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The Bottlenose Dolphin (Tursiops truncatus) as a Model to Understand Variation in Stress and Reproductive Hormone Measures in Relation to Sampling Matrix, Demographics, and Environmental Factors

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Technical Report

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National Ocean Service Charleston United States

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Our overarching goal was to develop indicators and methods to quantify chronic stress in bottlenose dolphins. Much research had focused on the stimuli which induce stress in marine mammals, as well as the hormonal mediators of the stress response. Stress may be induced by a variety of factors, including noise, pollutant or toxin exposure, presence of predators, loss of prey, human interactions, andor habitat changes. The stress response is complex and difficult to study experimentally in marine mammals due to ethical and logistical considerations, but has been well characterized in other laboratory mammal species. In mammals, as well as other vertebrates, the stress response has two modes of operation. The fast mode involves the rapid release by the medulla of fast-acting agents, such as catecholamines, which drive the fight-or-flight response, enhancing vigilance, alertness, arousal, and attention. The catecholamines in turn play a major role in excitation of the hypothalamic-pituitary-adrenal HPA axis, initiating a hormonal cascade which culminates in stimulation of the adrenal cortex to secrete glucocorticoids GCs. The delayed but more sustained response driven by GCs coordinates brain and body functions to cope with stress and facilitate recovery, adaptation, and re-establishment of homeostasis. These functions include mobilization of substrates for energy metabolism, suppression of immune and inflammatory reactions, and inhibition of bone and muscle growth. Studies of both captive and free-ranging individuals support the existence of these same stress response pathways in marine mammals. While the HPA axis and physiological processes driven by the GCs are essential for an individuals ability to respond and adapt to stress, prolonged stimulation can overly burden the bodys regulatory systems and induce deleterious effects.

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