Dwarf and pygmy sperm whales (Kogia sima and K. breviceps) are difficult to study using traditional visual observation methods. Their intensely cryptic behavior has resulted in few population estimates or reliable population trends for either species. Fortunately, both species use sound to navigate their ocean habitat, so even when they cannot be seen, their presence can be recorded. However, given their deep-diving behavior and avoidance of boats, Kogia are only rarely detected on towed arrays. In the North Pacific only a few high-quality recordings exist, with a total of <1,000 clicks. Unlike recordings from motorized platforms, drifting recorders move without generating ship noise or triggering avoidance behavior, which leads to higher rates of detection for species that are otherwise difficult to detect. Here we present a new dataset that greatly increases the number of Kogia acoustic detections in the North Pacific. We analyzed over 4,000 hours of recordings from drifting passive acoustic recorders (DASBRs), from the Main Hawaiian Islands, the Northwestern Hawaiian Islands and the Marianas Islands from 2018-2023 covering all months except December. Of the 83 DASBR deployments, 51 contained verified detections of Kogia clicks, for 165 total unique detection events, and a cumulative total of more than 12,000 clicks. There were no distinct spatial trends in click characteristics, with all regions and seasons being acoustically similar, and there was no clear separation of clicks into groups that might align with the two species of Kogia. However, there was a diel trend, with more clicks at night. Additionally, we highlight a case where a DASBR was deployed concurrent with a visual confirmation of K. sima, leading to 93 species-verified clicks. This is one of only a few confirmed recordings of K. sima globally. These recordings open new possibilities of inference and assessment for this mysterious, yet cosmopolitan genus.
Citation:
Merkens, K., J.S. Trickey, J. McCullough, and R.W. Baird. 2026. Kogia in the North Pacific: Spatial and Temporal Patterns in Click Characteristics from Passive Acoustic Monitoring. Presentation at the 26th Biennial Conference on the Biology of Marine Mammals, San Juan, Puerto Rice, 19-23 October 2026.