Authors of a recently published study discuss how their research discovered that seals exhibit avoidance of turbines during operation. This finding is important for industry developers and regulators, as lower numbers of seals close to the turbine reduces the potential for fatal collisions and injuries.
The rise of the tidal energy industry
The marine renewable energy sector is growing rapidly. Offshore wind is well established, and focus is now turning to other sources of energy, in particular wave and tidal. Tidal energy is a predictable resource, in terms of its location, timing and power. There are several designs of tidal turbines on the market, but most resemble a small wind turbine either mounted on the seabed, or floating at the sea surface, and have fast-moving blades that rotate at speeds of over 5m/s.
There is increasing evidence to suggest that marine mammals, including seals, are attracted to areas of high tidal flows for foraging. Therefore, as the industry expands, there is an inevitable overlap with areas used by marine mammals. This overlap raises a pressing question: what are the risks to seals from the rotating blades of tidal turbines? Previous research showed that turbine blades could injure a seal, so the question is whether or not animals show sufficient avoidance of operational turbines and limit the risk of collision between seals and the rotating blades.
New technology to monitor underwater animal movements
To determine how seals respond to such devices and assess the risk of collision, data are required on numbers and behaviour of seals present in close proximity to the turbine. However, due to the difficulty of collecting data in this challenging environment (high flow speeds and underwater), there has been a lack of data on behavioural responses of animals to tidal turbines.
A relatively new continuously is by using multibeam imaging sonars. Sonar, (Sound Navigation and Ranging) works by sending out sound waves and interpreting the echoes that bounce back, working similarly to radar technology. While radar is commonly used above water—sonar is its underwater counterpart. Multibeam imaging sonars allow for high-resolution monitoring of the turbine to take place 24/7, 365 days a year and be used to detect and track ‘targets’ in the data with high spatial accuracy.
Seal presence around the turbine
To measure the nature and number of interactions between seals and a tidal turbine, two multibeam imaging sonars were mounted on a seabed platform to monitor a tidal turbine located in the Pentland Firth, Scotland, for a year.
We observed 704 seals swimming close (within ~ 30 m) to the tidal turbine across a full year of monitoring. Analyses showed that seals were less likely to be present during high tidal flows (>2.3 m/s), during hours of daylight, and during the summer months (May-August).
Our findings also revealed a reduction in the numbers of seals around the turbine when it was operating (and the blades would be rotating), which is when risk of injury or mortality caused by a collision would be at its highest. This result combined with seals less likely to be close to the turbine at higher flow speeds (when the turbine is likely to be operating), reduces the risk of collision between seal and turbine.
Our research showed that irrespective of turbine operation, seals were less likely to be present at high flows. When the turbine was operational, there was a further reduction in seal presence of up to 77% indicating that seals are aware of, and avoid, the operating turbine.
Why avoidance matters
These results are important for developers and regulators, as lower numbers of seals close to the turbine at higher flow speeds during operation decreases the potential for fatal collisions and injuries. This, together with the new information on the temporal variation in the presence – over daily and annual cycles – can be used to predict the potential impacts of future tidal turbine developments.
This work was made possible thanks to the Natural Environment Research Council, the Scottish Government, SAE Renewables and MeyGen. In particular, we thank Fraser Johnson for all his support and guidance throughout the study.
Read the full article, “Seals exhibit localised avoidance of operational tidal turbines” in Journal of Applied Ecology.
