At Least 100,000 Years Ago, Great White Sharks Split Into Three Different Populations That Have Rarely Interacted With Each Other Since, Sparking Conservation Concerns
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.”
ramoncarretero – stock.adobe.com – illustrative purposes only, not the actual shark
In the study, the researchers analyzed the DNA samples of 89 great white sharks from all over the world to determine their genetic diversity. They used a statistical algorithm to group related genetic sequences together.
When they traced back the history of the sharks, they found that the lineages split into three different ones during the Penultimate Ice Age, when sea levels fell up to 490 feet below current levels.
They concluded that the three white shark groups are genetically distinct from one another, so if one of them vanished, unique genetic diversity would be lost as well.
It’s unclear why the populations split at all, but the researchers think that may have had something to do with the decrease in sea levels and changes in ocean temperatures and currents.
Conservation efforts should now focus on managing each group of great white sharks rather than proceeding with the view that they exist as a single global population.
If one group crosses into another group’s territory, they may start to interbreed and produce hybrid offspring that may not survive.
The study was published in the journal Current Biology.
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