A new six-year study off California’s coast found that vocalizations of blue whales dropped by nearly 40% during a recent marine heatwave.

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.