Whale sharks are nicknamed “Gentle Giants” for a reason. The world’s largest fish, they are colossal but harmless, spending most of their time filter-feeding on plankton at the ocean’s surface. Given their size, which usually sits between 18 and 40 feet and 15 and 20 tons, whale sharks essentially exist as swimming mouths, consuming vast quantities of food each day in order to survive. These tendencies, combined with their propensity for aggregating in tropical waters, have made them popular subjects of ecotourism.
Tourists observing whale sharks may see them employ two methods of feeding; the sharks either swim passively with an open jaw along the surface (Figure 1.A) or suction from below to increase their intake efficiency (Figure 1.B). Their gills and filter pads are specially designed to allow only the smallest of particles to pass through to the shark’s stomach, while large matter is expelled in a cough-like motion.
One lucky tourist recently witnessed a completely different feeding behavior though. On December 11th, 2022, in Baja California Sur, Mexico, a juvenile female whale shark was recorded diving to the ocean floor and suctioning along the sea bed (Figure 1.C). Although the incident lasted less than a minute, it has thrilled the scientific community, providing insight into the largely mysterious lives of these endangered animals.
Why would whale sharks want a mouthful of mud, you might ask? The Journal of Fish Biology reports on the topic, proposing that this behavior allows whale sharks to consume creatures buried in the sea floor, providing important nutrients when surface-level plankton quantities are low. Because whale sharks can dispel unwanted material, they do not actually ingest the sediment itself, only its biological inhabitants. Although this is the first time the behavior has been observed, previous studies on this species have revealed biochemical levels consistent with a benthic, or deep water, diet; now, scientists have an explanation for the previously baffling data.
The findings also have important consequences for global conservation efforts. Whale sharks are considered an endangered species, with rising sea temperatures and increased acidification altering traditional plankton blooms and feeding patterns. Thus, whale sharks’ exploitation of the sea bed for supplemental nutrition diversifies their diet and thereby strengthens their ability to survive. It also hints at whale sharks’ ability to adapt to changing conditions, giving hope for their future.
Another benefit arises from this discovery as well. Ecotourism, when practiced responsibly, has been celebrated as a way to increase the monetary value of sharks, thereby discouraging the harvest of sharks for fins, meat, medicine, and trophies. In other words, it makes living sharks more valuable than dead ones. But ecotourism’s role in uncovering this new behavior also emphasizes its importance in providing thousands of hours of raw observational data that would otherwise be impossible to collect. So witnessing benthic feeding in whale sharks is a win not only for the scientific community, but also for ecotourism and the potential it holds for combating anthropogenic destruction.
Although more research is needed to paint a complete picture of whale shark feeding behaviors, the first recording of sea bed foraging is a thrilling step towards new scientific horizons. And, perhaps, it could help in developing novel protection protocols for these animals as they struggle to stay afloat in the modern world.
Whitehead, Darren A., and Joel Gayford. “First record of bottom‐feeding behaviour in the whale
shark (rhincodon typus).” Journal of Fish Biology, vol. 103, no. 2, 2023, pp. 448–452, https://doi.org/10.1111/jfb.15457.