MARINE scientists have for the first time captured the vast soundscape of whales and dolphins off the west coast of Scotland, over an entire year.
A research team led by the Oban-based Scottish Association for Marine Science (SAMS) deployed underwater microphones between the Hebrides and the edge of the continental shelf between September 2020 and August 2021.
Known as passive acoustic monitoring, the microphones picked up sounds from a range of marine mammals, including dolphins and fin whales, minke whales, humpbacks and sei whales.
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The data collection, funded by the European Sea Fisheries Fund (EMFF) through the Scottish Government’s Marine Scotland Directorate, will help explain when migratory species arrive in Scottish waters, where they spend their time and how long they stay .
This information is crucial for regulators and advisers, such as Marine Scotland, as it will inform investment and mitigation strategies for renewable energy developments and other human activities at sea.
This will also assess how well populations are recovering since whaling ended in the 1950s. As sentinel species, cetacean movements can also show how climate change is affecting the ocean ecosystem. .
The results were published in a report titled Monitoring cetacean occurrence and variability in ambient sound in Scottish offshore waters in the journal Frontiers in Remote Sensing.
Dr Nienke van Geel, marine mammal expert at SAMS and lead author of the publication, said: “At the moment most of our predictive models on species distribution and population size are based on occasional observations in sea.
“Visual surveys usually take place near the coast and during daylight hours during the summer months, so we cannot provide a full picture.
“So we have large seasonal and night-time data gaps for marine mammals in Scottish waters and in particular in this area off the Hebrides to the edge of the continental shelf.
“This year-round collection of acoustic data on what is happening and when is extremely exciting and gives the best indication yet of the species we have in our own waters.
“For example, we detected a lot of dolphin activity – their sounds were detected almost daily throughout the year at some sites. There was also more whale and humpback whale song than we had intended.
The research team included scientists from Marine Scotland and the University of Plymouth and was carried out with the help of SAMS Enterprise and boat operator Seatrek Marine Ltd. To collect more than 12 terabytes of data, the team deployed 10 underwater microphones at depths between 60 and 175 meters, covering an area that stretched from Lewis and Barra west of St Kilda.
The researchers then used a combination of manual analysis of sound files and automated detection software to detect the species of interest. They also analyzed and compared the overall sound levels of the recordings and identified sources of natural sound from wind, rain and tides, as well as man-made noise, including noise from ships, echo sounders and military sonar.
The sound files collected will provide key baseline data for offshore developments such as wind farms, but will also feed into longer-term marine mammal distribution models under various climate change scenarios.
SAMS marine mammal ecologist and author of the publication, Dr Denise Risch, said: “Continued funding for such acoustic monitoring would be needed to provide crucial long-term data to help measure changes in the environment. .
“As the ocean warms, more species adapted to warmer waters are moving north. For example, in recent years we have seen more and more common dolphins following their prey as they migrate north.
“It will only take a few more decades for there to be a different species composition in Scottish waters.
“This kind of data is valuable for explaining how a warming ocean affects the movement of cetaceans and their prey, but it’s also the best way to know if certain species are recovering from the devastating effects of whaling and how we can protect them. current threats, such as entanglement in fishing gear and ocean noise.”