Blue whales go quiet off California after marine heat wave
A six-year acoustic study reveals a sharp drop in blue whale songs off the California coast following a record marine heat wave.
Jul 27, 2016; 8:40 AM ET Tourists in southern California are getting an awesome show of whale watching as plenty of Blue and Humpback whales make an appearance.
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. The study, which spanned six years of acoustic monitoring, revealed that blue whale vocalizations dropped significantly during and after the climate event known as “The Blob.”
Using underwater hydrophones, researchers tracked the sounds of three whale species — blue, fin and humpback — from 2015 onward. According to the Public Library of Science journal article, blue whale songs dropped by 40% during the study period, with the lowest point recorded in 2015, the year following peak heat wave activity.
The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whales (Mysticeti), and sometimes found in the Monterey Bay, California. (Photo credit: Getty Images)
The timing is no coincidence, researchers say.
“Analyzing baleen whale songs has revealed year-to-year variations that reflect changes in the availability of the species they forage on,” John Ryan, a biological oceanographer who leads MBARI’s Ocean Soundscape Team and was the study’s lead author, said. “These findings offer vital clues about how resilient different whale species may be in the face of changing ocean conditions.”
The 2015 marine heat wave, which was nicknamed “The Blob," created a swath of ocean water up to 4.5 degrees Fahrenheit above the historical average, covering over 2,000 miles of the Pacific. The temperature spike disrupted the marine food web, killing off krill, the primary food source for blue whales, and triggering harmful algal blooms that led to what Ryan described to National Geographic as “the most widespread poisoning of marine mammals ever documented.”
“It’s like trying to sing while you’re starving,” Ryan told National Geographic. “They were spending all their time just trying to find food...Possibly, when food is limited, whales need to dedicate more time to foraging and don’t have as much time to sing.”
A blue whale in the Gulf of Thailand. (Photo credit: Getty Images)
That lack of food may explain the silence. Blue whales, unlike humpbacks, rely exclusively on krill. When those tiny crustaceans vanish, so does the whales' ability to stay in one place long enough to sing or to mate.
Other whale species fared differently. Humpback whales, which feed on both krill and forage fish like sardines and anchovies, had more food options during the heat wave. Researchers noted that humpback whale songs actually increased over the same period, further highlighting how dietary flexibility may play a role in resilience to environmental disruption.
“Compared to humpback whales, blue whales in the eastern North Pacific may be more vulnerable due to not only a smaller population size but also a less flexible foraging strategy,” Ryan said, according to Newsweek. “These findings can help scientists and resource managers predict how marine ecosystems and species will respond to climate change.”
Blue whales may also use specific vocalizations to signal feeding opportunities to one another. “Hey, my fellow blue whales, I am yumming it up here. Krill’s up,” Ryan said, describing a call that has been observed drawing in other whales from miles away.
Acoustic monitoring is becoming an increasingly powerful tool for understanding ocean health. By analyzing patterns in whale song, scientists can track behavioral shifts, identify stress points in the ecosystem and anticipate how marine species may respond to a warming world.
“Just from picking up whale song you can start to make more inferences about the broader ecosystem,” Andy Rogan, a marine mammal biologist with Ocean Alliance, told Mongabay.
“There are whole ecosystem consequences of these marine heatwaves,” marine biologist Kelly Benoit-Bird of the Monterey Bay Aquarium told National Geographic. “If they can’t find food, and they can traverse the entire West Coast of North America, that is a really large-scale consequence.”
Dawn Barlow, an ecologist at Oregon State University, added that “where they are, and what they’re doing can tell you a lot about the health of the ecosystem.” She told National Geographic, “Now more than ever, it’s important to listen.”
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