Whale Shark Facts

A whale shark is a true cartilaginous fish, not a whale; the name reflects its whale-like size and filter-feeding habit. Adults typically run 18 to 40 feet long and weigh 15,000 to 40,000 pounds. Unlike predatory sharks with a mouth slung under the snout, the whale shark's mouth sits at the very front of its broad, flat head and can open nearly five feet wide. Inside are more than 300 rows of tiny teeth that play no part in feeding; the real tools are 20 spongy filter pads — modified gill rakers — that sieve food from the water. Its skin is up to four inches thick, and its spot pattern is unique to each individual, so researchers identify and track individuals from photographs using pattern-matching software originally built to map stars. It belongs to the carpet sharks (order Orectolobiformes), a group otherwise made up of much smaller bottom-dwellers, and is the only living member of its family, Rhincodontidae.

Whale sharks occur in all tropical and warm-temperate seas, generally between about 70°F and 86°F, and are highly migratory, following seasonal plankton blooms and fish-spawning events. They are mainly open-ocean animals but gather predictably at a handful of coastal sites when food is abundant — Ningaloo Reef in Australia, the Yucatán in Mexico, Donsol in the Philippines, and the coast of Tanzania among them. Tagging shows they also dive far below the sunlit surface, past 6,000 feet, to forage and manage body temperature.

Despite their size, whale sharks are filter-feeding carnivores that live on the ocean's smallest life: zooplankton, krill, copepods, and huge amounts of fish eggs, plus small schooling fish and squid. They feed two ways. In "ram filter feeding" the shark swims forward with mouth agape, forcing prey-laden water over the gill filters and swallowing the trapped food. In "active suction feeding," often used where prey is dense, it hangs vertically and pumps its gills to draw water in like a vacuum. At events such as mass fish spawning, a whale shark can take in enormous numbers of calories in a few hours.

Whale sharks are mostly solitary and make long ocean crossings alone, cruising at only about 3 mph, propelled by a slow sweep of the whole rear body rather than just the tail. Yet they tolerate one another well and gather by the hundreds at rich food blooms with no aggression or competition over the prey. They are famously docile around people and will let divers swim alongside, though touching them can strip the protective mucus layer from their skin.

Whale shark reproduction was a complete mystery until a single pregnant female was landed off Taiwan in 1995, showing the species is ovoviviparous: eggs hatch inside the female, which then bears live young. That one female carried over 300 developing pups — the largest litter known in any shark — each born about 16 to 24 inches long and fully independent. Where the young spend their early years is still largely unknown; pups are rarely seen and probably stay deep to avoid predators. Growth is very slow, with maturity taking up to 30 years, but survivors are thought to live 70 to 100 years.

The whale shark is Endangered with a declining global trend, and the main pressures are human. Swimming slowly at the surface leaves it very exposed to ship strikes from large freighters. It was historically hunted across Asia for meat, fins, and oil, and although now protected in many countries, illegal fishing and net entanglement continue. As a filter feeder it is also highly vulnerable to marine pollution, including microplastics and oil that foul its delicate gill rakers.

To learn more about the whale shark and global marine conservation efforts, consult the following authoritative resources:

• IUCN Red List of Threatened Species: Whale Shark
• World Wildlife Fund (WWF): Whale Shark
• Florida Museum of Natural History: Whale Shark
• Marine Megafauna Foundation