Whale Shark

The whale shark is the world's largest living shark as well as the world's largest living fish. The record-breaking whale was 20 meters in length and the whale shark weight was measured as 42 tonnes! Researchers and divers are drawn to this charming gentle giant.

Whale sharks are filter feeders, filtering seawater for food such as tiny fish and crustaceans with their large gaping mouths. Whale sharks, surprisingly, have rows of small teeth within their mouth, the purpose of which is unknown to experts! Despite the fact that they are a well-studied species, little is known about their reproduction process.

The whale sharks are mostly found in the open waters of the tropical oceans and are rarely found in water below 21 degrees celsius. Whale shark lifespans have been predicted to be 80 to 130 years based on studies of vertebral growth bands and free-swimming shark development rates. Whale sharks have enormous mouths and filter feed, a feeding habit shared by just two other sharks: the megamouth shark and the basking shark. They consume plankton and tiny fish nearly exclusively and pose little harm to people.

Reproduction in whale sharks happens through viviparity in which the embryos are supplied with nutrients from the yolk and stay within the mother’s body until it is ready to hatch. Only one pregnant female has ever been studied despite the fact that pregnant females are occasionally seen. She was discovered to be carrying 304 babies in various stages of development, all of whom were sired by the same male, implying that female whale sharks can retain sperm. This is considered to be the biggest shark litter ever.

Despite the fact that the whale sharks are big and dangerous they are found to be very vulnerable to overexploitation with the data collected suggesting that there is a 63% decline in the population of whale sharks in the Indo-Pacific region over the last seventy-five years. 

Over the years the whale sharks have been targeted by the illegal, unregulated and unreported (IUU) fisheries for their fine fins, oils, and meat. They have been found to be very susceptible to being hit by vessels in shipping lanes which have caused fatalities in the past. 

Here, we are going to discuss everything about the whale shark such as the whale shark size, whale shark length, description, habitat, whale shark lifespan. Also, a few of the most interesting and frequently asked questions related to whale sharks will be answered here. 

History of the Whale Sharks 

• A whale shark whose scientific name is Rhincodon typus is considered to be a slow-moving, filter-feeding carpet shark and is considered to be the largest known extant fish species. The longest confirmed individual measured 18.8 meters in length. The whale shark holds several world records for size, including being the world's largest living non-mammalian vertebrate. It is the only surviving member of the Rhincodon genus and the Rhincodontidae family, which belongs to the subclass Elasmobranchii of the class Chondrichthyes. It was previously categorized as Rhineodon in the Rhinodontidae family.

• The whale shark is a relatively new addition to the ocean's and its inhabitants' human record. However, this shark's ancestors may be traced back to the Jurassic and Cretaceous eras, when the current groupings of sharks first appeared 245-265 million years ago.

• The first whale shark specimen known to science was discovered off the coast of South Africa in 1828. Later that year, Dr. Andrew Smith formally identified this species as the ocean's largest living shark.

• The species of the whale shark is rare. There had been less than 350 verified reports of whale sharks globally, prior to the mid-1980s. Since then, there have been several sightings throughout Australia. The yearly arrival of the dugongs in Ningaloo Marine Park on Western Australia's northwest coast has spawned a profitable tourist sector.

Description of the Whale Shark

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• A whale shark's mouth consists of over 300 rows of tiny teeth and over 20 filter pads which it usually uses to filter feed. The whale shark’s mouths are located in the front of the head instead of the underline of the head. With two tiny eyes at the front corners, the head is broad and flat. Spiracles are found right behind the eyes. Whale sharks have five pairs of gills, each of which is rather big. Their skin is dark grey, with a white belly characterized by pale grey or white dots and stripes that are different for each individual. It has a 15-cm thick skin that is incredibly hard and harsh to touch.

• Three distinct ridges run along the sides of the whale shark, starting above and behind the head and ending at the caudal peduncle. Two dorsal fins, a pair of pectoral fins, a pair of pelvic fins, and a single medial anal fin make up the shark's body fins. The top lobe of the tail is bigger than the lower lobe (heterocercal).

• On the surface of their eyeballs, whale sharks have dermal denticles that are organized differently from their body denticles. These denticles, combined with the whale shark's ability to withdraw its eye deep into its socket, protect the eye from injury.

