Talk about the largest fish in the world, whale sharks (Rhincodon typus) come to mind. They are almost twice as large as the great white shark, which is the most feared predator on earth. Despite this shark’s enormous size, they do not pose any threat to humans.
Whale sharks (Rhincodon typus) are slow, filter-feeding carpet sharks, and the only living member of Family Rhincodontidae. They are easily recognized, not just for their huge size, but also for their unique patterns, which differentiates them from any other sharks.
You can find these sharks in all the tropical and temperate oceans in the world except the Mediterranean.
Kingdom – Animalia
Phylum – Chordata
Class – Chondrichthyes
Order – Orectolobiformes
Family – Rhincodontidae
Genus – Rhincodon
Species – R. typus
In 1828, Andrew smith described and named whale sharks based on a specimen caught in a harpoon in South Africa. There are many synonyms for family, genus, and specimen names. Despite Smith’s desired name of Rhineodon, the first scientific printing of the genus name appeared as Rincodon.
But, the International Commission on Zoological Nomenclature (ICZN) promoted the genus Rhincodon over others used in the past. This also applied to the family name as Rhincodontidae. The generic names used before including Rhineodon and Rhiniodon and the family names Rhineodontidae and Rhiodontidae.
Consistently, Taxonomists placed Rhincodontidae in the order of Orectolobiformes which includes families like Ginglymostomatidae (nurse sharks) and Orectolobidae (wobbegongs). The interrelationship between these sharks is based on morphological and anatomical similarities.
How to Identify Whale sharks
Whale sharks have a unique flattened broad head, a trim body, and two small eyes at the front corners of their head. Their mouth is traverse and very large, almost reaching the tip of their snout.
These sharks’ gill slits are huge and modified into filtering screens. These species’ first dorsal fin is larger than the second and positioned backward on their body. Adults Whale sharks tail is semilunate while that of the juvenile upper lobe is longer than the lower lobe.
Whale Sharks have a unique checkerboard color pattern of light stripes and spots on their body. Their skin can be up to 15 cm thick, very rough, and hard when touched.
These sharks have a greyish, bluish, or brownish coloration, with an upper surface pattern of creamy white spots between the vertical and horizontal stripes on their body. The function of the distinctive pattern on their body is unknown.
Though, many bottom-dwelling sharks tend to have bold, distinctive body markings that act as a camouflage. Whale sharks markings could be as a result of their evolutionary relationship with bottom-dwelling sharks. Unique markings in a pelagic species could have more to do with social activities like postural displays and recognition processes.
Inside their mouth, next to the pharynx, these sharks have 20 filtering pads in total. They have ten on each side of their jaw (the upper and lower). These filtering pads enable whale shark to sift through an average of 20,700 grams of planktons daily. Whale sharks’ teeth are tiny and pointed backward. They have about 300 rows of small teeth on each of their jaw.
These sharks have unique denticles .i.e, tooth-like scale structures, each with a solid central keel, a tri-lobed rear margin, and no lateral keels. It appears that the denticles are essential in their pelagic lifestyle.
Scientists estimate average adult size at 32 ft (9.8 m) length and 20,000 Ib (9 t) weight. Some evidence suggests that sexual maturity occurs at over 30 ft in length. There are also report of specimens near 18 m in length. Yet, they are scarce.
The largest total length these sharks can reach is uncertain due to a lack of data on how scientists measured them in many of the reported specimens. Adult whale sharks are difficult to measure both in the water and on the land.
Historically, methods such as comparisons to objects of known size and knotted ropes served for in-water measurements and may be inaccurate. Though, laser photogrammetry later came existence as a proposal to improve measurement accuracy.
Whale sharks spread across many waters, they occur in all tropical and warm temperate seas, apart from the Mediterranean. They occur throughout the Atlantic ocean, from New York through to the Caribbean to brazil central.
From Senegal to the gulf of guinea. These sharks also occur in the Indian ocean, all through the region, including the Arabian gulf and red sea. In the pacific ocean, they occur from Japan to Australia, off Hawaii, and from California to chile.
