Acoustic insights: monitoring Scotland’s cetaceans on stormy seas
Over five days at sea, our intrepid team of citizen scientists surveyed waters around Ullapool through storms and swell, gathering vital visual and acoustic data.
Each field season (April - Oct), we set sail on research expeditions across Scotland’s west coast, inviting passionate individuals to join us in safeguarding marine life. By collecting vital data, these hands-on voyages are helping to deepen the understanding of species and drive real change to protect the marine mammals of Scotland’s seas.
Over five days aboard Silurian, our team of citizen scientists experienced the full drama of the Hebrides; gale-force 8 winds, sudden rainbows, storm-driven swells, and surprise sightings! Amidst it all, we gathered vital visual and acoustic data, adding to HWDT’s long-term monitoring of whales, dolphins and porpoises.
Small pods of common dolphins joined Silurian, bow-riding and leaping through stormy seas, and a lunge-feeding minke whale thrilled near Isle Martin! Harbour porpoise, grey and common seals were spotted in sheltered waters, while seabirds - gannets, guillemots, razorbills, kittwakes and geese - filled the skies. Even a submarine made a surprise appearance near Rubha Reidh. From storm gales to minke whales, and from rainbows to birthday cake at sea, this was a voyage to remember.
Despite the challenging conditions, the crew aboard Silurian surveyed 277km of Hebridean waters, gathering 24 hours of visual and acoustic data through stormy seas. Five species of marine mammal were encountered across 26 sightings, including grey seals, common seals, harbour porpoises, common dolphins, and minke whales. 323 creels were recorded alongside 4 pieces of rubbish.
As sea state, visibility and swell height frequently combined to create ‘poor’ visual conditions for surveying, acoustic monitoring is a fantastic way to gather data and strengthen our understanding of Scotland’s whales, dolphins and porpoises.
Cetaceans live in a world of sound. Unlike us, they rely far more on listening than on sight. Dolphins and porpoises use echolocation clicks to navigate and hunt, while whales produce a variety of calls to communicate, find mates, and maintain social bonds.
Because so much of their behaviour happens below the surface, visual surveys alone can’t capture the full picture. This is where acoustic monitoring comes in:
Detecting the unseen: Hydrophones allow us to detect animals even when sea state, poor light, or swell make visual sightings impossible.
Understanding behaviour: Different sounds reveal different activities - from foraging clicks to social calls.
Tracking presence and movement: When and where species use certain habitats, even at night or in poor weather.
Measuring human impact: Acoustic data helps us understand how underwater noise from vessels or industry overlaps with the soundscape cetaceans rely on. Acoustic data also allows us to monitor the changing marine soundscape and the impact human activity is having on sound levels below the waves.
This is a screenshot of the PAMGuard Click Detector screen displaying a porpoise click detection (red triangles) amongst unidentified detections (black dots).
Using our towed hydrophone array and PAMGuard software, we were able to detect the presence of harbour porpoises even when they weren’t visible at the surface. Porpoises produce high-frequency echolocation clicks, far beyond the range of human hearing, which PAMGuard automatically detects and displays in real time. These detections confirm the species’ presence during poor visual conditions, evidence the use of specific areas by porpoises, and provide valuable information on distribution and activity. Acoustic monitoring like this ensures that quieter, less conspicuous species such as harbour porpoises are represented in our long-term dataset, even when the sea state makes visual sightings difficult. This is especially important as harbour porpoises are Scotland’s most abundant cetacean, yet often overlooked due to their small size and elusive surfacing behaviour.
Survey trackline from HWDT13.
A HUGE THANK YOU TO OUR TEAM OF CITIZEN SCIENTISTS WHO JOINED THIS EXPEDITION: NICKY, SILKE, PAUL, CHRIS, KATHY & RON