First Sighting Of Whale Sharks Bottom Feeding

Oct 17, 2023

In spite of their size, whale sharks (Rhincodon typus) are filter feeders, feeding on plankton, small fish, and other microscopic organisms. To capture their prey, they typically swim slowly near the water's surface, opening their massive mouths up to filter large volumes of water. In its throat, specialized structures called gill rakers filter out food particles while letting water pass through, and when it closes its mouth, it expels the excess water through its gills, swallowing the captured prey whole.

But does it feed any other way? It seems so.

In spite of their size, whale sharks (Rhincodon typus) are filter feeders, feeding on plankton, ... [+] small fish, and other microscopic organisms.

In Baja California Sur, Mexico, an ecotourism guide captured an unusual whale shark behavior on film and sent it to researchers for analysis. In the video, a 16.4 foot-long (5 meters) juvenile whale shark was seen sucking at the sand, gulping whatever it was finding in this deep area (about 20ft/6 m deep). "No one's ever seen this behaviour before," says Darren Whitehead at Shark Research Mexico, who studied the footage and wrote up a paper about the observation. Whale sharks are not known to partake in bottom feeding, which involves eating prey that resides on or near the seabed. You can see in the video how the juvenile whale shark tilts its head downward as it descends towards the sandy seabed, where it is probably finding prey. Nearing the bottom, it opens its mouth wide and sucks in water, capturing the microscopic organisms at the seafloor, as the gill rakers filter out the food particles.

The whale sharks' newly observed feeding behavior is likely an adaptation to maximize their opportunities for feeding within the ocean's water column by exploiting different food sources. This allows them to catch prey that may not be readily available on the surface of open water, such as benthic organisms (seafloor). However, it is important to note that most research has shown that their diet primarily consists of pelagic (open water) organisms, showcasing that bottom feeding is not a typical or predominant feeding strategy for whale sharks. But it is crucial to understand whale shark feeding behavior, including this occasional bottom feeding, in order to better understand their ecological role and assist in future conservation efforts. "We suggest that whale sharks actively feed upon benthic prey, either predominantly in deepwater environments or where the abundance of such prey exceeds that of planktonic food sources," says Whitehead. "[There is also] the potential for ecotourism and citizen science projects to contribute to our understanding of [this marine megafauna's] behavioural ecology."

The whale sharks' newly observed feeding behavior is likely an adaptation to maximize their ... [+] opportunities for feeding within the ocean's water column by exploiting different food sources.

There already exist several citizen science projects that involve whale sharks as their study focus, such as the ‘Wildbook for Whale Sharks’ and the ‘Shark Guardian Whale Shark Project’ projects. These initiatives engage volunteers in data collection, research, and public awareness efforts, allowing everyday citizens to contribute to science's understanding of these magnificent creatures. Whitehead believes those who swim with whale sharks can help capture more of this rare behavior, allowing scientists to understand its role in the shark's lifestyle.

Not only has this accidental video highlighted the versatility of their feeding strategies, but the whale shark's ability to adapt to changing food availability in their environment. It makes some shark scientists optimistics that perhaps there is hope for this endangered species in our ever-changing world.