Harbour porpoise (Phocoena phocoena) presence is reduced during tidal turbine operation

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.

A Review of Modeling Approaches for Understanding and Monitoring the Environmental Effects of Marine Renewable Energy

“…Noise levels from the operation of ME devices are generally not anticipated to be high enough to cause injury or hearing loss in marine mammals [1]. Behavioral responses such as avoidance are possible [78][79][80]; this is especially relevant for device arrays, where population-scale effects could occur if noise originates in or near foraging, breeding, or migratory areas [81]. Masking of intraspecific communication or signals of predators or prey is another way in which anthropogenic noise can alter behavior [82].…”

“…Agent-based models require detailed information about both general behaviors (e.g., swimming, diving, foraging) and responses to noise. Information about the latter is relatively scarce; passive acoustic monitoring of harbor porpoises and satellite telemetry of harbor seals have shown reduced density of individuals within the audibility range of operating turbines [79,80], but determining the specific cause of behaviors is complex.…”

“…Marine mammal behavioral responses to pile-driving noise have been monitored using satellite telemetry [78,118] or monitoring of communication such as porpoise clicks [117,125]. More recently, telemetry and acoustic monitoring have been used to monitor movement relative to tidal turbines [13,79,80]. Tagging or other monitoring protocols requiring direct interactions or extensive observations with marine mammals can be resource-intensive and may be regulated [13,120].…”

“…Field observation of animal behavior near turbines has been a fundamental challenge when estimating collision risk, and empirical parameterization of animals' behavior and density in models of collision risk remain rare [174]. Species such as harbor porpoises can be tracked by hydrophone, but such monitoring is limited to species that produce characteristic sounds and provides only partial information [2,79]. Logistical challenges for monitoring many species include inadequate light for video monitoring and acoustic blind spots near operating turbines for hydroacoustic monitoring.…”

“…Information about response behavior is scarce because there have been few operating ME devices, observing behavior near them is difficult, and observing behavior around larger arrays has not yet been possible. Recent studies monitoring porpoises and seals near small tidal turbine arrays have experienced limitations such as a lack of data before turbine installation or during multiple seasons and the inability to distinguish between individuals [79,80]. It is yet unknown how much device design and location affect behavior and thus how much species response data can be generalized.…”