One year of background underwater sound levels in Haro Strait, Puget Sound

Abstract

Haro Strait, on the west side of San Juan Island, WA, is the home range of the Southern Resident orca whales, a major shipping lane to and from Canada, and a center of private and commercial boating, especially in the summer. Four ITC hydrophones in a near-shore fixed array are used here to localize the underwater vocalizations of Southern Resident orca whales. The system operates 24 hours a day and has a frequency response of 100 Hz 10 kHz. Background sound levels are automatically characterized by half-hour reports that include: statistics and graphics based on mean sound levels (2-min running arithmetic mean pressure); a histogram of mean sound levels binned by frequency; and 2-s sound samples from maximum background events. Sound levels range from ∼90 dB re 1 microPa (quiet conditions) to ∼130 dB re 1 microPa when loud commercial ships are passing in the nearby shipping lane or speedboats are passing close to the hydrophone array. Complete results for one year of continuous monitoring will be presented, segmented by time (season, day of the week, hour in the day), frequency spectrum and dominant noise source class. [Work supported by 35 undergraduate researchers and the Colorado College.]