November Elasmobranch of the Month: Whale Shark
Whale sharks are the largest fish on the planet. They can grow to over 20 meters (40 feet) long and weigh 22.7 tons (50,000 pounds). Underneath they are white. On the top and sides they are blue-gray to brown with white spots and stripes. These markings create patterns that are unique to each individual. They have a flat head and very broad mouth. Their eyes are small. Their first dorsal fin is located midway down the back with the second dorsal fin located three-fourths down its body. Both dorsal fins have rounded tips and the second one is roughly half the size of the first. Its pectoral fins are broad and rounded. The front of the pectoral fins aligns approximately with the third gill slit. They also have three noticeable ridges on each side of their body. This shark species’ mouth contains ten filtering pads on each side. These pads are what filter its food. They also have 3,000 small teeth in their jaws, arranged in over 350 rows.
Image Credit: Michaela Palmer
Habitat and Distribution
The whale shark’s distribution is extremely widespread. They are found in all tropical and warm temperate waters, excluding the Mediterranean. They reside throughout the Atlantic Ocean, from New York, U.S. to the Caribbean to central Brazil and from Senegal to the Gulf of Guinea. In the Indian Ocean it resides throughout the area including Arabian Gulf and the Red Sea. In the Pacific Ocean, its range extends from Japan to Australia, Hawaii, and from California to Chile.
Whale sharks are pelagic, meaning they live in the open areas of the oceans away from the coasts. They are migratory animals and seem to prefer specific feeding locations. They can be seen at the surface as well as being able to reach depths of 1,928 meters (6325.5 ft).
Whale sharks are filter feeders, sucking water into their mouths and filtering out nutrients such as plankton, fish, squid, and crustaceans such as crab and shrimp. Using suction power enables them to take in larger amounts of food at a time than other filter feeders.
Much is still unknown about whale shark reproduction. Their reproductive method is ovoviviparous, where eggs develop and hatch inside the female then are birthed live. Based on a minimal number of specimens, it is believed the pups measure 55-64 cm (21.7-25.2 in.) long at birth. One specimen held 300 embryos, yet average litter sizes are not known.
The IUCN Red List of Threatened Species currently lists the Whale shark as Endangered, with a decreasing population trend.
The whale shark’s natural predators include great white sharks, tiger sharks, blue sharks and orcas. Due to the size of the whale shark, juveniles are preyed upon more often than adults.
They are targeted by the aquarium and commercial fishing industries. And like many other shark species, they are also caught as bycatch by commercial fishing methods. Additional threats include ship strikes and habitat destruction.
Florida Museum of Natural History
National Marine Sanctuary Foundation
Planet Shark Divers
The IUCN Red List of Threatened Species
Pierce, S.J. & Norman, B. 2016. Rhincodon typus. The IUCN Red List of Threatened Species 2016: e.T19488A2365291. https://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T19488A2365291.en. Accessed on 13 November 2022.