There is currently considerable uncertainty regarding the potential for lethal and injurious interactions between marine mammals and tidal turbines. This uncertainty is particularly concerning for harbour seals in the Orkney and North Coast management unit, where the population has been undergoing a protracted decline. This has led to constraints being placed on tidal developments in this area until more information is available on the real risks presented to this species by tidal turbines.
The aim of this research project was to provide improved assessments of the level of mortality to harbour seals potentially caused by tidal turbines in the Pentland Firth and Orkney Waters region, using recently available information from a number of areas of work. These include the consequences of collision for individuals, detailed information on tidal flow, updated tidal turbine parameters and data on temporal and spatial variation of harbour seals within the water column. Specifically, this project was developed to review the assessment process to determine areas where inputs could be refined to improve estimates in the short term; and to use the outputs of these reviews to generate an updated model that is fit for use to estimate the no-avoidance collision rates between seals and tidal turbines. Finally, this updated model was applied to an agreed envelope of consented tidal energy projects in the Orkney and Pentland Firth region. This envelope consisted of two projects: the MeyGen Phase 1a array of four turbines at the Inner Sound in the Pentland Firth, and the multiberth European Marine Energy Centre (EMEC) tidal test site at the Fall of Warness, Orkney.
In this report the word ‘collision’ is used to refer to the situation in which a transit through the swept area of a turbine would be predicted to result in physical contact between the marine mammal and the turbine blade. Unless otherwise specified, this refers to ‘no-avoidance’ collision, assuming no avoidance or evasive action is taken by the animal. This is the same as the definition of the term ‘encounter’ in Wilson et al. (2007), however here the word collision is chosen rather than encounter (unless specifically referring to the Wilson et al., 2007 model) because ‘encounter’ could be interpreted as an animal coming close to the device but without actual contact whereas ‘collision’ better reflects the potential for actual physical contact between the device and the animal that is the aim of the prediction. Where the text refers to ‘collision risk’, this is the probability of collision for an animal when ma king a single transit through the swept area of a turbine. Once account is taken of the likely number of such transits, ‘collision rate’ is the overall number of collisions estimated within a given period (usually one year).