Since tidal turbine technology was developed to generate clean electricity, conservationists have been concerned about wildlife collisions.
The blades spin super fast underwater, and it is important to be aware of the risks to sea life. In Scotland, seals are being tracked in the fast-flowing waters, but it is a tricky process near the active machinery.
Researchers needed to measure the actual risk, so they attached automated sonar to a turbine frame underwater. When seal movements through the channel were counted, they came to 704. How did the seals make it out without coming into contact with the blades?
How marine mammals are tracked in high-velocity waters
Normal cameras do not operate well in the low light and high silt levels around the turbine in the tidal channel. The monitoring problem was solved with multi-beam acoustic sonar.
The system provided almost continuous sonar monitoring and precise horizontal tracking around the turbine, though vertical information was limited.
The study saw 704 individual seal passes logged between May 2022 to June 2023 at the MeyGen tidal energy site in the Inner Sound of the Pentland Firth in Scotland.
Most of the animals stayed far away from the spinning blades. They either swam deeper to get under the turbine or they changed course to get around it before they got close. This meant that they stayed out of the danger zone completely.
However, there were a few that got much closer than most of the seals. The cameras recorded 16 events where the seals swam right into the plane of the blade motion.
The animals were now in the rotor collision zone, in theory.
Tracking logs allowed the researchers to isolate the few specific encounters, and now they have a better understanding of how seals behave in the vicinity of underwater rotors.
Rotor sweep encounters must be evaluated for wildlife safety insights
In the past, impact models have assumed that any marine mammal that gets in the way of an operating rotor will either be seriously injured or killed.
The steel blades weigh several tons, and when they sweep through the water, they become a mechanical obstacle in the path of seals diving in the water.
The 16 close passes that were recorded with sonar offer empirical data for testing collision assumptions. Acoustic reconstructions were also drawn up so that the seals’ exact trajectory could be recorded while they navigated the blades in real-life situations.
While no direct collisions were observed and most high-risk seals appeared to avoid the turbine blades, sonar limitations prevented researchers from ruling out collisions in every instance, leaving a few high-risk outcomes uncertain.
It is an unexpected outcome that has drawn attention to seals’ specific maneuvers and how they get through the turbine area unharmed.
Micro-avoidance tactics and hydraulic clearances prevent strikes
Reconstructing the acoustic tracks demonstrated fine-scale avoidance around the turbine, with seals swimming above or below rotor depth, turning sharply before reaching the blades, or passing horizontally rather than executing timed maneuvers between individual blades.
Because subsea tidal rotors turn relatively slowly, wide temporal gaps exist between passing blades, allowing seals to swim safely through open water intervals.
Real-world collisions are lower than models predicted
These fine-scale shifts enabled all 16 seals to reach the surface without physical impact.
Still, key scientific limitations remain.
Sonar tracks cannot confirm whether seals visually perceived the moving blades or simply reacted to localized hydrodynamic pressure changes.
Additionally, these 16 events reflect specific tidal velocity conditions at a single Scottish installation.
Observing 16 successful passes confirms that wild seals actively execute fine-scale micro-avoidance around operating tidal turbines, demonstrating that real-world collision risk is far lower than static predictive models previously suggested for this specific subsea installation site.
The full study can be read here: Montabaranom, J., Gillespie, D., Sparling, C., Longden, E., & Hastie, G. (2026). Evaluating the Risk of Collision of Seals Swimming Within Metres of Operating Tidal Turbines. Aquatic Conservation: Marine and Freshwater Ecosystems, 36(2), e70326.
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