Tracking and Monitoring Fin Whales Offshore Northwest Spain Using Passive Acoustic Methods

Abstract

Fin whales produce regular vocalizations with a dominant frequency of c. 20 Hz, similar to that of large airgun sources used in marine seismic surveys. Thus these vocalizations may be recorded on ocean bottom seismometers (OBS) or hydrophones (OBH) deployed during such surveys. We used data recorded by an array of 72 OBS/H with 4-6.5 km spacing, deployed offshore northwest Spain during June-August 2013, to study fin whale movements in this area. Whale vocalizations were identified automatically using signal processing techniques and localized using time delay estimates between several instruments. Airgun shooting took place during the deployment period, but we found no evidence for a correlation between vocalization detection rate and the presence or absence of shooting. Our analysis focused on six fin whale tracks identified during this period.Uncertainties in depth lead to poor confidence intervals, preventing effective analysis of diving behavior for the identified tracks. In the horizontal plane, the localizations had a higher degree of confidence. Use of a Kalman filter resulted in smoother tracks. Mean swim velocities range from 2 to 15 km/hr, and the animals traveled distances of 1.5-15 km in the periods analyzed.