Marine Creature of the Month June '20
Marine Creature of the Month
The votes are in! A landslide win for Destiny the whale shark!
Kingdom: Animalia
Class: Chondrichthyes
Conservation Status: Endangered (EN)
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| Picture from Scientific American |
WHAT IS DESTINY?
Destiny is a whale shark. Whale sharks cause some confusion: are they a whale or shark? They are sharks with a whale's diet. Simple! Destiny belongs to the largest species of shark and one of three which do not adhere to a typical "shark diet". The other two are basking sharks and megamouth sharks, if you are interested. More on this later. They belong to the family carpet shark which included species such as wobbegongs, nurse sharks, and epaulette sharks. I could honestly get super distracted talking about all these sharks - but some were featured on Sharks @ 7 & 3/4 so go watch those videos!
Whale sharks, on average, grow to be around 9.8m (32ft) but there has been a confirmed case of one being 18.8m (62ft). Generally, whales sharks over 12m (39ft) are uncommon, but it is still incredible how large these sharks grow on average. They weigh roughly 9t (20,000lb) which is a similar mass to a double-decker bus. They are one of the more colourful species of shark, being that beautiful shade of blue along the top half of their body. Their underside is light, a common camouflage colouring among sea creatures. Being dark on the top hides them from predators above by blending in with the shadows, while being light on the underside protects from below as they merge seamlessly in with the sea's surface above. Naturally at full size, the whale shark does not get many predators. However, they have to grow to that size and are vulnerable when young.
Destiny lives in the Marine Life Institute but her wild brethren live in tropical waters across the world. They tend not to venture into waters below 21C (70F). While considered a pelagic creature, one which lives in the open sea, they do not tend to dive to great depths. There are instances which contradict this, but they mostly remain near the surface. They can be spotted along coast lines during seasonal feedings and these tend to be clusters of whale sharks. Migration is a lifestyle for these behemoths. It is believed that the average lifespan of the whale shark is 80 years but could be as long as 130 years. It is a difficult thing to determine and measure, so these numbers are estimates only.
WHAT DOES DESTINY EAT?
Destiny is a filter feeder. This means they eat plankton and small fish. This is similar to the baleen whale, which was one of the reasons why they were dubbed the whale shark. The other being that they are of a similar size to whales. Whale sharks are active feeds who scoop up their food near the sea's surface, even hanging vertically and bobbing up and down to catch their dinner. The plankton they eat compromises of spawned fish eggs, copepods, krill, and Christmas Island red crab larvae.
While whale sharks have an incredible number of teeth - roughly 3,000 tiny teeth - they play no part in the feeding process. Instead, they filter their food through their gills, catching all the yummy bits in the bristles. They absorb vast quantities of water as they eat and need to expel it without ejecting their dinner too. The bristles, or filter pads, on their gills allow the water to pass through but catch their food and send it back towards their throat. It is a very efficient feeding method - otherwise they would not grow to the size they do! Juvenile whale sharks need to consume 21kg (46lb) every day! And they aren't even fully grown at that point!
To help them with their hunting methods, whale sharks have an extra large liver filled with oil. This is a buoyancy aid, keeping them at the surface as they feed. It contributes to roughly 20% of the whale shark's body weight. Perhaps this is why they do not tend to dive deep into the ocean - fighting a natural buoyancy aid is difficult. (I should know!) In addition to this, whale sharks have huge mouths - measuring up to 1.5m (5ft) across. This allows for massive amounts of water, krill, and plankton to make their way into the whale shark's tummy.
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| Picture from Oceanographic Magazine |
WHAT IS DESTINY'S LIFE CYCLE?
As I've already said, it is believed that whale sharks live for a long time. The way to measure their age is through studying growth bands on their vertebrae. It has been discussed for a very long time whether this is done annually or biannually. A study this year has confirmed that it is annually, after using the radioactive isotope Carbon-14 to identify growth bands put down during atomic tests during the 50s and 60s. More information on that, here. The specimen used in the study was calculated to be around 50 years old. Being able to identify a creature's age is massively important in their conservation as strategies can be compiled to suit their life span.
Being so long lived, they do not mature for a long time. Very little is actually known about the mating and birthing process with whale sharks. The first mating caught on camera was only last year and even that was unsuccessful! Certain areas have been deemed pupping areas due to increased sightings of pregnant and juvenile whale sharks, but the actual births have yet to be seen.
What is known is that these are among the ovoviviparious sharks. This is when embryos develop inside eggs and hatch inside the mother, who then gives birth to live pups. The females can carry a large number of eggs, up to 400, but they do not give birth all at once. It is believed they retain sperm from one mate and fertilise the eggs over a prolonged period. The pups are born 40-60cm (16-24inches).
WHAT THREATENS DESTINY?
Whale sharks are endangered. We do not have a clear picture of their population numbers but their slow maturity puts them at great risk. They fall victim to fisheries, by-catch, collisions, and the ever prevalent plastic pollution. If their numbers drop drastically then they will be unable to make them up, because they mature at such a old age. Thankfully, fishing of whale sharks has been banned in a number of areas - even as far back as 1998. Despite this, they are still illegally fished in parts of the world for their fins, skin, and oil.
In addition to this, they have been affected by disasters since. The oil spill off the coast of Mexico in 2010, for example, had an impact on the species. While no dead sharks were found, the oil was situated on the feeding ground of whale sharks. One third of the whale shark's estimated population has been seen in the Gulf of Mexico and many were seen to be struggling through the water.
Micro plastics interfere with their feeding process. More and more plastic particles are massing in the oceans and in feeding areas for these sharks. Much like with the turtles which mistake carrier bags for jellyfish, the whale shark will starve once its stomach is filled with plastic. Not only this, but they are being exposed to massive amounts of toxins from the plastics, themselves, poisoning these gentle giants from the inside out. Much like with most sharks, whale sharks are a vital part of their ecosystem and it would fall apart without their input. Without whale sharks eating the plankton, plants will suffocate and not get enough sunlight resulting in them dying out. Species dependent on those plants will die out. The species which rely on those will die out. And so on and so forth. Selfishly, this will lead to the ocean not providing 50% of our oxygen or being an abundant food resource.
If we cannot protect these sharks for their beauty, can we do it for that reason? (Personally, their beauty is enough for me!)
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| From Reader's Digest |
FUN FACTS
- You probably know this one, but what they hey! Whale sharks are the largest fish living in the ocean today.
- Their patterns of spots are unique to each shark, meaning you can identify them by spots alone. Find out more about it here!
- The family carpet sharks often have incredible markings, much like the whale shark does, which can resemble the patterns of tapestries or carpets.
- Whale sharks have the thickest skin of any living creature, with it being around 10cm thick. For some context, those Funko Pop figures are 10cm tall.
- 2011 saw the largest gathering of whale sharks recorded, 400 individuals off the coast of Yucatan.
- In Madagascar, the whale shark is called marokintana in their native language. This means many stars, a reference to the patterns on their back.
- The whale shark is featured on the reverse of the Phillipine 100-peso bill.
- Whale sharks do not like the bubbles produced by diving gear but are happy with snorkels!
And that is Destiny! Do you know any whale shark facts? Who should feature in my next MCotM poll? Which is your favourite filter feeder? Lemme know below!
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| Picture from Galapagos Conservation |
Listening to: Paaaarrrtttaaayy
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