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Abstract
Many cetaceans are exposed to increasing pressure caused by anthropogenic activities in their marine environment. Anthropogenic sound has been recognized as a possible stressor for cetaceans that may have impacts on health. However, the relationship between stress, hormones, and cytokines secretion in cetaceans is complex and not fully understood. Moreover, the effects of stress are often inconsistent because the character, intensity, and duration of the stressors are variable. For a better understanding of how anthropogenic sounds affect the psychophysiology of cetaceans, the present study compared the changes of cortisol concentration and cytokine gene transcriptions in blood samples and behaviors of captive bottlenose dolphins (Tursiops truncatus) after sound exposures. The sound stimuli were 800 Hz pure-tone multiple impulsive sound for 30 min at three different sound levels (estimated mean received SPL: 0, 120, and 140 dB re 1 μPa) that likely cause no permanent and temporary hearing threshold shift in dolphins. Six cytokine genes (IL-2Rα, IL-4, IL-10, IL-12, TNF-α, and IFN-γ) were selected for analysis. Cortisol levels and IL-10 gene transcription increased and IFNγ/IL-10 ratio was lower after a 30-min high-level sound exposure, indicating the sound stimuli used in this study could be a stressor for cetaceans, although only minor behavior changes were observed. This study may shed light on the potential impact of pile driving-like sounds on the endocrine and immune systems in cetaceans and provide imperative information regarding sound exposure for free-ranging cetaceans.
Highlights
Marine mammals use their auditory system for foraging (Madsen et al, 2006), socialization (Nowacek et al, 2007), and for communication and orientation (David, 2006)
This research investigated the effect of low-frequency multiple impulsive sounds on the cortisol and cytokine gene transcript profiles in blood and the behavioral response of captive bottlenose dolphins
Previous studies have showed that increased serum cortisol levels could be observed in captive beluga whales (Delphinapterus leucas) during physical examination (Schmitt et al, 2010) and in free-ranging bottlenose dolphins (T. truncatus) following chase capture for capturerelease health assessment (Hart et al, 2015)
Summary
Marine mammals use their auditory system for foraging (Madsen et al, 2006), socialization (Nowacek et al, 2007), and for communication and orientation (David, 2006) Noise in their habitat could lead to potentially harmful effects on these important activities. Exposures to sounds at high levels or for extended periods of time have the potential to cause hearing damage or physiological impacts (Nowacek et al, 2007; Erbe, 2013) Another effect caused by underwater sound from human activities is stress (Romano et al, 2004). If animals are in a constant state of stress for days or longer, stress responses may become maladaptive, that means crucial behaviors may be hampered, such as foraging ability, escape from predators, and socialization (reviewed in Chrousos and Gold, 1992)
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