Holy grail of shark science

Researchers uncover highly elusive shark birthing behaviors

Under a clear blue sky and rocking in rhythm with ocean waves, a mother receives her first ultrasound. Outside of a hospital setting, the procedure is far from typical. This mother is not an average patient — she is a scalloped hammerhead shark.

A new study published in the peer-reviewed journal Science Advances explores the previously unknown timing and location of tiger and scalloped hammerhead shark births. “A novel intrauterine satellite transmitter to identify parturition in large sharks” was published March 1, with funding for the research provided by Herbert W. Hoover Foundation.

James Sulikowski, co-author of the report and Senior Global Futures Scientist with the Arizona State University Julie Ann Wrigley Global Futures Laboratory, says understanding when and where sharks give birth can lead to more effective conservation efforts.

“Sharks are highly migratory and can travel thousands of miles a year, which makes it difficult to measure where they give birth,” said Sulikowski, who is also a professor in the New College of Interdisciplinary Arts and Sciences. “Previously, researchers would try to capture the babies close to shore to establish where the nurseries were. That isn’t always accurate. Baby sharks, even newborns, can travel hundreds of miles in very little time.”

Co-author Neil Hammerschlag, who conducted this research while a research associate professor at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, said other methods used to study shark reproduction are traditionally derived from sacrificing specimens and inspecting their reproductive organs.

“This new technology opens up a new path for generating accurate data on shark reproduction in a non-lethal way,” said Hammerschlag, the founder of Atlantic Shark Expeditions. “This is really important as sharks are among the most threatened vertebrates on the planet.”

The electronics of the birth alert tag were encased in an egg-shaped synthetic foam covered with a biologically inert sealant that, upon expulsion at birth, would float to the surface.

According to the International Union for Conservation of Nature, more than an estimated third of sharks are threatened by extinction. Overfishing is a major contributor: unsustainable fishing practices lead to habitat loss in addition to overexploitation of both shark and fish populations.

As apex predators, Sulikowski said sharks are paramount in regulating ocean ecosystems. The already elusive migratory creatures are also highly susceptible to anthropogenic and environmental change due to their slow growth and long life spans. Pollution and urbanization in particular are already disrupting shark nurseries, hence the need for proactive conservation efforts at vulnerable points in a shark’s life such as newborn stages and pregnancy.

“Our oceans in general need to be healthy, and sharks control all sorts of populations that could throw that health out of balance,” Sulikowski said. “Oceans provide invaluable food, economic services, and recreation; take sharks away and the world loses that.”

To discover where sharks are being born, Sulikowski and Hammerschlag implanted waterproof, satellitelinked intrauterine transmitters into pregnant scalloped hammerhead and tiger sharks. This is implanted via the cloaca, a cavity at the end of the digestive tract used for both excretory and reproductive purposes. The transmitters, created in collaboration with Lotek, a fish and wildlife monitoring company, act as a “birth alert tag.”

Contrary to some other methods of shark reproduction research, this process does not harm the sharks. The egg-shaped, six-centimeter-long by 2.5-centimeter-wide tag was designed to be inserted non surgically into a shark’s uterus and remain unobtrusive among the developing embryos without harming them. A satellite tag is also placed on the mother’s fin to track her location as she travels before the birth.

When the baby sharks are born, the egg-shaped transmitter is expulsed and floats to the ocean’s surface. Once buoyant, a flexible antenna points skyward and transmits messages in 15-second intervals until the battery expires.

This allows Sulikowski and Hammerschlag to pinpoint where the mother shark gives birth, and in turn, better understand where conservation efforts should be focused.

“In order to protect sharks as babies, we have to protect their moms,” Sulikowski said. “Being able to see exactly where sharks are giving birth — something we’ve struggled to do in the past — is the holy grail of shark science and conservation.”

Video: Shark intrauterine satellite transmitter https://www.youtube.com/watch?v=9mAlw7Cx_vE