White sharks form three different groups, and this could threaten their survival

Contrary to what many of us thought, great white sharks are not a single species, but are divided into three different populations that live in different parts of the world's oceans. The findings are a cause for concern among conservationists, as it appears that these different populations rarely interbreed.

The discovery was made by an international team of researchers who applied new, advanced genomic analyses to great white sharks from around the world. They found that the three distinct geographic lineages split between 100,000 and 200,000 years ago, during the penultimate ice age, and live respectively in waters of the South Pacific (Indo-Pacific), the North Pacific, and the North Atlantic and Mediterranean.

Despite their global distribution, previous research into the molecular population of great white sharks has been limited to opportunistic sampling from individual ocean basins or regions. Moreover, most of these studies have relied on the analysis of “microsatellites”, repetitive DNA segments that are repeated multiple times at specific locations in the genome, and small fragments of the mitochondrial control region that regulates RNA and DNA synthesis.

However, focusing on these markers produced a confusing picture that did not seem helpful in understanding the recent connections between great white shark populations. Therefore, the researchers in this study resorted to high-resolution genome-wide markers – called single nucleotide polymorphisms (SNPs) – which provided a reliable and reproducible picture of the situation, revealing the three distinct lineages.

This discovery is more than just a curiosity about an (un)famous marine species – it also draws attention to a significant problem of species conservation.

Crucially, the researchers found that the sharks do not interact with those of other populations. This means that the global white shark population is actually at greater risk of extinction than previously thought, as a loss of one lineage is unlikely to be compensated for by interbreeding.

“If all great white sharks belonged to one large, integrated global population, it would not be so bad if they disappeared from a particular area,” said Dr. Catherine Jones, lead researcher of the study at the University of Aberdeen, in a statement.

“However, if great white sharks are genetically separated populations, as is the case in the Mediterranean, and these were lost, the unique genetic diversity would also be lost.”

The research highlights that we need to better understand the distribution and health status of these different shark groups if we are to protect them in the future.

“Successful conservation requires the recognition of management units, but this is not available for great white sharks, which were thought to be the only global population,” added Les Noble, professor of aquatic life sciences at Nord University in Norway.

“Although it is not widely recognised, the future of humans is increasingly linked to that of the great white shark. As apex predators, they play a crucial role in maintaining the health and diversity of local marine ecosystems, which are responsible for 20 per cent of the protein in our diet. Over the last 50 years, the great white shark population has almost halved and it is considered critically endangered in Europe.”

If recent predictions are correct, the strength and direction of major ocean currents could change over the next 50 years. If this happens, the geographic boundaries between these shark lineages could break down, which in turn could lead to less productive matings and further threaten the great white shark and the overall diversity, health and productivity of the world's oceans.

“It has long been assumed that the loss of sharks in one area would be offset by the migration and mating of sharks from other areas. Our results suggest that this is clearly unlikely and that this, combined with bycatch fishing, depletion of their food reserves, pollution and poaching, could put this iconic apex predator at real risk of extinction,” Jones concluded.

The study was published in Current Biology.