Well, research by GMIT and IWDG in 2015 and 2016 showed that the continental shelf slopes to the west of I

Stranded Cuvier’s beaked whale

reland are home to year-round populations of Cuvier’s and Sowerby’s beaked whales and are used seasonally by Northern Bottlenose whales. These populations are not large with the total number of beaked whales in the region estimated to consist of only a few thousand animals during a 2007 EU funded survey. A French study published in 2012 found that only 8% of dead bycaught dolphins tagged and released offshore were subsequently recovered ashore. Thus the 70 dead beaked whales washed ashore on Irish and Scottish coasts in 2018 may have represented a mass mortality of up to 875 beaked whales or upwards of 8-20% of the estimated total beaked whale population for the region in 2007.

If military active sonar is causing the deaths of dozens, if not hundreds of beaked whales within the Irish Whale and Dolphin Sanctuary, how are to we prevent future deaths? In 2004, following research into a mass stranding in the Canary Islands linked to NATO exercises, Spain introduced a ban on the use of military active sonar in Canary Islands waters. Since that ban there has been no recorded mass strandings of beaked whales. Ireland could certainly adopt that approach and ban the use of military active sonar within the Irish Whale and Dolphin Sanctuary. However, it is not at all clear whether current national or international legislation allows the Irish government to restrict foreign naval vessel activity in this way, nor how any such ban could be enforced.

For now, the IWDG can only dread the next mass stranding and continues to push for adequate resources and funding to identify the causes of such mass standings when they do occur. We will also continue to ask the Irish government to find a way to prohibit the use of military active sonar within the Irish Whale and Dolphin Sanctuary.