• A complete and annotated genome of the whale shark was successfully released in the year 2017. Throughout history, there has been much evidence found that proves the fact that whale sharks can recover from any major injury and may even be able to regenerate small sections of their fins. The spot marking present on their body has been formed upon the previously injured areas. 

How Big is a Whale Shark?

• The whale shark is the world's largest non-cetacean mammal. Whale sharks are thought to have sexual dimorphism in terms of size, with males not becoming as large as females. The research looked at the growth of whale sharks during a ten-year period. It was discovered that males attain an average length of 8 to 9 meters, however, this does not reflect the greatest size conceivable. Based on more restricted data, the same research estimated that females would reach a length of about 14.5 m on average.

• Previous research on whale shark development and lifespan has yielded length estimates ranging from 14 to 21.9 meters. Limited data, primarily from males, shows that sexual maturity occurs at a length of 8 to 9 meters, with females maturing at a comparable or bigger size. Due to a lack of comprehensive documentation of the biggest documented individuals, the species' maximum length is unknown. There have been many reports of whale sharks up to 18 meters long.

• When it comes to large whale sharks it is very difficult to measure them both on water and on land. When measured on land, the overall length can be influenced by the position of the tail, which can be angled as it would be in life or extended to its greatest length. In-water measurements have traditionally been done using procedures including comparisons to known-size items and knotted ropes, which can be inaccurate.

Biology and Ecology of the Whale Sharks 

• This species of whale sharks are closely related to the wobbegong and other bottom-dwelling sharks (Orectolobiformes). Each shark's skin has a pattern of lines and spots that allows them to blend in with their environment. The sharks' 'camouflage' helps them blend in with their marine surroundings. Individual sharks may be identified by their distinct patterning, which does not appear to alter over time.

• The whale shark is one of only three filter-feeding sharks, the other two being the basking and megamouth sharks. It feeds on krill, crab larvae, jellyfish, and other small creatures. They have around 3000 small teeth, each measuring less than 6 mm in length, however, they do not utilize them during eating. The whale shark, on the other hand, can sieve prey as small as 1 millimeter through the fine mesh of its gill-rakers. They have the ability to extend their lips to a large breadth in order to maximize feeding efficiency.

• The whale sharks are also known to feed via suction while they are vertical in the water. When feeding behaviour data is coupled with sighting data, researchers may be able to better understand how shark presence is linked to natural occurrences in the ocean.

Distribution of the Whale Sharks 

• Whale sharks may be found in tropical and mild temperate waters, generally between 30°N and 35°S latitudes.

• They've been spotted in both deep and shallow coastal water, as well as lagoons on coral atolls and reefs.

• Whale sharks may be found in Australia, which is one of the most dependable places to look. Many other countries, including India, the Maldives, South Africa, Belize, Mexico, the Galapagos Islands, Southeast Asia, and Indonesia, have reported regular sightings.

• The species of the whale shark are widely distributed in Australian waters. Although sightings have been recorded further south than Kalbarri, they are most prevalent at Ningaloo Marine Park. Whale sharks have also been spotted between Australia and Indonesia in the Commonwealth seas.

• The whale sharks have been thought to prefer the surface seawater temperature which is between 21 to 25 degrees celsius. At Ningaloo Marine Park, however, sightings are more likely when the water temperature is approximately 27°C.

• Whale sharks have been seen in areas where seasonal food 'pulses' have been seen. The yearly whale shark aggregation at Ningaloo Marine Park is strongly connected to a rise in the region's production. This is linked to a mass coral spawn that happens every year in March/April.

Habitat of the Whale Shark 

• Whale sharks are fish, therefore they get oxygen through their gills. Unlike air-breathing whales and dolphins, they have no physiological need to swim near the surface. Despite the fact that whale sharks are most commonly seen swimming at the surface during seasonal aggregations, data from tracking studies conducted at Ningaloo Marine Park and other worldwide sites suggests that they may dive to tremendous depths of up to 700 meters. The whale sharks have the ability to stay away from the surface for lengthy periods of time.

• Individual whale sharks may stay close to Ningaloo Reef during the day and night, according to radio-tracking experiments conducted at Ningaloo Marine Park. Furthermore, using the Whale Shark Photo-identification Library, it was feasible to show that one recognized shark was recited in Ningaloo Marine Park on 14 different days over a 28-day span - all within a very small region. When sharks return to the Australian northwest coast, they appear to have a level of site attachment.

