A whale shark is a big fish with a big secret; one that has eluded researchers and observers for years. Despite being the largest fish in the ocean, very little is known about how whale sharks actually get here – their courtship and reproduction ritual is something scientists are still trying to piece together bit by bit… or should that be, bite by bite?

For the first time, researchers have witnessed a behaviour in the wild which could reveal critical clues about how the endangered whale shark goes about doing the deed. 

These are clues that arrive, according to the team of researchers at the Australian Institute of Marine Science behind the study, at a critical time. Given the endangered status of the ocean giant, developing a clearer picture of the pre-mating rituals of the elusive whale shark could prove to be vital knowledge when it comes to their conservation efforts.

It was during a 2024 expedition at Ningaloo Reef, off the coast of Western Australia – a spot at which research expeditions have routinely taken place at the peak of the seasonal aggregation of whale sharks each May since 2009 – that a team of scientists witnessed and recorded ‘following and biting’ behaviours by a sexually mature male whale shark and a smaller female.

Until now, everything we currently understand about the pre-mating rituals of whale sharks has been observed within aquariums or chance encounters in the wild. Footage captured of this ‘following and biting’ behaviour is, therefore, the first time it has been scientifically documented.

“Following and biting are common copulation behaviours in other species within the subclass of cartilaginous fish that the whale shark belongs to,” said Christine Barry, a PhD candidate from Murdoch University’s Harry Butler Institute and the Australian Institute of Marine Science. 

“This is also consistent with previous reports by fishers recounting behaviours they’d observed out on the water of sexually mature males towards females at different aggregation sites.”

The research team behind the recorded footage suggest that in this instance, the observed interaction “likely didn’t culminate in mating” owing to the difference in maturity between the two sharks. More likely was it that the juvenile female shark was attempting to evade the advances of the more mature male.

However, Ms Barry and the team have suggested that the whale shark’s mating behaviours resembled those of many other species of shark, adding that the existence of these records not only expands researchers’ understanding of the whale shark’s mating behaviours, but also provide insights into sex-biases reported in whale shark populations across various coastal aggregations. 

“At Ningaloo Reef, and many aggregation sites around the world, males outnumber females with a ratio of one female to three males,” said Ms Barry. “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.”

Ms Barry has – alongside PhD supervisor Dr Adrian Gleiss, a senior lecturer with Murdoch University’s School of Environmental and Conservation Sciences – been at the forefront of whale shark research and many a paper covering new ground with insights into the impacts of tourism on whale sharks and the predation of baitfishes associated with Ningaloo Reef whale sharks. 

Her latest research into the pre-mating rituals of whale sharks opens the door for new conservation efforts and further exploration into repopulation and protection of the species.

The paper was published in Frontiers in Marine Science earlier this month.

The study itself echoes similar research into the secret sex lives of sand tiger sharks off North Carolina which – by examining the gruesome bite injuries inflicted upon both participating parties – has gone some distance to prove that while love hurts, all wounds heal.

Published in journal Environmental Biology of Fishes in early December 2024, another study leads us into areas not for the faint of heart, describing the somewhat violent nature of shark sex; a process that requires them to press their bellies together while the deed takes place. For larger species, this is a tricky act to perform and requires, typically, the male to grasp the female with its teeth, often leaving bloody wounds on her in the process.

According to the new study, many males don’t leave unscathed, either. Some females bite back. 

For the study, lead author Jennifer Wyffels, a researcher at Ripley’s Aquariums and the University of Delaware examined the mating wounds left in sand tiger sharks – a critically endangered species that grows up to 10 feet long. 

The research first observed a group of sand tiger sharks in an aquarium, where mating activity had resulted in severe injury to a female. Based on these data, the researchers were able to establish a scale to describe the severity and healing stages of shark mating wounds, with one describing fresh wounds and four describing the initiation of scarring.

Using this, the team then analysed some 2,876 photographs of 686 sand tiger sharks taken between 2005 and 2020 off the coast of North Carolina. Their findings revealed an increase in stage one wounds were detected in late May, marking the start of a voracious mating season in the region. The peak levelled off in July, indicating that mating had become less aggressive by mid to late summer.

Photographs collected in this seasonal window provided more evidence, indicating that – out of the females that stuck around in the region at the end of mating season – bore stage three and four wounds. It was this that led researchers to conclude that while sand tiger shark mating is a particularly violent affair, sharks have an “unusually fast healing rate” in which deep wounds close after just 22 days and scarring finishes 85 days post injury.

“By combining aquarium and wild sand tiger shark wound healing observations, we were able to describe wound stages and a timeline for healing for this species,” said Wyffels. “This information was used to infer the mating season for wild sand tiger sharks.”

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