IAP2-22-481

Migratory patterns, diets, and death in stranded British odontocetes revealed through molecular and isotopic signatures

Background: Climate change poses an active threat to marine species worldwide, and British large marine animals in particular (Evans and Waggitt 2020). Warming ocean temperatures since about 1990 have altered these animals’ – including porpoises, dolphins, and toothed whales (i.e., odontocetes) – ecological distributions and impacted their health through changes in regional habitats and preferred prey availabilities (Thorne et al. 2022). As ‘sentinels’ of the ocean environment (Bossart 2006), odontocetes are considered important indicators of marine ecosystem health at local-to-larger scales, and their ecology and conservation is currently a topic of global interest (Williamson et al. 2021).

Ocean warming is actively restructuring patterns of habitat distribution in oceans worldwide and has especial impacts on odontocetes with respect to migratory pathways (c.f., beaked whales [van Weelden et al. 2021]) and interspecific competition (c.f., harbour porpoises and dolphins). Indeed, there is a clear increase in frequency of British warmer-water adapted large odontocete sightings and stranding events over the past three decades (Williamson et al. 2021), which might be related to changes in distribution and diet (van Weelden et al. 2021) through warming sea surface temperatures.

Based on sightings and historical stranding data, the more common warm-water cetaceans around British waters include harbour porpoise (Phocoena phocoena), short-beaked common dolphin (Delphinus delphis) and Sowerby’s beaked whale (Mesoplodon bidens). Common cold-water cetaceans include long-finned pilot whale (Globicephala melas), white-beaked dolphin (Lagenorhynchus albirostris), and sperm whale (Physeter macrocephalus). Despite habitat differences, in the northeast Atlantic, stomach contents of these species indicate overlapping prey preferences, although key questions about time since ‘last supper’ in stranded odontocetes remain open. By incorporating stable isotope analysis of tissue samples from stranding samples, further quantification of dietary niche and identification of specific feeding grounds is possible, allowing further monitoring of migration and competition. Multi-tissue isotopic analysis would furthermore determine feeding trajectory and timeline immediately prior to death. With this in mind, hydrogen and carbon stable isotope signatures of lipids and bulk tissue are exemplary proxies for gathering longer-term ecological data on these cosmopolitan and highly mobile animals (Whiteman et al. 2019).

Aims: We propose to use stable isotope signatures of lipids (δD and δ13C for e.g., alkanoic [fatty] acids) and bulk skin (δ13C and δ15N) from common species of stranded cold-water (G. melas, L. albirostris and P. macrocephalus; n >50 each) and warmer-water (P. phocoena, D. delphis and M. bidens; n >50 each) adapted Odontoceti species spanning 1992-2022 to reconstruct feeding grounds and dietary patterns in important British cetaceans. With these data, we aim to identify general foraging pathways and define ecologic stressors (i.e., overlapping prey preferences) that should be monitored. This research is crucial to establish an ecological framework for conservation management towards sustainable marine communities.

Methodology

This research will take advantage of state-of-the-art techniques in gas chromatography (GC) and mass spectrometry (MS) to characterize individual diagnostic whale-derived lipids – called ‘biomarkers’ – from skin and blubber samples in specimens recovered from regional British coastlines. Lipids will be extracted (via accelerated solvent extraction [ASE]) before isolation of biomarkers via ‘flash’ columns and liquid chromatography (LC) techniques. Target biomarkers will include metabolic compounds derived both from diet (e.g., omega-6 fatty acids) and from de novo synthesis (e.g., cholesterol) to maximise ecological insights. The PhD candidate also will have opportunities to optimise analytical techniques to enable complementary (geo)chemical detection of further compounds, such as hormones viz. oestrogens, and bulk isotopic analyses.

Inceptive samples are available or in-hand for this project, enabling the PhD candidate to start their analyses at the project’s start. The PhD candidate will likewise have opportunities to engage in regional fieldwork in Years 1 and 2 to augment their sample collection and furthermore interact with key partners and their respective scientific networks. Multidisciplinary project foci and fieldwork together with immediate policy relevance means collaboration will be crucial for the success of this endeavour, which will foster rich knowledge exchange and networking opportunities.

Project Timeline

Year 1

Literature review and techniques training. Fieldwork with Scottish Marine Animal Stranding Scheme (SMASS), followed by initial odontocete cetacean sample processing and analysis.

Year 2

Continued processing, collection and analysis of samples. Dissemination of initial findings at national conference and submission of first publication.

Year 3

Finalisation of data collection and interpretive directions. Thesis writing. Dissemination of results.

Year 3.5

Time devoted to thesis writing and publications.

Training
& Skills

This project will equip the student with a range of skills, including advanced lipid biomarker analysis, collaborative collections and fieldwork, ‘big data’ analysis and translation of science for wider audiences. Specific research skills will include:
• Gas chromatography-mass spectrometry (GC-MS)
• Stable isotope analysis
• Marine ecology
• Museum and coastal fieldwork
• Stakeholder engagement
• Biogeoscience statistics
• Conservation policy development

Facilities, equipment and expertise available within the institutions and supervisory team provide a combination of world-leading analytical, laboratory and field capability and technical support that ideally fits this PhD project maximising the expert training that will be available. The student will benefit from a network of collaborators at the Lyell Centre, Scottish Marine Animal Stranding Scheme (SMASS), and National Environmental Isotope Facility (NEIF).

References & further reading

Bossart, G.D., 2006. Marine mammals as sentinel species for oceans and human health. Oceanography 19, 134.

Evans, P., Waggitt, J., 2020. Impacts of climate change on Marine Mammals, relevant to the coastal and marine environment around the UK (MCCIP Science Review), Marine Climate
Change Impacts Partnership.

Thorne, L.H., et al., 2022. Rapid restructuring of the odontocete community in an ocean warming hotspot. Global Change Biology 28, 6524.

van Weelden, C., et al., 2021. Impacts of climate change on cetacean distribution, habitat and migration. Climate Change Ecology 1, 100009.

Whiteman, J.P., et al., 2019. A guide to using compound-specific stable isotope analysis to study the fates of molecules in organisms and ecosystems. Diversity 11, 8.

Williamson, M.J., et al., 2021. Cetaceans as sentinels for informing climate change policy in UK waters. Marine Policy 131, 104634.

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