A groundbreaking study has revealed that great white sharks, the apex predators of the ocean, are not a single, globally connected species, but rather three distinct groups that have been isolated for an astonishing 100,000 to 200,000 years. This discovery, published in the journal Current Biology, has profound implications for conservation efforts, as it highlights the need to protect each group independently to prevent their extinction.
The research, conducted by scientists who sequenced the genomes of 89 great white sharks (Carcharodon carcharias) from around the world, identified three distinct populations: the North Atlantic/Mediterranean, Indo-Pacific, and North Pacific. These groups, separated by vast stretches of ocean, have evolved independently and rarely interbreed.
The study authors emphasize that the existence of these distinct lineages means that if one population goes extinct, it cannot be replaced by individuals from another lineage. “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,” explained study 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.”
The researchers used mitochondrial DNA, which is inherited only from the mother, to trace the lineage divergence. They found that female sharks always return to their birth site to give birth, making their mitochondrial DNA a unique “passport” that reveals their origin. This confirms that the three distinct groups have remained geographically isolated for a very long time.
The study’s findings suggest that the separation of these lineages occurred during the Penultimate Glaciation Period, a time of significant climate change and sea level drops. The researchers believe that these environmental shifts may have created barriers that prevented the sharks from interbreeding and ultimately led to the formation of distinct genetic groups.
Despite their isolation, there is one documented case of hybridization between the Indo-Pacific and North Pacific lineages in the Bermuda Triangle. However, the researchers believe that such instances are rare, and that most hybrids likely do not survive due to natural selection.
The International Union for Conservation of Nature (IUCN) has classified the great white shark as vulnerable to extinction, and their population has declined by about a third between 1970 and 2018. While their numbers are slowly increasing thanks to global protection efforts, the new discovery emphasizes the importance of focusing conservation efforts on each individual population, as interbreeding between groups can lead to offspring that may not survive.
The disappearance of these apex predators would have dire consequences for the marine ecosystem and, ultimately, for humans. “Our fate is intimately bound with the great whites because we get about 20% of our protein from marine ecosystems, which the great whites keep healthy,” said Noble. “So [if] we lose the great whites, we might lose a lot of our protein from these ecosystems.”
The study’s findings highlight the urgent need for tailored conservation strategies for each distinct great white shark population. Recognizing the unique genetic heritage and ecological roles of these three groups is crucial for ensuring their long-term survival and the health of the marine ecosystems they inhabit.
