Whale sharks

Whale sharks (Rhincodon typus) are slow-moving filter-feeding carpet sharks and the largest known currently living fish species. 

The largest confirmed individual had a length of 12.65 m (41.5 ft) and a weight of about 21.5 t (47,000 lb).

Whale_shark_Georgia_aquarium

Whale shark from Taiwan in the Georgia Aquarium. image: wikipedia

 Unconfirmed claims of considerably larger individuals, over 14 m (46 ft) long and weighing at least 30 t (66,000 lb), are not uncommon. 

The whale shark holds many records for sheer size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate


Whale_shark_Australia

A whale shark in Western Australia. image: wikicommons/ Brocken Inaglory

It is the sole member of the genus Rhincodon and the only extant member of the family Rhincodontidae (called Rhiniodon and Rhinodontidae before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The species originated about 60 million years ago. 

The whale shark is found in open waters of the tropical oceans and is rarely found in water below 22 °C (72 °F). Modeling suggests a lifespan of about 70 years, but measurements have proven difficult. 

Distribution of whale sharks

Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and are not known to pose a threat to humans.

Scientific Classification

Kingdom: Animalia

Phylum: Chordata

Class: Chondrichthyes

Order: Orectolobiformes

Family: Rhincodontidae

(J. P. Müller and Henle, 1839)

Genus: Rhincodon

(A. Smith, 1829)

Species: R. typus

How it was discovered as a species

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" directly refers to the fish's size, being as large as some species of whales and also that it is a filter feeder like baleen whales.


Diet

The whale shark is a filter feeder – one of only three known filter-feeding shark species (along with the basking shark and the megamouth shark). It feeds on plankton including copepods, krill, fish eggs, Christmas Island red crab larvae and small nektonic life (actively swimming), such as small squid or fish.


How they filter feed

Feeding occurs either by ram filtration, in which the animal opens its mouth and swims forward, pushing water and food into the mouth, or by active suction feeding, in which the animal opens and closes its mouth, sucking in volumes of water that are then expelled through the gills. 

In both cases, the filter pads serve to separate food from water. These unique, black sieve-like structures are presumed to be modified gill rakers. 

Food separation in whale sharks is by cross-flow filtration, in which the water travels nearly parallel to the filter pad surface, not perpendicularly through it, before passing to the outside, while denser food particles continue to the back of the throat.

 This is an extremely efficient filtration method that minimizes fouling of the filter pad surface. Whale sharks have been observed "coughing", presumably to clear a build-up of particles from the filter pads. Whale sharks migrate to feed and possibly to breed.

A juvenile whale shark is estimated to eat 21 kg (46 pounds) of plankton per day.


The whale shark is an active feeder

They target concentrations of plankton or fish  and are able to ram filter feed or can gulp in a stationary position. This is in contrast to the passive feeding basking shark, which does not pump water. Instead, it swims to force water across its gills


Reproduction

Surprisingly, neither mating nor pupping of whale sharks has been observed.

The capture of a female in July 1996 that was pregnant with 300 pups indicated whale sharks are ovoviviparous.

 The eggs remain in the body and the females give birth to live young which are 40 to 60 cm (16 to 24 in) long. Evidence indicates the pups are not all born at once, but rather the female retains sperm from one mating and produces a steady stream of pups over a prolonged period. 

They reach sexual maturity at around 30 years and their lifespan is an estimated 70 to 100 years.


#InternationalWhaleSharkDay is on the 30th of August.


Source adapted from: Whale shark. (2017, August 30). In Wikipedia, The Free Encyclopedia. Retrieved 06:52, August 31, 2017 , from https://en.wikipedia.org/w/index.php?title=Whale_shark&oldid=798025860