Marino, L., Rose, N. A., Visser, I. N. et al. 2020. The harmful effects of captivity and chronic stress on the well-being of orcas (Orcinus orca). Journal of Veterinary Behavior 35, 69-82.

Orcas are large, deep-diving cetaceans who are known for their global distribution, wide-ranging behavior, intelligence, and social complexity. They possess one of the largest and most complex brains in the mammalian kingdom. However, they are the third most common species of cetaceans kept in aquariums and marine theme parks. Most spend many years, and sometimes decades, in captivity. At the time of writing, 60 individuals are held in concrete tanks globally. The scientific data on how both wild-caught and captive-born orcas fare in captivity are increasingly robust in demonstrating that they cannot thrive under artificial circumstances in concrete tanks. In captivity, orcas exhibit a wide range of abnormal behaviors and often die at an early age from infections and other health conditions that are uncommon in a wild setting. Though numerous papers and reports describe these adverse effects, they do not offer a clear and systematic explanation for why captive orcas suffer chronic stress and how it affects their well-being. We describe likely mechanisms for the high levels of morbidity and mortality in captive orcas, including the impact of chronic stress on physiology and illness. We conclude that orcas are poor candidates for maintenance in captivity and suggest that a radical shift is required in their treatment, to meet their complex needs.