Harbour porpoises exhibit localized evasion of a tidal turbine

Abstract

Tidal energy generators have the potential to injure or kill marine animals, including small cetaceans, through collisions with moving turbine parts. Information on the fine scale behaviour of animals close to operational turbines is required to inform regulators of the likely impact of these new technologies. Harbour porpoise movements were monitored in three dimensions around a tidal turbine for 451 days between October 2017 and April 2019 with a 12‐channel hydrophone array. Echolocation clicks from 344 porpoise events were localized close to the turbine. The data show that porpoises effectively avoid the turbine rotors, with only a single animal clearly passing through the rotor swept area while the rotors were stationary, and none passing through while rotating. The results indicate that the risk of collisions between the tidal turbine and porpoises is low; this has important implications for the potential effects and the sustainable development of the tidal energy industry.

Biological Consequences of Marine Energy Development on Marine Animals

“…The alteration or loss of pelagic habitat caused by well-sited marine energy will be small and animals are likely to adapt to these changes quickly. These pelagic animals are, however, more likely to be susceptible to injury or death from a rotating tidal turbine blade, although it is generally thought that collision with blades is likely to be very rare, based on the space available around devices in addition to the sensory, behavior, and swimming capabilities, such as evasion, of the pelagic species [6,81]. Additional observations and validated models of turbine blade encounter and collision are needed to better understand this dynamic, and mitigation strategies may be needed to lessen the likelihood or severity of such encounters.…”

“…Their ability to hear, locate, and respond to tidal turbines at a distance will modify their risk of collision, and fatal injuries are unlikely [8]. Collision risk and underwater noise from marine energy devices may cause severe injury or death to harbor porpoises; however, no increase in injured or dead porpoises has been observed near marine energy sites [6,50,51]. Recent research indicates that harbor porpoises have the ability to avoid tidal turbines in close proximity, which will limit their risk of collision [6].…”

“…To date, most efforts to relate the potential effects of marine energy on the environment have been approached from the perspective of the stressors, or portions of a device and associated systems that could cause stress, injury, or death to marine animals, or irreparable harm to habitats [5]. The large number of groups and species of marine animals and varied habitats that could be at risk from marine energy devices have limited the number of studies that examine the interactions from the point of view of the receptors (the animals and habitats that might be harmed by the devices and systems), except in very localized and species-specific instances [6][7][8][9], as well as in a small number of review papers (e.g., [10]).…”

A review of the UK and British Channel Islands practical tidal stream energy resource

“…In general, for a small number of marine mammal species, monitoring around single turbines and small arrays has provided evidence of avoidance in the range of hundreds to thousands of metres, which would lead to lower estimates of collision risk compared with worst-case assumptions [96][97][98][99][100]. A recent study provided the first evidence for fine-scale evasion of an operational tidal turbine by harbour porpoises [101]. Monitoring has provided evidence that some species of fish aggregate around turbines during periods with low current speeds, possibly to use the structure for shelter from the flow or for feeding strategies [102].…”

“…In general, for a small number of marine mammal species, monitoring around single turbines and small arrays has provided evidence of avoidance in the range of hundreds to thousands of metres, which would lead to lower estimates of collision risk compared with worst-case assumptions [96][97][98][99][100]. A recent study provided the first evidence for fine-scale evasion of an operational tidal turbine by harbour porpoises [101].…”