Stressful times

Sattler R, Bishop AM, Polasek L. 2020. Cortisol Levels for Pregnant and Non-Pregnant Steller Sea Lions (Eumetopias jubatus) in Human Care. Aquatic Mammals, 46: 146-151. Open Access

Feeling stressed? Repeating the Hitchhiker’s Guide to the Galaxy advice “Don’t Panic” to yourself? You’re not alone…in more ways than you may know!

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All animals experience ‘stress’. We’ve never had a Steller sea lion ask for pickles and ice-cream, but recent research published by Alaska SeaLife Center scientists in the journal Aquatic Mammals indicates that these pinnipeds have heightened stress during the breeding season. As part of a long-term study aimed at understanding the costs of reproduction for the endangered Steller sea lion, blood samples were taken throughout the year to quantify the amount of ‘cortisol’ in pregnant and non-pregnant females, and across reproductive seasons.

Kuliak with his mom, Eden.

Cortisol is a hormone is involved with many of your body’s processes, and plays a key role in how we respond to stress. While stress can lead to increased levels of cortisol, many other factors also raise our cortisol levels including time of day, food intake, and activity. Still, by measuring how much cortisol is circulating in the blood before, during or after an acute event we can gain a better understanding of the stress associated with natural patterns like pregnancy.

When assessing how stressful reproduction is for Steller sea lions in our captive population, scientists found that cortisol levels were highest during the breeding season; but in the non-breeding season, cortisol levels were similar between pregnant and non-pregnant animals. Having this reference information about stress, even from a small sample, can be valuable for the continued care, directed research, and health of marine mammals.

To take a step back, you might be wondering:

“How do you get a blood sample from a 660 lb animal?”

A female Steller sea lion undergoing routine veterinary check at the ASLC.

Voluntary blood draws and other procedures can be trained through positive reinforcement. This means that an animal presents its flipper, wing, leg to allow veterinary staff to take a sample. However, blood draws are often taken as part of larger health assessments that require handling or access to the animal under anesthesia. In those cases, restraint is required for the safety of the animal and staff; but positive-reinforcement can still play a key role. While the main aim of this study was to assess stress related to pregnancy, researchers also found that in general, animals that were trained to voluntarily place their face into an anesthesia mask had lower cortisol levels than those that required physical restraint.

In this video, one of the Steller sea lions at the ASLC, Mara, is having a check-up, and the team demonstrates how training can help our veterinarians monitor her health.

Interestingly, researchers also observed that across animals there were individual differences in how females responded (e.g. think of two dogs at the vet where one is happy to see a new person and the other is pacing anxiously). These findings emphasize that it is important to understand how stress-relieving behavioral, physiological, and medical markers together can be used to determine the appropriate sampling context instead of applying a one-size-fits-all approach to this and other species in human care.

While there were some patterns across treatments, scientists noticed the cortisol levels differed among individuals within those categories. For example, EJ06006 (dark blue), seemed to have consistently high cortisol levels across all contexts. (Figure 1: from Sattler et al. 2020)

All activities and photographs are taken under National Marine Fisheries Service Permits #18534 and #14334.

Written by: Dr. Amy Bishop

The donors that have made gifts to the research programs at the Alaska SeaLife Center are so appreciated.  Your  gifts have helped maintain our science programs.

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