Behavioral responses of humpback whales (Megaptera novaeangliae) to full-scale ATOC signals

Loud (195 dB re 1 mu Pa at 1 m) 75-Hz signals were broadcast with an ATOC p rojector to measure ocean temperature. Respiratory and movement behaviors o f humpback whales off North Kauai, Hawaii, were examined for potential chan ges in response to these transmissions and to vessels. Few vessel effects w ere observed, but there were fewer vessels operating during this study than in previous years. No overt responses to ATOC were observed for received l evels of 98-109 dB re 1 mu Pa. An analysis of covariance, using the no-soun d behavioral rate as a covariate to control for interpod variation, found t hat the distance and time between successive surfacings of humpbacks increa sed slightly with an increase in estimated received ATOC sound level. These responses are very similar to those observed in response to scaled-amplitu de playbacks of ATOC signals [Frankel and Clark, Can. J. Zool. 76, 521-535 (1998)]. These similar results were obtained with different sound projector s, in different years and locations, and at different ranges creating a dif ferent sound field. The repeatability of the findings for these two differe nt studies indicates that these effects, while small, are robust. This sugg ests that at least for the ATOC signal, the received sound level is a good predictor of response. (C) 2000 Acoustical Society of America. [S0001-4966( 00)02610-2].