Whale sharks filmed feeding off Western Australia

Off Western Australia, researchers have captured close-up footage of whale sharks to gain a clearer understanding of how they feed.

Recorded using small cameras temporarily attached to several animals, the footage offers a perspective rarely achieved in the marine environment. It reveals that these huge fish do not feed solely close to the surface, as was long assumed. Instead, they alter their technique according to depth, currents and the availability of food.

Cameras attached to the fins

The study took place around Ningaloo Reef, on Australia’s west coast. At certain times of year, this area is known to host large gatherings of whale sharks. Despite their considerable size, these animals are difficult to observe for long periods without affecting their natural behaviour.

Teams from the Australian Institute of Marine Science therefore attached tags to the fins of several individuals. Each unit combined tracking instruments with a miniature camera. The tags were programmed to release themselves naturally after 24 hours.

“The whale sharks continued on their way without altering their swimming, while the researchers recovered footage recorded within their environment.”

This technique marks a major advance over conventional tags. Standard devices chiefly provide information about an animal’s position, depth or route. They do not show exactly what it is doing while travelling. Video now allows scientists to connect movements with specific actions: opening the mouth, changing direction, accelerating or descending towards the seabed.

Thirty-six feeding behaviours identified

The researchers compared the filmed sequences with more than a hundred scientific publications devoted to the species. Their work produced a catalogue of 36 distinct feeding-related behaviours. According to the institute, it is the most comprehensive repertoire yet assembled for whale sharks.

The findings challenge a widely held assumption. These animals were mainly linked with feeding near the surface, where they can consume large amounts of plankton, fish eggs or tiny crustaceans. The footage shows that they actually search through much of the water column, including areas close to the seabed.

An open mouth, even while descending

One of the observed methods is particularly energy-efficient. The whale shark slowly descends towards the bottom with its mouth open. Water then passes through its gills, while its filtering structures retain edible particles. This method requires little energy, a valuable advantage in tropical oceans where prey is not distributed everywhere.

Conversely, the animal can display far more active behaviour. When a shoal of krill or a concentration of food appears near the surface, it speeds up and actively pursues the resource. It therefore does not rely on a single method, but selects its strategy according to the opportunity.

• Slow feeding during descents towards the seabed;
• Foraging at several depths;
• Faster pursuits close to the surface;
• Constant adaptation to areas where prey is concentrated.

A giant dependent on scattered resources

The whale shark is the largest fish known on Earth. Some individuals measure well over ten metres in length. Despite its size, it does not hunt large prey. It is a filter feeder: it draws in vast volumes of water before retaining the tiny organisms that make up its food.

Its diet may include zooplankton, larvae, fish eggs, crustaceans and krill. The difficulty is that these resources often occur in highly localised, short-lived patches. One area may be rich for a few hours, then nearly empty the following day.

“The filmed behaviours suggest that whale sharks compensate for the irregular availability of their resources with a far broader range of techniques than expected.”

This flexibility partly explains their ability to range across vast ocean spaces. However, it does not shield them from every threat. The species is classified as threatened and remains vulnerable to vessel strikes, accidental capture in fishing gear, habitat degradation and disturbance at heavily visited tourist sites.

Why these images could help protect whale sharks more effectively

Knowing where whale sharks genuinely feed could inform protection measures. If scientists establish that a section of seabed or a particular layer of water regularly serves as a feeding ground, they can assess more accurately the risks associated with shipping, fishing or certain offshore works.

Seasonal gatherings also draw many tourists. Supervised viewing can fund local research and raise public awareness, provided strict distances are maintained. Getting too close, having too many boats nearby or remaining for long periods in an animal’s path can disrupt its swimming and limit its access to food.

Monitoring that could expand to other oceans

The researchers now hope to fit cameras to more whale sharks at gathering sites in different parts of the world. Ningaloo Reef represents only a fraction of the vast range covered by the species, which occurs in warm seas across several continents.

The term “water column” refers to the space between the surface and the seabed. The new observations show that this entire space matters to whale sharks. Their feeding may begin near the waves, continue at mid-depth and sometimes end very close to the ocean floor. This mobility makes them harder to study, but it also provides a practical direction: protecting the animal means looking beyond the surface alone.