Fluctuations in Whale Song Reveal Link to Food Availability off California Coast

Researchers have found that the vocal activity of blue, humpback, and fin whales in a California marine sanctuary directly correlates with food availability, dispelling concerns about a potential silence among these majestic creatures. A study published last year by scientists at the Monterey Bay Aquarium Research Institute (MBARI) analyzed underwater recordings collected using hydrophones within the Monterey Bay National Marine Sanctuary, comparing them to fisheries data from the National Oceanic and Atmospheric Administration (NOAA).

Biological oceanographer John Ryan, lead author of the PLOS One study, explained that while whales utilize a range of vocalizations, male whales primarily engage in singing—a behavior thought to play a crucial role in attracting mates and facilitating communication. The ability to detect these songs highlights the vast range over which whales can communicate; a single whale’s song can be heard from distances spanning thousands of square kilometers.

The study’s origins lie in 2015, coinciding with a severe marine heatwave dubbed “the blob,” which severely disrupted the marine ecosystem and led to widespread food scarcity. That year marked the period with the lowest recorded levels of whale song. As ocean temperatures gradually cooled and the ecosystem began to recover, so too did whale vocalizations.

Between 2015 and 2018, blue whale singing experienced a significant upswing, followed by a decline between 2018 and 2020 before rising again in 2021. These fluctuations closely mirrored changes in the abundance of krill, the whales’ primary food source. Researchers suggest that limited food resources necessitate energy conservation, potentially reducing the amount whales dedicate to singing.

Skin sample analysis confirmed blue whales continued to consume krill even when its availability was reduced; humpback whales demonstrated greater flexibility, shifting their diet between krill and fish like anchovies and sardines. Consequently, humpbacks were the only species exhibiting a sustained increase in vocal activity throughout the six-year study period.

The MBARI findings align with a 2023 investigation published in Ecology and Evolution, which documented reduced blue whale calls off New Zealand during marine heatwaves. Both studies underscore the detrimental impact of rising ocean temperatures on whale populations. Marine heatwave events have dramatically increased over recent decades, with significant occurrences in both 2023 and 2024. While the current study’s data concludes in June 2021, ongoing monitoring continues to track whale song patterns. When questioned about a perceived silence among blue whales since that time, Ryan confirmed, “Nope.”

Blue whales remain significantly rarer than before widespread commercial whaling practices of the early 20th century. Following the implementation of hunting bans, their populations have been gradually increasing, though recent population estimates are several years old. A NOAA assessment indicates approximately 1,898 blue whales reside in the eastern North Pacific region.