The basking shark, Cetorhinus maximus, is the second-largest fish in the world’s oceans, surpassed only by the whale shark. This colossal marine animal can reach lengths comparable to a city bus. Its sheer size often leads people to assume it is a powerful predator, but its behavior of swimming slowly near the surface with an enormous, gaping mouth prompts curiosity about how this giant feeds. The question of whether it possesses the formidable dental structure typical of other sharks is a common inquiry about this gentle giant.
Vestigial Teeth and Their Structure
Basking sharks do possess teeth, but they are dramatically different from the large, serrated weapons found in predatory sharks like the Great White. These teeth are classified as vestigial, meaning they are remnants of an evolutionary past and serve virtually no function in the adult’s diet. They are exceptionally small, typically only a few millimeters long, often cited to be around 5 millimeters.
The tiny teeth are conical in shape and feature a distinct backward-pointing curvature. They are highly numerous, arranged in over a hundred rows within the shark’s mouth, with estimates suggesting six rows in the upper jaw and nine in the lower jaw. This dense arrangement is not designed for seizing, tearing, or chewing prey.
The function of these minute teeth remains largely a mystery, but they may have a non-feeding role. Scientists speculate the teeth may be involved in courtship or mating rituals, as individuals are sometimes observed with scars that align with the mouth size of other basking sharks. Another proposed role involves feeding before birth, where embryonic sharks may use them to consume unfertilized eggs within the mother’s womb.
How Basking Sharks Really Eat
The immense size of the basking sharkâs mouth is directly related to its unique, passive feeding strategy. The shark is an obligate ram feeder, meaning it must swim forward to force water and food into its mouth. It cruises slowly with its mouth held wide open, creating an opening over three feet wide.
Water flows into the cavity and is channeled out through five pairs of large gill slits that almost completely encircle the head. The food collection mechanism is located on the gill arches, consisting of specialized, bristle-like structures called gill rakers. These dark, comb-like filaments can be up to three inches long and are densely packed, totaling up to approximately 27,000 rakers.
These gill rakers form an efficient sieve that traps tiny prey items. The primary food source is zooplankton, specifically small crustaceans called copepods, along with small invertebrates and fish eggs. By filtering the water, the gill rakers strain the plankton, which is then periodically swallowed. A single basking shark can process over 1.3 million liters of water per hour while feeding, allowing it to collect vast quantities of microscopic food necessary to sustain its enormous body mass.
Defining Characteristics of the Basking Shark
The average adult basking shark reaches lengths of approximately 26 feet (7.9 meters) and can weigh over five tons; some individuals exceed 33 feet (10 meters). Despite their large size, they are known for their non-aggressive and placid nature.
They are a cosmopolitan, migratory species, found in temperate and boreal oceans across the globe, inhabiting both the Northern and Southern Hemispheres. Basking sharks are often observed near the surface, a behavior that earned them their common name, but they are also capable of deep dives, having been tracked at depths exceeding 3,000 feet (1 kilometer).
Their seasonal movements are driven by the search for concentrated patches of zooplankton, often resulting in trans-oceanic migrations.