Eavesdropping on baleen whale songs in the Pacific Ocean reveals year-to-year variations that track changes in the availability of the species they forage on, reports a new study led by John Ryan, of the Monterey Bay Aquarium Research Institute (MBARI), U.S., published February 26, 2025 in the open-access journal PLOS One.
In the vast oceans, monitoring populations of large marine animals can be a major challenge for ecologists. Scientists deploy underwater microphones called hydrophones to study and track baleen whales, which communicate over long distances through sound. In the new paper, researchers monitored songs from blue, fin and humpback whales off the West Coast of the United States for six years, to see what the song data could reveal about the health of their ecosystem.
The researchers saw large year-to-year variations in whale song detection. The amount of humpback whale song continually increased, with their songs being detected on 34% of days at the beginning of the study and rising to 76% of days after six years. These increases consistently tracked improved foraging conditions for humpback whales across all study years, large increases in krill abundance, followed by large increases in anchovy abundance. In contrast, blue and fin whale song rose primarily during the years of increasing krill abundance. This distinction of humpback whales is consistent with their ability to switch between dominant prey. An analysis of skin biopsy samples confirmed that changes had occurred in the whales' diets. Other factors, including the local abundance of whales, may have contributed to patterns in song detections observed in some years, but changes in foraging conditions were the most consistent factor.
Overall, the study indicates that seasonal and annual changes in the amount of baleen whale song detected may mirror shifts in the local food web. The results suggest that an understanding of the relationship between whale song detection and food availability may help researchers to interpret future hydrophone data, both for scientific research and whale management efforts.
John Ryan, a biological oceanographer at MBARI and the lead author of this study, adds: "Surprisingly, the acoustic behavior of baleen whales provides insights about which species can better adapt to changing ocean conditions. Our findings can help resource managers and policymakers better protect endangered whales."
In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/41jvLtU
Citation: Ryan JP, Oestreich WK, Benoit-Bird KJ, Waluk CM, Rueda CA, Cline DE, et al. (2025) Audible changes in marine trophic ecology: Baleen whale song tracks foraging conditions in the eastern North Pacific. PLoS ONE 20(2): e0318624. https://doi.org/10.1371/journal.pone.0318624
Author countries: U.S., Australia
Funding: The work of JPR, WKO, KJBB, CMW, CAR, DEC and YZ was funded by The David and Lucile Packard Foundation, through an annual grant to the Monterey Bay Aquarium Research Institute. The U.S. National Science Foundation funded installation and maintenance of the MARS cabled observatory through awards 0739828 and 1114794. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
