Oceans of noise - Whale and Dolphin Conservation Society

Location: Sarasota, Florida, USA• Preliminary analyses suggested that boat traffic affected bottlenose dolphin distribution,behaviour and energy requirements.• Significantly fewer dolphins were seen in boat channels on weekends (periods of high vesseltraffic) than on weekdays, suggesting a shift in distribution to avoid boat traffic.Ref: Wells 1993.Location: Cardigan Bay, Wales.• The responses of bottlenose dolphins were observed when exposed to speedboats andplaybacks of sounds produced by speedboats.• Observed responses included shorter surfacing periods and longer dive times observed fromvessels at distances of 150-300m.• The authors suggested that quieter boats travelling at high speeds disturb dolphins more thanslower, larger boats that emit higher intensity noise. The noise produced by a high speed boatonly rises above ambient levels shortly before its closest point of approach, eliciting a startleresponse.Ref: Evans et al. 1992.Location: Ensenada De La Plaz, Mexico.• No quantifiable adverse responses to boat traffic in Ensenada De La Plaz were recorded.Ref: Acevedo 1991.Beluga whales, Delphinapterus leucasLocation: St. Lawrence Estuary, Canada.• In 1991 beluga whale vocal behaviour was monitored before and after exposure to noise froma small motorboat and a ferry.• Vocal responses were observed in all trials but were more pronounced when exposed to theferry.• Responses included: (i) a progressive reduction in calling rate, (ii) brief increases in fallingtonal calls and three pulsed-tone call types, (iii) an increase in the repetition of specific calls,and (iv) a shift in frequency bands used by vocalising animals from 3.6kHz to 5.2-8.8 kHzwhen vessels were close (within 300m) to the whales.Ref: Lesage et al. 1999.140