IAP-24-118

Migratory patterns and feeding grounds of stranded beaked whales explored through biomarkers and isotopic signatures of blubber

Climate change poses an active threat to marine species worldwide, and British beaked whales (ziphiids) in particular [1]. Warming ocean temperatures since about 1990 have altered these animals’ ecological distributions and impacted their health through changes in regional habitats and preferred prey availabilities. As ‘sentinels’ of the ocean environment [2], beaked whales are considered important indicators of marine ecosystem health at local-to-larger scales, and their conservation is currently a topic of global interest [3].

Ocean warming is actively restructuring patterns of habitat distribution in oceans worldwide and has especial impacts on ziphiids with respect to migratory pathways [4] and interspecific competition [5]. Indeed, there is a clear increase in frequency of British warmer-water adapted Ziphiidae sightings and stranding events over the past three decades [6], which might be related to changes in spatial distribution and diet4 through warming sea surface temperatures. In the northeast Atlantic Ocean, ecosystem impacts of surface warming primarily propagate through food webs via ‘bottom-up’ effects on microalgae [7], which in turn affect higher trophic level organisms such as whales. Importantly, these effects can be tracked through lipid biomarker distributions and their stable isotopic signatures amid trophic cascade [8]. As such, the molecular isotopic signatures of diagnostic microalgae lipids incorporated in cetacean blubber offers an exciting opportunity to assess marine ecosystem resilience and trophic interactions despite notable complexities in regional food web structuring.

Based on sightings and historical stranding data, one of the more common warm-water ziphiids around British waters include Sowerby’s beaked whale (Mesoplodon bidens). Cold-water ziphiids include Cuvier’s beaked whale (Ziphius cavirostris) and Northern bottlenose whale (Hyperoodon ampullatus). Despite habitat differences, in the northeast Atlantic, stomach contents of these species indicate shared foraging grounds with overlapping prey preferences [3-6]. By incorporating powerful biomarker analyses of diagnostic algal lipids – called alkenones – that fluctuate alongside ocean temperature and are incorporated into cetaceans via trophic transfer, uniquely quantitative reconstructions of foraging ground location are possible. Complementary stable isotope (hydrogen [δD] and carbon [δ13C]) analysis of bulk blubber and its component biomolecules (viz. alkenones and fatty acids) allows further differentiation of dietary preferences and habitat between species vis-à-vis carbon flow and trophic structure. Considered together, molecular and isotopic signatures are exemplary proxies for gathering longer-term ecological data on these cosmopolitan and highly mobile animals [8].

Aims: We propose to use stable isotope signatures of blubber-associated lipids (δD and δ13C for alkenones and fatty acids) and bulk blubber (δ13C and δ15N) from common species of stranded whales adapted to colder-water (Z. cavirostris and H. ampullatus) and warmer-water (M. bidens) habitats. Samples will be selected from between 1992-2022 to reconstruct feeding grounds, dietary patterns and trophic interactions in the midst of large-scale climate change. With these data, we aim to identify general foraging pathways and define ecologic stressors (i.e., ocean warming, prey preference overlap, food-chain length, and the resilience of trophic interactions) that should be monitored. This research is crucial to establish an ecological framework for conservation management towards sustainable marine communities and has deep policy implications with respect tocetacean welfare.

This research will take advantage of state-of-the-art techniques in gas chromatography (GC) and mass spectrometry (MS) to characterize individual diagnostic organic molecules – called ‘biomarkers’ – from 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., alkenones) and from de novo synthesis (e.g., odd-numbered fatty acids) to maximize ecological insights. The scholar also will have opportunities to optimise analytical techniques to enable complementary (geo)chemical detection of further compounds, such as steroid hormones and bulk isotopic analyses.

Inceptive samples are available or in-hand for this project, enabling the scholar to start their analyses at the project’s start. The scholar 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. We expect that these opportunities will be student-led, and therefore can also incorporate additional aspects of fieldwork, laboratory work, outreach (e.g., citizen science) or developing policy. Multidisciplinary project foci means collaboration will be crucial for the success of this endeavour, which will foster rich knowledge exchange and networking opportunities.

Year 1

Literature review and techniques training. Fieldwork followed by initial blubber 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

Data analyses and synthesis with current literature. Dissemination at international conference and preparation of second publication.

Year 3.5

Time devoted to thesis writing and publications.

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).