Emily Chan
About 100,000 to 200,000 years ago, great white sharks split into three different groups that have rarely interacted with each other ever since.
These groups are located in the northern Pacific Ocean, the southern Pacific Ocean, the Indian Ocean, and the North Atlantic and Mediterranean. It appeared that ocean currents kept them separated.
“At the end of the Penultimate Ice Age — between 100,000 to 200,000 years ago — white shark populations appear to have divided into three discrete lineages which seldom interbreed,” Catherine Jones, a co-author of the study and a researcher at the University of Aberdeen in Scotland, said.
Great white sharks can grow up to 20 feet long and weigh more than 4,000 pounds. Their status on the IUCN Red List of Threatened Species is listed as “vulnerable.”
In Europe, they are considered to be critically endangered. Their populations worldwide have decreased to around 63 percent of their numbers in the 1970s due to several threats.
The sharks are often caught on accident by commercial fishers targeting other species, which can result in their injury or death. In addition, marine pollution, including chemical contaminants and plastic waste, affects the health of the sharks and their prey. Furthermore, overfishing reduces the food supply for great whites.
It doesn’t help that these sharks have a slow reproductive rate. They reach reproductive maturity at about 15 years old, and then they produce few offspring.
So, when their populations are experiencing declines, they are unable to bounce back very quickly. According to the new paper, the populations cannot be replaced if one of them goes extinct.
“Now we understand that if you wipe out sharks in a particular area, they’re not going to be repopulated by sharks from another lineage,” said co-author Leslie Noble, a molecular evolutionary ecologist at Nord University in Norway. “The so-called global population of white sharks has now shrunk to these three very discreet units. And it’s really quite concerning.”
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