David E. Bain
Marine World Foundation, 2001 Marine World Pkwy., Vallejo, CA 94589
Univ. of British Columbia, Vancouver, BC V6T 2A2, Canada
Marilyn E. Dahlheim
Natl. Marine Mammal Lab., Seattle, WA 98115
A study of hearing abilities of killer whales was conducted to help assess the impact of noise produced by vessels. The study had five objectives: (1) determine the range of frequencies that killer whales can hear; (2) determine the ability to hear these frequencies in the presence of bandlimited masking noise; (3) determine whether vessel noise affects the ability to hear pure tones; (4) determine whether noise from different directions has different masking properties; and (5) determine the ability to detect simulated killer whale sounds in the presence of vessel noise. Data were collected using conditioned responses of four captive killer whales. Conclusions reached include: killer whales are sensitive to a wide range of frequencies (0.5--105 kHz); noise reduces the ability to detect signals of similar frequencies; very loud, low frequency, noise reduces the ability to detect signals even at much higher frequencies; noise has the strongest effect when it comes from in front of the whale, and the least effect when it is from the side or behind; and the ability to detect broadband signals such as killer whale calls and clicks is not substantially affected by low levels of vessel noise.