Stress response of wild bottlenose dolphins (Tursiops truncatus) during capture–release health assessment studies

Abstract

There is a growing concern about the impacts of stress in marine mammals as they face a greater array of threats. The stress response of free-ranging dolphins (Tursiops truncatus) was examined by measuring their physiologic response to capture and handling. Samples were collected from 168 dolphins during capture–release health assessments 2003–2007 at two study sites: Charleston, SC (CHS) and the Indian River Lagoon, FL (IRL). Adrenocorticotropic hormone (ACTH), cortisol, aldosterone (ALD) and catecholamines (epinephrine (EPI), norepinephrine (NOR), dopamine (DA)), were measured in blood and cortisol in urine. Mean time to collect pre-examination samples after netting the animals was 22min; post-examination samples were taken prior to release (mean 1h 37min). EPI and DA concentrations decreased significantly with increased time to blood sampling. ACTH and cortisol levels increased from the initial capture event to the post-examination sample. EPI concentrations increased significantly with increasing time to the pre-examination sample and decreased significantly with time between the pre- and post-examination sample. Cortisol concentrations increased between the pre- and post-examination in CHS dolphins. Age- and sex-adjusted mean pre-examination values of catecholamines were significantly higher in CHS dolphins; ALD was higher in IRL dolphins. Significant differences related to age or sex included higher NOR concentrations in males; higher ALD and urine cortisol levels in juveniles than adults. Wild dolphins exhibited a typical mammalian response to acute stress of capture and restraint. Further studies that relate hormone levels to biological and health endpoints are warranted.