Optimising health and welfare of harbour and grey seals in rehabilitation

Student Spotlight - Michal Zatrak

PhD Research at Manchester Metropolitan University

Senior Technical Officer at University of Chester

Email: michal.zatrak@stu.mmu.ac.uk   Twitter: @MZatrak

Background

Harbour (Phoca vitulina) and grey seals (Halichoerus grypus) commonly encounter threats in their habitat that include climate change (Kovacs et al., 2012), predation (Brownlow et al., 2016), competition for food (Wilson and Hammond, 2019), pollution (Allen et al., 2012), and diseases (Härkönen et al., 2006). These threats can cause seal strandings, which either result in direct death or rescue. When rescued, trained wildlife rescuers assess each seal and determine whether treatment at a rehabilitation centre is required. Seal pups that come into rehabilitation centres require medical treatment and/or assisted feeding. The stress induced on the seals by these practices has the potential to negatively affect the outcome of rehabilitation (Trumble et al., 2013). Therefore, the overarching aim of my PhD research is to develop health and welfare assessment tools for harbour and grey seals in rehabilitation, in order to increase their odds of survival and release back to the wild.

Rehabilitation records- how are our seals doing?

The first study of my PhD investigated the causes of harbour and grey seal admittance to rehabilitation centres in the UK and Ireland, and identified factors that affect juvenile seal survival. It has just been published in the journal of Marine Mammal Science (https://doi.org/10.1111/mms.12983). This study involved the collection of rehabilitation records for 1,435 harbour and 2,691 grey seals from five rehabilitation centres (Figure 1) from 1988 to 2020.

The records showed that the most common reasons for seal admission to rehabilitation centres included malnourishment (37%), injuries (37%), maternal abandonment (15%), lethargy (12%), and parasite infections (8%). The frequent presence of malnourishment among stranded juveniles could be attributed to interruptions in the suckling regime of mother and juvenile pairs (Anderson et al., 1979), postweaning periods of juvenile seal fasting, and inefficient foraging due to inexperience (Muelbert et al., 2003; Nordoy & Blix, 1985). This is alarming as statistical modelling, in the form of a mixed effects logistic regression model, indicated that the odds of survival to release significantly increased with weight for both species (Figure 2), and that grey seals were almost five times more likely to survive than harbour seals.

This weight-dependent survival could be attributed to the importance of fat in thermoregulation, hydration, and buoyancy during foraging. Therefore, we recommended  seal rehabilitators to pay special attention to the weight of admitted juvenile seals during triage and treatment to enhance their odds of survival.

What's next?

My next studies will optimise the process of seal health and welfare assessments through the development of new tools that can be integrated into rehabilitation protocols. The first study focuses on identifying factors associated with elevated faecal cortisol metabolite levels in harbour and grey seals. This could help determine how these species cope with stress in rehabilitation and how their cortisol levels vary according to sex, season, individual differences, time in captivity, feeding methods and behavioural time budgets (Figure 3a). For the final study of my PhD, I will be developing a new lab-on-a-chip device to enable the detection and identification of seal lungworm infections in places where laboratory equipment is not readily available. This has the potential to enable rehabilitators, veterinary staff and any other user without prior knowledge in parasite identification to detect and identify lungworms in seal faecal samples faster and more accurately (Figure 3b). Overall, the outcomes of my PhD could improve the odds of survival and consequent release back into the wild for harbour and grey seals, and contribute to their population recruitment.

References

Allen, R., Jarvis, D., Sayer, S., & Mills, C. (2012). Entanglement of grey seals Halichoerus grypus at a haul out site in Cornwall, UK. Marine pollution bulletin, 64, 2815-2819. https://doi.org/10.1016/j.marpolbul.2012.09.005

Anderson, S., Baker, J., Prime, J., & Baird, A. (1979). Mortality in Grey seal pups: incidence and causes. Journal of Zoology, 189, 407-417. https://doi.org/10.1111/j.1469-7998.1979.tb03972.x 

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

Härkönen, T., Dietz, R., Reijnders, P., Teilmann, J., Harding, K., Hall, A., … Thomson, P. (2006). The 1988 and 2002 phocine distemper virus epidemics in European harbour seals. Diseases of aquatic organisms, 68, 115-130. https://doi.org/10.3354/dao068115 

Kovacs, K., Aguilar, A., Aurioles, D., Burkanov, V., Campagna, C., Gales, N., … Härkönen, T. (2012). Global threats to pinnipeds. Marine Mammal Science, 28, 414-436. https://doi.org/10.1111/j.1748-7692.2011.00479.x

Muelbert, M., Bowen, W., & Iverson, S. (2003). Weaning mass affects changes in body composition and food intake in harbour seal pups during the first month of independence. Physiological and Biochemical Zoology, 76, 418-427. https://doi.org/10.1086/375427

Nordoy, E., & Blix, A. (1985). Energy sources in fasting grey seal pups evaluated with computed tomography. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 249, 471-476. https://doi.org/10.1152/ajpregu.1985.249.4.R471

Trumble, S.J., O'Neil, D., Cornick, L.A., Gulland, F.M., Castellini, M.A. and Atkinson, S. (2013). Endocrine changes in harbor seal (Phoca vitulina) pups undergoing rehabilitation. Zoo biology, 32(2), 134-141. https://doi.org/10.1002/zoo.21036

Wilson, L., & Hammond, P. (2019). The diet of harbour and grey seals around Britain: Examining the role of prey as a potential cause of harbour seal declines. Aquatic Conservation: Marine and Freshwater Ecosystems, 29, 71–85. https://doi.org/10.1002/aqc.3131

Zatrak, M., Brittain, S., Himmelreich, L., Lovick‐Earle, S., Pizzi, R., Shaw, K.J., Grant, R.A. and Geary, M., 2022. Factors affecting the survival of harbor (Phoca vitulina) and gray seal (Halichoerus grypus) juveniles admitted for rehabilitation in the UK and Ireland. Marine Mammal Science. https://doi.org/10.1111/mms.12983