Measuring ADD Noise in TIdal Streams (MANTIS): Could Acoustic Deterrent Devices (ADDs) reduce risk of marine mammal collisions with tidal turbines?

潮汐流海洋可再生能源部门的扩展是可取的，但对周围海洋环境构成潜在风险。一个潜在的风险是海洋哺乳动物和其他物种与旋转的潮汐涡轮机叶片相撞。由于担心这些极具魅力的受保护物种可能因碰撞造成的死亡或伤害，监管机构(包括项目合作伙伴苏格兰海洋[MS]、苏格兰自然遗产[SNH]和自然资源威尔士[NRW])在考虑同意申请时采取了预防措施，导致MRE场地开发速度放缓。如果动物要避免碰撞，它们需要对涡轮机的存在发出足够的警告，以便及时采取行动。由于水流和游泳速度明显限制了视觉探测范围，远距离探测(即警告)将通过声学手段进行。然而，在这些能量旺盛的地方，动物是否能听到涡轮机的声音超过了自然产生的环境噪音(来自水流、泥沙输送和湍流)，还存在不确定性。因此，开发商和监管机构(包括MS)正在考虑是否在涡轮机上增加额外的噪声源，以确保动物可以感知并避开它们。其他行业，如水产养殖、渔业和建筑业，使用声学威慑设备(ADDS)通过发出响亮的、令人厌恶的声音来吓跑海豹和其他动物，使其远离潜在的危险区域。出于这个原因，ADDS目前被认为是减少潮汐涡轮机之间潜在碰撞风险的一种缓解方法。然而，人们担心动物可能长期被排除在大片区域之外，特别是因为潮流MRE涡轮机打算运行数十年，而不是短期。此外，考虑到涡轮机放置的目标环境已经很嘈杂，以及这种情况在潮汐周期中可能会如何变化，目前还不清楚会听到什么范围的增加。因此，迫切需要评估这些环境中ADDS的可探测性(或不可探测性)。总体项目目标是澄清实际潮汐河流环境中商业可用ADD的可探测性如何在与碰撞相关的空间尺度(至少数十至数百米，但可能进一步取决于环境噪声水平)以及在涨潮和大潮周期中变化。对现有潮汐流环境声学数据集的详细分析将使我们能够了解环境噪声水平如何在潮汐周期、与海洋哺乳动物听力相关的频率上发生变化。这将使改进的依赖于距离的声音传播模型得以开发，该模型描述了ADD信号在潮流环境中的传输。然后，将在不同的流动条件下对不同ADD信号的传输进行实验测试，以评估声学可检测范围，验证传播模型，并考虑对海洋哺乳动物的可能影响。这将提高我们对ADDS是否可以提供适当的缓解技术来降低海洋哺乳动物与潮汐涡轮机的潜在碰撞率的理解。这项提案的预期结果的影响将是允许监管项目合作伙伴(苏格兰海洋、苏格兰自然遗产和自然资源威尔士)制定长期的循证政策，将ADDS作为一种实用和相称的手段来减轻潮汐涡轮机可能造成的海洋哺乳动物碰撞风险。这些政策将有助于海洋环境教育部门的长期环境可持续性，并提高苏格兰和威尔士履行其在养护海洋哺乳动物和其他可移动海洋物种方面的(国家间)义务的能力。

Expansion of the tidal-stream marine renewable energy (MRE) sector is desirable but poses potential risks to the surrounding marine environment. One potential risk involves marine mammals and other species colliding with rotating tidal turbine blades. Concern about potential collision-driven mortality or injury of these charismatic protected species has led to regulators (including project partners Marine Scotland [MS], Scottish Natural Heritage [SNH] and Natural Resources Wales [NRW]) adopting a precautionary approach when considering consent applications, resulting in a slowdown in MRE site development. If animals are to avoid collision they will need sufficient warning of turbines' presence to take timely action. With water flow and swimming speeds significantly restricting visual detection ranges, long-range detection (i.e. warning) will be through acoustic means. However there is uncertainty over whether animals can hear turbines over naturally occurring ambient noise in these energetic sites (from water flow, bed load transport and turbulence). As a result, developers and regulators (incl. MS) are considering whether to add extra noise sources to their turbines to ensure animals can perceive and avoid them. Other industries such as aquaculture, fishing and construction use Acoustic Deterrent Devices (ADDs) to scare seals and other animals away from potentially dangerous areas by producing loud, aversive sounds. For this reason ADDs are currently being considered as a mitigation method to reduce potential collision risk among tidal turbines. However, concerns exist regarding potential undue long-term exclusion of animals from large areas, especially as tidal-stream MRE turbines are intended to operate for decades rather than short periods. Furthermore it is not clear over what range ADDs will be audible given the already noisy environments targeted for turbine placement, and how this might vary over the tidal cycle. There is therefore an urgent need to assess the detectability (or not) of ADDs in these environments.The overall project objective is to clarify how the detectability of commercially available ADDs in real tidal-stream environments varies across collision-relevant spatial scales (at least tens to hundreds of metres, but potentially further dependent on ambient noise levels) and across the ebb-flood and spring-neap tidal cycles. A detailed analysis of existing acoustic datasets from tidal-stream environments will allow us to understand how ambient noise levels vary across tidal cycles across frequencies relevant to marine mammal hearing. This will allow development of improved range-dependent sound propagation models describing ADD signal transmission in tidal-stream environments. The transmission of different ADD signals will then be experimentally tested under varying flow conditions to assess ranges of acoustic detectability, validate propagation models and consider likely impacts on marine mammals. This will improve our understanding of whether or not ADDs could provide a suitable mitigation technique to reduce potential collision rates of marine mammals with tidal turbines. The impact of the expected outcomes of this proposal will be to allow the regulatory project partners (Marine Scotland, Scottish Natural Heritage and Natural Resources Wales) to develop long-term evidence-based policies concerning the use of ADDs as a practical and proportionate means to mitigate marine mammal collision risk potentially posed by tidal turbines. Such policies will contribute towards long-term environmental sustainability of the MRE sector and improve Scotland's and Wales' ability to fulfil their (inter-)national obligations in terms of conservation of marine mammals and other mobile marine species.