Contrary to most sharks from the same order “Orectolobiformes” which are benthic species (live on or near the bottom), whale sharks are pelagic (open sea) species. Research reveals that these sharks can reach a depth of 6300 ft (1900 meters) and have a preference for warm waters, with a temperature of around 70-86°F (21-30°C), marked by significant productivity (plankton).
You can find these sharks offshore but usually, they come close to inshore, sometimes entering coral atolls or lagoons. These species segregate by sex and size in most of their coastal feeding areas.
Their coastal feeding areas consist of male juvenile sharks, with the largest congregation containing hundreds to thousands of individual sharks. Whale sharks show site fidelity, where they continue to return to the same feeding site but also engage in high migration, with the daily movement of about 15-18miles (24-29 km). These sharks’ movement likens to that of schools of pelagic fish that are feeding on the same prey as them.
Whale Sharks Migration
Whale sharks seem to prefer different geographical locations at various times of the year. They may undertake either localized or large scale transoceanic migrations, timing, and location of production pulses. Scientists postulate several areas for Seasonal migrations but they need more information to affirm these patterns. Every march and April, whale sharks congregate on the continental shelf of the central western coast of Australia, in the Ningaloo reef area.
There was a research in this area on the short term movement and behavior of these species of shark. Researchers believe Whale sharks migrate to the Ningaloo reef every year to take advantage of the high zooplankton concentrations in the area during that period. Scientists monitored a few whale sharks in Ningaloo Reef and made some behavioral observations.
The reaction of these species differs between ignoring them to slowly diving. Also, when water starts flowing out from the reef, transporting potential prey outside. Tracked whale sharks swam in large circles next to passes in the reef. Whale sharks also made a lot of dives throughout the observed period. It seems that these movements, up and down through the water column, has a link to feeding. These sharks have smaller livers than most sharks and could control their buoyancy by swallowing some air like the sand tiger sharks.
Whale sharks were observed near la Paz, Mexico. Researchers reported that these sharks were not feeding at the surface. They swam without gulping, head-turning, and were rhythmically opening and closing their gill when feeding. These sharks slightly opened their mouth. The flaps of skin over the gill slits vibrated as the water kept flowing out. This is typical of pelagic sharks. Because of whale sharks’ broad geographical range, two main sub-populations exist which vary in trend and size, Atlantic and Indo-pacific.
These sharks feed on a wide variety of planktonic and nektonic prey, such as small crustaceans, schooling fishes, and sometimes on squids and tuna. Also, phytoplankton and macroalgae may form a part of their diet.
In contrast to most plankton feeding vertebrates, whale sharks do not depend on a slow forward motion to filter. Instead, they depend on a versatile suction filter-feeding method which allows them to draw water into the mouth at higher velocities than other active filter feeders such as basking shark.
This behavior enables these sharks to capture more massive, more active nektonic prey as well as zooplankton aggregations. So, they are reliant on dense aggregations of prey organisms. When compared to other filter-feeders such as basking shark, whale sharks’ denser filter screens prove to be more efficient for sucking water than the flow-through system.
While feeding, these sharks tend to keep their head nearer to the water surface in an almost upright position. Whale sharks feed by opening their mouth, dilating their jaws, and sucking. After that, they close their mouth and the water flows of their gills.
During the little delay between closing the mouth and opening the gill flaps, plankton can get trapped against the dermal denticles lining the pharynx and the gill plates. A delicate sieve-like apparatus, a distinctive modification of the gill rakers, forms a blockage to the passage of anything apart from fluid, keeping all organisms of 0.08 inches (2mm) and above in diameter. Practically, nothing apart from water goes through the sieve.
Scientists observed Individual sharks coughing, a mechanism employed to flush or clear accumulated food particles from the gill rakers. As these sharks suck in water, they move their heads in a characteristic sideways motion getting planktons. This can also help them when in a school of prey to cut swathes. Some group of individuals has been observed feeding at dusk or in the middle of the night.
They can sense the density of plankton by their well-developed nostrils located on each side of their upper jaw, on the leading edge of their terminal mouth. Whale sharks’ small eyes are situated on the sides of their head. As a result, their vision may play a lesser role than olfaction in guiding the head turns during surface feeding.
