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Are Cetaceans in Human Care More Stressed Than Those in the Wild?

Philipp J. Kroiß

Those who want to bring an end to cetaceans in human care often claim that the animals experience increased stress in captivity. Is this true and can we trust these words? Let’s look at the scientific facts.

Cortisol, nicknamed “the stress hormone” is the primary glucocorticoid found in most mammals including humans and cetaceans. Cortisol levels can be used to measure stress in wild cetaceans as well as those in human care (Proie 2013).  There are two main samples that can be collected to determine cortisol levels; blood and excreta. Samples can be collected from animals in human care using husbandry methods, collected without husbandry behaviors from both animals in human care and in the wild.

Many scientific studies have been conducted using Atlantic bottlenose dolphins, as they are the most frequently seen cetacean seen at aquariums all over the world. In Proie’s study, mean cortisol levels were significantly higher in wild Atlantic bottlenose dolphins (Tursiops truncatus) compared to dolphins in human care (Proie 2013). When comparing samples of wild Atlantic bottlenose dolphins to those samples collected in human care without using husbandry behaviors, the data shows that the stress level is in these animals are nearly the same (Proie 2013).

Tursiops truncatus & trainer | Loro Parque

Philipp J. Kroiß

Further, it was clearly shown that the samples collected from Atlantic bottlenose dolphins during husbandry training sessions displayed significantly lower cortisol levels. This trend is mimicked in the beluga whale where mean cortisol levels were significantly higher in wild beluga whales (Delphinapterus leucas) than compared to samples collected from animals in human care during routine husbandry training sessions (Proie 2013). When we only compare samples of wild belugas to samples collected in human care not including husbandry behaviors, we can see that the stress level is nearly the same (Proie 2013).

Unfortunately, Proie could not compare cortisol levels of wild killer whales (Orcinus orca) to those in human care, as cortisol levels of wild killer whales were not evaluated. However,  orcas in human care showed the lowest cortisol level compared to belugas and Atlantic bottlenose dolphins both in the wild and in human care.

What can we learn from these findings? The notion that cetaceans in human care are more stressed than their wild counterparts is incorrect. The stress differences are not significant between animals in human care and their wild counterparts as indicated when comparing cortisol samples collected with non-husbandry methods.  Zoological Atlantic bottlenose dolphins and beluga whales have normal cortisol levels and they are not more stressed than their wild counterparts. A study comparing cortisol differences in other cetaceans in human care such as killer whales compared to wild populations would be advantageous to understand the role stress plays in each setting. It is expected that the results would be similar to Proie’s findings.

Additionally, the data shows that animals participate in training voluntarily. If the animals were forced to participate, there would likely be a significant increase in cortisol production, indicating that the animal was stressed. Husbandry training helps to reduce the stress that an animal experiences during medical procedures, thus this type of conditioning is beneficial to the animal and not harmful as some proponents against human care believe. Science does not support the claims of these proponents by refuting the notion that dolphins in human care suffer from stress or have greater stress than populations in the wild.

 

Proie, S., 2013. A SYSTEMATIC REVIEW OF CORTISOL LEVELS IN WILD AND (Doctoral dissertation, The Evergreen State College).




5 thoughts on “Are Cetaceans in Human Care More Stressed Than Those in the Wild?

  1. Midge

    I would like to suggest a correction to your article. Ms. Proie’s research was for a Masters Thesis, not a Doctoral Dissertation. I also think that it is important to point out, as Ms. Proie states multiple times in her thesis, that the chase, capture, restraint techniques used to sample wild cetaceans makes it difficult to compare wild to captive cortisol levels. Samples from wild animals likely do not reflect baseline levels. There are a number of reasons that cortisol levels in captive cetaceans are lower, including habituation or even dampened activity of the hypothalamic-pituitary-adrenal axis. The latter can be detrimental as well. The role of cortisol is actually more nuanced than just being involved in “stress.” At baseline levels, cortisol facilitates activity by mobilizing energy sources. The acute stress response (“fight or flight response”) is also adaptive because it quickly redirects energy away from non-essential physiological processes and behaviors, allowing the animal to cope with an immediate stressor. When animals are chronically stressed (in other words, the stressor is long-lasting), that is when they start to have lots of “wear and tear” problems. It is great that this meta-analysis found that animals in captivity had lower cortisol levels, but I feel it is difficult to compare captive levels to wild caught levels and make solid conclusions because of the different methods used to collect samples (Proie points this out as well). Furthermore, multiple samples over several points in time are necessary to get a comprehensive view of the hormonal profile of the animal. A single sample at a single time point is only a snapshot of that animals cortisol levels. Proie also suggests that future study is needed to really get an idea of what is going on (and she gives thoughts on what these future studies should focus on). I too feel like there is so much more going on than what your article suggests. Proie’s study is an excellent jumping off point, but not necessarily the final conclusion.

