Climate change may be pushing great white shark nurseries northward
The great white shark may be one of the ocean's top predators, but it's still affected by climate change, just like any other animal. That's what's indicated by a new study, which shows that young great whites in California are moving to the north.
Starting in 2002, biologists from the Monterey Bay Aquarium and elsewhere started tagging wild juvenile great white sharks off the coast of Southern California, in order to see where the fish spent their time.
Up until 2013, it was found that the young sharks ventured no farther north than a region near Santa Barbara, at a latitude of 34º N – this finding was backed up by historical records dating back to 1983. That changed in 2014, however, when the North Pacific marine heatwave (also known as The Blob) began causing a rise in water temperatures along the California coast.
As a result, some of the tagged sharks started showing up as far north as the waters of Bodega Bay, at 38.5° N. This was reportedly farther north than juvenile great whites had ever been found in California. Local people additionally started reporting sightings of juveniles, around the same time.
Although the marine heatwave may have dissipated somewhat since its peak, it's still producing an upward trend in water temperatures. This has resulted in the young sharks' range now reaching up to Monterey, at 36° N. It's worth noting that while water temperatures at Aptos, California, once averaged about 55º F (13 ºC), they have since climbed as high as 69º F (21 ºC), as recently as last August. Aptos is 146 miles (236 km) south of Bodega Bay.
The study concludes that such rises in water temperature may be causing the juvenile sharks not just to extend their range northward, but to actually shift it, as the Southern California waters are now simply getting too warm for them.
"Nature has many ways to tell us the status quo is being disrupted, but it's up to us to listen," says Monterey Bay Aquarium Chief Scientist, Dr. Kyle Van Houtan. "These sharks – by venturing into territory where they have not historically been found – are telling us how the ocean is being affected by climate change."
A paper on the study was recently published in the journal Scientific Reports.