The underwater noise of vessels in the Hervey Bay (Queensland) whale watch fleet and its impact on humpback whales

Abstract

In 1994 the underwater noise of 19 vessels involved in whale watching was measured. Vessels ranged from 1.5–70 tons and included yachts, runabouts and high-speed and displacement mono and multihulls. Except for one water-jet trimaran, all vessels were propeller driven. Unlike the directional patterns reported for merchant shipping, each vessel projected lobes of sound fore and aft with lower levels abeam. In the high speed planing vessels this was exacerbated by the deep propellers exposed forward, and the vessel squat while on the plane. All vessels displayed a linear relationship with broadband noise level and the logarithm of speed. Although unique for each vessel, as a rule of thumb doubling the speed doubled the detection range. The response of whales to vessel noise was as much a function of the rate of change of noise as its steady level. Rapid increases in noise produced more responses. Vessels which, by their design, required constant maneuvering to maintain station produced greater adverse responses from whales. Some design criteria important in reducing noise impacts from whale watch vessels include shielding of the propellers in the forward direction, windage in relation to draft, slow speed steerage, machinery noise reduction and passenger viewing access.