Marine mammals in the Anthropocene : informing management, planning and conservation

Abstract

Anthropogenic activities are ubiquitous in the world’s oceans. Understanding the scale and occurrence of threats, and their associated impact(s), is challenging, given many threats are mobile (e.g. maritime vessels), have a heterogenous distribution, and marine species differ in their vulnerability to each particular threat and stressor. Further, marine species, such as marine mammals, are often mobile and inherently cryptic, with heterogenous abundance across their range. The inherent challenges related to studying marine mammals and their threats has limited our understanding of anthropogenic threats to whales, dolphins and seals, and may ultimately result in conservation and mitigation efforts being insufficient or inappropriate. To contribute new understanding on this topic, this first chapter of this thesis develops an evidence base, via a systematic mapping process, to collate currently available knowledge relating to how anthropogenic threats affect nineteen marine mammal species. The resulting outputs highlight a disparity in the volume of records between species, geographic areas, and threats. The potential reasons and implications of such heterogeneity are discussed, and recommendations are provided for filling such gaps. The next chapter evaluated how multiple stressors to marine mammals are considered within the UK’s environmental assessment process. Many maritime industries (such as harbour or renewable energy developments) are legally required to conduct cumulative effects assessments (CEAs) in order to gain consent to carry out certain potentially impactful activities. However, comparison of CEAs found disparity in practice between sectors, despite them occupying broadly the same ocean space and potentially impacting the same marine mammal species. Again, I provide recommendations that will help to standardise practice when it comes to predicting cumulative impacts to marine mammals. Vessels are evidenced to pose multiple potential risks to marine megafauna, including underwater noise, disturbance and fatal or injurious collision. However, the data available to understand this risk is limited. Lack of data can preclude threats from being sufficiently considered within risk or impact assessments and consequently, management efforts. To this end, the remainder of this thesis focuses on exploring approaches to capture data on vessel presence and movement, to later allow for a more holistic evaluation of the occurrence of vessels, and the associated threat this poses to the marine environment. In these chapters, I explore whether the most commonly used vessel data (automatic identification system (AIS)) is reflective of real-world traffic, and thus sufficient for assessment and monitoring. Data gathered between 2019 and 2024 by trained volunteers under the ‘Scottish Vessel Project’ show that AIS data only represented 43% of vessel traffic in coastal areas, 41% of vessel traffic co-occurring with marine mammals, and 36% of vessel traffic in Marine Protected Areas. This new understanding of the volume and occurrence of all vessel traffic can support the more robust quantification of threats associated with vessels in Scotland’s coastal seas, including strike risk, disturbance and noise exposure. Together, this thesis identifies a number of knowledge gaps with regard to our current understanding of threats posed to marine mammals and the wider marine environment, particularly with in regard to evidence of threats from anthropogenic activities (Chapter 2), the way threats to marine mammals are considered by impactful maritime sectors (Chapter 3), and the data available to characterise threats (Chapters 4-6). Throughout, tailored recommendations are provided to address the evidence gaps identified, which, if implemented, could ultimately support the development of more effective threat mitigation measures.