A Rare Find

From Hsu et al, Journal of Fish Biology, 2014.

From Hsu et al, Journal of Fish Biology, 2014.

Research into the biology and ecology of the whale shark has increased dramatically over the past 15 years, but our understanding of much of the life cycle of these animals is still lacking.  In particular, little is known about their reproduction and the early life of young whale sharks.  Mating between whale sharks has never been observed, and while pregnant females can be seen in certain areas of the Eastern Pacific, no one has ever witnessed a whale shark giving birth.  In fact, only a single pregnant female has been scientifically documented, a 10.6 meter female that was caught in the Taiwanese fishery in 1995.  This animal carried more than 300 embryos in her uteri, and provided all the information currently known about whale shark reproduction.

Given the large number of offspring carried by this single female shark, it is mystifying that young whale sharks are so very rarely observed in the oceans.  In all of recorded literature there are only 18 previous reports of neonatal whale sharks, and these sightings span all oceans and many different habitats.  Where newborn whale sharks spend their time is therefore unknown, but the rarity of these animals suggests they may use isolated or deep water ecosystems.  Young whale sharks first appear at conventional feeding aggregations when they reach approximately 2.5 meters in length.  An aggregation in the Gulf of Tadjoura near Djibouti, Africa, has the overall smallest individuals, with an average size of just 4.5 meters, and individuals as small as 2.5 meters.

Hsu et al now describe the 19th recorded sighting of a neonatal whale shark.  This neonate was found off Green Island, Taiwan in October of 2013, where he was being chased by a school of giant trevally.  The male shark measured 78 cm total length, indicating that he was approximately 3 months of age.  Interestingly, the area where this individual was found is quite near where the pregnant female was caught in 1995.  The young whale shark was turned over to researchers at National Taiwan Ocean University, where he was measured and marked with a numerical tag, then released in deep water.  Let’s hope this small shark survives to be sighted again, teaching us more about the first year in the life of a whale shark.

The paper is online before print at: H. H. Hsu, C. Y. Lin and S. J. Joung. The first record, tagging and release of a neonatal whale shark Rhincodon typus in Taiwan (2014) Journal of Fish Biology doi:10.1111/jfb.12498.