Are Blue Whales Going Silent? What the Research Actually Shows

Short answer

• Blue whales have not stopped singing. A six-year MBARI-led study (2015 to 2021), published in PLOS ONE in February 2025, found that blue whale song detections off California tracked the availability of krill, falling sharply in the food-poor years that followed a major marine heatwave and rising again as food returned.
• News coverage in 2025 reported a drop of nearly 40 percent in blue whale song during the worst of those years. That figure describes song detected at one listening station off California, not a worldwide silence and not a population count.
• The researchers' explanation is energetic, not acoustic. Blue whales eat almost nothing but krill. When krill is scarce, the whales spend their time and energy searching wider for food, leaving less for singing. Lead author John Ryan of MBARI compared it to "trying to sing while you're starving."
• Separately, the pitch of blue whale song has been dropping for decades in populations around the world (documented since a 2009 study in Endangered Species Research). Why is still debated.
• What is not established: that blue whales are ceasing to sing altogether, or that the song pattern by itself proves a population decline. NOAA lists the species as endangered, and its main documented threats today are ship strikes and entanglement in fishing gear.

Introduction

In the summer of 2025, headlines around the world announced that blue whales, the largest animals that have ever lived, were “going silent.” The stories were alarming, and some of them went well beyond what the underlying science says. The research behind the headlines is real, careful work: a six-year acoustic study led by the Monterey Bay Aquarium Research Institute (MBARI), published in the journal PLOS ONE in February 2025. It found that blue whale song off California rose and fell with the supply of krill, the whales’ almost exclusive food, and that song detections dropped steeply during the years when a marine heatwave starved the ecosystem.

That is a significant finding, and it is not the same thing as whales falling silent for good. This article separates what the study measured from what the headlines claimed, explains the mechanism the researchers propose, and places the result in its longer scientific context: blue whale songs have also been getting deeper in pitch for decades, for reasons that remain unsettled, and the whales sing in an ocean that human shipping has made much noisier. It also states plainly what the research does not establish, because on this topic the gap between the data and the drama is the story.

What the Study Actually Found

The study behind the headlines is “Audible changes in marine trophic ecology: Baleen whale song tracks foraging conditions in the eastern North Pacific,” by John P. Ryan of MBARI and seventeen co-authors from institutions including Cascadia Research Collective, NOAA Fisheries and the University of Wisconsin. It was published in PLOS ONE on February 26, 2025.

The team listened through a hydrophone, an underwater microphone, mounted on the Monterey Accelerated Research System (MARS), a cabled seafloor observatory that MBARI operates on the continental slope outside Monterey Bay, California. The instrument sits about 891 meters (roughly 2,900 feet) below the surface, connected to shore by a 52-kilometer cable that delivers power and a continuous stream of data. From July 2015 through June 2021, the hydrophone captured recordings on 2,111 of the 2,192 days in the period, a 96 percent capture rate that let the researchers track song month by month rather than in scattered snapshots.

The timing was an accident with scientific value. Recording began in July 2015, while the Northeast Pacific was still in the grip of “the Blob,” the severe marine heatwave of 2014 to 2016 that warmed a vast stretch of ocean, suppressed the cold-water productivity the food web depends on, and was accompanied by toxic algal blooms. Ryan described those years bluntly in 2025 coverage of the study: the bloom “caused the most widespread poisoning of marine mammals ever documented. These were hard times for whales.”

Across the six years, the researchers found that detections of song from blue whales, fin whales and humpback whales moved with the food supply. Song from all three species was at its lowest during the worst of the heatwave. As conditions improved and prey rebounded, song rose. Blue whale song peaked in the third year of the study, when krill was abundant, fell again in the fifth year when krill crashed a second time, and rose again by 2021. In other words, the study’s central result is that baleen whale song tracks foraging conditions: the whales sing most when feeding is good.

Where the “40 Percent” Figure Comes From

When National Geographic reported the study in July 2025, setting off the wave of “going silent” coverage that followed in August 2025, it reported that blue whale vocalizations had dropped by nearly 40 percent alongside a collapse in krill and anchovy populations during the food-poor years. Most of the headlines that spread afterward kept the number and dropped the context.

