Acoustic interaction of humpback whales and whale-watching boats off Maui, Hawaii

Abstract

Whale-watching activities during the humpback whale annual winter sojourn in Hawaii have increased steadily over the past years. A concern of many is the possible detrimental effects of whale-watching boats on humpback whales; including the possibility of damage to their auditory system. To address this concern, the noise generated by five different types of whale-watching boats was measured, two with outboard engines, two with inboard diesel engines, and a seagoing vessel, in the near shore waters of west Maui. The first series of measurements was conducted at the peak of the whale season, and the boat noises were partially masked by humpback whales’ chorusing (boat noises and whale chorus levels were on the same order of magnitude). A 1/3 octave band spectral analysis indicated whale chorus levels as high as 136 dB re: 1 μPa with no whales in sight. Throughout the day humpback whale chorusing noise was present at similar levels for miles along the same coastline. Measurements taken close to the end of the season had about a 15-dB decrease in the humpback whale chorusing levels. Considering the high level of chorusing by humpback whales, the acoustic effects of the whale-watching boats should be relatively small or negligible.