Here’s Which Sea Animals Are Hurt Most by the U.S. Heatwaves


Heatwaves can have a devastating impact on some marine predators such as sharks but other species can adapt, scientists have discovered.

Marine heatwaves have become about 50 percent more frequent in the past 10 years, according to data from the National Oceanic and Atmospheric Administration (NOAA). They can lead to habitat loss and, in some cases, the deaths of marine mammals.

Scientists wanted to find out how marine life responded to the trend. Using data from tagged animals in the northeast Pacific, they found out how they redistributed themselves following heatwaves in 2014, 2015, 2019, and 2020.

Some predators, including sharks, mammals, seabirds, turtles and tunas, suffered “near total loss of habitat” due to the heatwaves, the study published in Nature Communications reported.

“There was a surprising diversity of impacts both across marine heatwaves, and across predators,” corresponding author Heather Welch, of NOAA, told Newsweek. “Predator habitat displaced in all four cardinal directions; some predators experienced a two-fold increase in habitat area during one heatwave, and then near-total loss of habitat area during another. So instead of being a story about winners and losers, this is a story of how variable marine heatwave impacts can be. To understand the full scope of impacts, we need to move beyond single-species, single-heatwave case-studies towards more holistic ecosystem-based investigations.”

Two tagged whales were among the animals assessed in a study on how heatwaves affect marine habitats. The consequences could be devastating for some species.
Elliott Hazen, Southwest Fisheries Science Center, NOAA

Bluefin tuna and blue sharks were the predators that suffered most from habitant loss in the 2015 heatwave. The California sea lion and elephant seal, however, experienced a two-fold habitat gain due the 2019 heatwave.

Some species can also redistribute themselves, and alter their migration patterns.

Around 11 to 31 percent of albacore, bluefin and yellowfin tuna habitat in Mexico switched to the U.S. during 2014 and 2015.

Although each habit change among these predators differed slightly, they were all “highly predictable,” the study reported.

“Importantly, we found that although marine heatwave impacts were highly variable, they were also highly predictable via models,” Welch said. “We can’t assume future heatwaves will impact species in the same way as past events, but we can predict the impacts of future heatwaves in real-time as they occur. Or better yet, we could forecast impacts ahead of time.”

Tagged sea lion
A tagged sea lion, also assessed in the study. Sea lions were able to adapt, it found.
Dan Costa, University of California Santa Cruz

Such habitat changes demonstrated that marine animals have early warning systems, similar in some ways to human weather forecasts, that alert them as to how a heatwave will impact their habitat.

Although studies have looked at long-term effects of marine heatwaves, less is known about the short term.

It is hoped that the study will help to produce predictions of where various species will be found, allowing better management of marine resources and preventing humans and wildlife coming into potentially dangerous contact.

“As adaptive management tools are needed to prepare nations and minimize future fishery conflicts, the authors also demonstrate a dynamic ocean management tool using their models that can produce daily predictions of the distribution for each species,” the study said.

“This early warning system would allow for proactive responses to new human-wildlife conflicts and changes in the availability of marine resources.”

“Such early-warning systems are particularly important because we found marine heatwaves can redistribute species across jurisdictional boundaries (e.g. national waters, the high seas),” Welch said. “Species jurisdictional redistributions have been observed in response to long-term warming (climate change), however we find that redistributions are also occurring due to the short-term episodic warming of heatwaves. Nations will need lead time to proactively plan ahead for species’ ingresses or egresses during heatwaves.”

Outside of marine heatwaves, all ocean basins have been steadily warming since the 1990s.

According to NASA, the ocean has absorbed 90 percent of the heat from global warming and 2020 was one of the warmest years recorded for ocean temperatures.

Data from the Climate Change Institute at the University of Maine has also shown that since mid-March 2023, the average sea surface temperature worldwide has been higher than it has ever been since accurate satellite temperature records began in 1981.

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