Basking shark

Presentation

The Basking shark is the second largest fish in the world after the whale shark, reaching over 9 meters in length. This giant of the seas feeds exclusively on plankton which it filters using immense gills. Despite its impressive size, it is completely harmless to humans and moves slowly on the surface with its mouth wide open. It is often observed alone or in small groups in temperate and cold waters, including sometimes in the Mediterranean. Its large liver, rich in oil, ensures buoyancy adapted to its pelagic life. The species has been heavily hunted in the past for this oil, which has significantly reduced its populations.

Massive gray-brown to blackish body, conical snout prominent in young birds. Very wide mouth that can open up to a meter, lined with extremely developed gills forming almost circular slits around the neck. High, triangular dorsal fin, often visible on the surface, and crescent-shaped caudal fin. Skin covered with rough dermal denticles as in other sharks.

Characteristics

Indicative values: they vary by subspecies, sex and region.

Habitat and distribution

Basking shark frequents temperate to cold coastal and pelagic waters, often near the surface. It favors areas rich in plankton, notably thermal fronts and coastal upwellings. It can also make deep dives in the open sea. Its presence is seasonal and linked to the abundance of food available.

Behaviour

Generally solitary species but sometimes observed in groups during surface plankton concentrations. A slow swimmer, it makes significant seasonal migrations following areas rich in food. It can dive deep, particularly in winter, a period during which its behavior remains poorly understood. Its peaceful behavior and tolerance of approaching boats made it an easy target for historic fishing.

Reproduction

The reproduction of Basking shark remains poorly documented, but the species is ovoviviparous. The gestation would be particularly long, possibly more than a year, or even several years depending on certain hypotheses. Females give birth to a small number of young, already formed and independent. Sexual maturity is late, reached only after several years of growth.

Peculiarities

Its name comes from its habit of swimming on the surface, as if on a pilgrimage. It shares with the whale shark the filter-feeding method, a rare adaptation among large fish. Its size and slowness make it an animal that is easily observed but also easily vulnerable to human activities.

Threats and conservation

The species has been historically overexploited for its liver oil, meat and fins. It remains threatened by accidental captures in fishing nets and collisions with ships. Its slow growth and low fertility slow down the recovery of populations. It now benefits from international protections in several regions.

References

Profile updated 28 August 2026 · Reviewed by the TunisieVet editorial team.