Basking Shark: where and when to see them

The basking shark is the world's second-largest living fish and a specialist feeder on tiny drifting animals. Despite its enormous mouth, it is not a predator of people or large marine mammals. Individuals sometimes feed close to the surface, making their dorsal fins visible from coastal viewpoints or vessel decks. Surface appearances are strongly influenced by plankton distribution, so a suitable season does not make encounters predictable or universal.

Size

6–8 m long

Weight

Not reliably established

Lifespan

Not reliably established

Status

Endangered

Basking sharks typically swim slowly while feeding, passing water through the open mouth and across filtering structures associated with the gills. They may gather where currents concentrate plankton, but these aggregations can disperse quickly. Tracking has revealed extensive seasonal movements and substantial changes in depth. Courtship-like circling groups have been documented, and occasional full-body breaches show that an apparently sedate shark can produce powerful bursts of activity. Individual basking sharks are often solitary, but they can form aggregations when food is abundant. Their slow, deliberate swimming style near the surface is primarily for continuous feeding, allowing them to process large volumes of water.

• Only the whale shark grows larger among living fishes.
• Its feeding apparatus includes gill rakers that retain small planktonic prey.
• Satellite tracking has shown that some individuals cross ocean basins.
• Basking sharks can breach completely clear of the surface.

Scottish surface observations are most plausible from late spring into early autumn, often with the strongest interest in summer. Plankton blooms, currents and weather vary annually. Calm conditions improve visibility from shore or decks but do not establish shark presence. In Scotland, the prime season aligns with increased plankton productivity, making sightings more frequent from May to September. Early mornings or late afternoons can sometimes offer calmer seas and better visibility for spotting these animals.

This marine shark inhabits temperate coastal and offshore waters, often near productive fronts, headlands and shelf seas. It is not confined to the surface or shoreline. Seasonal movements can take individuals far offshore and into much deeper water. Despite their size, basking sharks are highly migratory, often traveling thousands of kilometers across ocean basins. They are found in both the Atlantic and Pacific Oceans, generally preferring waters between 8 and 24 degrees Celsius.

Basking sharks filter zooplankton, particularly copepods, together with other small drifting crustaceans and planktonic animals. They concentrate feeding where prey density makes continuous swimming worthwhile. They do not chase seals or fish schools in the manner of large predatory sharks. Their gill rakers are specifically adapted to sieve microscopic prey from vast quantities of water, acting as a highly efficient filter-feeding apparatus. Basking sharks can filter up to 2,000 tons of water per hour to extract sufficient zooplankton.

Common name

Basking Shark

Scientific name

Cetorhinus maximus

Animal group

Marine life

Size

6–8 m long

Weight

Not reliably established

Lifespan

Not reliably established

Status

Endangered

Identification

Compared with other large sharks, the basking shark has exceptionally long gill slits nearly encircling the head and an enormous filtering mouth. Their dorsal fin is typically large and triangular, often visible above the water, while the caudal (tail) fin can also be seen, particularly the upper lobe. The skin is dark grey to brownish-black and often appears mottled or scarred.