There are several sites where large numbers of whale sharks aggregate, attracting tourists from all over the world. Most of the sharks present at these sites are juvenile males between four and nine meters in length. Of the 7,700 individual sharks identified in the global whale shark database around 2/3 are male.
Where are all the females? Where are the adults (and babies) of either sex?
At this stage, we know very little about whale shark reproduction and life history. Only one pregnant whale shark has ever been physically examined by scientists. This singular shark, caught in a fishery off Taiwan in 1995, carried over 300 pups inside her. That is almost twice as many as any other shark species. We do not know if this is normal. We still do not know how often females produce pups either.
Considering that the largest whale shark on record was reportedly 20 meters in length and that this specimen was relatively small at 10.6 meters total length (34.8 feet), it is believed that a whale shark could carry even more embryos at a time. It is well documented that the amount of embryos a fish can support increases exponentially with abdominal size.
The Galapagos Islands in Ecuador are the only known site where pregnant females are routinely seen, on a seasonal basis. Where do these huge sharks move before and after the season? Do they come to the Galapagos for breeding? To date, no one has ever witnessed a whale shark giving birth.
Through satellite tagging and tissue sampling paired with photo identification, we are hoping to answer questions about their location and movement patterns, their breeding grounds and reproductive frequencies, and the main human threats these endangered sharks are facing.
That allows us to calculate how quickly fisheries can reduce their populations, and how fast they can bounce back once human threats are removed by increasing protection for the species and its key habitats.
Broadly, large juvenile and adult females are the most important individuals to the species’ rebound potential. Identifying human threats to these life stages, and mitigating them, will be the most efficient means of reversing population decline.
This is a collaborative project in conjunction with the Galapagos Whale Shark Research Project and supported by the GLC Charitable Trust.