Whale Shark

Verified Timeline

Lore & Background

The species was distinguished in April 1828 after the harpooning of a 4.6 m (15 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, described it the following year. The name 'whale shark' refers to the animal's appearance and large size; it is a fish, not a mammal, and, like all sharks, is not closely related to whales. Since the 1800s, there have been accounts of very large whale sharks. In 1868, the Irish natural scientist Edward Perceval Wright obtained several small whale shark specimens in the Seychelles. Wright was informed of one whale shark that was measured as exceeding 45 ft (14 m). Wright claimed to have observed specimens over 50 ft (15 m) and was told of specimens upwards of 70 ft (21 m). Hugh M. Smith described a huge animal caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, and no measurements were taken. Smith learned through independent sources that it was at least 10 wa. Later sources have stated this whale shark as approximately 18 m (59 ft), but the accuracy of the estimate has been questioned. In 1934, a ship named the Maunganui came across a whale shark in the southern Pacific Ocean and rammed it. The shark became stuck on the prow of the ship, supposedly with 15 ft (4.6 m) on one side and 40 ft (12.2 m) on the other, suggesting a total length of about 55 ft (17 m).

In Their Own Story

The whale shark is an active filter feeder, primarily consuming plankton, krill, fish eggs, and small schooling fish such as sardines and anchovies. The shark can process over 6,000 liters of water per hour through its specialized sieve-like gill pads. Highly migratory, the whale shark travels thousands of miles across tropical oceans to exploit seasonal food sources, with large, predictable feeding aggregations occurring at coastal sites such as Ningaloo Reef in Western Australia, the Yucatan Peninsula in Mexico, and off the coast of Gujarat and Kerala in India. Evidence suggests that whale sharks can recover from major injuries and may be able to regenerate small sections of their fins. Their spot markings have been shown to reform over a previously wounded area. The complete and annotated genome of the whale shark was published in 2017. Rhodopsin, the light-sensing pigment in the rod cells of the retina, is normally sensitive to green and used to see in dim light, but in the whale shark two amino acid substitutions make the pigment more sensitive to blue light instead, the light that dominates the deep ocean. One of these mutations makes rhodopsin vulnerable to higher temperatures. This pigment becomes unstable in shallow water, where the temperature is higher and the full spectrum of light is present. To protect from this instability, the whale shark deactivates the pigment when in shallow water. In the colder environment at 2,000 meters below the surface, it is activated again. The mutations thus allow the shark to see well at both ends of its great vertical range.

Reader's Guide

Whale sharks inhabit the open waters of all tropical oceans. They are rarely found in water below 21 °C (70 °F). The lifespan of a whale shark is estimated to be between 80 and 130 years, based on studies of their vertebral growth bands and the growth rates of free-swimming sharks. Whale sharks possess a broad, flattened head with a large mouth and two small eyes located at the front corners. Unlike many other sharks, whale shark mouths are located at the front of the head rather than on the underside of the head. Their mouths can be exceptionally wide; a 12.1 m (39.7 ft) individual was reported to have a mouth measuring 1.55 m (5.1 ft) across. Whale shark mouths can contain over 300 rows of tiny teeth and 20 filter pads which it uses to filter feed. The spiracles are located just behind the eyes. Whale sharks have five large pairs of gills. Their skin is dark grey with a white belly marked with an arrangement of pale grey or white spots and stripes that is unique to each individual. The skin can be up to 15 cm (5.9 in) thick and is very hard and rough to the touch. The whale shark has three prominent ridges along its sides, which start above and behind the head and end at the caudal peduncle. The shark has two dorsal fins set relatively far back on the body, a pair of pectoral fins, a pair of pelvic fins and a single medial anal fin. The caudal fin has a larger upper lobe than the lower lobe (heterocercal). Whale sharks have been found to possess dermal denticles on the surface of their eyeballs that are structured differently from their body denticles. The dermal denticles, as well as the whale shark's ability to retract its eyes deep into their sockets, serve to protect the eyes from damage.

Did You Know?

• The whale shark can process over 6,000 liters of water per hour through its specialized sieve-like gill pads.
• The skin of a whale shark can be up to 15 cm (5.9 in) thick and is very hard and rough to the touch.
• Whale sharks have been found to possess dermal denticles on the surface of their eyeballs that are structured differently from their body denticles.
• The complete and annotated genome of the whale shark was published in 2017.
• The whale shark's rhodopsin pigment becomes unstable in shallow water, so the shark deactivates it there, then reactivates it in the colder environment at 2,000 meters below the surface.