Marine scientists spent a year listening to the “vast soundscape” created by whales and dolphins off the Scottish coast.  

Researchers recorded the iconic undersea calls and clicks of the ocean-going mammals using sophisticated underwater microphones to better understand when migrating species arrive, how long they stay and when they depart.  

The project will help inform safe development of the undersea environment, such as the placement and mitigation strategies for renewable energy and other human activity at sea. 

It will also provide information about the habits of migrating cetaceans as their behaviour changes in response to warming sea temperatures, and allow an assessment of how well populations are recovering since the end of whaling in the 1950s. 

Already, scientists have been surprised by the number of sie and humpback whales recorded in Scottish waters. 

The researchers heard humpback whales

Common dolphins - pic: Nienke van Geel

Dr Nienke van Geel, a marine mammal expert at SAMS and lead author on the research, said: “At the moment, most of our predictive models on species distribution and population sizes are based on occasional sightings at sea. Visual surveys typically take place inshore and during daylight hours in the summer months, so can’t provide the full picture. 

“We therefore have large seasonal and night-time data gaps for marine mammals in Scottish waters and particularly in that offshore area from the Hebrides out to the continental shelf edge. 

“This year-round acoustic data collection of what’s happening and when is extremely exciting and gives the best indication yet of which 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 sei and humpback whale songs than we had expected.” 

The data collection, funded by the European Marine Fisheries Fund (EMFF) via the Marine Scotland directorate of the Scottish Government, was carried out using microphones between the Hebrides and the continental shelf edge between September 2020 and August 2021. 

Overall, the area covered stretched from Lewis and Barra to the west of St Kilda. 

SAMS marine mammal ecologist and research author 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. 

She said: “As the ocean warms, more species that are adapted to warmer water come north. For example, in recent years we’ve seen more common dolphins follow their prey as they migrate northwards. It will only take a couple more decades for there to be a different species composition in Scottish waters.  

“This kind of data is valuable in explaining how a warming ocean is affecting the movement of cetaceans and their prey, but it is also the best way to find out whether certain species are recovering from the devastating effects of whaling and how we can protect them from current threats, such as entanglement in fishing gear and ocean noise.”