Marine Mammal Science & Conservation

Risso's dolphin

Risso’s dolphin (Grampus griseus)

Group formation: Social groups 5-50

Size: 2.6-4 m (male and female same size), calf 1.1-1.7 m

Weight: 300-500 kg, calf 20 kg

Age: 40 yrs

Sexual maturity: males 10-12 yrs, females 8-10 yrs

Gestation: 13-14 mths, with 2-4 yrs in between

Weaning: unknown (probably 1-3 yrs)

Diet: mostly squid, nocturnal feeders.

Distribution: Cosmopolitan species that lives in deep water preferably close to continental shelves, close to land (400-1000m) prefer temperate, subtropical and tropical waters but the range is 60° N to 60° S.

Raja Ampat: they have been sighted rarely in small groups (25), but nothing is known about them.

Population size: unknown

Conservation Status: Least Concern ver 3.1, Pop. trend: unknown

Threats: Whaling (Faeroe Islands, Japan, Sri Lanka, Indonesia, West Indies), chemical and plastic pollution, man-made noise impacts (seismic surveys, military sonar), entanglement in fishing gear, over fishing, captivity.


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