Long-term monitoring of Ziphius cavirostris behavior using 3D tracking from fixed hydrophone arrays off Southern California

Goose-beaked whales ( Ziphius cavirostris ) are a deep-diving toothed whale species and top predators in deep sea ecosystems. Much is yet to be learned about their social and foraging strategies due to their elusive behavior, but this information is increasingly relevant given their demonstrated behavioral changes in association with anthropogenic sound. This study used direction-of-arrival (DOA) localization to track the position of goose-beaked whales from echolocation clicks recorded on seafloor-mounted hydrophone arrays offshore Southern California. Overall, 2738 tracks of diving goose-beaked whales were processed from acoustic recordings collected at four long-term monitoring sites between 2018 and 2023. Results highlight distinct spatial use patterns driven by bathymetric features at each site, with whales foraging closer to the seafloor at sites with complex bathymetry and showing a preference for certain bathymetric features. Group sizes at depth ranged from 1 to 9 individuals with a mean of 2.34 and exhibited site-specific seasonal variability as well as a strong diel trend at one site. During many of these encounters, individuals exhibited highly coordinated behaviors. This study demonstrates the value of long-term passive acoustic tracking for studying elusive, deep-diving species and provides significant advancements in understanding goose-beaked whale behavior at depth over long time scales.