8 Fascinating Facts About the Majestic Basking Shark

The basking shark (Cetorhinus maximus) is the second largest fish in the world. Found throughout the world’s oceans, these sharks are mostly gray in color and have five large gill slits on either side of their head. Their most recognizable feature is their huge open mouth—it's close to 4 feet wide—which they use to filter microscopic prey at the ocean’s surface.

These majestic sharks are endangered, with a declining population due to overfishing, hunting, entanglement in fishing nets, and collisions with boats. From their unusual dining style to their ability to hurl themselves into the air, here are a few things you may not know about the amazing basking shark.

1. Basking Sharks Are the Second Largest Living Fish

Just behind the whale shark, the basking shark is the second biggest fish in the world. They typically range from 23 to 26 feet in length, although the largest basking shark recorded was over 40 feet long. Basking sharks weigh around 8,500 pounds, and males are larger than females.

Found primarily in the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean and Black Seas, these migratory sharks have a wide range that includes boreal and temperate waters, areas close to land, and those far offshore.

2. They Eat Zooplankton

Although they are giant sharks, large mammals have nothing to fear from the zooplankton-loving basking shark. Among sharks, exclusively eating zooplankton is rare. Only two other sharks share this trait—the whale shark and the megamouth shark. All three have hundreds of small teeth to help filter what comes into their mouths, and gills to push the water back out. But unlike the other two, the basking shark doesn’t suck in water, it only filters what flows into its open mouth.

In order to feed, the basking shark just has to open its large mouth wide. The creature's gill rakers catch the food while the rest of the water flows out of the shark’s five gill slits on either side of its head. It filters more than a half-million gallons of water (two million liters) per hour through its gills.

3. They Aren't Really Basking

While a basking shark moving slowly along the surface of the water may look to casual observers like it is basking in the sun, the shark is actually just filtering food. They're most commonly seen doing this during summer months, when zooplankton is abundant at the surface. Sometimes they roll while basking, doing a full 360-degree turn.

When they were first discovered, basking sharks were called sunfish due to their frequent appearance seemingly floating in the water toward the sunlight. Welsh naturalist Thomas Pennant renamed the fish basking shark to differentiate the species from ocean sunfish.

4. They Can Breach

A surprising skill of the slow-moving basking shark is its ability to breach. Like its relatives the great white shark and the mako shark, basking sharks can leap in the air. Researchers studying the breaching ability of basking sharks recorded individuals at a starting depth of 90 feet below the surface reach speeds of over 11 miles per hour and travel four feet above the water’s surface at a nearly vertical position. This is particularly impressive given the basking shark's large size and its ability to accomplish this from a nearly horizontal position underwater.

Basking sharks are thought to breach for a number of reasons. They sometimes leap from the water to rid themselves of parasites and exhibit the behavior during mating season. Some evidence points to breaching playing a role in acoustic communication between distant groups of sharks and is likely to be related to "intra-specific signalling" of some kind.

5. They Sometimes Socialize

Basking sharks are seasonally social. During certain times of the year and in portions of their range, basking sharks are mostly solitary or travel in pairs. But during the summer months in the northern part of their range, they are seen in larger groups of 100 or more individuals. Basking sharks have been observed traveling primarily in same-sex groups with individuals of a similar size.

The gestation period for female basking sharks is estimated at about three years. During this time, female sharks are not frequently seen. Once the pups are born, they are immediately independent without any parental involvement. Oceana reports, "As opposed to whale sharks, which give live birth to hundreds of small babies, basking sharks give birth to only a few, quite large babies."

6. They Are at Risk

Basking sharks are endangered with a declining population. Because these sharks have a long gestation cycle and are not able to reproduce until they are about 11 years old, they are highly susceptible to continued rapid population decline.

Basking sharks have been hunted for centuries for their fins, liver, and oil. These majestic sharks continue to be hunted for their livers even today, which are rich in squalene, an ingredient frequently used in medicines and cosmetics. Demand for their large fins for shark fin soup has led to overfishing, and they are often unintentionally caught in fishing nets. Because these sharks are surface feeders, collisions with commercial and recreational boats are also a threat to them. Boaters are urged to stay at least 330 feet (100 meters) away if these sharks are seen at the surface.

Basking sharks are protected in portions of their range, including regionally in the U.S. and in EU territorial waters, and via trade restrictions under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

7. They Are Highly Migratory

Basking sharks follow the food, and in the case of these Lamniformes, that food is zooplankton. They travel north through the summer months and head south for the winter when the plankton supply begins to diminish. Basking sharks have been observed as far south as South America and South Africa. They migrate to coastal areas to breed from May through July.

Not only do they migrate great distances, but basking sharks also migrate vertically from the ocean’s surface to depths of over 4,000 feet. This makes them difficult to study, hence the gaps in scientists' knowledge about their lifestyles.

8. They Move Slowly

Notoriously slow swimmers, basking sharks are always on the move, so they cover great distances. When migrating, basking sharks travel at a rate of 2.4 mph, which is slightly faster than their 1.9 mph rate when they are filtering food. Because they have five gill slits on each side, basking sharks need to move slowly to allow their massive filtration system to operate.