The effects of underwater sound on fishes are of concern because fishes use sound to find prey, avoid predators, and for social interactions (see How do fish communicate using sound? and How do fish use or make sounds when feeding?). Studies that investigate the effects of sound on fishes have been limited. More emphasis has been placed on studying the effects of sound on marine mammals, partly due to the fact that marine mammals are protected by federal regulations. In addition, marine mammals are easier to study in the wild since they come to the surface where behavioral reactions to sound can be measured. Fish experiments have primarily been conducted in laboratories where fishes can be observed, but the laboratory setting makes it difficult to work with loud sounds (1).

Several studies demonstrated an effect of sounds produced by airguns on fish behavior. In two studies, catch rates of commercially important species including cod, haddock, blue whiting, and Norwegian herring declined in areas where seismic exploration was conducted with airguns (2,3). These studies also showed that catch rates of these species increased 30-50 km away from the sound source, suggesting that fishes avoided the areas where the airguns were operating. A study of caged pink snapper suggested that fish would have fled when they heard an approaching airgun array if they had been able to swim away (4). In another study with airguns, rockfishes began to exhibit behavioral changes at 161 underwater dB. When the sound level was 180 underwater dB, blue rockfish swam in tight circles and schools of black rockfish moved to the seafloor (5).

Black rockfish in Monterey Bay National Marine Sanctuary, California. Photo courtesy of NOAA Photo Library.

Concern over the effect of the ATOC sound source on the distribution and behavior of fishes prompted a study on three species of rockfish (6). Rockfishes were kept in an enclosure and observed before being exposed to sound (a "control" period), during ramp-up of transmissions similar to those of the ATOC source, and during a 20-minute ATOC-like signal. The fishes did not move towards or away from the sound source despite receiving levels of sound of 145-153 underwater dB. They also did not change their behavior between the control period and the exposure periods. Though fish were not exposed to the actual ATOC source under true operational conditions, the results suggest that there may be possible ways of reducing the potential effects of some anthropogenic sounds on fishes.

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