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When the largest fish in the world rams in
Published on: Sunday, March 12, 2023
By: Kan Yaw Chong
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Whale shark rams its big mouth into a krill boom to filter feed. (Pic by Bob Hartley.)
FOUR whale sharks between 13ft and 20ft long swam into Gaya Island waters over the last three weeks, just 10 minutes from Sabah’s Capital City and stayed around for four weeks.

“I never get tired of seeing whale sharks no matter how many times I have seen them,” said Clement Lee, veteran diver and co-founder of pioneering diving outfit Borneo Divers.   

A plankton bloom, krill boom and lower water temperature are “sure” signs that these enormous creatures would be ramming in and he got what he wanted – another “sensational experience” after leading a group of whale shark enthusiasts, including Gillian Tan, to mount a total of six dives.

Which raises a key question: Can Kota Kinabalu become a whale shark watching destination?

The largest recorded whale shark in record measured 61.7ft (18. 9m).

Inset: Head of a whale shark – broad and flat.

This is the most accurately measured giant specimen because the enormous female was caught by whale shark fishing off the coast of India in the Arabian Sea and verified by a study on Marine Megafauna done in 2015 by McClain and team. Yet marine scientists remain open to the known 2015 ‘largest in record’ may not necessarily be the largest in legend, meaning the maximum could have been or could still be lurking around undetected. 

But according to one writer awestruck by the immense mouth of this broad and flat headed ocean giant,“ even without those chart topping winners (undetected maximums), it is likely that whale sharks are not just the largest fish on earth but also the largest fish ever lived”!

This is also why it was first distinguished as a whale shark as far back as 1828 by a man because one specimen killed off the coast off Table Bay was as big as some species of whales!

Super size explained  

As Clement Lee and Gillian Tan noted, its super size grabs their awe.

Of course, genetics determine its maximum size. A clear example is its dimorphic nature which dictates separate size for male and female where the mature female is twice as big.

“But these are very big animals and when you have a huge animal you need lots of food,” says fish biologist Dr Mark Meekan of the West Australian Institute of Marine Science.

The question is how does a fish gets enough nutrients and energy to sustain such a gigantic body 100 years which is its estimated life span?

A ‘plankton patroller’

Again, its genetic characteristics as an omnivore – an inherent ability to eat and survive on both plants and animal matters as a plankton patroller filter feeder that doesn’t need to hunt their food makes a difference. All it needs to do is just open its big mouth, gulp down large amounts of water as it swims and let its body sort through it. 

This is particularly true when it sees large concentrations of planktons, krills, fish eggs and larvae and rams through them and gulp in as much water as possible. This diet can contribute to the massive size of the whale shark because small ocean life are the most numerous in volume so it’s not hard for this slow mover to hunt, raking up a reported 45kg of food per day for even juveniles, so says an online report.

A close look at how the whale shark is gulping in a concentration of krills. (Picture courtesy of Gillian Tan.)

Worthy of note is whale sharks grow up very fast.

Though born small at just 21-25 inches, their growth is reportedly very rapid which soon outpaces peers and within a few years there isn’t any predator that wants to play around with a whale shark based on its bulk alone, it is noted.     

One surprise from study 

But this is frankly a surprise that challenges the traditional mindset about the key position of krills and planktons in sustaining the immensity of whale sharks.

“Everything we thought we knew may not actually be true,” noted Dr Mark Meekan who led a study off Western Australia’s Ningaloo reef.

“We have seen them coming to Ningaloo and we have seen them feeding on krills and we’ve thought, ‘Boom there’s the answer’.

It turned out that the ocean giant routinely enjoy a seaweed salad alongside hefty helpings of krills, according to an Australian Associated Press report.

Group of whale shark buffs with Clement and Gillian off Bungaraya Island Resort.

Two ocean giants as seen from below. 

So an indepth probes into its microchemistry, analysis of possible food sources, from minute planktons to large seaweeds and skin samples ensued.       

They were eating “quite a bit of plant materials, more so in fact than krill,” Dr Meekan was quoted as saying. 

One part of the study involved collecting and testing whale shark excrement.

Yes, the results showed that they were “certainly eating krill – but were not metabolising much of it”.  

Metabolism by definition refers to the chemical process that that converts food into energy, nutrients and elimination of wastes. 

So although krills look like a star attraction to whale sharks they may not be its prime sustenance after all.


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