Whale shark: size, longevity, IUCN status, and responsible observation

In February 2012, a female whale shark measuring 10 meters and weighing about 7 tons was recovered in Pakistan. Its vertebrae, later dated using carbon-14 left in the oceans by nuclear tests in the 1950s and 1960s, indicated it was 50 years old. This is the highest validated age ever recorded for the species.

This figure challenges many existing fact sheets still circulating, which claim a lifespan of 150 years and a weight of 34 tons without any source. So, everything was reviewed, from size to IUCN status, to verify what needs to be known before swimming next to it.

Rhincodon typus remains the largest living fish. The rest deserves some nuances.

What size and weight does the whale shark really reach?

The greatest length reported in the wild is about 20 meters, for an individual observed off Taiwan, and the official Australian fact sheet retains the same maximum. Weight is much less documented. The most solid data concerns the Pakistani female of 10 meters, estimated at about 7 tons.

The 34 tons figure circulating online has no verifiable source.

But most whale sharks encountered by swimmers are far from these measurements. According to the Australian fact sheet, males become adults between 7 and 9.2 meters, and females around 9 meters. An animal of 6 meters has therefore not finished growing. Its size is still impressive. The growth model published in 2020 predicts a theoretical maximum length of 21.9 meters, which fits quite well with the Taiwanese record.

Characteristic	Accepted Value	Remark
Maximum reported length	About 20 m	Individual from Taiwan
Size at maturity	Males 7 to 9.2 m, females around 9 m	FRDC fact sheet
Documented weight	About 7 t for a 10 m female	Ong et al., 2020
Oldest validated age	50 years	Vertebrae dating
Estimated longevity	60 to 100 years	Estimate, FRDC fact sheet
Maximum recorded depth	At least 1,928 m	Electronic tag
Embryos in a female	About 300	Only one documented case
IUCN status	Endangered (EN)	2016 assessment

How to recognize a whale shark and where does it live?

You recognize it by its broad, flattened head, its mouth located at the very tip of the snout, and its bluish-gray back covered with light spots and lines forming a checkerboard pattern. It lives in tropical and warm temperate seas, near the coast as well as offshore.

This spot pattern is unique to each individual. Researchers use it like a fingerprint, based on photos taken on the flank. Thus, a simple image can enrich a photo-identification catalog, provided it was taken without chasing the animal or blocking its path as it passes. The large pectoral fins and ridges running along the back complete the portrait. It is impossible to confuse it with another shark.

The Mediterranean is not part of its range, according to the official Australian fact sheet dedicated to the species.

One might imagine it stuck to the surface. Tags tell a different story, as a whale shark has been recorded at at least 1,928 meters depth, well beyond any recreational dive. With its filtering mouth, it is also among the strangest sharks in the world.

What does the whale shark eat and how does it filter water?

The whale shark feeds by filtering. It is one of only three species of filter-feeding sharks, along with the basking shark and the megamouth shark. It swallows large volumes of water loaded with plankton, krill, eggs, and small fish, then the water exits through the gill slits while the prey remains trapped.

It does have teeth, though. Thousands of tiny ones, aligned in tight rows. They are not used for chewing and their exact function remains debated. The work is done further along, in the sieve formed by its gill arches, which retain the prey. It can filter while swimming with its mouth wide open, or hold itself almost vertically and suck in water in bursts, a posture often photographed during observation outings.

The spectacular figures about thousands of tons of water filtered per hour are not based on any measurements we could find, so we leave them aside.

This diet makes it very different from the great white shark, a major predator of marine mammals. It does not hunt any prey larger than a small fish.

How long does a whale shark live?

The oldest whale shark whose age has been validated was 50 years old. The study published in 2020 in Frontiers in Marine Science counted the growth bands of its vertebrae and calibrated them against the carbon-14 from nuclear tests. The Australian fact sheet mentions a longevity estimated between 60 and 100 years.

