Killer whale predation of harbour seals in the coastal waters of Scotland: investigating the ecological drivers and consequences of an apex predator-p

Foraging animals make decisions about where, when, and what to eat, the outcome of which can be critical to determine their fitness. Animals that are prey to others must also balance foraging benefits and safety from predation. Responses such as fleeing to a refuge can cost prey time and energy but ensure their survival1,2. Predators, in turn, must respond strategically to prey behaviour to maximise their foraging success. Predator-prey interactions provide a mechanistic basis to predict food web structure and understand the dynamics and resilience of ecological communities3

Harbour (Phoca vitulina) and grey (Halichoerus grypus) seals are closely related species with overlapping distributions in the UK. Killer whale (Orcinus orca) predation of both species is frequently observed in some parts of Scotland; however, the scale of predation is largely unknown4,5. In contrast to sub-populations of Pacific killer whales ('ecotypes'), killer whales in the Atlantic may feed on both mammal and fish prey6-8. Their prey selection is likely to be influenced by both prey availability (distribution and abundance) and traits (e.g., age class, body size). For example, grey seals are larger in size and are more abundant than harbour seals in Scotland but tend to forage further offshore9. Quantifying the spatial and temporal patterns of predation events and understanding the behavioural and bioenergetic dynamics of seal predation are key to understanding killer whale foraging and their potential impacts on seal populations in Scotland.

This PhD project will investigate killer whale predation of harbour seals with the ultimate goal to inform the conservation of both the apex predator population and their mammal prey. The project will take a bioenergetics approach to study predator-prey interaction in situ by integrating and modelling existing datasets, and collecting new field data in Shetland. The key objectives of the PhD are to 1) provide age stage-specific (e.g. adult/pup) estimates of grey and harbour seal consumption by killer whales in coastal waters of Scotland, 2) quantify spatial and temporal variation in seal predation, and 3) investigate whether predation rates could lead to observed declines in harbour seal population numbers.



References
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3. Portalier, S. M. J., Fussmann, G. F., Loreau, M. & Cherif, M. The mechanics of predator-prey interactions: First principles of physics predict predator-prey size ratios. Funct. Ecol. 33, 323-334 (2019).
4. Bolt, H. E., V, H. P., Laura, M. & Foote, A. Occurrence of killer whales in Scottish inshore waters: temporal and spatial patterns relative to the distribution of declining harbour seal populations. Aquat. Conserv. Mar. Freshw. Ecosyst. 19, 671-675 (2009).
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9. Thompson, P. M., Mcconnell, B. J., Tollit, D. J., Mackay, A. & Racey, P. A. Comparative Distribution, Movements and Diet of Harbour and Grey Seals from Moray Firth. J. Appl. Ecol. 33, 1572-1584 (1996).