whale shark

Whale Sharks are easily recognized by their immense size and a two-tone pattern of light spots and lines on a base coloration ranging from gunmetal grey to black to dusky blue, mocha brown, or bronze upper surface and a white underbelly.

The whale shark has a broad, blunt head; three prominent ridges running transverse along its body. It's enormous mouth is located at the front of the head, and can be opened wide to filter large amounts of water for small fish, squid, crustaceans, and other plankton organisms. The Whale Shark is ovoviviparous and gives birth to live young measuring approximately 70cm in length. The Whale Shark is not only the largest shark species, it also has the largest litter size of all sharks.

Very little is known about the habits of the Whale Shark. Sub adults may live in small groups, but these are seen only very rarely. Adults are usually solitary and nothing is known about the way these giants find each other, or how and where their mating occurs.

Whale Sharks are on many peoples "must do" list and in spite of their general scarcity, encounters with these gentle giants can be had off Sodwana Bay annually between October and April due to their natural migratory patterns.Globally, Whale Sharks also appear often around the Seychelles, Similan Islands (Thailand), Christmas Island, Ningaloo Reef (Western Australia), India, Sri Lanka, Belize, Mexico, Kenya and Mozambique.

Physical Characteristics

The largest shark, which was accurately measured at 12,18 meters (40 feet, 7 inches) in length and weighing a hefty 11 metric tons by fishermen who netted a specimen off the coast of Bombay in 1983 and has been less accurately reported in other instances at 18 meters (60 feet).  Whale Sharks are estimated to be approximately 70 cm at birth.  Very little information exists of juveniles measuring less than 3 m in length as the majority of encounters occur with animals between 3 - 8m.

Epidermis

The skin of an adult whale shark may attain a thickness of over 100mm, limiting its possible predators to great white sharks, tiger sharks and orcas, and although none have been observed attacking a whale shark, some individuals show scars and bite marks from apex predators. Scientists call the contrasting coloration of a dark upper surface and light lower surface counter shading, a trait indispensable for stealth and protection. Another possibility is that these pigment patterns could be an adaptation for radiation shielding, important in a species that may spend a significant proportion of time in surface waters possibly exposed to high levels of ultraviolet radiation.

Eyes

Whale Sharks eyes are situated in front of the pectoral fins and gill slits where the polka dotted, dark upper surface joins the snowy underbelly, and two rounded recessed orifices on either side of the head.  The larger of the orifices houses an unblinking eye the size of a golf ball.  The eyes show no expression other than the wide-eyed stare of a large black pupil that swivels to follow any activity going on around it.  

If an object approaches the eye too directly the eyeball swivels backward into the cavity and a tough flap of skin slides forward to cover the opening to the vulnerable sensory organ.  
Once the shark perceives that the threat has passed, the skin flap retracts and the eye returns to its wide-open stare.  
Other shark species posses a similar shielding eyelid (called a nictitating membrane) which slides forward to protect the eye, but the whale shark’s sight protection adaptation is unique and is as yet unclassified.

Spiracle

A slightly smaller opening spaced back from the eye and ahead of the gill slits marks the site of the spiracle chamber.  The spiracle functions as a vestigial first gill slit, allowing water to be taken in and oxygen extracted, whereupon the oxygenated blood is pumped directly to the eye and the brain via a separate blood vessel.  

More commonly associated with sedentary, demersal sharks, sawfish, guitarfish and stingrays. The spiracle in this non-bottom-dwelling shark was one of the criteria that led taxonomists to make the whale shark the sole representative of the family Rhincodontidae in the Orectolobiformes order (an order comprised of nurse, zebra and carpet sharks.)  Whale sharks and other Rhincodontidae also have five gill slits, two dorsal fins, a single anal fin and a mouth termination in front of the eyes.

Mouth

The mouth extends across the width of the flat, blunt snout and ends well before the eyes.  
A mouth running the width of a whale shark’s head can reach tremendous proportions: the 12,18m specimen’s head measured 1,36m across, in the slack repose of death; alive and in the process of feeding, it can possibly extend two or three times that width.

Smell

Like bottom-dwelling sharks, the whale shark has twin nasal slits and sensory barbells (a trait it shares with the nurse shark) in front of its blunt snout on the upper surface above the mouth.  

In sharks, the nasal openings do not lead to the mouth nor do they play any part in respiration, their purpose is to augment the shark's sense of smell, enabling it to detect prey without relying on sight.  

The majority of other shark species have a ventrally located mouth and an elongated snout, which provides a greater surface area for the receptors of the ampullae of lorenzini - the sensory organs which detect weak electronic fields and provide sharks with sensory information when their vision is hampered.  

Placed, far forward and extending over the mouth, the whale sharks barbells augment the ampullae of lorenzini and signal the location of prey, guiding the whale shark's mouth towards its reward.

Teeth

Some scientists believe the whale shark's teeth to be vestigial.  Their function has not been observed, but it seems probable that they are used in processing larger food items, such as small tuna and mackerel that are occasionally captured but are too large to pass through the whale shark's gullet.