On the 3rd of January 2025, a baby swell shark named Yoko was born at the Shreveport Aquarium in Louisiana. The fascinating part is that the tank does not house any male sharks, only two females.

These females have not encountered a male in over three years! So, how was Yoko conceived? The aquarium’s team has proposed two potential explanations for this unexpected birth: delayed fertilization or parthenogenesis.

Delayed fertilization occurs when a female stores sperm from a male. She then uses it to fertilize eggs at a much later time.

But this seems unlikely considering the length of time since the females last interacted with a male.

Parthenogenesis is a form of asexual reproduction where an egg develops into an embryo without fertilization. While rare, this has been documented in various species, including some sharks, reptiles, and birds.

In sharks, parthenogenesis is typically considered a last-resort mechanism for females isolated from males. The females basically “clone” themselves, and are able to reproduce without male contribution.

Interestingly, Yoko’s birth is not the first instance of a shark being born through parthenogenesis in an aquarium.

Previous cases have been recorded in species such as bonnethead sharks, zebra sharks, and blacktip sharks.

In 2001, a bonnethead shark at a Nebraska aquarium gave birth without mating. In 2016, a zebra shark in an Australian aquarium produced offspring after years of isolation from males.

These cases provide evidence that parthenogenesis is a reproductive strategy used by sharks in captivity. Once Yoko is big enough for DNA extraction, scientists will determine the cause of her birth.

This genetic testing will show whether Yoko’s conception resulted from parthenogenesis or delayed fertilization. Regardless of the outcome, this event highlights the resilience and adaptability of sharks.

Swell sharks (Cephaloscyllium ventriosum) are native to the coastal waters of the eastern Pacific Ocean, ranging from central California to southern Mexico.

There is also an additional population off the coast of Chile. They are known for their unique defense mechanism: swelling!

When threatened, they can swallow water to swell their bodies. That makes it difficult for predators to bite or dislodge them from crevices. Swell sharks are oviparous, meaning they lay eggs.

Females produce egg cases, often referred to as “mermaid’s purses,” which they wrap around coral using tendrils. The gestation period for these eggs ranges from 9 to 12 months, depending on water temperature.

Once hatched, there is no parental care, meaning the pup needs to survive on its own from birth.

Yoko’s birth provides a valuable opportunity for scientists to deepen their understanding of shark reproduction and parthenogenesis.

Studying parthenogenesis cases can offer insight into the evolutionary biology of sharks. With this knowledge, better conservation strategies can be implemented.