Abstract
Abstract Uptake of tidal turbine technology to generate renewable energy has been partly limited by poor understanding of ecological impacts, including the potential for collisions between cetaceans and rotating turbine blades. To address this concern, it is necessary to identify whether cetaceans behaviourally respond to operating turbines. A turbine in Scotland was instrumented with hydrophones to detect cetacean vocalizations. A generalized additive model was used to investigate temporal variability in harbour porpoise presence close to the turbine. As there were incidentally periods when the turbine was not operating, it was possible to determine the effect of blade rotation, whilst accounting for the potentially confounding effect of tidal flow. Harbour porpoise presence varied intra‐annually, diurnally and with tidal state. Peak presence occurred during winter (September–February), at night and at high flow speeds on the flood tide. Porpoises exhibited significant avoidance of the tidal turbine when it was operating; avoidance increased with flow speed, whereby mean porpoise presence was reduced by up to 78% (95% CIs, 51%, 91%) on the flood tide and up to 64% (95% CI, 3%, 91%) on the ebb tide. The temporal variability in encounter rate in the present study highlights that collision risk assessments assuming static densities probably fail to capture the temporal variability of collision risk. Future studies should conduct long‐term baseline monitoring to derive encounter rates at larger spatio‐temporal scales and as a reference from which to measure change in habitat use. It is also critical that the generality of the avoidance rates presented here is assessed for other sites, turbine types, array sizes and cetacean species. As the tidal industry expands, it will be important to reconcile the benefits of avoidance responses from a collision risk perspective with potential chronic effects of displacement from, or barriers between, important habitats.
Highlights
In response to climate change, ambitious green energy targets have driven the expansion of the offshore renewable energy sector
Porpoises exhibited significant avoidance of the tidal turbine when it was operating; avoidance increased with flow speed, whereby mean porpoise presence was reduced by up to 78% on the flood tide and up to 64% on the ebb tide
Porpoise presence was reduced by up to 78% within tens to 150 m of Whilst the percentage of deviance explained by the model was relatively low (9%), there was sufficient statistical power to identify a significant behavioural response to operation of the turbine
Summary
In response to climate change, ambitious green energy targets have driven the expansion of the offshore renewable energy sector. Noise emitted by tidal turbines (Schmitt et al, 2018; Pine et al, 2019) could lead to disturbance, resulting in habitat displacement or barrier effects, and there is potential for fatal collisions with turbine blades, as has been observed in the wind farm industry for birds (Zimmerling et al, 2013) and bats (Johnson et al, 2004). To assess whether these concerns are valid, data on the occurrence and movements of porpoises and dolphins around operational tidal turbines is urgently required.
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