Inter-specific interactions: Investigating the role of grey seals in the harbour seal decline

The UK hosts two species of seal: the harbour (Phoca vitulina) and grey seal (Halichoerus grypus) which are key top predators in UK seas. These species have broadly similar resource requirements but are showing contrasting population trajectories around the UK since the early 2000s, harbour seal populations have been declining dramatically along the north and east coasts of Scotland but increasing in the southern North Sea. Meanwhile, grey seal populations around the UK coast are increasing or stable.
Competitive and predatory interactions between species are widely understood to be two of the most important processes determining the structure of natural communities. The coincident changes in grey and harbour seal population sizes suggest that there may be a causal link between the trends of the two species. Furthermore, many other potential drivers of harbour seal decline, such as direct anthropogenic factors and large-scale disease events, have been ruled out. Grey seals, which are larger than harbour seals, may impact harbour seal populations through multiple potentially interacting mechanisms. Grey seals predate harbour seals (Brownlow et al. 2016) but it is not clear if the level of predation is sufficient to significantly influence population dynamics. Grey seals may also compete with harbour seals either indirectly by depleting their common prey species (exploitative competition) and/or directly through interfering with the acquisition of prey (interference competition).
Since the early 1990s, the Sea Mammal Research Unit (SMRU) at the University of St Andrews along with the University of Aberdeen have used telemetry tracking devices to study the movements and foraging behaviour of both species at sites around the UK. This has produced an extensive seal telemetry database which includes data from over 600 harbour and 400 grey seals. In most regions, there are longitudinal data representing seal behaviour at multiple points along the population trajectories of both species. The student will make use of these large archives of foraging and movement patterns together with spatially detailed long-term population data (>25 years), range-wide diet data and information on causes of death from strandings data to examine the evidence for the role of grey seals in regional harbour seal declines.
This research will be focused in three areas:
1) Is there evidence of a link between grey and harbour seal densities and trends (at sea and on land)?
2) Is there evidence, from telemetry data, of inter-species competition?
3) Could grey seal predation have caused the regional decline in harbour seals?

References
Brownlow A, Onoufriou J, Bishop A, Davison N, Thompson D (2016). Corkscrew seals: Grey seal (Halichoerus grypus) infanticide and cannibalism may indicate the cause of spiral lacerations in seals. PLoS ONE 11(6): e0156464. https://doi.org/10.1371/journal.pone.0156464
Russell, D. J. F., McClintock, B. T., Matthiopoulos, J., Thompson, P., Thompson, D., Hammond, P. S., Jones, E. L., McKenzie, M., Moss, S. & McConnell, B. J. (2015). Intrinsic and extrinsic drivers of activity budgets in sympatric grey and harbour seals. Oikos, 124(11), 1462-1472. DOI:10.1111/oik.01810
Russell, D. J. F., Jones, E. L., & Morris, C. (2017). Updated Seal Usage Maps: The Estimated at-sea Distribution of Grey and Harbour Seals. Scottish Marine and Freshwater Science. 8(25). Scottish Government. DOI: 10.7489/2027-1
SCOS (2017) Scientific advice on matters related to the management of seal populations. Natural Environment Research Council, 144pp.
http://www.smru.st-andrews.ac.uk/files/2018/01/SCOS-2017.pdf