Baffling: Swell shark cub born in all-female tank

The birth of a baby swell shark born in a Louisiana aquarium that houses only females has flummoxed marine experts. Yoko, the swell shark pup, hatched on  January  3 after an egg was spotted by the US aquarium’s animal husbandry team eight months ago. The egg could have gone undetected for up to two months prior to that, according to the Shreveport aquarium.

The two female sharks present in the tank had not been in contact with a male for more than three years, the team says. This suggests either a process called parthenogenesis, a rare form of asexual reproduction, or delayed fertilisation may have occurred.

A DNA analysis once the pup is big enough for a blood sample to be taken will determine the truth about the mysterious birth, but that will take months. “This situation is incredible and shows the resilience of this species,” said Greg Barrick, the curator of live animals at Shreveport aquarium. “We are very excited in the coming months to confirm whether this was indeed a case of parthenogenesis or if it was delayed fertilisation.”

The baby shark – named after the Native American Chumash people’s word for shark, “onyoko” – was said to be thriving, although the aquarium acknowledged that sharks born though such reproductive events often face significant challenges. Should Yoko’s time with us be short, they said, she will leave an “unforgettable legacy” to the study of shark reproduction and conservation.