JOINT INSTITUTE FOR MARINE
OBSERVATIONS
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STUDY OF WHALE WATCH VESSEL AMBIENT NOISE IN THE HARO STRAITJohn Hildebrand (SIO)Link to NOAA Strategic Plan: NOAA's Mission Goal 1: Protect, Restore, and Manage the Use of Coastal and Ocean Resources through Ecosystem-based Management; Goal 4: Support the Nation's Commerce with Information for Safe, Efficient, and Environmentally Sound Transportation RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEMThe objective of this project is to analyze acoustic data on ambient noise collected in the Haro Strait. The Northwest Fisheries Science Center is examining the potential impact of ambient noise on the Puget Sound population of Southern Resident Killer Whales. Specific goals of this study are to survey environmental noise in the Haro Strait region at different depths from calibrated vertical hydrophone array data, characterize acoustic source levels for whale watch vessels under typical operating conditions, and characterize the ambient sound level produced by multiple vessels operating simultaneously including the sound directionality. Data collected previously on whale watch and commercial vessel ambient noise were analyzed. The hydrophone system used to collect these data was calibrated. Noise output of 5 vessels was calculated for a standardized set of operating conditions including: idle, cruising speed (~10 knots) and power acceleration. RESEARCH ACCOMPLISHMENTSNoise spectra from four whale watch vessels collected under a controlled protocol and one commercial container ship collected opportunistically are represented in Table 1. Table 1. Vessel parameters and operating conditions examined in this study
For this analysis, calibrated noise measurement of five vessels encountered in the Haro Strait was presented. 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 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. The Mercury, the jet drive vessel, was the quietest vessel (Figure 1) at high frequencies, and the Olympas, the largest, produced the highest sound pressure levels at high frequencies. The Mercury is unusually quiet for its size and speed, with bubble (cavitation) noise less than 5 dB above background levels at cruise speed at 219 m range and there is no appreciable rotating equipment noise detected. The anomalously low underwater noise levels for this size vessel are presumably due to the jet drive system. High levels of ambient noise encountered in the Haro Strait hampered the ability of this study to separate the noise of individual vessels from others operating in the vicinity. This was the case both for vessels that were cooperating with the study and operating under controlled conditions, and those that were measured opportunistically. It is recommended 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.
Fig. 1 Acoustic source spectra at cruise speed for each of the five vessels in this study.
Fig. 2 Noise study area in the Haro Strait, adjacent to Limekiln Lighthouse on the west coast of San Juan Island. |
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