Temporal Trends in Fin Whale ( <i>Balaenoptera physalus</i> ) Vocalizations Off the West Coast of South Africa

ABSTRACT Long‐term acoustic monitoring of whale vocalizations offers valuable information on cetacean population biology and ecology and has become an essential tool for stock management. This study investigated seasonal and interannual variation in fin whale call characteristics off the west coast of South Africa using passive acoustic data across two periods: July 24, 2014 to January 13, 2017, and March 3, 2023 to September 27, 2024. Fin whale call presence along the west coast increased during austral autumn ( p  = 0.027). Social calls exhibited a peak frequency decline from 19.00 Hz to 18.75 Hz ( p  < 0.001), while accompanying high frequency notes decreased from 96.00 Hz to 94.92 Hz ( p  < 0.001). Short and long inter‐note interval lengths increased between the two periods ( p  < 0.001), while overall song complexity decreased ( p  < 0.001). Although eastern Antarctic fin whales have historically been assumed to migrate to this region, increased occurrence of high frequency notes below 90 Hz, inter‐note intervals of 15 s, and backbeat presence—all acoustic signatures of the western Antarctic fin whales—suggest previously unrecorded western Antarctic individuals. This study provides the first quantitative description of fin whale call changes in the southeastern Atlantic Ocean enhancing our knowledge of the species' acoustic ecology in the data‐deficient Benguela ecosystem.