Abstract

Harbor seal pups in rehabilitation and in the wild were compared using two metabolic hormones (cortisol and TT4), two cellular immunity components (lymphocytes and eosinophils) and morphometric measurements. Neonatal harbor seals in two rehabilitation facilities, the Alaska SeaLife Center and The Marine Mammal Center in California were compared to wild harbor seal pups from Tugidak Island, Alaska. Total thyroxine (TT4) concentrations in the rehabilitation pups ranged from 0.7 to 11.4 ng/ml in animals age 2 days to 14 weeks. Cortisol concentrations ranged from 2.3 to 76.4 ng/ml. The wild pups' TT4 ranged from 1.61 to 7.62ng/ml and cortisol ranged from 7.07 to 20.57 ng/ml.

In the pups undergoing rehabilitation, there were indications of hormonal changes due to locale variations, introduction of other animals, and alternating feeding regimes (live fish, different prey). High levels of cortisol at weaning suggest a change in metabolic rate due to diet adjustment in pups during rehabilitation. The lower cortisol concentrations post-weaning indicate that pups in rehabilitation had overcome the challenge of pre-weaning diet or environment and avoided chronic stress, through to adaptation to the rehabilitation facility. TT4 concentrations were significantly higher in wild pups, likely attributed to a more energetic and demanding life in a dynamic environment.

The rehabilitated pups showed lower percentages of lymphocytes, but not eosinophils compared to wild pups. When comparing the post weaned pups in rehabilitation and wild harbor seal pups using morphometric parameters, the wild pups were heavier and were longer. It is probable that the animals in rehabilitation were compromised, maternally abandoned, or presented with a level of disease process, but it is also possible that current rehabilitation practices do not equally mimic what a healthy pup would receive from its mother in the wild, thus pups undergoing rehabilitation likely remain smaller and possibly immunologically challenged despite repeated and constant care in rehabilitation.