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).
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).