Abstract

A comparison between rehab and free-ranging harbor seals was designed utilizing metabolic hormones; cortisol and thyroxine, and cell mediated immunity factors; lymphocytes and eosinophils. Neonatal marine mammals that are admitted to rehab facilities are more inclined to suffer from immunosuppression due to abandonment, malnourishment and anthropogenic tension. Analysis of hormone concentrations, immune function, and body condition via morphometrics can give an indication of an animal's physiology. Immunocompetence in an individual animal or species is a complex series of metabolic and physiological parameters. Hormones, such as cortisol (an adrenal hormone) and total thyroxine (TT4, a thyroid hormone), are good indicators of metabolic state and potential stressors to an animal's physiological system. Spikes or depressions of these metabolic hormones can aid in determining the fitness of an animal. Cortisol and TT4 abnormalities based over time have been found to cause forms of immunosuppression in other pinniped species.

This study examined cortisol levels, TT4 levels, and leukocyte subsets (lymphocytes and eosinophils) in neonatal harbor seals from two rehabilitation facilities and in wild pups sampled in the field. Preliminary results indicate that TT4 concentrations in the rehab 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.

Spikes in cortisol and thyroxine were expected at times of weaning. High levels of cortisol at weaning suggest a change in metabolic rate due to diet adjustment in 66% (19 in 29) of rehab pups. TT4 was elevated in 59% (17 in 29) rehab pups. Most pre-wean marine mammals have elevated TT4 which increases their metabolic rate to compensate for life out of the womb, especially thermoregulation. The pre-wean rehab pups did have elevated TT4 supporting the theory of metabolic and thermoregulatory issues in neonatal seal pups. The results show that wild harbor seal pups have the highest concentration of both cortisol and total thyroxine (TT4) of the three groups of pups compared. Pre-wean rehab harbor seal pups exhibit the lowest levels of both leukocyte types of all three groups compared.

Baseline information on circulating metabolic hormones and standards of hormone concentrations in neonate seals is one approach to further the investigation of immunocompetence of the species. Stress is one of the hardest states to try to quantify in research. However, examining these results from five consecutive years of rehab pup sampling and three years of wild pup sampling at the same location, the preliminary results show that no one particular group of animals exhibits hormone ranges out of the norm on a regular basis. If anything, the wild harbor seal pups are showing elevated levels of both metabolic "stress" hormones and one of the leukocyte populations. This information is pertinent to the survival of marine mammal rehabilitation facilities, in that the results do not show an undone amount of chronic stress states in the hormone levels of harbor seal pups admitted and treated in rehab centers.

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