Whale shark

• 1. Introduction

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  The whale shark, Rhincodon typus, is the largest known living fish. The biggest measurement scientists trust comes from a single female in the Arabian Sea. She was reported in 2001 with a standard length of 15 m and an estimated total length of 18.8 m. A 2015 study of the size of marine megafauna, led by McClain and colleagues, judged her the most reliable and accurately measured giant on record. Even that figure comes with a caveat, because nobody has pinned down how large these animals can really grow. Some reports claim far more. This documentary asks how a fish of that scale lives on some of the smallest food in the ocean. It asks how anyone measures an animal that will not hold still, and why a creature so gentle has such a hard time staying common. It also asks how much of its life remains unseen.

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• 2. Name and Ancestry

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  In April 1828, a harpoon struck a 4.6 m fish in Table Bay, South Africa, and science gained a new species. Andrew Smith, a military doctor attached to the British troops stationed in Cape Town, described it the following year. The name he settled on is misleading. This animal is a fish, and like every shark it is not closely related to whales. It earned the label from its looks and its enormous size. Other cultures reached for the sky instead. In Madagascar it is marokintana, meaning many stars, after the pattern on its back. Eastern Java calls it gegar lintang, star-backed, while Sulawesi and Papua say gurano bintang. In Japan it is jinbei-zame, because the markings resemble patterns seen on jinbei garments. Vietnamese speakers call it ca ong, literally sir fish. In the Philippines it is butanding or balilan, and it appears on the reverse of the 100-peso bill. The Maldivian 1000 rufiyaa note from the 2015-2017 edition also carries it, beside a green turtle. Scientific naming has shifted too. Before 1984 the genus was spelled Rhiniodon and the family Rhinodontidae. Today Rhincodon typus is the only living species in its genus and the only extant member of the family Rhincodontidae. It sits among the carpet sharks, in the same class as all sharks and rays. The lineage is old. The earliest known fossil teeth come from the Late Oligocene of South Carolina. From the Early Miocene onward, teeth turn up more widely, in the eastern United States, southern France and Costa Rica. One extinct relative, Rhincodon ferriolensis, was described from the Late Burdigalian stage in Europe, probably in Spain.

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• 3. Measuring a Giant

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  In 1868, the Irish natural scientist Edward Perceval Wright collected several small whale shark specimens in the Seychelles, then heard much bigger stories. He was told of one measured at more than 45 ft. He claimed to have seen specimens over 50 ft, and he was told of some upwards of 70 ft. In 1919, Hugh M. Smith described an animal caught in a bamboo fish trap in Thailand. It was too heavy to haul ashore, so nobody measured it. Smith learned from independent sources that it was at least 10 wa, a local unit. Fishermen's usage suggested a wa meant either 2 m or roughly 1.7 to 1.8 m. Later writers repeated the shark as about 18 m, but that estimate has been questioned. In 1934, a ship called the Maunganui rammed a whale shark in the southern Pacific Ocean. The animal lodged on the prow, reportedly with 15 ft on one side and 40 ft on the other, which suggests about 55 ft. Satellite tracking by Scott A. Eckert and Brent S. Stewart followed 15 sharks from 1994 to 1996. Two of them were females reported at 15 m and 18 m. A stranded whale shark of 20.75 m was reported on the Ratnagiri coast in 1995. On the 7th of February 2012, a carcass was found floating 150 km off the coast of Karachi, Pakistan. It was said to be 11 to 12 m long and to weigh around 15000 kg. Sharks of 18 to 20 m appear in scientific literature, but the largest are poorly documented, and most whale sharks seen are smaller. Measuring is hard even with the animal in hand. On land, the total length changes depending on whether the tail is angled as in life or stretched out. In the water, divers once relied on objects of known size and knotted ropes, which can mislead. Photogrammetry, both underwater and from the air, is now used to tighten the numbers.

