Certainly, the whale shark (from its Latin name Rhincodon typus) accumulate records. Already the holder of the title “world’s largest fish”, this peaceful sea giant is now driven to the first place on the podium of the largest omnivorous animals, that is, whose diet consists of both plants and animals.
A podium where the whale shark now takes the place of the kodiak bear – the largest subspecies of brown bear – since this fish was not even there at the beginning, and for good reason: we put it away from a food point of view, among carnivores!
“It makes us question everything we thought we knew about what whale sharks eat.“, Dr Mark Meekan, ichthyologist (fish biologist) at the Australian Institute of Marine Science (AIMS), said in a statement.
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In fact, prior to the publication of the study by Dr. Meekan and his colleagues in the scientific journal Ecology (19/7/2022) whale sharks have been known to feed almost exclusively on krill – a small crustacean which they filter through their gills by swallowing large amounts of seawater in their mouths and only releasing the liquid.
Until then, whale sharks’ consumption of algae was considered involuntary, as the plants should not strictly be part of their “diet”.
Determine the foods that contribute to the growth of the whale shark
The study’s authors collected algae and plankton available from the whale shark’s environment in Ningaloo Reef, Western Australia. They then took skin samples from 17 individuals – a painless process for the animal – to analyze their biochemical composition of fatty acids and amino acids.
The researchers thus concluded that certain molecules in the tissues of the Ningaloo whale sharks corresponded to those contained in sargassum, brown algae, proving that a nutritional assimilation of these plants by the animal had taken place.
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“We believe that during evolution, whale sharks have acquired the ability to digest some of the sargassum that enters their intestines.“, Dr. Mark Meekan interprets.”So the vision we have of whale sharks coming to Ningaloo to feast on these tiny krill was only half the story. In fact, they also eat quite a bit of algae.“
In the past, scientists relied mainly on the composition of feces to see what had or had not been digested by animals. This new study, on the other hand, uses the technique of “isotope analysis of specific compounds” (CSIA) – which indirectly makes it possible to determine which foods have specifically served the animal for its energy and growth.
“On land, the largest animals are always herbivores. In the sea, we thought that animals that had grown very large, such as whales and whale sharks, fed one step higher up the food chain – by consuming animals such as crustaceans and small fish.” says the lead author.”It turns out that the development system on land and in water might not be so different after all.“
In their study, however, the researchers warn against the danger posed by the plastic in the water. By consuming algae, whale sharks would be more likely to ingest this source of pollution at the same time, which is detrimental to their digestion.
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Harmless to humans like the vast majority of shark species, the whale shark is classified as “threatened” by extinction on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, mainly due to its intentional or unintentional capture by fishing vessels, as well as maritime collisions .
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