Blue Whales Are Going Silent. Scientists Warn It’s a Cry for Help

For centuries, the deep, resonant songs of blue whales have travelled across entire oceans, carrying messages between the planet’s largest creatures. Now, these voices are fading. A new six-year study off California’s coast suggests that marine heatwaves and noise pollution are altering the soundscape of the sea, and scientists warn the silence signals serious trouble. 

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Beneath the waves, the ocean is never truly quiet. The crackle of shrimp, the rumble of distant storms, and the haunting calls of whales create a constant chorus. Capturing these sounds is a small metal hydrophone anchored 3,000 feet below the surface of California, part of a network that allows researchers to eavesdrop on the underwater world year after year.

“When you start listening closely, you realise just how many creatures contribute to the ocean’s soundtrack,” said Jarrod Santora, an ecosystem oceanographer at the National Oceanic and Atmospheric Administration (NOAA), in an interview with National Geographic.  

When the researcher team – led by Monterey Bay Aquarium Research Institute’s Biological Oceanographer John Ryan, began monitoring in 2015, they had no idea a record-breaking marine heatwave was about to reshape the region. 

The marine heatwave, later dubbed The Blob, was first detected in 2013 as a warm patch in the Bering Sea. It expanded south along the Pacific Coast, stretching from Alaska to Mexico by 2016. In some places, water temperatures climbed more than 15C above normal, disrupting currents and scattering prey. 

For blue and fin whales – species that rely almost entirely on dense swarms of krill – this was devastating. Krill numbers plummeted, and those that remained were harder to find. The study found blue whale vocalizations dropped by nearly 40% during the heatwave years. 

“When we have these really hot years and marine heatwaves, it’s more than just temperature,” Kelly Benoit-Bird, a Monterey Bay Aquarium’s Marine Biologist and co-author of the paper, told National Geographic. “The whole system changes, and we don’t get the krill. So the animals that rely only on krill are kind out of luck.”

Humpback whales, which have more varied diets, continued to sing through the disruption. But for blue whales, whose feeding strategy depends on massive, high-reward gulps of krill-rich water, lean years means quieter oceans. 

“We don’t hear them singing,” said Ryan, referring to underwater sound recordings from that year. “They’re spending all their energy searching. There’s just not enough time left over – and that tells us those years are incredibly stressful.”

A Pattern Across Oceans

This decline was not limited to the eastern Pacific. In New Zealand’s South Taranaki Bight, researchers found a similar pattern between 2016 and 2018. Blue whale “D calls”, linked to feeding, fell during warm-water years, and their patterned mating songs decreased the following season. 

“When there’s less food, they invest less in reproduction,” said Dawn Barlow, a Marine Ecologist at Oregon State University. “It’s a clear indicator of ecosystem stress.” 

Barlow calls blue whales “sentinels” of ocean health: because they integrate signals from across vast feeding grounds, changes in their behavior reflect larger shifts in the marine environment. 

Extreme Heatwaves Are Here to Stay

Marine heatwaves are becoming more frequent, longer lasting, and hotter. Their average duration has tripled since the 1940s, with some events spiking ocean temperatures by up to 5C, according to an April study. These extremes ripple through the entire food web, from plankton to predators. 

“If whales that can travel thousands of kilometers, still can’t find food to eat, it’s a sign of large-scale disruption,” said Benoit-Bird. In some cases, repeated heatwaves may permanently alter ecosystems, affecting carbon storage, fisheries, and biodiversity.

Listening as a Conservation Tool 

Sound is one of the few ways scientists can track ocean changes over vast areas. But to measure disruption, they need to know what a healthy ocean sounds like – a baseline that is surprisingly hard to capture. 

The Covid-19 lockdown offered an accidental experiment. As shipping traffic dropped, underwater noise levels fell, and marine animals shifted into areas usually disrupted by human activity. “It is like seeing wildlife reclaim city streets, only underwater,” said Benoit-Bird. 

Long-term acoustic monitoring could help policymakers respond faster to environmental stress, regulate industrial noise, and identify critical feeding or breeding habitats before they are lost.

A Race Against Time

Blue whales can live for 80 years or more, meaning population trends play out slowly. Only a few dozen generations have passed since commercial whaling ended, and scientists say we cannot afford to wait centuries to act. 

“The science is clear – climate change is transforming the oceans,” said Barlow. “We see it from the smallest plankton to the largest predators. Listening to these ecosystems is essential if we hope to protect them.”

For now, the message from the ocean’s largest singers is simple and urgent: their songs are growing quieter. Whether we answer that warning or not could determine not just the fate of the blue whale, but the health of the oceans we all depend on.

Featured image: OSU Marine Mammal Institute/Oregon State University via Flickr.