Who’s the daddy? Baby shark hatched at aquarium with no males might not have one

When an egg appeared one day in a shark tank at a Louisiana aquarium, staff were puzzled. The tank only has two resident sharks — and they’re both female.

What’s more, neither of them have had contact with any males in over a decade. 

“[There was] definitely surprise,” Greg Barrick, curator of live exhibits at the Shreveport Aquarium, told As It Happens host Nil Köksal.

But, he added, a fatherless shark — while rare — is “not out of the realm of possibility.”

Who’s the momma?

Staff at the Shreveport., La., facility first found the egg about eight months ago, though they suspect it was laid a few months before that. 

It went undetected because staff had no idea one of the tank’s two inhabitants — female swell sharks named Ethel and Lucy — was pregnant.

Then, on Jan. 3, 2025, the little pup hatched. Barrick named it Yoko, short for Onyoko, the Chumash word for shark.

“She’s doing great,” Barrick said, noting they’ll need a few months to confirm the pup’s sex. “I’m saying ‘she’ for now. But that might change.”

The aquarium still isn’t sure which of the two adult females is Yoko’s mother, and they have no idea who the pup’s father is — or if it even has one.

There are two possible explanations for Yoko’s sudden appearance. Either the pup’s mother reproduced asexually by creating a genetic copy of herself, a phenomenon known as parthenogenesis. Or she stored away sperm from a previous sexual encounter and saved it for later, a process known as delayed fertilization.

And while neither method of reproduction is a shark’s first choice for making babies, they’re also not as unusual as you might think.

‘Not exactly cloning’

Parthenogenesis occurs when a female of reproductive age is continuously ovulating, but never encounters a male to mate with, says shark scientist Bob Hueter, who is not associated with Yoko or the Shreveport Aquarium. 

“Over time, there’s an adaptation where the females can actually self-fertilize their own eggs,” said Hueter, senior advisor for the marine research organization Ocearch.

“It’s not exactly the same thing as cloning. But they’re basically producing a sort of a copy of themselves.”

Parthenogenesis was first documented in sharks in 2007 when a hammerhead had a virgin birth at a U.S. zoo. It has since been observed in about a dozen species of sharks, Hueter says. 

It’s also been documented in other animals, including fish, snakes, grasshoppers, Komodo dragons, and condors, to name a few. 

“It’s something that evolution has built into most of the vertebrate groups of animals,” Hueter said. “It doesn’t occur in mammals — as far as we know yet.”

Saving sperm for better days

The other possibility is sperm storage, or delayed fertilization, an ability first documented in the 1970s in blue sharks

A female shark mates with a male, then stores her lover’s sperm inside her oviducal or nidamental gland until she’s ready to give birth or lay eggs  — sometimes for months, or even years.

Sometimes, Hueter says, fertilization is delayed until the mother reaches her breeding grounds. Sometimes it’s delayed until bad weather passes by, or until food becomes more abundant. 

“Her body chooses to hold on to those sperm and keep them fertile, keep them viable, for a period of time until the conditions change,” Hueter said.

“It’s another very interesting and beautiful example of evolutionary adaptation to, you know, environmental conditions.”

Male-free since 2014

So is Yoko a genetic copy of Ethel or Lucy? Or is she the delayed result of a long-ago tryst?

Only genetic testing will confirm for sure, says Barrick, and that has to wait a few more months until Yoko is big enough to draw the necessary blood without causing harm. Samples will also be collected from Ethel and Lucy.

“Is this [shark pup] genetically identical to either of the females? And if so, it’s parthenogenesis,” Barrick said. “Or is this different from both the females? And if so, then it’s delayed fertilization and there was a father involved.”

The latter, he says, is unlikely. Ethel and Lucy have been with the Shreveport Aquarium for three years, with no access to males. Before that, they lived in an all-female tank at another facility, going back to at least 2014.

“So if it is delayed fertilization, it is the first of its kind for that length,” Barrick said.

While it’s not clear how long a female shark can store sperm, Hueter agrees it would be “a real stretch to imagine that it could go on for that long.”

Parthenogenesis, though, could have its downsides.

Hueter says it’s a last-ditch reproductive technique, because it doesn’t allow a species to carry forward genetic diversity.

That’s bad news for a species in the wild if it goes on long enough, he said. But a single generation of parthenogenesis in an aquarium environment is probably fine. 

Still, Barrick says there have been examples of problems occurring in parthenogenesis offspring.

“Unfortunately,” he said, “it can cause some recessive traits that can cause some health problems to come into play.”

Staff are keeping a close eye on Yoko, Barrick said. But so far, the unexpected pup of unknown parentage seems both hale and hearty.