Marine mammal bycatch in southwest England: Taking a holistic approach to assess causes, impacts and evidence-based solutions

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Background: The Cetacean Strandings Investigation Programme (CSIP) at ZSL has been running since 1990 and is funded by Defra and the Devolved Government of Wales. It coordinates the investigation of all whales, dolphins and porpoises, marine turtles, seals and large bodied sharks that strand around the English and Welsh coastline. As well as documenting each individual stranding, they conduct post-mortem examinations to investigate causes of death and learn more about the threats large marine vertebrates face in UK waters. Since its inception in 1990, CSIP have noted that accidental entrapment of marine mammals in commercial fisheries (bycatch) has been a consistent finding in every year of study and represents the largest direct anthropogenic driver of mortality in stranded cetaceans examined at necropsy (n=782, 1990-2019, data UK strandings dataset). The southwest of England and Wales, particularly Cornwall, is a hotspot for bycatch-related mortality. For example, 64% of all bycatch cases diagnosed in UK of stranded common dolphins examined at post-mortem examination (1990-2019) were recorded in Cornwall. During 2020, approximately one-third of post-mortem examinations of stranded cetaceans in Cornwall were diagnosed as bycatch cases.It is likely that bycatch in the region is driven by multiple sectors and multiple fleets impacting on species across the region; and inside/outside of the UK Exclusive Economic Zone (EEZ). Marine mammals from across the wider north Atlantic region, including common dolphins, harbour porpoises and grey seals, are known to succumb to bycatch in this area. Bycatch is therefore an international issue impacting marine mammals at regional, national and international levels. In addition, locally discrete and small marine mammal populations (e.g. coastal/inshore bottlenose dolphin communities) will be highly vulnerable to any bycatch-related mortality. Bycatch may therefore also pose a significant conservation issue for some species/populations.There is currently relatively limited information on the main drivers of bycatch in the area, and information such as the spatial and temporal overlap between species distributions and fisheries, and the types of gear used are essential for informing policies aimed at managing the threat.Aims and Approach: This project would take an interdisciplinary approach to informing our understanding of marine mammal bycatch in southwest waters. There is scope for the student to develop the specific objectives of the project depending on their skills and interests but suggested aims include;1) Ecology/Pathology: Assess the existing evidence base for gear types thought to impact on cetaceans in the region. Determine whether additional forensic evidence of bycatch could be gathered during investigation of strandings to help improve data collection and diagnosesa. The student would work with strandings scientists and veterinary pathologists from CSIP and the wider UK strandings network to design a series of experiments to test how interactions with different gear types may present in bycaught animals.b. Assess existing sources of bycatch, strandings and other ancillary data to synthesise a more holistic understanding of bycatch related impacts across different marine mammal species, including temporal and spatial variation.2) Oceanography: Develop methods for identifying potential factors that may influence the spatio-temporal patterns of bycatch-related strandingsa. By inverted particle tracking within a numerical coastal ocean model, backwards track bycaught animals from their stranding location to estimate the potential location for the animals interacting with fishing gearb. Identify the spatial extent of 'high risk' fishing activities in southwest regional waters using a number of data sources (e.g. Inshore Vessel Monitoring data and landings information).3) Policy analysis: Develop policy options to support design improvement and potential solutions