There is perhaps more to the largest shark in our waters than we previously understood to its reputation as a gentle monster. Filter feeders, whale sharks (Rhincodon typus) are supposed to methodically scour the seas for microscopic creatures like krill.
Greens made up of algae and other photosynthesizing organisms are among the myriad of small swimmers they scoop up.
This cannot be avoided, however scientists have questioned whether this flora serves as more than just a garnish for the carnivore or if it acts as the side salad that keeps it afloat.
Researchers have discovered what these 10-meter-long (32-foot) ocean hoovers are actually using from the enormous pools of water they suction through their systems by analyzing excrement and skin samples.
According to Patti Virtue, a biological oceanographer at the University of Tasmania, “the faeces did suggest that they were consuming krill.” But not much of it is being metabolized by them.
Whale sharks, which are actual sharks with cartilage in place of bones, instead seem to be removing nutrition from a ton of algae.
The fish scientist at the Australian Institute of Marine Science, Mark Meekan, states that “this compels us to reevaluate everything we thought we knew about what whale sharks consume.” And what they are doing on the open ocean, in truth.
The tissue study performed by Meekan and colleagues also uncovered a fatty acid composition that was more in line with omnivory than carnivory. They discovered skin that was abundant in arachidonic acid (ARA), which is only present in sufficient amounts to account for the levels seen in whale sharks.
Using tissue samples, a different research in 2019 discovered evidence that whale sharks do, in fact, consume at least some creatures that are low on the food chain, such as plants and algae. Additionally, they are not the only omnivorous sharks; bonnethead sharks (Sphyrna tiburo) also consume a lot of seagrass.
When these creatures, which are also known as shovelheads for obvious reasons, pursue tiny food like crabs, mollusks, and fish in thick seagrass ecosystems, they usually devour the plant components as a result. So it’s possible that their capacity to digest it developed as a result of their need to deal with this plant stuff moving through their bodies.
The researchers speculate that the whale sharks may have experienced the same thing. The creatures that live on algae (epibionts), which they may have first consumed in the course of their evolution, may now also be digested and utilized by them.
Meekan says that the image of whale sharks traveling to Ningaloo just to feed on these little krill is only partially accurate. They are in fact there and devouring some algae as well.
Unfortunately, the whale sharks must follow oceanic characteristics like surface currents that assemble these floating food sources in order to find enough of this floating organic stuff. The whale sharks unintentionally consume these contaminants since these features also collect ocean pollutants like trash.
Meekan has seen evidence of some of this plastic making it into the whale sharks’ excrement. However, the researchers cautions in their study that it’s probably going to decrease their stomach capacity, stall their digestion, or make them vomit their meal. These threatened species, whose populations have declined by 62 percent over the previous 75 years, may be harmed by this.
Meekan claims that all of the largest terrestrial creatures have historically been herbivores. “In the water, we always assumed that the larger species, such as whales and whale sharks, were eating higher on the food chain creatures like shrimp and tiny fish.
It seems that the systems of evolution on land and in water may not be all that dissimilar after all.
This research was published in Ecology.