Acoustical monitoring of finback whale movements on the New Jersey Shelf

Abstract

Acoustical monitoring of finback whales is performed by using a data set collected over a 3-week period in December of 2003 on the New Jersey Shelf. One-second-duration 20-Hz signals of finback whales were recorded on three vertical line arrays (VLAs) and a bottomed horizontal line array (HLA.). One-second-duration pulses are separated by about 10 s and there is an approximately 2-min-long silent period between 10- to 18-min-long pulse trains. A 30- to 60-min silent period after 5 to 10 pulse trains is also common. Modal analysis of individual pulses indicated that most signals contained two acoustic modes. Arrival-time and group-speed differences of these modes are used for remote acoustic ranging. These modal characteristics are also exploited in a broadband matched-field algorithm for depth discrimination. Bearing estimation of individual whales is obtained by performing horizontal beamforming on the HLA data. Range estimation results are verified by time-of-flight triangulation using single hydrophone data from each VLA location. Acoustic monitoring results indicated that most finback whales traveled near the shelf break front where food might be abundant. Relations between silent periods and acoustic range/depth monitoring results are also investigated. [This work was supported by the ONR.]