The basking shark (Cetorhinus maximus) is the second-largest fish species in the world, regularly reaching lengths of 26 feet (8 meters) and occasionally exceeding 33 feet (10 meters) with a weight of several tons. This immense fish is typically grayish-brown with a large, conical snout and a massive mouth that can open over three feet wide. Basking sharks are found worldwide in temperate and boreal waters, inhabiting continental shelf areas. Despite their intimidating size, basking sharks are not considered dangerous predators to humans, with zero recorded unprovoked attacks.
Basking Shark Diet and Temperament
The biological reason for the basking shark’s harmless nature lies in its feeding strategy. Basking sharks are obligate filter feeders, meaning their diet consists entirely of zooplankton, tiny organisms drifting in the water column. They feed by opening their enormous mouths and swimming forward slowly, a method called ram feeding. This process forces water across specialized gill rakers, which strain microscopic crustaceans from the water.
Unlike predatory sharks, the basking shark has only hundreds of tiny, backward-curving teeth that are not used for biting or hunting. The shark’s throat is also relatively narrow, preventing it from swallowing anything larger than its planktonic food source.
The shark’s cruising speed is slow, and its temperament is inherently passive and docile. They are often observed “basking” near the surface, which is how they got their name. Researchers have often noted that basking sharks will simply detour around objects, including divers, rather than engaging with them. This non-aggressive behavior reflects their low-energy feeding lifestyle.
Defining the Risk to Humans
Any potential danger posed by a basking shark is entirely accidental, stemming from its sheer size and power. The primary risk comes from the possibility of an accidental collision with a person or a small vessel. When feeding near the surface, a shark unaware of its surroundings could unintentionally strike a swimmer or diver with its massive body or powerful, crescent-shaped tail.
Another accidental risk is associated with the shark’s habit of breaching, where it leaps partially or fully out of the water. While extremely rare, a multi-ton shark landing on a small boat could cause severe damage and injury. Furthermore, the shark’s skin is covered in abrasive placoid scales, known as dermal denticles, which can inflict a rough scrape or abrasion upon contact.
To ensure a safe encounter, guidelines recommend maintaining a distance of at least 100 meters from the animal to avoid disturbing its natural behavior. Approaching too closely also increases the risk of entanglement in the shark’s large fins if it decides to change direction abruptly. Respecting the animal’s space prevents both accidental injury to humans and disturbance to the shark.
Human Impact on Basking Sharks
The danger dynamic is largely reversed, with humans posing a far greater threat to the basking shark. Historically, basking sharks were heavily hunted in the mid-20th century for their large, oil-rich livers and for their fins in the international shark fin trade. This exploitation, combined with their slow growth and long gestation period, led to significant population declines.
Modern threats continue to put pressure on the species, which is currently listed as Endangered on the IUCN Red List. The slow-moving sharks are highly susceptible to vessel strikes, especially when feeding near the surface, which can cause serious injury or death.
They also suffer from accidental entanglement in fishing gear, known as bycatch, which can lead to drowning or severe injury from the lines and nets. Environmental factors driven by human activity, such as pollution and climate change, also impact the sharks indirectly. Changes in ocean temperatures and currents can affect the distribution and abundance of the zooplankton they rely on for food.