A live whale shark pup separated from its dead mother was kept and maintained in captivity in Japan. The young shark did not eat at first for 17 days, although it swam continuously. This indicates that the pup had much endogenous energy stored.
Researchers observed Birth of whale sharks, but their mating has only been seen twice in St Helena. Their mating was first filmed off Ningaloo reef via airplane in Australia in 2019 when a massive male whale shark tried to mate with a smaller, immature female. Whale sharks are ovoviviparous. The study of a female whale shark captured in July 1996, helped to prove this. This pregnant female was with 300 pups.
The eggs remain in the body of the mother, and the females give birth to live pups which are 40 to 60 cm long. Evidence shows these pups are not born at once, but instead, the female keeps sperm from more than one mating and produces a regular stream of pups over a long period. It was unclear to researchers if these sharks developed growth bands each year or in two years. Of course, in the study of growth, age, and lifespan, the formation of growth bands in the vertebrae is of the essence.
Growth and Lifespan
Researchers who picked interest in the study of the growth and lifespan of whale sharks found that they deposited growth bands each year. This study which took place in 2020 involved scientists comparing the ratio of carbon-14 isotopes present in whale sharks’ growth bands to events of nuclear testing occurring between the 1950s and 1960s. The result of this study led to the presumption that a 33 ft (10 m) long female whale shark was 50 years.
This means that whale sharks have late sexual maturity; the estimate for sexual maturity in males is 25 years. Different studies looking at vertebra growth bands and measuring these sharks in the wild have estimated their lifespan from 80 years to 130 years.
Marine scientists in the Philippines found the smallest living specimen of whale sharks on March 7, 2009. Scientists found a juvenile shark measuring only 15 in (38 cm) with its tail tied to a stick at a beach in Pilar Sorsogon in the Philippines and released into the water. Based on this discovery, some researchers no longer believe this area may be just a feeding ground.
They believe that this site might also be a birthing ground for whale sharks. During summertime in the South Atlantic (St. Helena) waters, there are so many whale sharks present in the location. This includes predominantly the Juveniles and adult pregnant females.
Scientists found a young shark in the stomach of a blue shark (Prionace glauca). They found another specimen in the gut contents of the blue marlin (Makaira nigricans). At Ningaloo Reef, tiger sharks and great white sharks attack whale sharks when they congregate. A lot of Parasitic copepods were discovered on the lining of the pharynx of a young whale shark in Taiwan.
Relationship with Humans
Importance to Humans
Whale sharks contribute to the national and international trade, essential to marine tourism. Fisheries take them as bycatch. The only fishery that exists in the Atlantic was located in Cuba, which captures about Nine sharks every year but was later shut down and banned in 1991.
As a result, in the indo-pacific, the amount of whale sharks targeted by fisheries has increased over the years because of the increasing economic value of whale sharks meat. Up till 2008, Taiwan captures an average of 100 whale sharks every year for oil, meat, aquaria, and fins.
Though whale sharks are rare in the market, however, when they appear marketers overprice them because of their hard preparations and trophy-like status. Due to their value, opportunistic finning started in several countries, including Taiwan.
In India, by harpooning these sharks, they get access to their flesh and liver oils. Although whale sharks are now protected both in India and the Philippines, harpooning fishes developed in other countries like Pakistan and Iran. Their liver oils are usually used for waterproofing fishing boats and other appliances for the manufacture of shoe polish and as a cure for some skin diseases while they consume their flesh.
Whale sharks have been kept in specialized aquaria in Georgia, China, and Japan, only their large size and specialized diet exempt these species from the mainstream aquarium. In some locations where the presence of whale sharks seems to be predictable, these sharks, only targeted by commercial tourist operations. By taking advantage of whale sharks’ surface feeding habits, the tourism industry expanded rapidly around the world, generating millions of dollars per country every year.
Threats to Humans
In general, Whale sharks are harmless to humans. Yet, there are reports of few cases of these sharks ramming sportfishing boats, after being provoked. However, this is not always the case as it is more likely for a vessel to ram into whale sharks as they feed or bask on the surface.
