Scottish Marine and Freshwater Science Vol 7 No 17
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.
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A review of collision risk models revealed a number of key areas where current models could be refined. The model selected for refinement was the modified Band collision risk model (Band, 2000; 2012a; Scottish Natural Heritage, 2016). The avenues identified for refinement of the model were grouped into a number of areas: 1) consideration of site specific detailed information on seal movement and behaviour, 2) the consequences of collision, i.e. relaxing the assumption that every collision would end in death for the animal, 3) evasion and avoidance behaviour in response to the turbine itself, 4) properties of individual turbines, and 5) uncertainty in input parameters. The review revealed that sufficient data were available to inform an assessment of refinements of the model for Areas 1), 2) and 4). For 5) it was concluded that, although uncertainty in some input parameters (e.g. animal density) would be relatively straight forward, explicit incorporation of all sources of uncertainty into estimates of collision and mortality rates would require more resource than was available for this project. There are currently very little empirical data to inform refinements based on 3) evasion and avoidance so all calculations presented in this report assume no avoidance or evasion, with the exception of the comparison in Table 24 in Section 10 where a range of avoidance rates are adopted to provide a comparison to previous estimates.
Marine Scotland Science
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