Whale Shark (Dotty Giant of The Sea)
The whale shark (Rhincodon typus) is the largest shark, the largest known extant fish species, and the largest known non-mammalian vertebrate. This magnificent creature, even during mature adult life stages, holds a wide variety of noticeably size records among individuals. Reaching 18-32.8 feet long, with an average lifespan of 70 years and the most unique and beautiful patterns, the whale shark is certainly a wonder to dive with.
In fact, their stunning spotty pattern is so unique to every individual that scientists and divers use their spots and blue, grey or brown shadings to identify each shark. Not only this, but whale sharks use a camouflage known as countershading. When viewed from above, their dark colouring blends in with the dark ocean environment, whereas when they’re viewed from below, their lighter white tummies blend in with the sunny sky above.
Whale sharks are slow-moving filter-feeders; by continuously opening and closing their giant mouth they’re able to suction water into their mouth and out their gills where the red-blood-cell layer on the inner side of the gills collect the oxygen from the water; this feeding technique is known as “cross-flow filtration.” While the shark does this mouth movement, food will find its way into the shark’s mouth and become trapped inside denticles which are sieve-like structures formed by the teeth almost like scales. Whale sharks prey on organisms such as tiny crustaceans, squid, plankton, tuna and so much more!
These fascinating sharks prefer warmer waters and thus they populate all tropical seas; every spring they are also known to migrate to central west, Australia in the continental shelf. This is because of the coral spawning of the area’s Ningaloo reef provides a feast of plankton for whale sharks.
Despite their unusually giant size, the whale shark is an extremely docile fish and they continue to be a favourite species for divers to swim with. But how does the whale shark swim? They use their caudal fin to move forward and their pectoral (side fins) fins to move side-to-side and up and down. Their dorsal fins (fins on their back) stabilise them in the water.
All sharks have a natural negative buoyancy, meaning they sink. Recently, scientists have found a connection between their buoyancy and large size. This is as their weight is stronger than their buoyancy force. The buoyancy force of their specialized oils within their liver pulls the shark up: if this was stronger and caused the shark to float then it would be called positive buoyancy. The shark’s weight drags the shark downwards: if this was just as strong as the shark’s buoyancy force and the shark stays still when unmoving, it would be called neutral buoyancy. However, the whale shark’s weight is stronger than the shark’s buoyancy force, this gives the shark a negative buoyancy so when the shark is unmoving, the shark naturally sinks. This may sound like an evolutionary failure, however, it’s a clever adaptation the whale shark has taken to another level. By growing larger and therefore heavier, the whale shark has a stronger negative buoyancy than other sharks. Now, sharks have cartilage as a skeleton instead of bone which is almost 50% less dense than bone which makes them lighter so their buoyancy force isn’t too heavy.
Their pectoral fins are specially designed to generate a lift beneath them when swimming similar to how a bird’s wings are shaped to help lift the bird. This method is called “dynamic lift.” So why does the whale shark have this adaptation and why does the whale shark have stronger negative buoyancy than other sharks? Interestingly, whale sharks save up to 30% of their energy by sinking deeper or even reaching the ocean floor to feed on tiny prey which seek shelter in deeper waters; this adaption allows the whale shark to use their conserved energy to stay warmer for longer which can, in turn, allows the whale shark to feed for longer in colder depths. Their critical organs have large areas of white muscle around them that help insulate the shark for longer periods of time also. The larger the whale shark grows, the more heat it can conserve and whale sharks are known to dive up to 500m of water, sometimes deeper. The whale shark even outgrows many whales!
Furthermore, in spite of these many specialized adaptations the whale shark has gained through evolution, they spend 60% of their lives at the water surface where they swim in warmer waters.
Unfortunately, whale sharks are currently listed on the IUCN Red List as endangered, meaning they’re at high risk of extinction. Though scientists aren’t confident in what would happen if they go extinct, they do know that if that were to happen, an expansion of small organisms would be apparent and this could have a negative impact on our precious ecosystems. In the past 75 years, sadly, their population has decreased by 50%.
Their filter-feeding method makes them vulnerable to ocean pollution in specific, from microplastics to macroplastics, and even fishing gear. Thankfully there are some things you can do to help save our wonderful whale sharks:
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