Determining Fin Whale Call Counts in the Northeast Pacific using Hydrophone Data

Abstract

Fin whale call counts in the Northeast Pacific, between 2015 to 2020, were determined using hydrophone data from the Ocean Observatories Initiative’s regional cabled array database. This study sought to determine if fin whale call counts in the NE Pacific increase in support with the 7.5% annual abundance increase estimated from visual surveys. A regional cabled array station at the base of the Axial seamount was used, and the hydrophone data was analyzed by spectrogram cross-correlation that detected the 20 Hz down swept call made by fin whales. From 2015 to 2018, fin whale call counts showed a continuous increase. Call counts between 2018 and 2019 decreased. From 2019 to 2020, call counts showed a significant increase. Fin whale call counts in the NE Pacific between 2015 and 2020 showed a 10.2% annual increase. However, the fit to a linear trend is weak and the data does not rule out a calling rate that is unchanged with time. Sea-surface temperature in the winter showed significant variations from year to year and there were fewer calls in the years when winter water temperatures were anomalously high. This suggests that fewer fin whales congregated near Axial temperatures when temperatures are warmer, but then returned the following year when the water temperature was more normal.