The climate crisis is pushing great white sharks into new waters, where it is diving populations of endangered wildlife, research has shown.
Ocean warming, which reached a record level in 2020, has resulted in young great white sharks moving 600 km (373 miles) north of the California coast in waters that were previously too cold since 2014. At that time, there was a dramatic increase in sea otters killed by white sharks, with the number in Monterey Bay falling by 86%.
The overall range suitable for sharks in the region has shrunk as more areas have become too hot, forcing predators and prey closer together. The shark is the best predator, and its movement is upsetting ecosystems with populations of fish such as salmon also falling. There is also concern about the potential for new encounters between sharks and humans, although the rate of shark attacks has fallen sharply in recent decades.
Scientists hope that the disruption of the habitat of a sensational shark will highlight how global warming is pushing marine animals to the poles and confusing the species found in the oceans’ ecosystems, with unpredictable and damaging consequences.
“White sharks are not just another species – they are a top predator and all eyes are on them in the sea,” said Kyle Van Houtan, of the Monterey Bay Aquarium in California. The shift of species’ varieties is a global phenomenon, he said. “What we discover here is just a harbinger of much broader patterns.”
“The sharks are not the problem – climate change is the problem,” he said. “The sharks are telling us that the ocean is changing and that now is the time to do something about it.”
Prof Malin Pinsky, of Rutgers University, USA, and not part of the research team, said: ‘This is a particularly noteworthy example of the mass movement of marine life currently taking place on our coast, with everything from mangroves to cod. Climate change is disrupting our ocean ecosystems and sometimes it produces surprises with many teeth. ”
The new research, published in the journal Scientific Reports, analyzed the location of great white sharks and the temperature of the sea using millions of measurements, from labels placed on the sharks to observations reported by amateur game watchers.
“We can document a dramatic increase in juvenile white sharks in Monterey Bay that started in 2014 with a marine heat wave,” Van Houtan said. Juvenile great sharks are less than 2.5 meters long. Unlike adults, the juveniles are too small to maintain their body temperature in the usually cold waters of Monterey Bay.
The marine heatwave in the North Pacific lasted from 2014 to 2016. It was called ‘the spot’ and harmed other marine animals, including the death of a million seabirds. “Fascinatingly, after the heatwave stopped, it was still hot, and the whites had not left – they are still here,” Van Houtan said.
The scientists showed that the cold limit for the young sharks moved northwards on average 600 km between 2014 and 2020. “It’s an incredible distance in a few years,” he said.
Young great white sharks eat fish before migrating to seals and sea lions as adults. The young white sharks are thought to kill the sea otters as they learn to hunt mammals. “Sea otters are an endangered species and very important to the California coast as ecosystem engineers, both in kelp forests and seagrass meadows,” Van Houtan said.
The scientists found that the area of the ocean outside California with temperatures suitable for young sharks – 15C to 22C – shrank by about 5%. “It does not look big in the overall scheme, but predators and prey are now compressed into a smaller place where prey has fewer hiding places. “So you see a rapid decline in fish, including salmon,” he said.
Ocean ecosystems are already being damaged by overfishing, pollution and noise. “They need all their components to survive and thrive, and throwing extra factors into the equation, such as warm-ups and youthful whitening, only exacerbates the situation,” Van Houtan said.
One particularly hot part of Monterey Bay attracts people as well as the young sharks. “It has definitely become a local problem and public safety concerns have been raised on beaches,” he said. “Even if it’s just juveniles, six or 7 feet tall and eating so-called fish, it definitely raises your awareness.” Recent research has shown that the number of shark attacks in California has dropped by 91% since 1950 thanks to people who have better information to avoid encounters.
Prof Pinsky said: “This research is also a good example of the power of civil scientists. Without people recording what they saw with apps like iNaturalist, this massive expansion of withaai youths would have gone unnoticed. ”