Whale sharks (Rhincodon typus) are the biggest fish on the planet, with some clocking in at 60 feet long. Now, for the first time, we might have some clues to how these endangered gentle giants mate. During a research expedition to Western Australia’s Ningaloo Reef in May 2024, a team of scientists observed sexually mature male whale sharks following and biting smaller females. This biting could be a precursor to mating and the findings are detailed in a study published January 2 in the journal Frontiers in Marine Science.
CREDIT: Christine Barry Research
Previously, fishers in the area had reported this behavior of the sexually mature males swimming towards females at different aggregation sites. Whale sharks typically gather around Ningaloo Reef every year from March through July to feast on the plankton and krill that are abundant after the reef spawns. While they are usually found in tropical coastal waters, juvenile males often make up the majority of these populations.
This new study was part of an annual research trip to the reef when the sharks are typically there in their highest numbers. On May 14, a boat pilot alerted the team to the location of a female whale shark that was about 22 feet long. Shortly after, an adult male whale shark appeared and followed about 6.5 to 10 ten feet behind the female.
“The male was observed to open its mouth and lunge forward towards the caudal fin of the female,” the authors write in the study. “The male shark increased its swimming speed and lunged again at the caudal fin of the female, this time making contact and briefly biting the tail. The female responded by rapidly pivoting with pectoral fins pointing downwards to face the male.”
The team ultimately did not see these interactions culminate in mating. However, the following and biting are similar to the early mating behaviors seen in shark species, including tiger sharks (Galeocerdo cuvier), zebra sharks (Stegostoma fasciatum), basking sharks (Cetorhinus maximus). Observing this behavior not only expands our understanding of how whale sharks might mate, but offers some insight into the sex imbalances at these sites where whale sharks gather.
“At Ningaloo Reef, and many aggregation sites around the world, males outnumber females with a ratio of 1 female to 3 males,” Christine Barry, a study co-author and PhD candidate at Murdoch University in Australia, said in a statement. “This could explain why female whale sharks may be avoiding aggregation sites. Particularly for juvenile female sharks, the energetic costs of unwanted attention from males could imply a reason for strong male biases.”
[ Related: Orcas observed preying on massive whale sharks. ]
This research also opens up new avenues for conservation efforts for this struggling fish species. Whale sharks have been classified as Endangered on the IUCN Red List of Threatened Species since 2016. While their numbers are difficult to document, some scientists estimate that there are 130,000 to 200,000 whale sharks swimming in the world’s oceans. In addition to Australia, there are other documented aggregation sites in the Galapagos, Philippines, Mexico, Thailand, and Mozambique.
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