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The climate crisis is pushing great white sharks into new waters where they are plunging populations of endangered wildlife, research shows.
Ocean warming, which reached an all-time high in 2020, has led young great white sharks to travel 600 km (373 miles) north off the coast of California since 2014, in previously too cold waters . During this period, there has been a dramatic increase in the number of sea otters being killed by white sharks, with the number in Monterey Bay dropping 86%.
The overall range suitable for sharks in the region has diminished as more areas have become too hot, forcing predator and prey to come close. The shark is the main predator, so its change is disrupting ecosystems with populations of fish like salmon also declining. There are also concerns about the potential for further encounters between sharks and humans, although the rate of shark attacks has fallen sharply in recent decades.
Scientists hope that a large-scale shark habitat disruption will highlight how global warming is pushing marine animals toward the poles and scrambling for species in ocean ecosystems, with unpredictable and damaging consequences .
“White sharks aren’t just another species – they’re a supreme predator and all eyes are on them in the ocean,” said Kyle Van Houtan, of the Monterey Bay Aquarium in California. The displacement of species ranges is a global phenomenon, he said. “What we have detected here is just a harbinger of much larger models.”
“Sharks are not the problem – climate change is the problem,” he said. “Sharks tell us that the ocean is changing and now is the time for us to do something.”
Professor Malin Pinsky, of Rutgers University, USA, and not part of the research team, said: “This is a particularly interesting example of the mass movement of marine life that is currently taking place. off our coasts, involving everything from mangroves to cod. . Climate change is confusing our ocean ecosystems and sometimes producing surprises with a lot of bite. “
The new research, published in the journal Scientific Reports, analyzed the whereabouts of great white sharks and ocean temperature using millions of measurements, from tags placed on sharks to sightings reported by observers. from wildlife.
“We are able to document a dramatic increase in juvenile white sharks in Monterey Bay that began with a marine heat wave in 2014,” Van Houtan said. Juvenile great white sharks are those less than 2.5 meters (8.2 feet) in length. Unlike adult adults, juveniles are too small to maintain body temperature in the normally cold waters of Monterey Bay.
The marine heat wave in the North Pacific lasted from 2014 to 2016. It was called “the gout” and affected other marine animals, including the deaths of a million seabirds. “Fascinatingly, after this heat wave ends, it’s still hot and the white sharks haven’t gone away – they’re still there,” Van Houtan said.
Scientists have shown that the cold limit for young sharks shifted north by an average of 600 km between 2014 and 2020. “It’s an incredible distance in just a few years,” he said.
Young great white sharks eat fish before moving on to seals and sea lions as adults. Young white sharks are believed to kill sea otters by learning to hunt mammals. “The sea otter is an endangered species and very important to the California coast as ecosystem engineers, both in kelp forests and seagrass beds,” Van Houtan said.
Scientists have found that the ocean area off California with temperatures suitable for young white sharks – 15 ° C to 22 ° C – has shrunk by about 5%. “It doesn’t look big in the general scheme of things, but predators and prey are now squeezed into a smaller place, where prey has fewer places to hide. So you see a very rapid decline in fish, including salmon, ”he said.
Ocean ecosystems are already damaged by overfishing, pollution and noise. “They need all of their components to survive and thrive and adding additional factors into the equation, like warming and juvenile white sharks, only exacerbates this plight,” Van Houtan said.
A particularly warm part of Monterey Bay attracts both people and young sharks. “It has definitely become a problem locally, and there has been a concern for public safety on the beaches,” he said. “Even though they’re just juveniles, six or seven feet long, and supposed to eat fish, it definitely awakens your consciousness. Recent research has shown that the rate of shark attacks in California has dropped 91% since 1950 thanks to people with better information on how to avoid encounters.
Professor Pinsky said: “This research is also a great example of the power of citizen scientists. Without people recording what they saw with apps like iNaturalist, this massive expansion of juvenile white sharks may have gone unnoticed.
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