• In the year 2011, more than 400 whale sharks gathered off the Yucatan coast and it was considered to be one of the largest gatherings of the whale sharks ever recorded. Large numbers of whale sharks congregate in that location every year between May and September, making it one of the most dependable seasonal gatherings known for whale sharks. Ecotourism as a result has exploded to unsustainable proportions.

Reproduction and Growth of the Whale Shark

•  The whale shark's development, lifespan, and reproduction are all unknown. There was some debate on whether vertebral growth bands occur yearly or biannually, which is crucial for calculating whale shark age, growth, and lifespan.

• Various studies that have been conducted throughout the years in which the vertebrae growth bands were studied and the measuring of the whale sharks in the wild have estimated that the lifespan of the whale shark is approximately 80 years and if they are not deprived of their diet, they could live up to 130 years. 

• There is much evidence that suggests that the male grow faster than the females in the earlier stages of their lives but at the end reach a smaller maximum size. Whale sharks are known to exhibit late sexual maturity. One study suggests that the age at which the male sharks reach sexual maturity is at the age of 25 years. 

• Whale sharks have not been seen pupping, although they have been seen mating twice in St Helena. When a larger male failed to mate with a smaller, immature female, mating in this species was seen for the first time in whale sharks off Ningaloo Reef in Australia by aircraft in 2019.

• Whale sharks are ovoviviparous, as evidenced by the catch of a 10.6 m female in July 1996, who was pregnant with 300 pups. The eggs stay in the female's body, and she gives birth to live young that are 40 to 60 cm long. Evidence suggests that the puppies are not all born at the same time, but rather that the mother keeps sperm from each mating and produces a continuous stream of pups over time.

• Marine biologists in the Philippines discovered what is thought to be the smallest live whale shark specimen on March 7, 2009. The juvenile shark, which was found with its tail attached to a post on a beach in Pilar, Sorsogon, Philippines, was released into the wild, measuring just 38 cm. Some experts now feel that this region is not just a feeding place, but also a birthing ground, as a result of this study. Young whale sharks and pregnant females have been seen in the South Atlantic Ocean off the coast of St Helena, where many whale sharks may be seen throughout the summer.

What Do Whale Sharks Eat?

• The whale shark is a filter feeder which is that they are the only three known filter-feeding shark species along with the basking sharks and the megamouth shark. 

• Plankton such as copepods, krill, fish eggs, Christmas Island red crab larvae, and small nektonic life such as small squid or fish are eaten by whale sharks. It also eats clouds of eggs laid by fish and corals during mass spawning. The numerous rows of vestigial teeth have no function in the eating process. Ram filtration, in which the animal opens its mouth and swims forward, forcing water and food into the mouth, or active suction feeding, in which the animal opens and shuts its mouth, sucking in large amounts of water that is subsequently ejected via the gills, are the two methods of eating.

• The filter pads of whale sharks are used to isolate food from the water. It's thought that these unusual black sieve-like structures are modified gill rakers. Whale sharks use cross-flow filtration, in which water passes almost parallel to the filter pad surface, rather than perpendicularly through it, before flowing to the outside, while heavier food particles remain at the rear of the throat. This is a very effective filtering technique that prevents the filter pad surface from being fouled. The "coughing" of whale sharks has been seen, probably to remove a build-up of particles from the filter pads. Whale sharks travel in order to eat and potentially reproduce.

• The whale shark is a voracious eater who hunts for plankton or fish in high quantities. It has the ability to ram filter feed or swallow when stationary. The basking shark, on the other hand, is a passive feeder that does not pump water. It swims instead to push water through its gills. A young whale shark is thought to consume 21 kilograms of plankton each day.

• Whale sharks have been observed preying on a variety of planktonic and tiny nektonic species that are spatially and temporally variable. Krill, crab larvae, jellyfish, sardines, anchovies, mackerels, tiny tunas, and squid are some of these. The fish moves forward at a steady pace with its mouth completely open, straining prey particles from the water using forward propulsion. This is also known as 'passive feeding,' because it happens when prey is present in low numbers.