Species profile
Cetorhinus maximus
Basking shark
EN · Endangered — Endangered — very high risk of extinction in the wild
About this species
Basking shark (Cetorhinus maximus) is part of the curated SpeciesWatch catalogue and is classified as Endangered. The basking shark — the second-largest fish on Earth — cruises with its metre-wide mouth open, filtering up to 1,800 m³ of seawater an hour for plankton. The overall trend remains uncertain or is not applicable, so it should not be inferred from a small number of observations.
Habitat, behaviour and ecological role
This profile associates the species with marine, pelagic. These labels summarise environments used during different stages of its life rather than drawing an exact range boundary. In spring they gather in circles at the surface, a behaviour once thought to be courtship and now believed to be social feeding. Its anatomy and behaviour are responses to those environments, while movement can connect distant places requiring different forms of management.
Why this species is at risk
Basking sharks can lose their filtering gill rakers in winter when plankton is scarce — they literally rebuild their feeding apparatus each spring. The catalogue records 3 principal pressures for this profile: Bycatch, Fin trade, Ship strikes. They should not be treated as isolated causes. Habitat change, exploitation, pollution, disease and climate stress can reinforce one another, while the importance of each pressure varies between regions and through time.
Conservation outlook
Fishery management needs enforceable limits, more selective gear, bycatch reduction and coordinated compliance across jurisdictions. Direct protection needs to combine enforcement with conflict prevention, demand reduction and local benefits that make coexistence viable. Actions need long-term monitoring and revision as evidence changes; a positive intervention in one place does not by itself represent recovery across the species.
Editorial review: 2026-08-21
Threat factors
Known occurrences
Dots are georeferenced occurrence records from OBIS (marine) and GBIF (global), not individual animals and not a complete range map. Up to 500 recent API results are cached; the profile renders at most 500 points.
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