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• 4. Built to Filter

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  A whale shark of 12.1 m was once reported with a mouth 1.55 m across. Unlike many sharks, it carries that mouth at the front of the head instead of underneath. Inside sit more than 300 rows of tiny teeth, yet these vestigial teeth play no part in feeding. The work falls to 20 black, sieve-like filter pads, which are presumed to be modified gill rakers. The shark can run over 6,000 liters of water per hour through them. It feeds in two ways. In ram filtration, it swims forward with the mouth open. In suction feeding, it opens and closes the mouth to draw in water and then expels it through the gills. Either way, the water travels nearly parallel to the pad surface, and denser particles slide on toward the throat. This cross-flow design is very efficient and keeps the pads from clogging. Even so, the sharks have been seen coughing, presumably to clear built-up particles. The menu is wide. It includes copepods, krill, chaetognaths, jellyfish, fish eggs, Christmas Island red crab larvae, and small squid or fish such as sardines, anchovies, mackerels and small tunas. They also eat Sargassum and partly digest it, which makes them omnivores. A juvenile is estimated to eat 21 kg of plankton a day. Only two other sharks filter feed, the basking shark and the megamouth. The basking shark is a passive feeder that simply swims to push water across its gills. The whale shark is active and seeks out dense patches of prey. The BBC program Planet Earth filmed one timing its arrival to a mass spawning of fish, then feeding on the clouds of eggs and sperm. That diet has a modern cost. Microplastics have now been confirmed in whale shark scat.

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• 5. Skin and Sight

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  No two whale sharks wear the same pattern. Each has pale grey or white spots and stripes over dark grey skin, with a white belly beneath. The skin can be up to 15 cm thick and feels hard and rough. Three prominent ridges run along each side, from above and behind the head to the caudal peduncle. The head is broad and flattened, with two small eyes at the front corners and five large pairs of gills. Two dorsal fins sit far back on the body, and the tail has a bigger upper lobe than lower. The eyes are unusually armored. Their surface carries dermal denticles that are built differently from those on the body. The shark can also retract each eye deep into its socket. The animal heals well. Evidence suggests it recovers from major injuries and may regenerate small sections of fin. Spot markings have been shown to reform over a wounded area. Vision may be the strangest feature. Rhodopsin, the pigment that lets rod cells see in dim light, is normally most sensitive to green. In the whale shark, and in the bottom-dwelling cloudy catshark, two amino acid substitutions shift it toward blue, the light that dominates the deep ocean. One substitution makes the pigment vulnerable to heat. In humans, a similar mutation causes congenital stationary night blindness, because body temperature makes the pigment decay. In warm shallow water, the shark switches its pigment off, which would otherwise interfere with full color vision. At 2,000 meters, in colder water, the pigment switches back on. The eyes have also lost every cone opsin except LWS. The complete annotated genome of the species was published in 2017.

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• 6. Ocean Wanderers

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  The deepest recorded dive of a whale shark reached 1,928 m. Tracking off the northeast Yucatan Peninsula reveals a daily rhythm. The sharks swim at the surface near shore between sunrise and mid-afternoon. They then spend the afternoon and night oscillating up and down in oceanic waters. About 95% of the oscillating time was spent above 200 m. Regular deep dives passed 500 m, often in brief stutter steps, perhaps for foraging. Some sharks stayed below 50 m for three days or more. The species ranges across tropical and warm-temperate seas, usually between 30 degrees north and 35 degrees south, and is rarely found in water below 21 C. Individuals have still been spotted as far north as the Bay of Fundy and the Sea of Okhotsk, and as far south as Victoria, Australia. There are two subpopulations. The Atlantic one stretches from Maine and the Azores to Cape Agulhas, South Africa. The Indo-Pacific one holds 75% of all whale sharks. Seasonal feeding gatherings form at coastal sites including the Persian Gulf, Ningaloo Reef, Darwin Island in the Galapagos, Mafia Island in Tanzania, Inhambane in Mozambique, the Seychelles, Qatar, Taiwan and the Gujarat and Kerala coasts of India. In 2009, more than 400 whale sharks gathered off the Yucatan coast, one of the largest gatherings recorded. Most years, large numbers appear there between May and September. The tourism these gatherings attract has grown to unsustainable levels. Divers also meet whale sharks in places such as Honduras, Thailand, the Maldives, the Red Sea and Tofo Beach in Mozambique. Despite their size, they pose no danger to people, and younger ones can be playful near divers. Photographers such as Fiona Ayerst have captured them swimming close to people. At Darwin Island, a study between 2011 and 2013 found that 91.5% of the whale sharks seen were adult females.

