In a groundbreaking study conducted along the Sea of Japan, researchers from Kyoto University have deployed passive acoustic monitoring to unveil new insights into the elusive behaviors of small odontocetes—particularly dolphins and porpoises—frequenting Wakasa Bay and Aso Bay. This pioneering effort marks a significant advance in marine mammal science by capturing vocalizations that illuminate how these cetaceans navigate and communicate within complex coastal soundscapes.
The Sea of Japan, hemmed in by Japan’s archipelago and the Eurasian continent, has undergone rapid environmental changes that have blurred previous scientific understanding of its marine inhabitants. While dolphin sightings and incidental captures have been sporadically reported, comprehensive ecological data concerning small toothed whales remained scarce. Motivated by local fishermen’s observations, the team sought to clarify which species were present and how they utilized these coastal waters.
Between January 2022 and November 2024 in Wakasa Bay, and from March 2023 through October 2024 in Aso Bay, scientists deployed underwater acoustic recorders designed to capture the high-frequency echolocation clicks and signature whistles typical of odontocetes. These devices passively listened to the underwater soundscape, providing continuous, non-invasive recordings. A unique feature of the study was direct collaboration with local communities who assisted with equipment deployment and contributed sighting reports alongside photographic evidence.
Despite low detection rates—approximately one acoustic event every ten days—the monitoring yielded crucial acoustic profiles of the dolphins’ whistles. Notably, sounds recorded in Aso Bay, distinguished by a noisier ambient environment, exhibited distinct whistle characteristics compared to the quieter Wakasa Bay. Although it remains uncertain whether these acoustic variations stemmed from environmental soundscapes or intrinsic differences among the animals, the collected data strongly suggests the presence of Indo-Pacific bottlenose dolphins in these areas.
This research not only establishes baseline knowledge on the temporal and spatial occurrence of small odontocetes along the Sea of Japan’s coast but also underscores the efficacy of passive acoustic monitoring as a vital tool in marine ecology. Traditional observational methods often falter with infrequently sighted species, whereas acoustic techniques can detect elusive animals continuously and remotely.
Looking forward, the team’s work opens the door to enhanced, long-term ecological monitoring that could prove instrumental in detecting shifts in marine biodiversity due to environmental stressors, climate change, or human activity. Such insights are crucial for informing conservation strategies and ensuring the sustainable management of coastal marine resources in collaboration with local populations.
First author Satoko S. Kimura emphasized the symbiotic relationship fostered between scientists and fishers, noting, “By listening to the sea with the community’s support, we are beginning to unravel the hidden lives of dolphins in waters familiar to us all.” The study offers hope for integrating traditional knowledge with cutting-edge science to better protect marine ecosystems sharing the Sea of Japan’s dynamic coasts.
Subject of Research: Animals
Article Title: Occurrence and Whistle Characteristics of Small Odontocetes in Two Coastal Regions of the Sea of Japan
News Publication Date: 25-May-2026
Web References: http://dx.doi.org/10.1111/mms.70200
Image Credits: Chihiro Kinoshita
Keywords: odontocetes, Indo-Pacific bottlenose dolphins, passive acoustic monitoring, marine mammals, Sea of Japan, echolocation, whistle characteristics, coastal ecology
