Abstract

Wild and captive dolphins are known to contract a number of illnesses such as respiratory, cardiovascular, dermatological, and digestive tract infections, including gastric ulcers.¹ Causes of gastric ulcers in dolphins include bacterial infection by Helicobacter sp., parasitic infections, high dietary histamine, foreign body ingestion, and stress.^1,2,3,4,5 However, there have been instances where gastric ulcers have occurred in species such as common bottlenose dolphins (T. truncatus) without any obvious attributable cause, and these occurrences may be a manifestation of stress.^3,6,7 The uShaka Sea World bottlenose dolphins (Tursiops sp.) are divided into three groups: five females, three males, and a bonded pair (male and female). Routine gastroscopies, a trained medical procedure performed as part of the standard cetacean preventative health program, suggested that the dolphins in the female group were more predisposed to recurring lesions in the first stomach, compared to the male group and the bonded pair. These mucosal lesions, or gastric ulcers, may be attributed to social stress, as bottlenose dolphins are highly social animals. Anecdotal daily observations of the dolphins by their trainers indicated that the social interaction within the female group was more dynamic than in the other two groups. As part of uShaka Sea World’s animal welfare programme, a research project was initiated to test if a link existed between social stress and the pathogenesis of gastric lesions in the dolphins. Voluntary gastroscopy (n=88) was performed on each dolphin bi-monthly for a period of six months, in conjunction with a rigorous behavioural observation regime amounting to 137 hours of observations, conducted between October 2017 and April 2018. An ethogram was developed from the observations, detailing the social and solo behaviours occurring within the male and female groups. The social dynamics observed during poolside monitoring of the two mono-sex groups were assessed on association patterns, social interactions, and synchronous swimming. Results indicate that the association patterns in the female group changed significantly four times over the study period, whereas the males’ association patterns did not. The males engaged in a greater number of social interactions and took part in more synchronous swimming than the females. Additionally, the presence and severity of gastric ulceration (graded on a scale of 1=no lesions; 2=<10 lesions; 3=>10 lesions, <50% area covered; 4=>50% area covered) was significantly higher in the female group than the male group. Changes in social structure in the female group indicate that social stress is present, which is reflected in the higher ulceration rate of the females. Therefore, gastric ulceration may potentially be used as an indicator of social stress in captive bottlenose dolphins.

Acknowledgements

The authors wish to thank the Mammal and Bird Department and the Animal Health Department of uShaka Sea World. The authors thank the South African Association for Marine Biological Research’s Sea World Foundation for the financial support of this project.

* Presenting author

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