Behavioural and faecal cortisol metabolite monitoring of harbour (Phoca vitulina) and grey seal pups (Halichoerus grypus) in rehabilitation centres (2026)

Zatrak, M., Shaw, K. J., Geary, M. et al.

Abstract

Harbour (Phoca vitulina) and grey (Halichoerus grypus) seals face numerous anthropogenic and environmental threats around the UK and Ireland. These commonly lead to seal pups becoming stranded and in need of rescue and rehabilitation. Although rehabilitation supports the recovery and welfare of stranded seals, the process can expose individuals to a range of stressors, such as handling, intensive medical treatments, assisted feeding and confinement. Effective methods for assessing seal health and welfare in response to these challenges remain limited. This study investigated whether faecal cortisol metabolites (FCMs) and behavioural indicators can effectively monitor welfare in rehabilitating harbour and grey seal pups. A total of 479 faecal samples were collected from 19 seal pups (Harbour n = 8, Grey n = 11), and 3864 h of footage was collected for 25 seal pups (Harbour n = 11, Grey n = 14), all rehabilitated at Tynemouth Seal Hospital (North Tyneside, UK). The effect of sex, time of day, feeding method, water access, body condition, and day of rehabilitation on both FCM concentrations and behavioural time budgets was investigated. Changes in FCM levels did not correspond to any of the predictor variables and highlights the complexity of interpreting FCMs in rehabilitation settings, likely reflecting individual variation, allostatic load, and limited sensitivity to short-term stressors. In contrast, seal pup behaviour was significantly affected by rehabilitation variables, including feeding method and access to water. Although assisted feeding is essential for the survival of malnourished pups, it caused decreased displays of vigilance in both species, and a decrease in tactile and locomotion behaviours with an increase in stereotypic behaviours in grey seals. This warrants enrichment plans to be incorporated into the care of these seal pups to counteract any negative impacts on their welfare. Similarly, water access for swimming should be provided as soon as possible to ensure that the sufficient development of natural locomotory and tactile behaviours is facilitated. Overall, these results could be used to optimise behavioural welfare assessments and the rehabilitation protocols currently in place for both harbour and grey seal pups, improving seal pup welfare in captive settings.