Currently, there is no full estimate of the global population of whale sharks. These species are considered “Endangered (EN)” by the International Union of Conservation of Nature (IUCN) due to the influence of fisheries, vessel strikes, and bycatch losses, together with their long lifespan and slow growth rate.
The Philippines in earlier on banned all selling, fishing, importing, and exporting of these sharks for commercial purposes, followed by India and later Taiwan. All these actions are attempts to preserve the population of this species.
These sharks are the largest fish on earth which means they need a huge aquarium to keep them. They also need some specialized feeding. These sharks are famous in the few public aquariums that keep them.
But, their large size and iconic status have fueled opposition to keeping them in captivity, particularly after the death of some whale sharks that were held in captivity. The initial effort at keeping whale sharks in captivity was in 1934 when a specimen was kept for about four months –off the natural bay in japan.
The first attempt at keeping them in aquariums was initiated in 1980 by Okinawa churaumi aquarium in japan. After 1980, a lot of whale sharks have been kept at Okinawa, usually obtained from incidental catches in coastal nets set by fishers, only two were strandings. Several of these sharks were already weak from the stranding/capture and were later freed, but survival rates were low at first. After scientists resolve the first difficulties in maintaining these species, some have survived in long term captivity.
The world record for a whale shark in captivity is an individual that has lived for 18 years or more in the Okinawa churaumi aquarium. After Okinawa, the Osaka aquarium began to keep whale sharks too, and these institutions conducted most of the necessary research on the keeping of these sharks. Since the mid-1990s, other aquariums in japans, South Korea, China, Taiwan, India, Dubai have kept these sharks.
Whale shark that was kept at Dubai Atlantis was saved from shallow waters in 2008, with a lot of abrasions to the fins. After the rehabilitation of this shark, they released it in 2010, after living in captivity for 19 months. Beyond Asia, the first and only place to keep whale sharks is Georgia aquarium in Atlanta, U.S.
Human Culture and Whale sharks
Whale sharks in Madagascar are called Marokintana in Malagasy which means “Many stars” due to the markings on their back. In the Philippines, these sharks are called Balilan and Butanding. The reverse of the Philippines 100-peso bill featured whale sharks.
In their law, snorkelers must maintain a distance of four feet from these species, and there is also a fine and possible prison sentence for anyone who touches them. Whale sharks are also known as “Jinbel-zame” in japan because their markings resemble Jinbel.
Five Interesting Facts about Whale Sharks at a Glance
1. These Sharks are the Largest Fish In The World
Although there are difficulties in measuring whale sharks, the longest verified whale shark is 40 feet in length, about 1.5 tons in weight.
2. Whale Sharks Neither Bite nor Chew
Despite whale sharks’ enormous size, they can’t bite or chew their food. They feed via suction and they only feed on krill, fish, and plankton.
3. These sharks are Migratory
Scientists don’t understand whale sharks migratory habits fully, but they tend to gather in mass in specific places at specific times. For instance, a large group of schools visits exotic locales like the Yucatan peninsula and the Galapagos every summer to feed on plankton.
4. Scientists Don’t Know How Old Whale Sharks Can Get
Most scientists agree that these sharks reach sexual maturity around age 30, but their total life span is unknown. As reported by some ichthyologists, whale sharks probably die in their sixties. Others believe that these sharks can live up to 100 to 150 years. But, scientists aren’t sure about their lifespan, but they are now known to reach 70 years of age or more.
5. Whale Sharks Have Thousands of Teeth
Other sharks have about 20 to 30 rows of teeth but these sharks have more than 300 rows which means they have about 3000 individual teeth.
- “Discover Fishes: Rhincodon typus, Whale Shark”, Florida Museum of Natural History.
- “Maldives Whale Shark Research Programme”.
- “Fisheries Fact Sheet: Whale Shark”.
- “Whale Shark”, National Geographic.
- “Whale Shark (Rhincodon typus)“, IUCN Red List of Threatened Species.
- “Whale Shark”, Wikipedia (accessed May 2020).