Automated acoustic detection of fin whale calls off Kushiro-Tokachi at the deep sea floor observatory

Automatic acoustic detection and tracking were useful methods for understanding the behavior and population of marine animals. The seismometer and hydrophones were set in the ocean bottom off Kushiro in Japan. The acoustic data were recorded at a sampling frequency of 100 samples per second by 4 ocean bottom hydrophones. The fin whale calls, consisting a frequency down sweep in the range 20–15 Hz with duration of about 1 second, were recorded at these data. In this paper, the fin whales calls were automatically detected by extracting such down sweep signals from the acoustic data at 1457 days, ranging from 2009 to 2012. The acoustic data were transformed into the spectrogram by using short FFT. The fin whale calls were detected by computing the correlation between the measured spectrogram and the criterion spectrogram, which was computed from the typical fin whale call, at each time. It was demonstrated that the call detections increased from October to February. In addition, the movements of the fin whales could be estimated by temporal changes of time differences between calls detected at two hydrophones.