Pregnancy can be a tough time for any mother, but if there's one thing we humans can be thankful for, it's that our babies don't come 20 at a time – and they aren't equipped with multiple rows of razor-sharp teeth!
This incredible sonogram of a pregnant tiger shark was recorded by researchers from the University of Miami (UM) and University of New England (UNE), during an expedition to study shark behaviour at Tiger Beach in the Bahamas.
The site is known for its year-round abundance of tiger sharks, and thanks to these new methods, we're beginning to form a clearer picture (pun intended) of why they hang out here.
It all started back in 2003, when UM shark biologist Dr Neil Hammerschlag made an interesting observation: many of the sharks in the area were female. We've come to learn much about sharks over the years, but the details of their reproduction remain a mystery for most species.
Where do they go to mate? How many pups do they have? When do they become sexually mature? In the past, scientists had to rely on observations of dead animals during necropsies when trying to answer such questions.
So Hammerschlag and UNE marine biologist Dr James Sulikowsky put on their thinking caps, taking inspiration from human over-the-counter and in-hospital pregnancy tests to develop a non-invasive method to look for shark "baby bumps".
"Our data suggests that Tiger Beach may function as a refuge habitat for females to reach maturity as well as a gestation ground where pregnant females benefit from calm, warm waters year-round that help incubate the developing embryos and speed up gestation,” says Hammerschlag.
The team used the same imaging technology used by medical professionals on pregnant women, only modified for use at sea. A screen was replaced with goggles and waterproof casings were added.
Getting the sharks on board and prepped for the procedure is something that takes an incredible amount of finesse and teamwork. Sharks are quite sensitive to stress, so "check-ups" like this must be done quickly and gently.
A quick blood sample also allowed the team to test the levels of circulating sex hormones, just like those an obstetrician would test for on a human patient.
"We don’t fully remove sharks from the water," the team explains. "We use a specially designed platform that is partially submerged to secure them."
You might notice the shark in the video is clamping down on a pipe. This pump actually helps the shark during work-up (the term used to describe a shark check-up) by keeping oxygenated ocean water flowing over the gills. All said and done, the entire procedure takes under twenty minutes.
Sharks bite when they're stressed, explains the team. So in a way, the water pipe acts as a pacifier. When the shark is calm, the work-up can proceed without any trouble, and the shark swims safely away once the tag is placed.
Research has shown that although tiger sharks produce large litters, the pups are inefficient swimmers, and extremely vulnerable to predation as they grow – especially by other sharks. Learning where these threatened animals go to breed, and how they use that environment, is a crucial step in better protecting them. This vital intel can help us ensure that these cosmopolitan swimmers don't overlap with fisheries during the most critical stages of life.
Data from the sharks' satellite tags – which will pop off on their own and cause the sharks no pain – will help the team better understand where these females are going.
"I think a lot of people have been waiting for this,” Hammerschlag told TakePart earlier this year. “In 2011, James and I published a paper saying we need to come up with these non-lethal alternatives. People at the time said the tech’s not out there. When this study came up we wanted to prove it for ourselves. It can be done."
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The full study can be found in the Journal of Aquatic Biology, here.
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