Over half of vessels operating in Scotland’s coastal waters are effectively “invisible”
to standard maritime tracking systems, according to a new Heriot-Watt University
study.
Researchers say only 43% of vessels within 10 km of the Scottish coast broadcast an Automatic Identification System (AIS) signal, the standard global tool to monitor ship movements.
The figure is even lower for the Western Isles according to the study which claims only 20% of vessels observed during the study hours were transmitting AIS data, despite the area being a hotspot for ecotourism, fishing, and aquaculture.
The Heriot-Watt team says this lack of visibility poses significant risks to marine
life, safety, and sustainable ocean management.
Smaller vessels, such as fishing boats under 15m, recreational craft, and jet skis, accounted for much of the missing data. They are not legally required to carry AIS.
The study, which relied on over 1,800 hours of land and sea surveys conducted between 2019 and 2024, covered nine of Scotland’s 11 marine regions and showed huge regional and seasonal disparities in AIS visibility.
It was published in the academic journal Marine Policy.
Much of the data was collected by citizen scientists from several organisations; volunteers were trained to follow a standardised method to survey and quantify ships.
Volunteers from the Hebridean Whale and Dolphin Trust, Whale and Dolphin Conservation Shorewatch in Shetland, and the Community of Arran Seabed Trust all participated.
Dr Emily Hague from Heriot-Watt’s School of Energy, Geoscience, Infrastructure and
Society said: “This data challenges the assumption that we can rely on AIS to tell
us what’s really happening in our coastal seas.
“In some areas, over 75% of vessel activity goes unrecorded.”
The study highlighted significant regional variations. Compared to the Outer Hebrides rate of 20% of vessels observed transmitting AIS data, Orkney Islands showed 58% of vessels broadcasting.
In the Forth and Tay, home to some of Scotland’s busiest ports, AIS coverage reflected
true traffic only 8% of the time, raising questions about under-represented commercial
and recreational traffic.
Dr Hague said: “AIS data is used by governments, conservation bodies and researchers
to model vessel-related impacts such as underwater noise pollution, whale and dolphin
collision risk, anchor damage to the seabed, greenhouse gas emissions and climate
impact.
“But if over half of vessel movements in inshore waters are missing, existing models may be severely underestimating these impacts. This could lead to inadequate management, conservation and safety policies."
Dr Lauren McWhinnie said: “Scotland’s coasts are a vital habitat for species like bottlenose dolphins, minke whales and orca. Without accurate data, it’s difficult to assess and mitigate threats to these species.”
The authors suggest that where there are high volumes of non-AIS vessels, AIS data
should be supplemented with other tracking methods, such as land-based observations
and citizen science, to build a complete picture.
Dr McWhinnie said: “Ideally, even smaller vessels would broadcast their position using AIS.
“Improving data will benefit coastal communities, providing information that will
allow them to balance tourism and other vessel-based activities with local sustainability
and environmental objectives.
“It will also enable researchers and conservation groups to provide better evidence when it comes to measures for protecting marine life.
“With an improved understanding of the activities and movement of different types of vessels, marine planners and policymakers could tailor regulations to maximise their potential effectiveness.
“The wider maritime sector could further benefit through improved safety and awareness.”
80% of marine traffic off the Hebrides ‘invisible’ to tracking according to study
17 April 2025