Postural instability and akinesia in a pantropical spotted dolphin, Stenella attenuata, in proximity to operating airguns of a geophysical seismic vessel

Aberrant behaviour including erratic locomotion was observed in a pantropical spotted dolphin 600. m ahead of an airgun array during 3D seismic explorations off Liberia in March 2009. The dolphin, presumably in acoustic distress, lifted its head and cervical region above the surface in an oblique, strikingly rigid posture during 5. min. Turbulent white-water evidenced a major propulsory thrust. Incremental postural instability and apparent exhaustion progressed to a catatonic-like state of akinesia as the dolphin rolled over onto one side, then its back before sinking virtually motionless close to the airgun array. Unless it recovered full locomotory control, asphyxiation was inevitable. Potential internal injury is discussed, both acoustic-mediated and from extreme exertion (exertional myopathy, rhabdomyolysis and myoglobinuric nephrosis). As behaviour was spatially and temporally closely associated with firing seismic airguns, we suggest a cause-effect relationship. Differential diagnoses of pre-existing morbidity, senescence, or intoxication are considered possible but unlikely.