Three qualifications matter. First, the figure concerns song detections at a single listening station off central California over a six-year window, not a global survey of the species. Second, the study period began in the middle of a marine heatwave, so the early years were unusually bad years for food; measured from that starting point, singing rose substantially as the ecosystem recovered before falling back in the second krill crash. By the end of the study period, all three species were being heard more than at the beginning. Third, a hydrophone counts songs, not whales. Fewer detections can mean whales singing less, whales feeding somewhere beyond the instrument’s range, or both. The study’s own design links the pattern to prey data, which is why the researchers interpret it as a singing response to food scarcity; it is not, and was never presented as, a census.

Read carefully, the study is better described as showing that blue whale song is a sensitive gauge of feeding conditions, rising and falling with the krill supply, than as showing a one-way slide into silence.

Why Hungry Whales Sing Less

The mechanism the researchers propose is about energy budgets. Only male blue whales sing, and scientists believe the song is a mating advertisement, produced over long periods while the whales are dispersed. Singing is therefore, in effect, optional spending: important for reproduction, but not what keeps a whale alive this week.

Blue whales are extreme specialists. NOAA Fisheries notes that they feed almost exclusively on krill, straining huge volumes of water through their baleen plates, and that the biggest individuals may eat up to six tons of krill a day. Unlike humpback whales, blue whales cannot switch to fish when krill fails. The study supported this with chemical analysis of whale skin samples, which showed that in lean years the blue whales were ranging farther and wider in search of krill. A whale that is spending its days searching a larger ocean for scattered food has less time and less energy left over for song. That is the finding Ryan summarized for National Geographic: “When you really break it down, it’s like trying to sing while you’re starving. They were spending all their time just trying to find food.”

The fin whales in the study, which also feed almost exclusively on krill, showed the same pattern as the blue whales. That parallel strengthens the food explanation: two krill specialists quieted in the same lean years, while a generalist did not.

The Humpback Contrast

The study’s most instructive comparison is the humpback whale. Humpbacks eat krill too, but they also eat small schooling fish such as anchovies and sardines, and the study’s chemical evidence showed them switching between krill and fish as availability changed. Their song, instead of dipping, rose continuously across the six years, the only one of the three species to do so.

MBARI’s own summary of the research draws the lesson explicitly: blue whales feed exclusively on krill and are especially vulnerable to disruptions in that single food supply, while humpbacks are more resilient because of their flexible diet. The whale song archive, in other words, recorded two different strategies meeting the same ocean shock. The specialist absorbed the shock in its behavior, singing less. The generalist switched menus and kept singing. That is why the researchers describe whale song as a window into ocean health: it registers, species by species, how hard conditions are below the surface.

A Separate Puzzle: The Songs Are Also Getting Deeper

Long before the heatwave study, researchers had documented a different change in blue whale song, one that has nothing directly to do with how much the whales sing. Since at least the 1960s, the pitch of blue whale song has been steadily dropping.

Mark McDonald of WhaleAcoustics, with John Hildebrand of the Scripps Institution of Oceanography and Sarah Mesnick of NOAA Fisheries, analyzed thousands of recordings from blue whale populations around the world and published the result in Endangered Species Research in 2009. The tonal frequency of the songs had fallen by fractions of a hertz every year, in every population with data, even though the song styles differ between oceans. In the best-studied population, off California, the pitch dropped by 31 percent over the study period. The drift was steady enough that researchers had to keep recalibrating their detectors to lower frequencies to keep tracking the songs.

Why it is happening remains genuinely unsettled, and the scientists involved say so. McDonald and his co-authors weighed several hypotheses, including rising ocean noise, changes in ocean chemistry and temperature, and changes in the whales themselves. Their favored explanation was demographic: as blue whale numbers slowly recover from the whaling era, males may not need to sing as loudly to reach the same number of listeners, and singing louder is physically easier at higher frequencies. NOAA’s own public summary of the phenomenon is candid: scientists found that blue whales have been singing at lower frequencies over the past fifty years, and the reason remains a mystery.

The honest position is that two distinct things are true at once. Blue whale song volume, in the sense of how much singing researchers detect, rises and falls with food conditions on timescales of years. Blue whale song pitch has been sliding downward for decades for reasons nobody has proven. Neither finding supports the claim that the species is on its way to total silence.

Singing in a Louder Ocean

There is a third strand of context that the “going silent” headlines usually blur into the heatwave story, and it should be kept separate: the ocean has become a much noisier place, and noise interferes with whale communication in its own right.

