Rare video captures following and biting courtship behavior in elusive whale sharks

Courtship and procreative behavior in many species of elasmobranchs—cartilaginous fish including rays, sawfish, sharks, and skates—may include following and biting. However, there has been little research on procreative behavior specific to whale sharks (Rhincodon typus). Now a multi-institutional research team from Australia has observed a sexually mature male whale shark following and biting a smaller female in the wild.

The researchers report their findings in a Data Report Article in Frontiers in Marine Science.

Since 2016, whale sharks have been classified as Endangered on the IUCN Red List of Threatened Species. Though these sharks are usually found in the coastal waters of warm and tropical areas throughout the world, juvenile males often comprise the majority of these populations, and observations of their behavior inform much of the existing research.

Adults are more elusive, according to the research team. “Our knowledge of adult whale sharks, particularly their reproductive and behavioral ecology, is largely derived from chance observations of sharks caught by fisheries or from animals held in aquaria,” they write.

Few existing reports of observed courtship behaviors

In fact, existing reports of whale shark courtship and procreative behaviors include only two locations in the wild: in the waters around the Saint Helena Islands of the South Atlantic Ocean, and at Western Australia’s Ningaloo Reef.

On various occasions in Saint Helena, fishers reported a male following a female and nudging her caudal fin, and also described seeing males following females, then positioning themselves with their ventral sides up beneath the females, presumably to introduce their claspers.

The Ningaloo Reef sighting came in 2019 from the pilot of a small plane who was providing aerial spotting to scientists on a research vessel. She noticed an adult male approach a smaller female and rotate himself, ventral side up, with his claspers out. The female avoided him, but not before the pilot managed to capture images of the activity.

The newest observation

The newest observation also occurred at Ningaloo Reef. From 2009–2024, the researchers made yearly field expeditions in early May, to coincide with the peak of the seasonal whale shark aggregation. The pilots of light planes worked with them to report sightings and direct the vessel to them.

During these observations, the research team recorded the sex ratios of males to females, omitting individuals sighted multiple times within a season and individuals whose sex could not be determined.

On 14 May 2024, a pilot summoned them to the location of a female whale shark, which they photographed and measured to be 7 meters in total length. Shortly afterwards, a male (presumed to be an adult due to its calcified claspers and 8.5-meter size) appeared and began following 2–3 meters behind the female’s caudal fin.

The researchers describe what happened next: “The male was observed to open its mouth and lunge forward towards the caudal fin of the female. 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.

“After a brief pause in forward movement, the female again turned rapidly, with contact occurring between the snout of the male and the caudal fin of the female. The female then rapidly descended to depth followed by the male. At this point, the researchers lost sight of the sharks from the surface.”

Interestingly, the researchers report, “the behaviors we observed and those reported by Gudgeon (2019) did not appear to result in successful mating. Although it was possible that mating could have occurred after the sharks that we followed descended to deep water, the female appeared to actively resist the attention of the male.”

They speculate that this may be due to the male having pursued a sexually immature female. Sexually mature females measure 10–12 meters; the females in both cases measured 6–7 meters.

Ningaloo’s whale shark ecology may play a role in unsuccessful mating attempts

Furthermore, the local ecology may be a factor. For decades, the majority of Ningaloo’s shark population has been female—between 15 and 17% from 1992–2004, a ratio of approximately 1:5—according to studies published in 2006 and 2007. The researchers of the latest observation report a female whale shark population averaging 22% (a ratio of about 1:3) in Ningaloo from 2010–2024, based on their sampling trips during these years.

“As the sex ratio of males and females at birth is roughly 1:1, as it is for most other species of sharksthis implies that some female whale sharks may be actively avoiding aggregation sites,” they write.

There are varying hypotheses for why this is the case, but exactly why is unknown. The researchers of the new report note that they have not recorded any females of mature length, though they have observed juvenile females feeding with males.

Nevertheless, the team concludes that although the interaction they report “did not likely culminate in mating, our observations suggest that pre-copulatory behaviors of whale sharks resemble those of many other species of shark. Such records do not just expand our understanding of reproductive behaviors but may also provide insights into the potential drivers of sexual segregation reported in populations of whale sharks at many coastal aggregations.”

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