Silurian monitors Joint Warrior on our latest acoustic survey
THE FINAL ACOUSTIC SURVEY OF THE SEASON MONITORED JOINT WARRIOR, EUROPE’S LARGEST MILITARY EXERCISE, TO HELP US TO UNDERSTAND THE IMPACT it may HAVE ON CETACEANS IN THE HEBRIDES.
Joint Warrior brings together the Royal Navy, the Royal Air Force and the British Army, as well as forces from other nations. These exercises typically occur twice a year in spring and autumn. During these exercises a joint task force run several training scenarios into anti-submarine and anti-surface warfare, mine counter measures, intelligence gathering, GPS jamming and electronic warfare training.
Here at the Hebridean Whale and Dolphin Trust we are concerned about how these exercises and training scenarios may be impacting the whales, dolphin and porpoise in our waters. We are best placed to assess these impacts as we are the only organisation collecting long term monitoring data in the Hebrides. Military sonar used during these exercises can disturb cetaceans, who live in a world of sound, relying on their hearing to navigate, find food and communicate with one another. This year we are running a series of acoustic surveys where our hydrophone (underwater microphone) allows us to detect marine mammals and monitor underwater sound. During this survey we were also able to monitor any military sonar in the area and assess how this may affect the presence and behaviour of the cetaceans that we encountered.
Silurian set off on the 8th of October and immediately sailed north, where we knew military activity was taking place. As we made our way past the Small Isles and up the Sound of Sleat we encountered several pods of common dolphins that appeared to be feeding in the area. With the weather expected to deteriorate, we sailed for over 11 hours the next day, reaching the Outer Isles that evening so that we were tucked away from the incoming storm. This was definitely the right decision as howling northerly winds hammered the sails constantly throughout the day. With conditions settling down we made our way across the Minch and recorded our first instances of military sonar. We heard sonar consistently throughout the next four days, some of which we could hear through the headphones without even putting them on - from the next room! We could even hear sonar when we were storm bound and tucked away in the Summer Isles.
With the military exercise drawing to a close we decided to head south and survey the waters across the Sea of the Hebrides, before heading south of Mull and collecting data around Colonsay. It was here that we saw the first minke whales of the trip! They were certainly worth the wait as we encountered six individuals in less than an hour, some of which were lunge feeding, displacing huge amounts of water as they gulped down their prey. We ended the trip in Crinan basin, where Silurian will remain for the winter between surveys, getting much needed rest and maintenance work.
In total, we covered over 550 nautical miles and collected over 85 hours of acoustic recordings.
Tracklines showing where Silurian travelled on our lastest acoustic survey
We recorded military sonar on 14% of the track lines conducted on the survey and dolphins whistles on 50%. The hydrophone also picked up over 250 harbour porpoise, with over 1380 individual clicks. Five species of marine mammals were visually recorded including harbour porpoise, common dolphins, minke whales and grey and common seals.
