Biology
The Mechanics of Filter Feeding in Basking Sharks
Quick fact
A single basking shark can filter up to 2,000 tons of water per hour through its gills, capturing up to 4.5 pounds of plankton per hour.
Why this is interesting
Imagine a shark the size of a bus, yet it feeds on creatures so small you can barely see them. How does it manage to eat enough to survive?
Read the full explanation
Understanding The Mechanics of Filter Feeding in Basking Sharks
Basking sharks are filter feeders, meaning they don't chase after big fish like great whites. Instead, they swim slowly near the surface with their enormous mouths wide open, letting water flow in. As water passes over their gills, fine, comb-like structures called gill rakers trap tiny plankton, which the shark then swallows. This is called 'ram filtration' because the shark relies on forward motion to push water through its mouth. It's a bit like how a whale uses its baleen, but instead of baleen, the shark uses its gill rakers. This method is efficient for scooping up large quantities of small prey, but it requires the shark to constantly swim to keep water flowing.
A deeper explanation
The key to basking shark feeding is the structure of its gill rakers. These are long, thin, bristly structures made of keratin that line the gill arches. When a shark swims with its mouth open, water flows in and across the gill rakers, which act like a fine-mesh sieve. Plankton, being larger than the spaces between the rakers, gets trapped while water flows out through the gill slits. The shark periodically closes its mouth and swallows the accumulated plankton. This system is highly effective because it allows the shark to process a massive volume of water with minimal effort. However, it imposes a physical constraint: the shark must swim fast enough to generate sufficient water flow, but not so fast that it creates excessive drag or energy costs. The trade-off between speed, drag, and feeding efficiency is a classic example of biomechanical optimization. Basking sharks typically cruise at around 2.5 mph, a speed that balances water intake with energy expenditure. This feeding strategy also ties into the shark's migration patterns, as they travel to areas where plankton blooms are dense, ensuring they get the most out of each mouthful.