Sonar versus whales: noise may disrupt neural activity in deep-diving cetaceans.

INTRODUCTION In humans, and other terrestrial animals, acoustic and non-acoustic detrimental effects of noise have been described long ago (1,2). In the recent years there is an increase in public and expert interest in the potential damaging consequences of acoustic pollution to marine life. The general increase in underwater noise and the use of sonar (1,2) have been associated with behavioral (3, 4) and pathological changes (5) in diving mammalians exposed to such an environment. Among these last, the connection established between the use of high-intensity sonar and the stranding and acute death of whales (6,) is particularly striking. It has been suggested that sonar activity per se may induce either bubble formation similar to decompression sickness (DCS (7)), or direct tissue disruption in diving mammalians (8,9). This may be true at the proximity of high intensity sonars (10,11). But the general signs of DCS observed in stranded cetaceans that were presumably exposed to the mid-range sonar activity at distance (5) suggest a behavioral cause: an accelerated ascent from deep water after being affected by the sonar. We postulate here novel auditory and sensorineural mechanisms by which sonar, and intense noise, may disrupt the behavior of diving cetaceans. Together with this, we also propose that the effects of noise at frequency may be enhanced during deep diving due to a synergistic combination with the adaptive response of the central nervous system (CNS) at high pressure.