Noise propagation from vessel channels into nearby fish nesting sites in very shallow water

Noise exposure has been shown to have negative impacts on fish. This study introduces the F-weighting function for assessing the effects of audible sounds on fish. Sound levels with the F-weighting function emphasize the frequencies that the fish can detect and suppresses frequencies the fish cannot detect. A hydrophone was placed at locations of shelters or “dens” colonized by oyster toadfish Opsanus tau in very shallow water (1 – 2 m depth). Sounds produced by three representative passing vessels – an inboard boat, an outboard boat, and a tugboat pushing a barge – in nearby channels were recorded. Each vessel produced sounds at the den location at levels audible to the fish. The vessel sounds were not loud enough to produce temporary threshold shifts or permanent hearing losses in the fish, but they were loud enough to produce behavioral effects, masking of conspecific and predator sounds, the Lombard effect, and possibly an increase of stress hormones. Also, for comparison with the noisy site, sounds were measured at a quiet site where no vessels were present. The loudest sounds at the quiet site had similar sound pressure levels to the quietest sounds at the noisy site at a time when no vessels were detected.