However, the “100 to 150 years” still found in some sources have no solid published basis. The same goes for the “oldest specimen of 70 years.” The measured growth is very slow, with a coefficient of 0.014 per year in the 2020 study model. A female therefore takes decades to reach adult size. The authors also warn that underestimating the longevity of a species distorts the management of its fishing.

Regarding reproduction, only one pregnant female has been documented to date in the literature, with about 300 embryos.

The gestation period remains unknown. The “two years” suggested by some fact sheets is a supposition. We therefore still do not know how often a female reproduces, which makes any estimate of the species’ capacity to recover fragile. For comparison, our list of marine animals that live the longest shows much higher records.

Why is the whale shark classified as endangered?

Since 2016, the IUCN Red List has classified the whale shark as “Endangered.” The assessment, signed by Simon Pierce and Brad Norman, estimates that the Indo-Pacific population has declined by 63% over three generations, or 75 years, and the Atlantic population by at least 30% over the same period.

The causes are known. Fishing, targeted or accidental, has long weighed heavily, for its meat and fins. However, a more discreet threat appears in monitoring. The Australian fact sheet notes that propeller injuries are commonly recorded during surveillance programs. An animal that spends time near the surface remains exposed to every fast boat crossing its feeding area.

Unregulated tourism is also listed among the threats.

Its biology does not help either. A species that grows slowly and becomes adult late takes decades to replace each loss, a point that the authors of the 2020 study emphasize for fisheries managers. The status therefore does not change quickly.

How to observe a whale shark without disturbing it?

You observe it at the surface, with fins, mask, and snorkel, alongside an operator who applies a written code of conduct. Keep your distance, do not touch the animal, do not cut its path, and limit the number of swimmers around it. Exact rules vary from country to country, so ask for them before booking.

The most cited sites are Holbox in Mexico, Ningaloo in Australia, Donsol in the Philippines, Nosy Be in Madagascar, and South Ari in the Maldives. The seasonal windows displayed by booking platforms vary from page to page and are almost never dated. Impossible to decide from here. Yet, this question determines your trip. Ask the operator for their observation rates from previous seasons, month by month, and what they offer if the animal does not show up.

No serious operator can guarantee you an encounter.

For what level? On most outings, you swim at the surface, so the question is less about your certification than your comfort in open water, far from shore and sometimes with currents. Clear water says nothing about the current. The current decides more than the photo. Listen to the briefing, note how the boat recovers swimmers, and keep in mind why we never touch marine life. Also think about your sunscreen, which ends up in the water.

In short, this filter costs you an hour of research and sometimes a more expensive outing, against the risk of paying for an entire trip to a site where sharks are fed to keep them in place.

FAQ

Is the whale shark dangerous to humans?

It does not hunt humans and feeds on plankton and small fish. The risk comes from its mass, with a possible tail fin strike if a swimmer gets too close. Keeping your distance protects you and the animal.

Does the whale shark have teeth?

Yes, thousands of tiny teeth lined up in rows. They are not used for chewing, as the whale shark filters water through its gill arches to trap its prey.

How long does a whale shark live?

The oldest individual whose age has been validated was 50 years old, according to a study published in 2020. The official Australian fact sheet estimates its longevity between 60 and 100 years. The often-cited 150 years has no published basis.

What is the IUCN status of the whale shark?

It has been classified as “Endangered” on the IUCN Red List since 2016. The assessment estimates a 63% decline in the Indo-Pacific population and a decrease of more than 30% in the Atlantic over 75 years.

Sources

• Annual Bands in Vertebrae Validated by Bomb Radiocarbon Assays Provide Estimates of Age and Growth of Whale Sharks (Ong, Meekan, Hsu, Fanning and Campana, Frontiers in Marine Science, 2020)
• Whale Shark, Rhincodon typus. Report Card (Fisheries Research and Development Corporation, Australian government, 2023)

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