Shark Niño? The powerful climate pattern could send more dangerous sea creatures to the West Coast. Experts expect unusual sharks, snakes and stingrays.
Ocean heat and El Niño pose challenges for marine life
There is growing concern about the potential impacts of El Niño and marine heatwaves on marine life when they occur simultaneously.
An intensifying El Niño is forecast to make it “a sharky summer” off the California coast, with greater numbers of white sharks arriving with warmer waters from the south, but they are far from the only marine life expected to make surprise visits.
Strong El Niños can move several species of sharks, as well as rays, tropical fish, birds and even sea snakes northward into waters where they rarely appear.
“We expect to see all kinds of weird tropical things come up with this warm water,” said Douglas McCauley, director of the Benioff Ocean Initiative at the University of California, Santa Barbara.
The strongest El Niños – and this one is forecast to be among the very strongest – can alter entire marine ecosystems, shifting both animals and the food they need to survive.
Its ripple effects in winds, rain and ocean currents can extend across the world’s oceans. Studies have linked El Niño and its cooler water counterpart – La Niña – to starving sea lions in Peru, changes in sea turtle behaviors in the Caribbean and fisheries successes in the Amazon and Congo rivers.
El Niño can trigger “a lot of animal movement,” said Nate Jaros, a vice president of animal care at the Aquarium of the Pacific.
This summer, juvenile sharks and other aquatic visitors are turning up early, thanks to the effects of an intense marine heat wave already in place before El Niño arrives, McCauley said.
“We’re already seeing Mahi mahi. You’ll see more bluefin tuna, and you see weird stuff, like we’ll see more sea turtles and sea snakes,” McCauley said.
The yellow-bellied sea snake, “a highly venomous sea snake,” turns up only during unusually warm periods and should not be handled, he said. “Some of these kinds of interesting oddities that are never a part of California will become part of this temporarily tropical El Niño-heated California.”
A ‘whole different ocean’
El Niño and La Niña – phases of the El Niño Southern Oscillation – have cascading effects across global oceans, affecting distribution and abundance of marine life, even in the year after the event. El Niño brings warmer-than-normal water to the eastern Pacific.
Normally in the California current off the Pacific coast, colder, nutrient-rich water flows up from below, bringing nutrients that fish, kelp forests and other marine life depend on. El Niño can suppress upwelling and cut off the supply of zooplankton, small fish and other prey items.
“We get this whole different ocean,” said Chris Lowe, a professor of marine biology and director of the Shark Lab at Long Beach State University.
Squid, anchovies and sardines get pushed north. Tiger sharks and bull sharks have been caught off California during previous El Niño events.
Hammerhead sharks arrive following mahi mahi, and can be more aggressive when chasing fish, Lowe said. During the 2015-2016 El Niño, two hammerhead shark bites were reported offshore.
This year, between the marine heat wave and rapidly expanding El Niño, scientists expect to see more of the same.
The Shark Lab is working to help prepare fishermen, surfers and others that they’re going to be sharing the ocean this summer and fall with animals “they’re not used to sharing it with,” Lowe said. “They may have to change their behavior to be safe.”
‘A sharky summer’
Among the most striking changes that occur off the California coast are the white sharks that arrive, primarily large numbers of juvenile sharks that follow warmer water temperatures within the very narrow range that is their comfort zone. Because of their limited size, they’re like Goldilocks, McCauley said. They want the water “just right.”
During the strong El Niño in 2015, there was also a blob of warm water offshore, and juvenile white shark numbers doubled and pushed north all the way to Monterey, Lowe said.
“They came out of nowhere and we couldn’t explain where they were coming from,” he said. “All we knew was water temperatures down off San Diego hit a record high of 80 degrees for the first time ever.” He later learned from colleagues in Mexico that their fishermen saw white shark numbers plummet.
Because of the marine heat wave, a UC Santa Barbara project that uses drones to observe sharks at a nearby beach has seen a twofold increase in white sharks so far this year, McCauley said. The initiative collaborates with the Shark Lab to share sightings with the public and lifeguards in the SharkEye project.
The increase in mostly smaller-sized white sharks does not necessarily increase the risk for beachgoers, the scientists said.
The bigger concern might be the increase in rays, Lowe said. Warmer water tends to bring more brown stingrays, a favorite of juvenile sharks.
“When I say this is going to be a sharky summer, what I should also say is it’s going to be a stingray summer as well, and we’re probably going to have record numbers of stingray injuries to people,” Lowe said. One of his students recently found that California lifeguards treat at least 10,000 people a year for stingray injuries, he said. “I’m predicting it’s going to go way higher this summer.”
History shows El Niño’s global ocean impacts
Previous El Niño and La Niña events demonstrated an influence far beyond extreme weather, showing how interconnected the world’s oceans really are.
During the 1982-1983 El Niño, sea birds on Christmas Island abandoned chicks to search for food and fur seal and sea lions were starving in Peru. Already this year, Reuters has reported hungry pelicans in Peru.
During the 2023-2024 El Niño, California sea lion pups saw lower growth rates, the National Oceanic and Atmospheric Administration reported. Fishing boats as far north as Alaska caught unusual species, and fewer tiny crustaceans known as copepods were found off the Oregon coast.
In the Atlantic, El Niño can not only suppress hurricanes, it can increase rainfall in the Amazon and Congo river basins, influencing the harvest of shrimp and other marine species, according to a study in the journal Nature Reviews Earth and Environment. It has been linked to shifts in abundance of fish along parts of the Atlantic coast in Africa and South America.
Scientists have not seen any effect of El Niño on white sharks along the U.S. Atlantic coast, Greg Skomal, one of the nation’s leading white shark researchers and a senior fisheries biologist with the Massachusetts Division of Marine Fisheries, told USA TODAY.
Studies have linked El Niño and La Niña events to prey availability and nesting in sea turtles, but correlating numbers of nests to these events “is really tricky and not straight-forward since a lot of factors go in to when and how frequently individual turtles nest,” said Kate Mansfield, a professor and director of the Marine Turtle Institute at the University of Central Florida. When less food is available, it may take longer for sea turtles to “bank” the energy needed to migrate back to their breeding areas and reproduce, she said.
‘A double whammy’
Scientists are growing especially concerned about the prolonged impacts of the warming waters associated with this El Niño, in light of the forecast.
“It’s going to be a double whammy,” McCauley said. With El Niño stacking new heat on top of the warmth already present from the heat wave and climate change, it’s likely to reveal more about how consequential the pattern could be in a warming world.
“It’s going to be a weird and interesting fall and winter, that’s for sure,” with a clearer picture emerging by October, he said. “But I can tell you it’s not going to be normal. So we’re watching with great interest all facets of the ocean, including sharks.”
Dinah Voyles Pulver, a national correspondent for USA TODAY, has written about sharks, climate change, violent weather and other news for decades. Reach her at [email protected] or @dinahvp on Bluesky.
