Basking shark

At first glance, the world’s second largest fish might seem menacing: Its gaping mouth has six rows of teeth in its upper jaw, and nine rows below, for a total of about 1,500 tiny, hooked teeth. The basking shark’s scientific name, Cetorhinus maximus, roughly translates to “great-nosed sea monster” in Greek.

In reality, these placid sharks, found the world over, are totally harmless. One of only three filter-feeding shark species, basking sharks eat tiny organisms called zooplankton. Swimming with their three-foot-wide mouths agape allows them to take in water and filter out plankton using gill rakers, special organs that prevent their food from escaping through the gills. Scientists believe their teeth—which are not used in feeding—are instead part of the mating process.

Moving at a speed of around two miles per hour, basking sharks can filter around 2,000 tons of seawater an hour. Unlike the two other filter-feeding sharks—whale sharks, the biggest fish on Earth, and megamouth sharks—basking sharks are passive feeders and do not actively suck in water.

In the past, people thought the fish were basking in the sun as they cruised near the surface—hence their name.

Where are they found?

Basking sharks are highly migratory. In spring and summer, they travel to coastal, nutrient-rich waters to feed, such as the western coast of Scotland, Isle of Man, the northeastern U.S., and Canada.

Rarely seen in winter, scientists have only recently discovered that basking sharks do not hibernate, as was once believed, but instead hang out in deeper and more distant waters. For instance, basking sharks often seen in Scotland and the Isle of Man during the summer have been recorded swimming to Spain, Morocco, and the Faroe Islands, while others stay in deep waters off the Scottish continental shelf. Scientists don’t yet know what drives these migrations, though possible theories include searching for a mate, food, or suitable temperatures.

Satellite tags have also revealed basking sharks can dive incredibly deep, over 3,000 feet. A few sharks have even swam to depths of almost 5,000 feet, or nearly a mile.

Basking sharks are also the biggest sharks that can breach, propelling their huge bodies out of the water, sometimes up to four times in a row. Breaching is still not totally understood, but the behavior could dislodge parasites or serve as a courtship ritual. Whatever the reason, breaching is very important to the fish: It takes up to 32 times more energy than swimming.

Reproduction

Usually solitary, males and females come together to mate during the summer. Males are believed to reach sexual maturity at around 12 to 16 years, while females reach maturity at about 20 years. Although mating has never been scientifically observed, scars on female sharks suggest that males use their teeth to hold onto while mating. 

Based on their estimated growth rate, length and number of rings on their vertebrae, basking sharks are thought to have a gestation period of up to three and a half years. 

Overall, very little is known about basking shark reproduction: Only one pregnant female has ever been captured and studied, off Norway in 1943. While being towed, she gave birth to five live pups and one stillborn, all measuring between 4.5 and 6.5 feet: as large as a full-grown whitetip reef shark.

Conservation status

During the 20th century, basking sharks were widely fished for their liver oil—used in lamps, cosmetics, perfumes, and lubricants—as well as their meat, skin, and large fins. It’s believed that as many as 100,000 sharks were fished from the North Atlantic and, with populations on the brink of collapse, many countries began prohibiting the catch of basking sharks in the 1990s.

However, the fish still get caught in fishing nets, are hit by boats, and ingest harmful microplastics. Climate change may also affect plankton numbers. 

As a slow-growing species that produces very few young, basking sharks are particularly vulnerable to extinction, which is why the animal is listed as endangered by the International Union for Conservation of Nature.

Aside from fishing bans, other conservation efforts have helped the species. In 2020, the Sea of the Hebrides off Scotland’s western coast became a marine protected area to protect basking sharks from fishing. Basking sharks are now one of the most highly protected sharks in European waters.