- New genetic studies have revealed at least two distinct groups of tiger sharks in the Atlantic and Indo-Pacific ocean basins, as well as a third, smaller population near Hawaii.
- These results are a slight surprise, due to the versatility and long swimming ranges of tiger sharks.
- Fisheries managers should take precautions to protect these distinct genetic populations, the researchers ask.
Tiger sharks sometimes swim for thousands of miles, far enough to roam the oceans. Their flexible diet and adaptable behaviors make them successful jet-setters, scouring the globe and mingling with distant members of the tiger shark society.
But new research shows that tiger sharks in different ocean regions are not as friendly with each other as expected. In fact, tiger sharks from the Atlantic and Indo-Pacific basins have diverged into at least two genetically distinct groups, according to a recent report published in the Journal of heredity.
A team of scientists from the Shark Research Center of the Save Our Seas Foundation at Nova Southeastern University in Dania Beach, Florida compared the genomes of 242 tiger sharks from 10 locations around the world. The authors, led by marine biologist Andrea Bernard, analyzed small genetic markers scattered throughout the tiger shark genome.
Their results exposed many contrasting markers between Atlantic Tiger Sharks and their Indo-Pacific counterparts. The researchers anticipated some differences based on their preliminary analysis of these sharks in 2016, but found even more variation than expected.
âIf this differentiation continues over time, these groups will be on the path to speciation,â said lead author Mahmood Shivji, director of the foundation’s Shark Research Center. “But they’re not there yet, at least in our opinion.”
Tiger Sharks (Galeocerdo cuvier) are smooth, striped top predators that can reach over 5 meters in length. They are not picky eaters; their prey includes fish, turtles, seabirds, snakes, dolphins and other sharks.
Tiger sharks seem content, whether they hover in the open sea, hunt in meter-deep waters near shore, or roam coral reefs. âHonestly, I can’t think of any other shark that does this,â Shivji said. But bycatch from fishing and the fin trade have made these versatile predators a Near Threatened species, according to the IUCN.
Despite their long journeys, Tiger Sharks appear to be homebody when it comes to breeding. âI’m not exactly shocked with the results,â said marine biologist Chris Lowe, director of the Shark Lab at California State University, Long Beach. Lowe noted that researchers still don’t know why tiger sharks travel so far or how climate change may affect their movements.
Scientists haven’t observed any physical or behavioral distinctions between Atlantic and Indo-Pacific populations, but they haven’t had a reason to look so closely. âTiger sharks are just these big things with stripes on them,â Shivji said. “Why would anyone even think it could be two different groups?” “
Now, environmentalists have a reason to look for different traits or behaviors between the two groups. And conservationists can develop fisheries policies to protect sharks in both populations.
A third group with more subtle variations has also emerged: tiger sharks around the long chain of the Hawaiian Islands.
âFortunately, a large part of the Hawaiian archipelago is protected,â said Shivji. âBut these tiger sharks don’t know it. They can travel enormous distances and they go well outside the protective limits. “
Next, the group wants to do whole genome sequencing to get a better idea of ââthe difference between shark populations. They also want to use the current analysis to compare the tiger shark with its evolutionary cousins, such as silky sharks or sandbank sharks.
Lowe said he looks forward to seeing this type of high-resolution global genetic study applied to other species. He thinks this could inform the management and conservation of fisheries in the future.
âTiger sharks captured my imagination because phylogenetically they are really weird,â Shivji said. Understanding the genetic origins of their idiosyncratic charm can make the importance of protecting them even more clear.
- Bernard, AN, Finnegan, KA, Pavinski Bitar, P., Stanhope, MJ, Shivji, MS (2021). Genomic assessment of global population structure in a highly migratory and versatile apex predator, the tiger shark (Galeocerdo cuvier). Journal of heredity, 112 (6), 497-501. doi: 10.1093 / jhered / esab046
Graycen Wheeler (@GraycenWheeler) is a graduate student in the Science Communication program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.