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• 7. Slow Life

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  For years, nobody knew whether whale shark vertebrae laid down growth bands once or twice a year. A 2020 study settled it using Carbon-14 in the bands, compared against nuclear testing in the 1950s and 1960s. The bands form annually. That study found a 10 m female was 50 years old and a 9.9 m male was 35. Lifespan estimates run from about 80 years up to about 130. Males appear to grow faster early on but end smaller. Maturity comes late; one study of free-swimming sharks put male maturity at about 25 years. Limited evidence, mostly from males, places maturity around 8 to 9 m. Growth models have produced asymptotic lengths from 15 to 21.9 m. A separate 2020 study tracked growth around Ningaloo Reef for 10 years and found females grow larger than males. Males averaged 8 to 9 m, while females averaged around 14.5 m, dropping to 12.1 m if aquarium animals were included. The authors stressed these are average asymptotic sizes, not maximums, and that sizes may vary by region. Earlier studies leaned on mostly immature males, and none had data from sharks over about 10 m. Mating has rarely been seen. It was witnessed twice at St Helena. In 2019 it was filmed from an airplane off Ningaloo Reef, where a larger male failed to mate with a smaller, immature female. Birth has never been observed. A female of about 10.6 m caught in July 1996 carried about 300 pups, which showed the species is ovoviviparous. Eggs stay inside the mother, and the young are born live at 40 to 60 cm. Evidence suggests the female stores sperm from one mating and releases pups gradually. On the 7th of March 2009, scientists in the Philippines found a 38 cm whale shark with its tail tied to a stake on a beach in Pilar, Sorsogon. It is believed to be the smallest living specimen known, and it was released. The find led some scientists to suspect the area is a birthing ground. In the first half of 2019, WWF Philippines logged 168 sightings, including 64 re-sightings, and identified very young juveniles in Ticao Pass.

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• 8. Peril and Protection

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  Between 130,000 and 200,000 whale sharks are thought to live in the world's oceans, and the number is falling. Over the past 75 years the population has dropped by about 50%. The decline is about 63% in the Indian and Pacific Oceans and over 30% in the Atlantic. The causes are fishing bycatch, ship strikes and pollution, and the International Union for Conservation of Nature lists the species as endangered. In 2010, oil from the Gulf of Mexico spill spread over an area where one-third of recent sightings in the northern gulf had occurred. The sharks could not avoid the slick, which lay on the surface where they feed. No dead whale sharks were found. A 2014 report said hundreds were illegally killed each year in China for fins, skins and oil. Protection has arrived in steps. The Philippines banned commercial fishing, selling, importing and exporting of whale sharks in 1998, followed by India in May 2001 and Taiwan in May 2007. In 2003 the species joined Appendix II of the Convention on International Trade in Endangered Species. It is also listed with six other shark species under the CMS Memorandum of Understanding on the Conservation of Migratory Sharks. In June 2018, New Zealand classified it as Migrant, with the qualifier Secure Overseas. Touching or riding whale sharks is forbidden in most countries and can bring a fine. In the Philippines, snorkelers must keep 4 ft away, and touching one risks a fine and possible prison. Captivity is contested. The first attempt came in 1934, when a shark spent about four months in a netted bay at Izu, Japan. The Okinawa Churaumi Aquarium began keeping them in an aquarium in 1980. One of its sharks had lived there more than 26 years as of 2021. Outside Asia, only the Georgia Aquarium in Atlanta keeps them. Its sharks needed 28 to 36 hours of transport. Ralph and Norton died in 2007, Trixie in 2020, Alice in 2021 and Taroko in 2025. As of August 2025, the aquarium keeps one male, Yushan, who arrived in 2007. All came from Taiwan's commercial fishing quota, a fishery Taiwan closed entirely in 2008.

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