The number of humpback whales frequenting Glacier Bay has been decreasing in recent years while the number of whales in the Fredrick Sound and Stevens Passage area has been increasing. A study was made to determine the acoustic characteristics of both areas and measure the influence of man-made noise sources on ambient levels. ‘Transmission loss (TL) in selected regions of both areas was measured and ambient noise spectra obtained. The TL characteristics for a shallow source and receiver were observed to have a 20 log (range) dependence below 1 kHz in both areas. In Glacier Bay a shallow surface duct was observed which changed the TL to approximately 10 log (range) dependence above 1 kHz. Low ambient noise levels were observed in the absence of boat and ship traffic. Thus the sound from louder vessels dominated the ambient out to a range of up to six miles in some measurements. A significant low-frequency noise contribution, believed to be due to glacier motion, was observed at some locations in Glacier Bay. [Work supported by NOAA, NMFS and National Park Service.]

A procedure was developed for observing the track patterns and behavior of migrating gray whales off Soberanes Point south of Monterey, California. A series of acoustic playbacks were made at realistic levels from an anchored vessel to simulate the presence of oil and gas development and production activities. In another series of tests, a seismic survey vessel with a 4000-in.3 air-gun array was navigated at progressively decreased ranges from the migrating whales. This was followed by a test sequence using a vessel with a single 100-in.3 air gun. Source characteristic and acoustic transmission loss measurements were made to permit prediction of the noise exposure for the nearby subject animals. Exposure levels for which observed behavioral changes occurred were determined. [Work supported by Dept. of Interior, Minerals Management Service.]

Results of recent studies involving gray, humpback, and bowhead whales show that whales tend to avoid areas with high underwater noise levels. Data obtained from whale behavioral observations during controlled exposure to representative industrial noise sources permit determination of the probability of avoidance Pa of the source region as a function of the noise level Ln. The zone of influence of a source may be defined as the region where Pa > 0.5. While the Ln required to produce this degree of avoidance has been found to depend on whale species and source type, some generalizations may be made. For low-frequency continuous noise, 50% of the whales exposed have been observed to avoid regions where the overall Ln is higher than 115 to 125 dB (re: 1 μPa). Sound transmission conditions at a specific site determine the distance from the source, where Ln falls below the Pa = 0.5 criterion level. The zone of influence thus has been found to vary considerably for the test sites investigated. For example, a drillship operating at a test site off the Alaskan Beaufort coast has an estimated zone of influence radius of 4 km, but, off the coast of California, the estimated zone of influence radius is reduced to 1 km. [Work sponsored by the Minerals Management Service.]