As interest and knowledge grows in marine mammal rehabilitation and research, there is an increased level of hands-on interaction and potential for stress. Acute stress is defined as a controlled response to a stressor where the overall effect is not harmful (Goldstein 1995). Stress becomes detrimental, (i.e., chronic) when a state of distress causes the organism to respond to the stimuli in an excessive or uncontrolled manner (St. Aubin and Dierauf 2001).
Surgical procedures in marine mammals are on the rise due to the increased numbers of animals and improved techniques in rehabilitation programs. Endoscopic procedures have been refined in bottlenose dolphins (Tursiops truncates), California sea lions (Zalophus californianus) (Dover and Van Bonn 2001) and sea otters (Enhydra lutris) (Larson et al 2002). Chemical immobilization agents are routinely used for various species of cetaceans and pinnipeds (Haulena and Heath 2001). The only current method to assess the effect of these surgical and anesthetic procedures has been indirectly through survivorship rates.
A finer scale interpretation of the effects of these now common procedures on stress hormone levels is being investigated, particularly if protocols can be modified to effectively reduce stress and increase survival rates. The focus of this study was to validate existing methods of steroid hormone analysis in marine mammals to enable the quantification of stress hormones in rehabilitated California and Steller sea lions. Fecal corticosterone analysis is a non-invasive method to monitor glucocorticoids in organisms. Fecal samples are easily collected and provide an integrated response that represents longitudinal data over a period of time as opposed to serum cortisol levels that can change quickly from sample to sample (Möstl and Palme 2002). A double antibody RIA kit (MP Biomedicals (formerly ICN Biomedicals), Costa Mesa, CA) was used for fecal corticosterone analysis.
California Sea Lions
Four experimental groups were opportunistically selected from existing procedures that California sea lions routinely undergo during rehabilitation at The Marine Mammal Center (TMMC), Sausalito, CA: (Group A: restraint for blood draw (n=10), Group B: anesthesia, no surgery (n=10), Group C: anesthesia, minor surgery (n=10), Group D: anesthesia, abdominal surgery (n=5)). Feces were collected opportunistically up to 72hr prior and 72hr post procedure for corticosterone analysis. Results indicate substantial individual variation in fecal corticoid responses. Only group C had a significant (P < 0.05) difference between fecal corticosterone concentrations before and after surgical procedures
Steller Sea Lion
In May 2002, a female Steller sea lion pup (EJS-02-01) was sighted separated from her mother after strong storms in Southeast Alaska. After 5 days of observations, EJS-02-01 was transferred to the Alaska SeaLife Center (ASLC) in Seward, Alaska. During 11 months of rehabilitation at ASLC, body weights were monitored and opportunistic fecal samples (n=86) were analyzed for corticosterone concentrations. Fecal corticosterone concentrations ranged from 15-3805 ng/g for EJS-02-01. Peak corticosterone values reflected responses to acute stressors during rehabilitation: changes in management (i.e., socialization with other animals), and end of rehabilitation quarantine and preparation for release. Pre-release preparations included anesthesia for hot branding to track post-release survival and long-term identification. EJS-02-01 was successfully released at Gran Point, Alaska in April 2003.
The stress response is a series of complex reactions that can be measured non-invasively with fecal corticosterone. Fecal corticosterone assay monitoring provides a valuable addition to hematological diagnostics to ensure that a wild animal is responding to various stressors within normal ranges for that species and is useful in monitoring long-term situations, like rehabilitation. This non-invasive method to monitor stress longitudinally is especially well-suited for an endangered marine mammal, such as the Steller sea lion, and is an excellent method to non-invasively monitor the stress response to varying surgical and non-surgical techniques.
We thank TMMC and ASLC rehabilitation programs, veterinary services staff, interns and volunteers; especially Michelle Caudle, Millie Gray, Denise Greig, Frances Gulland, Marty Haulena, Tim Lebling, Lisa Phoenix, Pam Tuomi, and Deb Wickham for sample collection and coordination. Support for this project was provided by the Alaska SeaLife Center Steller Sea Lion Program with funding through the National Marine Fisheries Service.
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