Seasonality of Fin Whale Calls Detected from the Deep Sea Floor Observatory off Kushiro–Tokachi

Automatic acoustic detection is a useful method for monitoring phonating marine animals. Fin whale calls consist of frequency down-sweeps at around 20 Hz with a duration of approximately 1 s. These low frequency acoustic data were recorded with four hydrophones located on the ocean floor off Kushiro and Tokachi, Hokkaido, Japan. The fin whale calls were automatically detected by calculating the ratio of signal energy to background noise and the duration of the calls. With respect to manually detected calls, correct detection and false alarms using the proposed method were 69.5% and 4.4%, respectively. A total of 2,865,403 calls were detected from data collected during 2,981 days from January 2007 to February 2015. The number of detected calls showed clear seasonal differences, high in October to February period.