Whale watch vessel ambient noise in the Haro Strait
Hildebrand, J., M.A. McDonald, J. Calambokidis, and K Balcomb. 2006. Whale watch vessel ambient noise in the Haro Strait. Joint Inst. For Marine Observations Report on cooperative agreement NA17RJ1231. MPL TM-490. August 2006, 24 pp.
This report provides a partial analysis of Haro Strait whale watching vessel noise data collected during fieldwork conducted May 28th to 31st, 2004 under contract to the NOAA Northwest Fisheries Science Center. The goal of this project was to measure representative calibrated noise levels of whale watching vessels and commercial shipping vessels operating in the Haro Strait and to examine differences in noise between vessel types. The Haro Strait is the site of high levels of vessel activity, both from the whale watching industry and from commercial vessel traffic.
One outcome of this work will be a better evaluation of the potential impact of vessel noise on southern resident killer whales. The Haro Strait is an important habitat for southern resident killer whales, a population designated as an endangered species owing to declines in their numbers. By characterizing the noise of vessels operating in the Haro Strait, the potential for noise to impact killer whales will be better understood.
Two concerns related to the impact of noise on marine mammals are behavioral impacts and masking noise. Behavioral impacts may range from short-term changes in activity to complete displacement from key habitat. Masking occurs when noise interferes with the animals’ ability to communicate with conspecifics, or to use echolocation for foraging or other functions. Killer whale communication whistles are centered at about 8 kHz (Thomsen, 2001) and the average intensity of stereotyped whistles is 153 dB re 1 µPa at 1 m (Miller, 2006). Their echolocation clicks are centered near 50 kHz on axis (although off-axis frequency peaks may be lower) and source levels are 194-225 dB re 1 µPa at 1 m on axis (Au et al., 2004).
For this analysis we present calibrated noise measurement of five vessels encountered in the Haro Strait. Field noise data were collected for a total of fifteen vessels under controlled conditions, and for a larger number measured under opportunistic conditions. Analysis of the complete vessel dataset will be the topic of future study. Four of the vessels considered in this preliminary study were small boats used for whale watching; one vessel was a large commercial container ship.
The noise produced at low frequencies (below 1 kHz) by the vessels examined in this study is thought to be due both to cavitation (bubble creation and collapse) and rotating machinery. Above 5 kHz the noise comes almost entirely from cavitation of the vessels’ propellers or bubble creation by jet drives.
High levels of ambient noise encountered in the Haro Strait hampered the ability of our study to separate the noise of individual vessels from others operating in the vicinity. This was the case both for vessel that were cooperating with our study and operating under controlled conditions, and those that we measured opportunistically. We recommend that future noise measurements for whale watching vessels operating in the Haro Strait should be conducted in an isolated setting, to allow better characterization of vessel noise generation under a wider range of operating conditions.