Fecal hormone analysis has recently become a common method for assessing
the physiological health of wild animals. Most vertebrate species excrete
increased levels of certain steroid hormones (such as glucocorticoids)
and experience a decrease in reproductive steroids while under stress.
Stress hormones are released by the bile into the gut, and excreted from
the body through the feces. Measuring the concentration of fecal hormones
has already provided insight into the physiological health of a large
number of species. This technique has great potential for the study of
marine mammals, such as Steller sea lions, but must be validated before
being widely used.
Researchers Kathleen Hunt, Samuel Wasser and Andrew Trites believe that
measuring the concentration of glucocorticoid metabolites released by
Steller sea lions may be particularly useful for assessing the physiological
status of sea lions in Alaska. If the technique can be proven,
it would offer a cost-effective means of assessing the physiological
health of sea lions. In addition, it could potentially serve as an early-warning
indicator of when a population is in trouble, or on the path to recovery.
Pup counts have been the most reliable means to date for monitoring the
status of Steller sea lions. However, this method may not reflect current
conditions, given the long time lag associated with sea lions attaining
sexual maturity and giving birth.
Fecal hormone analysis is a potentially powerful technique for monitoring
the physiological health of Steller sea lions given that scat (fecal)
samples can be easily collected from where sea lions rest (haul-outs and
rookeries), and that fecal glucocorticoids are known to reflect a variety
of ecological stressors in terrestrial species.
The first step in applying this technique to Steller sea lions is to validate
it using an adrenocorticotropic hormone challenge, also referred to by
biologists as an ACTH challenge. In a recently published paper, Hunt and
her colleagues describe how they injected four Steller sea lions at the
Vancouver Aquarium Marine Science Centre with ACTH, and collected feces
prior to – and after - the injection. Each of the collected scats
was analyzed to determine whether the glucocorticoid steroids expected
to have been produced by the sea lions in response to the ACTH challenge
appeared in the fecal sample.
Hunt and colleagues found that all of the animals showed the expected
peak of fecal glucocorticoid excretion after the ACTH injection. They
therefore concluded that their fecal glucocorticoid assay accurately reflects
the endogenous adrenal activity of Steller sea lions. Their study marks
the first time this technique has been validated for a marine mammal specie.
Validating the fecal hormone technique for Steller sea lions is an important
first step towards using it throughout their range. This method could
potentially become extremely useful for monitoring Steller sea lions,
and assessing the factors responsible for their population decline in
Alaska.
abstract
The Steller sea lion (Eumetopias jubatus) is listed as endangered in
parts of its range and is suspected of suffering from ecological stressors that
may be reflected by fecal glucocorticoid hormones. We validated a fecal glucocorticoid
assay for this species with an adrenocorticotropic hormone (ACTH) challenge. Feces
were collected from captive Steller sea lions (two males and two females) for
2 days before injection with ACTH, and for 4 or more days postinjection. Feces
were freeze-dried, extracted with a methanol vortex method, and assayed for glucocorticoids.
The assay demonstrated good parallelism and accuracy. All animals showed the expected
peak of fecal glucocorticoid excretion after ACTH injection. However, the two
males had higher baselines, higher peaks, and more delayed peaks than the females.
Peak glucocorticoid excretion occurred at 5 and 28 h postinjection for the two
females, and at 71 and 98 h for the two males. Correction for recoveries by the
addition of tritiated hormones produced ACTH profiles that were virtually identical
in pattern to uncorrected data, but with higher within-sample coefficients of
variation. Based on these results, we conclude that this fecal glucocorticoid
assay accurately reflects endogenous adrenal activity of Steller sea lions, and
that recovery corrections are not necessary for this species when using the methanol
vortex extraction method. More research is needed to address possible sex differences
and other possible influences on fecal glucocorticoid concentrations.
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