Whale Shark Reproduction

Over the last 20 years, whale sharks have made a spectacular increase in popularity with the general public.  As more places become tourist friendly, the Gentle Giant is being sighted more often than ever before.    However, it the largest fish in the sea is still a mystery to researchers.  After years of study and observation,  no one has reported a mating or a birthing.  It is only hypothesized that mating grounds exist.  Last summer, the largest whale shark population ever recorded was reported off the northern coast of the Yucatan Peninsula. Could this be where they meet?

Mature male whale sharks, as in other shark species, can be identified by their claspers. These claspers extend from the inner edges of the pelvic fin, located underneath male sharks and rays. Some species of shark are also known to bite their partner during intercourse. Some whale sharks have been seen with what is hypothesized as potential bite marks, but evidence is lacking. The male shark injects his sperm into the females two uteri. Females are identified by their lack of claspers. However, until a whale shark reaches sexual maturity (approximately 15 feet or 30 years old), it is difficult to determine the sex.

Until 1996, it was unclear whether whale sharks were oviparous (egg-laying), viviparous (live birthing) or ovoviviparous (both). In 1953, a fishermen in the Gulf of Mexico, brought up an egg sack containing a whale shark. This led to the possibility of an oviparous species. However, there was no other evidence to support this theory. However, in 1996, a fisherman in Taiwan, brought in a female that was observed to have nearly 300 young contained in both uteri–in varying stages of development. The largest were ready to be born, survived their mothers slaughter, and were raised in captivity for a short spell. This one report proved that the whale sharks are ovoviviparous. They start off in egg sack, but then exit them within the womb where they continue to grow, and then are given birth to live. As far as why there were so many, and in a diverse stages, brings up a whole new set of questions for scientists to ponder and study.

This was exciting news in the shark world. Potentially, the whale shark had mated with several males over the course of several years.  Or, the whale sharks grew depending upon certain conditions. Hypotheses and theories are many, and conclusions are still sought.  Pups were measured from 3 inches to 2 feet in length.  It is thought that 1.5 foot to 2 feet is birthing size. The only other information that has been gathered regarding the mating habits of whale sharks in the last 20 years is speculative at best.

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