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.

As blue whales struggled, humpbacks adapted. Unlike their strictly krill-dependent cousins, they feed on sardines and anchovies too—fish that weren’t impacted by The Blob. Humpback whale songs increased during the study, rising from 34% to 76% of days recorded.