Effects of Sounds from a Geophysical Survey Device on Behavior of Captive Rockfish (Sebastes spp.)

Behavior of rockfish (Sebastes spp.) exposed to air-gun sounds was examined to establish parameters in a subsequent fishing experiment to determine the effects of a geophysical survey device on fishing success. Rockfish observed in a field enclosure showed startle and alarm responses during 10-min exposures to sounds from a single 1639-cm3 air gun. For olive and black rockfish (S. serranoides and S. melanops), the threshold for the startle responses lay between 200 and 205 dB re 1 μPa. Under sound presentation, blue rockfish (S. mystinus) milled in increasingly tighter mills, and schools of black rockfish collapsed to the bottom. Vermilion (S. miniatus) and olive rockfish formed stationary schools near the bottom and, on sound presentation, either rose in the water column or moved to the bottom and became almost motionless. The general threshold for the alarm responses was about 180 dB re 1 μPa. Regression analyses of changes in depth distribution and shifts to active behaviors suggested that more subtle behavioral responses to sounds might become evident at 161 dB re 1 μPa. These initial responses were sustained only for a few minutes and may differ from those of unconfined fish.