NOAA Fisheries explains the core problem as masking. Whales rely on sound to communicate, navigate, and detect predators and prey. When background noise from human activity rises, especially in and near commercial shipping lanes and busy ports, a whale’s calls can be drowned out for other whales, shrinking the area over which it can be heard. NOAA scientists model this as a loss of “communication space,” and the agency warns that these effects, repeated over long periods and combined with other stressors, can affect the health, reproductive success and survival of whales. The 2009 pitch study raised a related point: ambient noise in the oceans has increased substantially over the past half-century, largely from shipping, although the researchers noted that noise alone does not neatly explain the pitch drop, because an animal trying to be heard over noise would be expected to sing higher, not lower.

Noise is therefore a real, documented pressure on whale communication, and NOAA treats reducing ocean noise as part of blue whale conservation. But it is not the mechanism the MBARI study measured. The California song pattern tracked food, year by year, in an ecosystem recovering from and relapsing after a heatwave. Folding the two stories into one vague claim about whales “going silent” because of noise misstates what this study found.

Blue whales are not the only whales affected: killer whales, which hunt in pods and rely on sound to find food, also struggle in a louder ocean.

How Scientists Listen to an Ocean

The study was possible because ocean listening has changed. A cabled observatory like MARS delivers a continuous, years-long recording from a fixed point in the deep ocean, something that battery-powered recorders, which must be retrieved and serviced, cannot easily match. MBARI recorded on 96 percent of days across six years, and the team processed that archive with automated tools: a deep-learning model trained to recognize humpback song patterns, and a signal-energy method for the lower, tonal blue and fin whale songs, both checked against manually reviewed spectrograms.

This kind of long-term acoustic monitoring is now a standard way to track whales that spend most of their lives far from shore and out of sight. It detects presence and behavior cheaply and continuously, and, as this study showed, it can register ecosystem changes, in prey abundance, in the whales’ behavior before those changes are obvious any other way. Its limits follow from the same design: one station hears one region. A quiet month at the MARS hydrophone is evidence about conditions and behavior in the whales that use that region, which the researchers then tie to prey surveys and chemical evidence. It is not a headcount of the species.

What the Research Does Not Show

Because this topic attracts exaggeration, the limits deserve their own summary:

• It does not show that blue whales have stopped singing. Within the study itself, song rose markedly in the recovery years and all three species were heard more at the end of the period than at the start.
• It does not show a population decline. The study measured song detections and linked them to prey data. NOAA’s species assessment is a separate matter: blue whales are listed as endangered under the US Endangered Species Act and protected under the Marine Mammal Protection Act; NOAA estimates roughly 10,000 to 25,000 blue whales worldwide, describes populations as increasing globally from their whaling-depleted low, and names vessel strikes and entanglement in fishing gear as the primary current threats.
• It does not show a permanent trend. Six years, one region, and a period that began mid-heatwave cannot establish where song levels go over decades. What it establishes is a relationship: when krill fails, krill-specialist whales sing less.
• It does not identify a single villain. The heatwave, toxic algal blooms, prey dynamics, ocean noise and a recovering population’s shifting song pitch are separate threads of evidence. Careful coverage keeps them separate; the whales’ situation does not need the threads tangled to be serious.

Blue Whale Basics, Briefly

The animal at the center of this story needs little embellishment. NOAA Fisheries describes blue whales as not only the largest of the rorqual whales but the largest animals ever to live on Earth, reaching about 110 feet in length. They are found in all oceans except the Arctic, in five recognized subspecies, and they feed almost exclusively on krill. Commercial whaling in the early twentieth century reduced them to a small fraction of their earlier numbers, which NOAA estimates at roughly 300,000 before whaling; hunting was banned internationally in 1966, and the slow recovery since is part of the backdrop to everything researchers now measure, including, possibly, the deepening of their song.

Only males sing, and the song, very low in frequency and among the most powerful sounds made by any animal, can carry across enormous distances underwater, which is what makes a single hydrophone off California able to hear whales across a wide region, and what makes the species so well suited to being studied by ear.

Frequently Asked Questions

Are blue whales actually going silent?

No. A six-year study off California (2015 to 2021) found that blue whale song detections rose and fell with krill availability: low during the marine heatwave years, higher when food returned. Headlines in 2025 reporting a drop of nearly 40 percent referred to the food-poor years in that study, at one listening station, not to a worldwide or permanent silence.

