Eavesdropping on whale songs over the last six years is providing new information vital to answering questions about these giants of the ocean.
The number of whale songs detected is associated with shifting food sources, according to the California scientists—and the number of days humpbacks have been singing has nearly doubled.
When monitoring baleen whale songs in the Pacific Ocean, researchers found year-to-year variations corollated with changes in the availability of the species they forage on.
In vast oceans, monitoring populations of large marine animals can be a “major challenge” for ecologists, explained Dr. John Ryan, a biological oceanographer at the Monterey Bay Aquarium Research Institute in California (MBARI).
Their team deployed underwater microphones called hydrophones to study and track baleen whales, which communicate over long distances through sound.
“Surprisingly, the acoustic behavior of baleen whales provides insights about which species can better adapt to changing ocean conditions,” said Dr. Ryan, a lead author of the study.
They also monitored songs from blue, fin, and humpback whales off the West Coast of the U.S. to see what the song data could reveal about the health of their ecosystem.
The findings, published in the journal PLOS One, showed “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,” said Dr. Ryan.
“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.
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“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.”
He explained that 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.”
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“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”, which could better protect endangered species.
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