The waters off California have grown quieter, and scientists are listening. New research from the Monterey Bay Aquarium Research Institute (MBARI) has found a sharp decline in the number of blue whale songs detected in the California Current Ecosystem following a prolonged marine heat wave.

Blue whales, once known for booming their deep, sonorous songs across the California Current Ecosystem (CCE), are going silent—and scientists believe it’s a warning we’d be foolish to ignore. A six-year study published in the Public Library of Science tracked the vocal activity of blue,