    Reply
    1. Philipp KroissPhilipp Kroiss Post author

      Please keep in mind, that the article compares samples that was collected with non-husbandry methods, when it compares cortisol levels of the animals. Of course it would make no sense, if we would compare samples that were collected in a different ways. But this does not happen. Please read this sentence of the article: “The stress differences are not significant between animals in human care and their wild counterparts as indicated when comparing cortisol samples collected with non-husbandry methods.”

      You write: “It is great that this meta-analysis found that animals in captivity had lower cortisol levels”. The article explains, that there are no signifant differences, when we compare cortisol levels collected with non-husbandry methods in human care and in the wild.
      It furthermore explains, that samples that were collect with husbandry methods (during a trainings session) are lower that those samples that were collected with non-husbandry methods.
      The article is not claiming “that animals in captivity had lower cortisol levels”. The article only refutes “that the animals experience increased stress in captivity”.

      Reply
    2. Danny StantonDanny Stanton

      Midge,

      First off I must say that it is nice to see that you have done some reading of your own. We do get a fair share of comments, but it is a breath of fresh air to talk science. I understand your position very well. You bring up some interesting and very valid points. I also think there are a few things that you might want to consider about this particular study within the confines of your comments. Philipp did not address any other research and was just trying to highlight this thesis. You are right in that it is important to consider the HPA axis as well due to the number of hormonal releases and responses that originate from there. With science the goal is always to eliminate as many variables or in other words to normalize the experiment to be as consistent and to reduce the variability of the outcome. With that being said the baseline is also important and this is how you arrive at what the baseline should be. I agree that using training in husbandry introduces an additional variable that cannot be accounted for in wild populations. This is the very reason why wild cortisol collection compared to cortisol collection without using training is stressed. The initial cortisol spike form collection would be considered normalized, as it would be expected also in cortisol collection in wild animals. Therefor the response is negated in the study. And the difference in cortisol level would be a true measurement between the two groups. The point of adding the inclusion of cortisol collected with husbandry behaviors is to show that the level was further reduced and makes the point that training for procedures reduces stress. I would also agree that a time study could show variability in normal cortisol production, however it is likely that that difference could be negligible unless there was an event to trigger an cortisol spike.

      To your other major point about the HPA axis: Habituation or dampening of the HPA response could happen for many reasons in both wild and captive animals. Again this is why it is important to considered different variables to determine the baseline for the study. Likewise acute Reponses are highly variable. One could actually argue that in a wild environment animals are subjected to much more variability than animals in human care, therefore they have more chances to mount an acute PA response. While this hypothesis was not tested, I personally believe that it would be a reason to expect animals in human care would have a stress level no grater than wild animals because the opportunity to become acutely stressed is reduced in a consistent environment. This would actually speak to your habituation point as well because stress then becomes reduced in human care because it is attenuated over time. Additionally, for animals born in human care they do not know any different and see their environment as what they have always known.

      I agree that there is always room of additional studies. I just wanted to respond and give you a few things to think about. This study is a great start, but more needs to be done. I do believe the data and the trend. It would be nice to have additional pieces of evidence such as behavioral studies and other studies using different markers of stress. The HPA axis as you suggested would be a great place to start. If we know the series of events and the hormones released through the HPA cascade in wild animals vs animals in human care, then we will be even more informed.

      Reply

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