As fascinating and awe-inspiring as they may be, we know very little about great white sharks. Basic facts like where they mate, where the females go to birth, and where the pups live before swimming to rejoin the adults in the open ocean is still a mystery, even to biologists, writes Peter Hess for Inverse. Now, a team of scientists led by evolutionary biologist Toby Daly-Engel is uncovering some of these mysteries while building a great white shark family tree.
With her colleagues Mauricio Hoyos Padilla and Michelle Wcisel, Daly-Engel began her search in a bay off of Baja, California, and located a nursery of baby sharks. With the help of local fishermen, they used a specially constructed longline fishing rig to catch the baby sharks, and collected tissue samples from over the side of the boat.
In addition to finding the nursery, the team set off to locate the females that birthed the babies, wanting to understand where the babies were coming from (mothers gestate for two years, but leave after giving birth). They tracked the adults down to nearby Guadalupe Island, and collected tissue samples from eight adult sharks using a punch biopsy tool attached to the end of a spear. They also attached radio antennae to three pregnant females.
With the DNA samples and the antennae, they hoped to draw a clear connection between the adult sharks in one place and the baby sharks in another, Hess explains. To their shock, the DNA sample results revealed that two pairs of baby sharks, born two years apart from each other, turned out to be from the same mating pair of adults. “It was so surprising and so different,” says Daly-Engel. “It would be like picking two people out of a crowd, days apart from one another, and yet finding out that they’re brother and sister.” She believes that this shows just how small the population of great white sharks may be. The results can help scientists develop a better understanding of the issues facing great white shark populations.