The whale shark, the ocean’s largest fish, is a gentle giant known for its docile nature. Reaching lengths of up to 18.8 meters (61.7 feet), these creatures pose no threat to humans. Their diet primarily consists of microscopic plankton and small nekton. As filter feeders, they use unique methods to gather the tiny organisms that sustain their massive bodies.
Main Dietary Components
Whale sharks consume a diverse range of small organisms. Their primary food sources include various forms of zooplankton, such as copepods, krill, and chaetognaths. They also feed on marine larvae, including fish eggs and Christmas Island red crab larvae. Microscopic plants, known as phytoplankton, and larger marine algae like macroalgae, are also eaten.
Whale sharks also target small, free-swimming animals, referred to as nekton. This includes small schooling fish like sardines, anchovies, mackerels, and even small tunas. Small squid are also part of their diet. They seek out dense concentrations of these prey items. A juvenile whale shark can consume approximately 21 kilograms (46 pounds) of plankton daily.
Filter Feeding Explained
Whale sharks use a filter-feeding mechanism to collect their prey. They have large mouths, capable of opening up to 1.5 meters (4.9 feet) wide. Inside, a filtering apparatus composed of 20 specialized filter pads separates food from water. These pads, modified gill rakers, feature a reticulated mesh with small openings, typically averaging 1.2 millimeters, designed to retain organisms larger than 2 to 3 millimeters.
Whale sharks use two main feeding techniques: ram filtration and active suction feeding. During ram filtration, the shark swims forward with its mouth open, allowing water and food to be continuously pushed in. They typically maintain slow speeds, around 1.1 meters per second. Active suction feeding involves opening and closing their mouths to draw in large volumes of water, a method executed while stationary or in a vertical orientation. This suction allows them to capture prey at higher velocities than other filter feeders.
The filtering process separates food particles from the water, which is then expelled through the gills. Water travels parallel to the filter pad surface in a process called cross-flow filtration, preventing clogging. Periodically, whale sharks perform a “coughing” motion, believed to clear accumulated particles from their filter pads. Despite possessing numerous rows of small, vestigial teeth, these play no role in feeding.
Food Sourcing and Habitat
Whale sharks inhabit tropical and warm-temperate waters, generally avoiding temperatures below 21°C (70°F). While primarily open-ocean (pelagic) dwellers, they are also found in coastal areas. Their movements are significantly influenced by the availability of preferred food sources.
These sharks often migrate to coincide with seasonal plankton blooms or mass spawning events of fish and corals. Areas like the Yucatan Peninsula in Mexico and Ningaloo Reef in Australia are known aggregation sites where whale sharks gather to feed. They seek out nutrient-rich currents and zones where deep, cold waters rise to the surface, fueling plankton growth. Whale sharks possess a developed sense of smell, enabling them to detect chemical cues, such as dimethyl sulfide, associated with dense aggregations of krill and other prey.