Basking shark (Cetorhinus maximus)

Physical characteristics

Key features include a huge, gaping mouth, numerous long gill rakers used to strain tiny animals from seawater, and a tall, triangular dorsal fin that is frequently visible as the animal moves near the surface. The body is stout and can appear dark grey to brown; unlike the whale shark, it does not display a distinctive spotted pattern. The basking shark is a classic filter-feeding species, relying on continuous swimming to force water through its gills and capture food.

Behavior and ecology

Basking sharks feed primarily on plankton, small crustaceans and fish larvae. They are most often seen alone or in small groups and may form larger aggregations where plankton concentrations are high. These sharks undertake seasonal movements and can be coastal or oceanic depending on food availability. Although they appear slow and harmless to humans, their size and gill structures require cautious interaction and respectful viewing distances.

Reproduction and life history

The reproductive biology of the basking shark remains incompletely understood. It is believed to be ovoviviparous—females carry eggs that hatch internally, later giving birth to live young—but details such as gestation length and pup size are not well documented. Basking sharks mature slowly and have low reproductive rates, traits that make populations vulnerable to overexploitation.

Human interactions and conservation

Historically targeted for liver oil, fins and meat by coastal fisheries, basking sharks experienced significant declines in many regions during the 19th and 20th centuries. Today they are protected in portions of their range and are considered vulnerable or threatened in several jurisdictions. Conservation measures include fishing restrictions, protected areas, and guidelines for whale- and shark-watching to minimize disturbance. Because they follow plankton blooms, basking sharks can serve as informal indicators of ecosystem productivity and attract ecotourism.

Notable distinctions and facts

• Second-largest living shark species after the whale shark.
• Often mistaken for other large filter-feeders; its anatomical details—especially the long gill rakers and lack of spot patterns—help distinguish it.
• Alternative common names include sunfish (not to be confused with the unrelated mola), bone shark, elephant shark, sailfish shark and big mouth shark.

Importance and research

Scientists study basking sharks to learn about migration, feeding ecology and the health of plankton communities. Sightings contribute to citizen-science databases and inform management decisions. Continued monitoring and international cooperation are important to ensure the species persists in the face of fisheries impacts, bycatch and changing ocean conditions.

For general background on filter-feeding sharks and conservation, see related resources: filter-feeding sharks overview, shark biology and whale shark comparisons.