Effects of capture stress on free-ranging, reproductively active male Weddell seals
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Physiological stress responses to capture may be an indicator of welfare challenges induced by animal handling. Simultaneously, blood chemistry changes induced by stress responses may confound experimental design by interacting with the biological parameters being measured. Cortisol elevation is a common indicator of stress responses in mammals and reproductive condition can profoundly influence endocrine response. We measured changes in blood cortisol and testosterone induced by handling reproductively active male Weddell seals (Leptonychotes weddellii) early and late in the breeding season. Weddell seals have the highest resting cortisol levels of all mammals yet showed a clear, prolonged elevation in cortisol in response to capture. Responses were similar when first caught and when caught a second time, later in the breeding season. Baseline testosterone levels declined over the breeding season but were not altered by capture. Administering a light dose of diazepam significantly ameliorated the cortisol response of handled animals without affecting testosterone levels. This may be an effective way of reducing acute capture stress responses. Male breeding success in years males were handled was no different to the years they were not, despite the acute capture response, suggesting no long-term impact of handling on male reproductive output.
KeywordsMarine mammals Leptonychotes weddellii Handling stress Cortisol Antarctica
We would like to thank the staff of Scott Base and Antarctica New Zealand who provided excellent field support for 4 years of this study. We thank Dudley Bell, Tony Dorr, and Sarah Winter for field assistance. Randy Davis, Terrie Williams, Tom Gelatt and Mike Cameron provided invaluable support at various times. Two anonymous reviewers provided comments which improved the manuscript. The study was supported by the Seaworld Research and Rescue Foundation, the Australian Research Council, the Graduate School of the Environment, Macquarie University, the Department of Biological Sciences, University of Waikato and the Antarctic Scientific Advisory Committee. Permission to conduct the study was obtained from the Environmental Assessment and Review Panel of Antarctica New Zealand, the Department of Conservation, New Zealand and the Animal Ethics Committee of the University of Waikato.
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