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In a first, scientist observe time and place of shark births

By Nicholas Gerbis
Published: Friday, March 3, 2023 - 5:15pm

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For the first time, scientists have pinpointed the moment and location of shark births.

As reported in a paper published in the journal Science Advances, the two landmark events were made possible by egglike tags implanted in the mother’s wombs.

“One of the biggest mysteries for us that we really consider the Holy Grail is where some of these really highly mobile species are going and spending their time,” said lead author James Sulikowski of ASU. “Particularly moms — what are their migration corridors? What trials and tribulations are they encountering?

The Birth-Alert-Tags (BATs), exited the tiger shark and scalloped hammerhead with their newborn pups, then surfaced and signaled satellites.

“She gave birth and that tag popped out,” said Sulikowski. “It was like Christmas morning; it was just incredible.”

James Sulikowski.
ASU professor James Sulikowski (left) and his team insert a birth-alert tag into a pregnant shark. The tags track the shark's birthing location to help protect nursery grounds.

Previously, scientists inferred nursery ground locations and birthing seasons from pregnant or newborn sharks that they captured and dissected. That left the where-and-when open to speculation within bounds loosely set by those observations, which came at a high price for endangered species.

“It’s a real needle-in-the-haystack for us,” said Sulikowski. “Because we're going out there and looking to catch a shark of a very specific size, a very specific sex and a very specific stage in its life history — a pregnant shark.”

Even if, as some believe, certain shark species return to their own birthplaces to deliver pups, they might gestate or seek nurseries elsewhere, Moreover, young sharks can swim quite far soon after birth.

Sulikowski and his coauthor, tiger shark expert Neil Hammerschlag of University of Miami, spent six years finding a solution rugged enough to survive saltwater conditions but gentle enough not to harm pups in utero.

“It was a big challenge to get this to work the way that we wanted it to, but, you know, nothing comes easy, right?” he said.

Researchers have used similar transmitters since the 1980s to study birth patterns in invasive land species like wild boars. Only recently have technical advances and strides in miniaturization made studying shark births with the BAT possible.

Researchers implant the device by placing the shark on its back in a trancelike state called “tonic immobility.” Once a ruggedized ultrasound confirms the shark’s pregnancy, scientists use a purpose-made instrument to implant the 42-gram BAT in the uterus via the cloaca, an orifice that does triple duty for the digestive, reproductive and urinary tracts.

“We can use the same technology that a human female would go to the doctor to receive, or that you would take your dog or cat to a vet to receive an ultrasound, or maybe an animal at the zoo,” said Sulikowski.

The shark population in the open ocean has dropped more than 70% in the past 50 years, and more than three-quarters of species face possible extinction, mostly due to overfishing.

The insights made possible by BAT observations could aid conservation efforts. By locating birthing areas and nurseries, and by understanding what makes them appealing to sharks, conservationists can better target their efforts and identify biomes to safeguard against threats like human construction and climate change.

Sulikowski says he eventually hopes to build a global monitoring network for sharks and other species.

“Our ultimate goal is to get this tag in as many different shark species as possible and really see how it might work in stingrays or other species that are mobile,” he said.

James Sulikowski.
A close-up look at a birth-alert tag.

Science Sustainability