Fish
Basking Shark
Cetorhinus maximus · also called sunfish (historical), bone shark, elephant shark
The basking shark is a giant that lives on some of the smallest food in the sea. Second only to the whale shark in size, it cruises the cool surface waters of the world’s temperate seas with its cavernous mouth held open, quietly straining plankton.
Overview
Basking sharks are found in temperate coastal and continental-shelf waters around the globe. In spring and summer they appear near the surface in the North Atlantic, North Pacific, and around New Zealand and southern South America, often close inshore where currents and fronts concentrate plankton. The name comes from their habit of swimming slowly at the surface as if basking in the sun — really, following the plankton that gathers in the warm surface layer.
The living net
A feeding basking shark swims steadily forward, mouth open to nearly a metre across, and lets water pour in and out through gill slits that almost wrap around its head. Thousands of comb-like gill rakers filter out copepods and other zooplankton, and the shark swallows the catch in gulps. Passing water at a rate of around 2,000 tonnes an hour, it is a purely passive filter — when plankton runs low it stops feeding, sheds its gill rakers, and regrows them for the next season.
Behaviour
For such a large, slow animal, basking sharks do surprising things:
- They breach, launching their whole body clear of the water and crashing back down — possibly to dislodge parasites or as a social signal.
- They form schools and courtship groups, sometimes swimming nose-to-tail in circles (“torus” formations) thought to be part of mating.
- They undertake long migrations and deep dives, disappearing from the surface for months at a time.
Threats and recovery
The basking shark is listed as Endangered, though the trend is now upward. Historic liver-oil and meat fisheries killed vast numbers and wiped out local populations. Since then it has gained legal protection across much of its range, is listed on CITES and CMS, and is a prized subject for wildlife tourism in places such as the Isle of Man, Scotland, and Ireland. Ongoing threats are bycatch, boat strikes, and entanglement in fishing gear and marine debris, and because the shark reproduces very slowly, recovery is measured in decades.
Basking Shark: common questions
Is a basking shark dangerous?
Not at all. It has no interest in and no ability to harm people — its teeth are tiny and non-functional for feeding, and it eats only plankton. Basking sharks are slow, placid, and often let boats and swimmers approach closely. The only real hazard is their size — an accidental swipe from the tail of a startled five-tonne animal, or a collision with a boat, can injure someone.
How does a basking shark feed?
Passively. It swims forward with its enormous mouth wide open, and water flows in and out over five pairs of gill slits that nearly encircle the head. Bristle-like structures called gill rakers, several thousand of them, trap the copepods and other tiny animals in the water, and the shark periodically closes its mouth to swallow the concentrated catch. Unlike the whale shark and megamouth shark, it does not actively pump or suck — it relies on forward motion, so it stops feeding and its gill rakers are shed and regrown when plankton is scarce.
Where do basking sharks go in winter?
For a long time nobody knew, and it was assumed they hibernated on the seabed. Satellite tagging has since shown they keep swimming, often descending to depths of several hundred to over 1,000 metres and travelling long distances — some North Atlantic sharks cross to the Caribbean and West Africa, and Pacific ones move to the tropics. They follow deep layers of plankton rather than resting.
Why were basking sharks hunted, and are they recovering?
Mainly for the oil in their giant liver, used for lamp fuel, machine lubricant, and later cosmetics and health supplements, and for their meat, skin, and fins. Targeted fisheries off Ireland, Scotland, Norway, and California killed tens of thousands and collapsed regional populations through the 20th century. The species is now protected across much of its range and listed on CITES, and some populations, such as in the northeast Atlantic, show early signs of recovery, but the shark's slow growth and low reproductive rate mean full recovery will take decades.