Neonatal marine mammals are more inclined to suffer from immunosuppression due to abandonment, malnourishment and anthropogenic contaminants. Analysis of hormone concentrations and body condition via morphometrics can give an indication of an animal's physiology. Hormones such as cortisol and thyroxine, if levels are altered due to such stresses on a neonate, can cause changes in metabolic rate, calcium absorption and blood pressure control. This study examines cortisol and thyroxine (total T4) levels in neonatal harbor seals in two rehabilitation facilities. The hormones were assayed using solid phase RIA (radioimmunoassay) techniques. The data collected from these assays are being used to form clinical diagnostic baseline values on pups that are admitted into these two rehab facilities.
Preliminary results may indicate that total T4 concentrations ranged from 0.70 to 11.4 ng/ml (µ=3.89ng/ml) in animals age 2 days to 14 weeks. Cortisol concentrations ranged from 2.56 to 56.37 ng/ml (µ= 12.14 ng/ml) in animals age 2 days to 14 weeks. Cortisol levels in rehab animals suggest high variability based on circadian cycles and feeding regimes. High levels of total T4 at weaning suggest a change in metabolic rate due to diet adjustment. This is shown in approximately 75% of weaned pup samples (n=12). Cortisol was more variable and showed a rise at time of weaning in 50% of pups sampled (n=12). Four pups showed their highest cortisol level at admission whereas two pups showed their highest level at the last sampling. 50% of the pups showed their highest total T4 at admittance whereas none of the pups sampled showed their highest total T4 at release or even last death prior to a death. These results suggest that; (a) total T4 is a more stable indicator of stress in the rehabilitation environment than that of cortisol and (b) that there may be some habituating to the anthropogenic stressors in the rehabilitation facility environment. Samples from free-ranging pups will be used to compare with rehab seals enabling researchers to evaluate and improve rehabilitation techniques.
This work was made possible by EVOS (Exxon Valdez Oil Spill Trustees Council), The Marine Mammal Center and the Alaska SeaLife Center.