Geneticist seeks DNA from our whale sharks

Scientists have discovered that whale sharks, the biggest fish in the ocean, get around —- as in really get around.

A just-released study by Chicago-based geneticist Jennifer Schmidt found that the bus-sized sharks not only swim across oceans, they apparently breed with their counterparts in far-flung areas of the globe.

Schmidt, a University of Illinois at Chicago associate professor of biological sciences, now wants to expand the study by taking DNA samples from the four whale sharks at the Georgia Aquarium in downtown Atlanta. The aquarium houses the only captive whale sharks outside of Asia.

The world’s biggest indoor aquarium obtained its whale sharks from Taiwan, an area not covered by Schmidt’s DNA study of 68 whale sharks in the wild.

“The opportunity to characterize these sharks genetically would nicely complement the existing study,” Schmidt said.

The study by Schmidt and her colleagues is one of the most comprehensive to date on the little-understood shark. It sheds new light on the behavior of the polka-dotted, filter-feeding giant that can reach 50 feet in length and weigh more than 20 tons.

Scientists know little about whale shark breeding activity or reproduction. The oceangoing fish are extremely difficult to study in the wild and have only recently become the focus of marine biologists around the world.

Schmidt said the study has significant implications for efforts to protect whale sharks, which are listed as a threatened species but are still killed for their fins, which fetch big bucks in some Asian markets.

“These animals move, and they move long distances,” Schmidt said. “Whale sharks from protected areas probably don’t stay in those areas but can move to areas where they are not protected.”

Schmidt looked at DNA from whale sharks from the Caribbean to the Indian and Pacific oceans. Results of the study showed little genetic variation between the different populations, indicating the big fish migrate across oceans and breed with other whale shark populations thousands of miles away.

Gregory Bossart, the Georgia Aquarium’s chief veterinary officer, said the facility is open to Schmidt’s proposal about testing its whale sharks.

“I would encourage anything like this where we could learn more about the species,” Bossart said. “We would encourage any sort of collaboration like this.”

The aquarium has funded some whale shark research in the wild, including the collection of DNA samples from whale sharks off Isla de Holbox, Mexico.

Florida-based shark scientist Bob Hueter has studied that Yucatan whale shark population, and two years ago contributed to a DNA study by Brazilian scientist Andrey Castro. Taken together, the two genetic studies come to similar conclusions on the big sharks, Hueter said.

“It shows the males might be rovers more than the females,” Hueter said. “This kind of theme is emerging in many, many different types of migratory sharks.”

Hueter said female whale sharks also roam great distances, but might be more prone to return to feeding and nursery areas.