Urinary glucocorticoids in harbour seal (Phoca vitulina) pups during rehabilitation

Abstract

ABSTRACTThe glucocorticoid (GC) hormone cortisol is often measured in animals to indicate their welfare and stress levels. However, the levels of other naturally occurring GCs are usually overlooked. We aimed to investigate whether aspects of the care and conditions of harbour seal (Phoca vitulina) pups in rehabilitation centres are reflected in urinary concentrations of four endogenous GCs. Urine samples were collected non-invasively from pups taken in as “orphans” at five different rehabilitation centres: three on the Irish Sea and two in the southern North Sea. Concentrations of urinary cortisol, cortisone, prednisolone and prednisone were analysed by mass spectrometry. Urinary concentrations of endogenous prednisolone and prednisone occurred in similar magnitude to cortisol, for the first time in any mammal species. The levels of all GC concentrations decreased as pups gained mass, but the most significant effect was for prednisone. Pups with mass less than 11kg, i.e. healthy average birth mass, had significantly higher levels of prednisone (but not of the other GCs) than pups of 11kg or more. Cortisol, cortisone and prednisolone concentrations were slightly higher for pups without access to water than those with water; however, we found no significant effect of social group on GC levels. Based on these findings, we tentatively suggest that the GCs may be elevated in harbour seal pups during rehabilitation in response to some physiological factors deviating from the norm of free-living pups. Our findings highlight the importance of measuring other GCs, in addition to cortisol, for understanding stressors affecting the welfare of seal pup in rehabilitation.