Occurrence and Whistle Characteristics of Small Odontocetes in Two Coastal Regions of the Sea of Japan

This study investigated the occurrence and whistle characteristics of small odontocetes in Wakasa Bay and Aso Bay, located in the coastal waters of the Sea of Japan, where ecological data are limited. Passive acoustic monitoring using A‐tag and SoundTrap was conducted from 2022 to 2024, with detections on 8.8% and 12.4% of monitoring days at the two sites, respectively. Broadband clicks were detected at both sites. Visual sightings reported by fishers, together with photographic confirmation by experienced observers, supported the occurrence of Indo‐Pacific bottlenose dolphins ( Tursiops aduncus ) in both bays. Compared with Wakasa Bay, Aso Bay showed a higher proportion of constant‐frequency whistles, lower overall whistle frequencies, and higher ambient noise levels. In Wakasa Bay, detections were concentrated in the early morning, while in Aso Bay, they increased in the early morning and evening under low water temperature conditions. Statistical models further suggested that diel and seasonal variations in occurrence might be influenced by environmental factors. These findings provide new insights into the spatiotemporal occurrence of small odontocetes in the Sea of Japan and establish a baseline for future ecological research and conservation. Continued monitoring across diverse coastal habitats is essential for understanding odontocete distribution and behavior in this region.