Shifts in acoustic signature of Southern Hemisphere fin whales: Declining peak frequency of high-frequency components.

Population-specific acoustic features are vital for using passive acoustic monitoring to study marine mammal populations in remote regions. Southern Hemisphere fin whale (Balaenoptera physalus) songs include region-specific high-frequency components, with the 86- and 99-Hz high-frequency components present in the Atlantic Sector of the Southern Ocean. Using long-term passive acoustic monitoring data, we show that, despite gradual interannual and intra-annual variabilities, these features remain distinct and recognizable across regions and years. Our findings support their use as reliable acoustic markers for monitoring fin whale populations, providing valuable insights into distribution and population structure.