Thomas F. Norris
Dept. of Vertebrate Zoology, Moss Landing Marine Labs., P.O. Box 450, Moss Landing, CA 95039
The effects of boat noise on cetacean acoustic behavior are not well understood. To examine these, real sources of boat noise were experimentally introduced to singing humpback whales (Megaptera novaeangliae). Humpback whales were chosen as subjects because they sing long songs that are easy to record. Also, they are often distributed in nearshore environments with heavy boat traffic. Songs from nine animals were analyzed (n=9). Ten variables describing time and frequency characteristics of humpback song signals and the structure of song patterns were compared before and during exposure to boat noise. Means of two variables (unit duration and phrase duration) were significantly less during boat passes than during control periods. Means of eight other variables were not significantly different. The statistical power of detecting a difference between the means was >90% for all variables describing frequency characteristics of songs. Because the durations of some variables were shortened, these results indicate that boat noise might affect humpback whale singing behavior. However, power analyses indicate that frequency structure is probably not affected. The significance of these effects concerning the behavioral biology of humpback whales is uncertain at this time.