Basking sharks (Cetorhinus maximus) are the world’s second-largest living fish after whale sharks, yet they feed on tiny zooplankton rather than large prey. These highly migratory sharks use coastal and open-ocean habitats across temperate seas. They are globally Endangered, and their slow recovery makes careful wildlife watching and effective protection especially important.
Basking shark facts at a glance
| Fact | Current evidence |
|---|---|
| Scientific name | Cetorhinus maximus |
| Conservation status | Endangered globally on the IUCN Red List |
| Size | Adults commonly measure about 6.7–8.8 m (22–29 ft); large individuals can approach 10 m (33 ft) |
| Diet | Zooplankton, including small crustaceans, invertebrate larvae, fish eggs, and fish larvae |
| Feeding method | Ram filter feeding with rows of gill rakers |
| Range | Temperate and cool waters across the Atlantic, Pacific, and other ocean regions |
| Habitat | Coastal shelf, bays, open ocean, surface waters, and deeper parts of the water column |
| Risk to people | Not predatory toward humans, but their size and power require a respectful distance |
| Reproduction | Believed to be live-bearing; gestation length, breeding areas, and reproductive rate remain uncertain |
What is a basking shark?
The basking shark is a large, slow-moving shark in the family Cetorhinidae. It is second in size only to the whale shark. Together with the whale shark and megamouth shark, it is one of three large filter-feeding shark species.
Its huge mouth can look intimidating, but the animal is adapted to strain small organisms from seawater. It does not use its teeth to seize seals, large fish, or people. This combination of immense size and a plankton-based diet makes it distinct from many better-known types of sharks.
How to identify a basking shark
A feeding basking shark is difficult to confuse with another species at close range. The clearest identification features are:
- an enormous, rounded mouth that opens while the shark swims forward;
- five exceptionally long gill slits that almost encircle the head;
- dark gill rakers visible inside the gill openings;
- a conical snout, small eyes, and grey-brown to nearly black upper body;
- a tall triangular dorsal fin and crescent-shaped tail.
Basking sharks have hundreds of tiny, often hooked teeth. Those teeth are real, but they are not the main feeding apparatus. The gill rakers—comb-like structures inside the gill arches—retain food as water flows out through the gill slits.
How big do basking sharks get?
Adult basking sharks commonly measure about 6.7–8.8 m (22–29 ft). NatureScot reports that they can grow to about 10 m (33 ft). Some older accounts describe animals longer than 10 m, but visual estimates and historical measurements are not equally reliable, so extreme figures should be treated cautiously.
The shark’s mass varies with length and body condition. A large liver helps with buoyancy and once made the species a valuable target for commercial oil fisheries. Size alone does not reveal age because growth, maturity, and longevity remain difficult to measure in a wide-ranging marine animal.
What do basking sharks eat?
Basking sharks eat zooplankton: drifting animals and early life stages small enough to be filtered from seawater. Their diet includes copepods and other tiny crustaceans, marine invertebrate larvae, fish eggs, and fish larvae. They concentrate their feeding in productive water where currents and ocean fronts gather dense plankton patches.
How ram filter feeding works
- The shark swims forward with its mouth open.
- Seawater enters the mouth and passes toward the gills.
- Gill rakers trap suitable plankton while water exits through the gill slits.
- The retained food is swallowed.
This is called obligate ram filter feeding because forward swimming supplies the water flow. Whale sharks and megamouth sharks can supplement forward movement by actively drawing or pumping water through the mouth. Estimates of how much water a basking shark filters per hour vary widely with body size, swimming speed, and methodology, so a single dramatic figure is less useful than the mechanism itself.
Where do basking sharks live?
Basking sharks are coastal-pelagic animals found across much of the world’s temperate and cool ocean waters. They occur in the North Atlantic and North Pacific, parts of the Southern Hemisphere, and some connected seas. Their habitat includes continental shelves, shelf edges, bays, productive coastal fronts, and open-ocean water.
Seeing a shark at the surface does not mean it lives only in shallow water. Basking sharks move vertically as well as horizontally, and tagging studies have recorded them far below the surface. Their location changes with season, plankton availability, water structure, and other factors that researchers are still investigating.
Where can you see basking sharks in the UK and Ireland?
Surface sightings are most common from spring through autumn, especially along the west coasts of Scotland and Ireland and around southwest England. In Scotland, the Sea of the Hebrides is an important summer area. The Shark Trust describes April through October as the main recording season, although wildlife never follows a guaranteed timetable.
How far do basking sharks migrate?
Basking sharks can travel thousands of kilometres, but they do not all follow one fixed route. In a 2017 satellite-tracking study, researchers deployed 70 tags off western Scotland and the Isle of Man. Data from 28 longer deployments showed a median minimum movement of 3,633 km (2,258 miles).
Some tagged sharks remained around the UK, Ireland, and the Faroe Islands. Others moved toward the Bay of Biscay, the Iberian Peninsula, or North Africa. The same study found use of both continental-shelf and oceanic habitat, mostly within the upper 50–200 m of the water column. These movements cross national boundaries, which is why conservation cannot be handled by one country alone.
Older theories suggested that basking sharks became dormant in deep water during winter. Electronic tagging instead shows continued movement and repeated vertical changes, making true winter hibernation unlikely.
Basking shark behavior below the surface
The name “basking shark” comes from the animal’s slow surface swimming, which can look like basking in the sun. Surface observations reveal only part of its life. A 2021 animal-towed-camera study recorded six sharks for a combined 123 hours in the Sea of the Hebrides. Feeding occurred close to the surface, but individual sharks spent as much as 88% of recorded daylight time near the seabed.
