Female whale sharks may have a built-in sperm bank

The filter-feeding whale shark is the biggest fish in the ocean. A recent study indicates that female whale sharks may be able to save sperm from a single mating session and fertilize their eggs at a later time.

This investigation of the whale sharks' mating habits was led by Jennifer Schmidt from the University of Illinois at Chicago. The study ("Paternity analysis in a litter of whale shark embryos") was published in Endangered Species Research. From the absract:

A 10.6 m female whale shark Rhincodon typus caught off the coast of eastern Taiwan in 1995 carried 304 embryos that ranged in developmental stage from individuals still in egg cases to hatched and free-swimming near-term animals. This litter established that whale sharks develop by aplacental yolk-sac viviparity, with embryos hatching from eggs within the female. The range of developmental stages in this litter suggested ongoing fertilization over an extended period of time, with embryos of different ages possibly sired by different males [...] We determined the paternity of 29 embryos representing 10% of the original litter, and spanning most of the range of size and developmental stage of the 304 embryos. All were full siblings sired by the same male, suggesting that this male may have sired the entire litter. Probability analysis indicates that a second male could go undetected if it sired less than 10% of the litter. The range of developmental stages of embryos from this single sire further suggests that female whale sharks may have the ability to store sperm for later fertilization.

You can read the full study here. Whale sharks cruise the seas at a leisurely 3.1 mph, become sexually mature at the ripe age of 30, and could live to be over 100 years old. It's unsurprising that their sex lives would be equally unhurried. It's like, "Have your pups? Sorry, I've got two months worth of listless bobbing booked. I'll pencil you in around Christmas."

[Photo via The American Littoral Society]