Why do blue whales sing less when food is scarce?

Because singing costs time and energy that a hungry whale needs for finding food. Blue whales eat almost exclusively krill and cannot switch prey. Chemical evidence in the MBARI-led study showed the whales ranging farther in lean years, and lead author John Ryan compared the result to trying to sing while starving. Fin whales, also krill specialists, showed the same pattern; humpbacks, which can switch to fish, did not.

Why is blue whale song getting lower in pitch?

Nobody knows for certain. A 2009 study by McDonald, Hildebrand and Mesnick documented the pitch dropping in every blue whale population with data, by 31 percent off California since the 1960s. The authors’ favored hypothesis links it to slowly recovering population numbers after the whaling ban, but they and NOAA both treat the cause as unproven.

Does ship noise stop blue whales from singing?

Noise is a separate, documented problem: NOAA explains that rising background noise, mainly from shipping, masks whale calls and shrinks the area over which whales can hear each other. It is not the explanation the MBARI study found for the California pattern, which tracked food supply year by year.

How do scientists hear whales they cannot see?

With hydrophones: underwater microphones. The 2025 study used one mounted on MBARI’s MARS cabled observatory, about 891 meters deep outside Monterey Bay, which recorded nearly continuously for six years. Automated analysis, including a deep-learning model for humpback song, processed the archive, checked against human-reviewed spectrograms.

Are blue whales endangered?

Yes. NOAA Fisheries lists blue whales as endangered under the Endangered Species Act and protected under the Marine Mammal Protection Act, with an estimated 10,000 to 25,000 worldwide, increasing from a whaling-depleted low. NOAA names vessel strikes and entanglement in fishing gear as the primary current threats.

Conclusion

“Going silent” is a headline, not a finding. The finding, from MBARI and its partners in February 2025, is subtler and more useful: the amount of blue whale song in the ocean off California is a living readout of the food supply, dropping when a marine heatwave empties the water of krill and recovering when the krill return. Around that result sit two other honest stories: a decades-long, unexplained deepening of the song’s pitch, and a noisier ocean that makes every call harder to hear. The whales are still singing. What the science actually shows is that when the largest animal on Earth goes quieter, it is usually telling us the pantry is empty, and that is worth hearing precisely.

Sources & references

• Ryan, J.P., and co-authors (MBARI, Cascadia Research Collective, NOAA Fisheries, University of Wisconsin), "Audible changes in marine trophic ecology: Baleen whale song tracks foraging conditions in the eastern North Pacific," PLOS ONE 20(2), February 26, 2025: study design, MARS hydrophone data from July 2015 to June 2021, song tracking foraging conditions, skin-sample chemical evidence, species diet differences.
• Monterey Bay Aquarium Research Institute (MBARI), Annual Report 2025, "A tale of two whales: Songs reveal levels of resilience among whales": blue whales feed exclusively on krill and are especially vulnerable; humpbacks more resilient due to flexible diet.
• National Geographic (nationalgeographic.com), July 2025, "Blue whales are going eerily silent, and scientists say it's a warning sign": the nearly 40 percent drop in blue whale vocalizations during the food-poor years, the Blob's effects, and John Ryan's "sing while you're starving" and "most widespread poisoning of marine mammals" quotations.
• McDonald, M.A., Hildebrand, J.A., and Mesnick, S., "Worldwide decline in tonal frequencies of blue whale songs," Endangered Species Research, 2009 (via Scripps Institution of Oceanography news release): global pitch decline, 31 percent off California since the 1960s, candidate explanations with population recovery favored, cause unproven.
• NOAA Fisheries (fisheries.noaa.gov), "Blue Whale" species page: largest animal ever to live; feeds almost exclusively on krill, up to six tons a day; endangered under the Endangered Species Act, protected under the Marine Mammal Protection Act; found in all oceans except the Arctic; five subspecies; primary threats are vessel strikes and entanglement.
• NOAA Fisheries, "The Big-Hearted Blue Whale" feature story: population estimate of about 10,000 to 25,000 worldwide and about 300,000 before whaling; only males sing; song frequency has fallen over the past fifty years and the reason remains a mystery.
• NOAA Fisheries, "A Whale's World of Sound" (Ocean Noise): masking explained, loss of communication space, effects concentrated near shipping lanes and ports, repeated impacts can affect health, reproductive success and survival.