Blue whales off the coast of California have mysteriously gone silent, with their songs dropping by nearly 40 percent over the past six years, according to a new study by the Monterey Bay Aquarium Research Institute. Researchers warn this silence signals a deeper crisis in the oceans as climate change accelerates.
The study, published in August 2025, used underwater microphones along a 32-mile cable off Monterey Bay to monitor whale sounds. It found that major marine heatwaves, particularly 'The Blob' which began in 2013 and raised ocean temperatures by over 4.5°F, devastated krill populations—a key food source for blue whales. 'It's like trying to sing while you're starving,' said biological oceanographer John Ryan.
The heatwave also triggered toxic algae blooms, causing widespread poisoning of marine mammals. 'These were hard times for whales,' Ryan told National Geographic. Blue and fin whales, which feed almost exclusively on krill, were heard far less often, while humpbacks with more varied diets continued singing normally.
Researchers observed similar silence in blue whales off New Zealand between 2016 and 2018 during the same heatwave. 'We were interested in understanding blue whale ecology,' said ecologist Dawn Barlow. 'And without trying, we ended up studying the effects of marine heatwaves.'
With krill numbers plummeting and their behavior disrupted by warmer waters, whales are spending all their energy searching for food. 'We don't hear them singing,' Ryan said. 'They're spending all their energy searching. There's just not enough time left over.'