The cameras also documented a complete breach, short-lived groups, and behavior interpreted as possible courtship. These observations are important but should not be stretched into claims that basking sharks form permanent families or teach young sharks migration routes. Researchers still do not know where many breeding events occur or what every aggregation means.
Reproduction and lifespan remain poorly understood
Basking shark reproduction is one of the largest gaps in the species’ biology. The sharks are believed to give birth to live young after embryos develop inside the mother, but very few pregnant females or newborns have been documented. Exact gestation length, litter size, mating grounds, nursery areas, and age at maturity remain uncertain.
A lifespan of roughly 50 years is often cited, but it is an estimate rather than a precise limit. What conservation scientists can say with more confidence is that basking sharks grow slowly and produce relatively few young. Populations therefore cannot quickly replace mature animals lost to fishing gear, vessel collisions, or targeted killing.
Are basking sharks dangerous to humans?
Basking sharks are not predators of humans. They feed on plankton and generally pose no deliberate attack risk to a passive observer. Their immense body, powerful tail, rough skin, and unpredictable movement still make close contact unsafe. A calm species is not the same as a harmless object.
- Do not touch, feed, chase, or swim directly in front of a basking shark.
- Never place a boat, paddleboard, or kayak across its direction of travel.
- Reduce speed and avoid sudden course changes when sharks are nearby.
- Give the animal room to feed, dive, turn, and leave.
- Follow local wildlife law and an applicable marine-watching code.
Why are basking sharks endangered?
The IUCN Red List classifies the basking shark as Endangered globally. Historic fisheries removed large numbers of mature sharks for liver oil, meat, skin, and fins. In the Northeast Atlantic, the last targeted British fishery closed in 1995 after the familiar pattern of high initial catches followed by falling landings and economic collapse.
Protection has reduced legal targeted fishing in many regions, but it does not remove every source of mortality. There is no reliable single count for all basking sharks worldwide, and trends can differ between regions. Their slow growth and low reproductive output mean that recovery may take decades.
Main threats to basking sharks
| Threat | Why it matters |
|---|---|
| Entanglement and bycatch | Sharks can become caught in nets, ropes, pot lines, and other fishing gear. Entanglement can cause deep wounds, prevent feeding, or lead to death. |
| Vessel strikes | Surface-feeding sharks may not evade an approaching boat, leaving them vulnerable to hull and propeller injuries. |
| Disturbance and harassment | Boats and swimmers can interrupt feeding, courtship, or other natural behavior and may cause direct injury. |
| Trade in body parts | International trade in fins and other products is regulated, but demand and illegal or poorly monitored trade remain concerns. |
| Historic depletion | Past fisheries removed mature animals faster than this slow-reproducing species could replace them. |
How basking sharks are protected
Basking sharks receive legal protection in the UK and Ireland, and fisheries rules prohibit targeted capture and retention in UK and EU waters. Internationally, the species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), which regulates international trade. It is also listed in Appendices I and II of the Convention on Migratory Species (CMS), reflecting the need for cooperation between range states.
Scotland designated the Sea of the Hebrides Marine Protected Area in December 2020 partly for basking sharks. Protection of a summer hotspot helps, but satellite tracking shows that individual sharks may move through several national jurisdictions and the high seas. Effective conservation therefore also depends on safer fisheries, vessel management, international monitoring, and better data.
These measures matter beyond one species. Understanding how sharks support marine ecosystems helps place basking shark protection within wider ocean conservation.
How to watch and help basking sharks responsibly
- Watch from land when possible. Binoculars and elevated viewpoints reduce disturbance.
- Use a responsible operator. In Scotland, look for an operator trained through the WiSe wildlife-watching scheme.
- Keep movement predictable. Approach slowly, avoid surrounding the shark, and leave an unobstructed route.
- Do not seek contact. Touching, feeding, chasing, or repeatedly positioning for a close photograph can harm the animal and may violate wildlife law.
- Record useful observations. Note the date, time, location, number of sharks, and visible injuries without putting yourself or the animal at risk.
- Submit sightings. The Shark Trust Basking Shark Project accepts records and photographs that can support verification, movement research, and photo identification.
Responsible sightings can contribute to research; crowding an animal cannot. Readers looking for broader action can also explore practical ways to help animals facing extinction.
Frequently asked questions
Are basking sharks dangerous to humans?
No. Basking sharks are not predators of humans and feed on zooplankton. Their size, powerful tail, and rough skin can still cause accidental injury, so keep a respectful distance and never touch or obstruct one.
How big do basking sharks get?
Adults commonly measure about 6.7–8.8 m (22–29 ft), while large individuals can approach 10 m (33 ft). Some larger historical estimates are difficult to verify.
What do basking sharks eat?
They eat zooplankton, including small crustaceans, invertebrate larvae, fish eggs, and fish larvae. Gill rakers retain this food as seawater passes through the gills.
Where do basking sharks live?
Basking sharks occur in temperate and cool waters across several ocean basins. They use coastal shelves, bays, open ocean, surface waters, and deeper habitat, moving seasonally between productive areas.
Why are basking sharks endangered?
Historic targeted fisheries severely depleted populations. Entanglement, bycatch, vessel strikes, disturbance, and trade remain concerns, while slow growth and low reproductive output make recovery slow.
Do basking sharks have teeth?
Yes. They have hundreds of tiny teeth, but they do not use them to capture large prey. Their gill rakers filter plankton from seawater.
A giant shark that depends on small food and careful protection
Basking sharks show why appearance is a poor guide to ecological role. One of the ocean’s largest animals survives by tracking concentrations of some of its smallest. Their migrations connect coastal feeding sites with offshore and international waters, while their slow life history leaves little room for preventable deaths. The most useful response is simple: protect productive habitat, reduce human-caused injuries, observe without interference, and turn credible sightings into better data.