Corticosterone as an Indicator of stress during estrus and pregnancy in captive sea otters (Enhydra lutris)
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Sea otter populations are at risk of extinction because population size has not recovered from the drastic reduction caused by the hunting and fur trade of the 18th and 19th centuries. With a small population facing extinction and a captive population maintained, researchers began to focus their efforts reproduction in captivcity. Corticosterone and cortisol are the principle glucocorticoids that regulate metabolism, immunosupression, and stress responses in many species and these hormones also appear to mediate stress-induced inhibition of reproductive functions (Rivier and Rivest 1991). Thus, corticosterone levels may be a useful indicator of stress related to reproduction, and monitoring these levels would allow for a better understanding of successful sea otter pregnancies in captivity. Therefore, the purpose of our study was to record corticosterone levels during successful and unsuccessful pregnancies in captive sea otters in an attempt to identify causes of captivity-induced stress and increase reproductive success of the otters. We monitored corticosterone in the sea otters through fecal samples collected over their captive lifetimes. We also measured body mass and used it as a health indicator. We paid special attention to the pregnant versus nonpregnant corticosterone levels to indicate trends in stress during certain reproductive times such as estrus, pregnancy, and motherhood. Peaks in stress were correlated with probable causes noted in the animal health records during the fecal collection date. Although no significant differences in corticosterone and body mass were found during successful and unsuccessful pregnancies, the most important information that we found was that each pregnancy and female is different and trends can be found in that variation. Overall, this information would allow reproductive efforts in captivity to become more precise and furthermore would increase the likelihood of recovery of the wild populations through transplantation efforts.