Researchers have made a surprising discovery about the eating habits of whale sharks, giving the largest fish in the sea another world title.
It turns out that the giants of the ocean regularly enjoy a seaweed salad along with plenty of krill, meaning they’ve officially dethroned the Kodiak bear as the world’s largest omnivore.
Scientists made the discovery while studying whale sharks on Western Australia’s Ningaloo Reef, and say it’s cause for rethinking what actually keeps the species so large.
“Everything we thought we knew may not be true,” said Dr Mark Meekan, a fish biologist at the Australian Institute of Marine Sciences.
“We’ve seen them come to Ningaloo and we’ve seen them feeding on krill and we thought, ‘Boom, there’s the answer.’
“But with sophisticated methods that look at the microchemistry of these animals, this story becomes much, much more complex.”
The scientists carefully analyzed possible food sources, ranging from small plankton to large algae, for amino acids and fatty acids.
Then they looked at what was in the whale shark skin samples.
“This study suggests that they feed on quite a lot of plant material, more in fact than krill,” Meekan said.
He believes the whale shark’s size has triggered an evolutionary response that has effectively turned bycatch, such as the brown twill seaweed common in Ningaloo, into food.
“They’re very big animals and when you’re a huge animal you need a lot of food,” he said.
“But it takes a lot of energy to push your mouth, open like a huge net, through the water. When you have a gut full of food but there’s also a lot of algae, what do you do?
“Do you throw it away? Energetically, this is a very expensive thing to do because you just spent all that energy collecting it.
“Whale sharks have simply overcome this in an evolutionary sense by being able to digest algae. They are making bycatch a part of their diet.”
Another part of the study involved collecting and testing whale shark poop, with the results showing that they certainly ate krill, but didn’t metabolize much of it.
“They are much less efficient than we expected them to be if they had evolved just to eat krill,” Meekan said.
The study has been published in the journal Ecology.