The Ocean Observatory Initiative (OOI) Regional Cable Array (RCA) and the Ocean Networks Canada NEPTUNE cabled observatory provide an opportunity for long-term studies of the distribution and behavior of calling marine mammals. We will present the results of a study to build a database of “20-Hz” fin whale calls that spans from 2015 to present. Fin whale calls were collected by bottom-mounted low-frequency hydrophones and seismometers deployed on the OOI RCA and are detected automatically by spectrogram cross-correlation with a detection kernel that sweeps down linearly from ∼26 Hz to ∼19 Hz with a duration of ∼0.8 s. The kernel is tuned to detect the high amplitude portions of both the high- and low-frequency calls of the doublet calling pattern which is currently the dominant fin whale song in this area. Preliminary results show significant interannual variations at a given site in the distribution of calls during the fall and winter calling season. The onset of calling appears to be significantly earlier near the continental slope off central Oregon than at Axial Seamount, 450 km offshore. There also appears to be a higher overall rate of calling nearer the continental slope.