Whale Shark, Rhincodon typus
Whale Shark, Rhincodon typus versus Human, Homo sapiens. Size comparison.
Whale Shark, Rhincodon typus, Juvenile. Photograph taken adjacent to Gordo I, Baja California Sur, July 2009 as a juvenile approached a drifting Mexican panga. Length: approximately 8.0 meters (26 feet).
The Whale Shark, Rhincodon typus, is a member of the Whale Shark or Rhincodontidae Family and is known in Mexico as tiburón ballena. This fish is the sole member of the Rhincodon genus and of the Rhincodontidae Family. The Whale Shark is the largest living fish.
The Whale Shark is the largest animal in the animal kingdom. They have a dark brown background dorsally and transition to white ventrally. They are covered with a pattern of light spots and stripes that give them a checkerboard appearance that varies from individual to individual. Looking down at them from above, they initially appear as a strange, ginormous, and slow-moving white rock. They have robust bodies with a broad flattened head, small round eyes, and a five-foot wide oval mouth equipped with 300 to 350 rows of tiny teeth and ten filter pads. They have five large gill slits, the last three located over the pectoral fins. Their caudal fin is crescent-shaped and asymmetrical with a larger lower lobe that is enhanced in juveniles; their first dorsal fin is over the pelvic fins and is much larger than their second dorsal fin, which is over the anal fin and both dorsal fins are well back on the body. Their skin can be up to four inches thick.
The Whale Shark is a pelagic migratory species that resemble a small submarine slowly cruising all open oceanic waters at depths up to 1,800 m (5,900 feet). The largest documented Whale Shark measured 12.65 meters (41 feet 6 inches) in length and weighed 21.5 tons (47,000 lbs) with numerous undocumented reports that they can be much larger. They prefer water temperatures greater than 22°C (72°F). They are normally found offshore but are known to enter lagoons and coastal areas near the mouths of estuaries and rivers. They migrate to feed and reproduce. They feed almost exclusively on plankton (concentrated collections of copepods, crab larvae, jellyfish, krill, small squid, and freshly released fish eggs), utilizing a ram filtration system whereby they swim at a slow constant speed with their mouth agape, a feeding mode known only in two other sharks, the Basking Shark, Cetorhinus maximus and the Megamouth Shark, Megachasma pelagios. They have modified gill rakers that filter food from water. Juveniles have been documented to consume 21 kg (46 lbs) of plankton per day. Reproduction is ovoviviparous with internal fertilization and the birth of at least 300 live miniature adults that are 40 cm (16 inches) to 60 cm (24 inches) in length, born over an extended period of time. Neither the mating or pupping of Whale Sharks has been observed. They have a lifespan between 70 and 100 years and have been dated to 60,000,000 years.
The Whale Shark is a resident of Mexican waters of both the Atlantic and the Pacific Oceans and are known to form large seasonal aggregations in coastal waters off Isla Mujeres and Isla Holbox in the Yucatan, in Bahia de los Angeles, Baja California, and in La Paz, Baja California Sur.
The Whale Shark is easy to identify due to its size and body coloration.
From a conservation perspective the Whale Shark is currently considered to be Endangered and are modestly protected on a global basis by various organizations. The global populations of Whale Sharks are unknown. They are currently maintained on a very limited basis in aquariums in Atlanta, Georgia, China, Japan, and Taiwan. They are harmless to humans. They are docile animals that will allow swimmers to hitch a ride and will play with divers, thus they have spawned a rapidly growing ecotourism business for divers that is not sustainable.
Note: I have had the good fortune of having several encounters with Whale Sharks as they have been common at certain times of the year around Gordo I, seven miles east of Puerto Los Cabos, Baja California Sur. They are curious animals and will approach a drifting panga. I have also seen one cruising the shoreline immediately off Palmilla Beach.