Risso’s dolphin
Grampus griseus
biology
Newborn Risso’s dolphins are about 1.1 m to 1.5 m long and appear brownish-grey. Adults reach lengths of 2.6 m to 3.8 m and weigh between 300 and 500 kg. They have 2 to 7 pairs of stout teeth only in the lower jaw. Their lifespan is estimated to be at least 40 years.
Risso’s dolphins are robust, blunt-headed animals without a distinct beak. A unique feature is the vertical crease on the front of their squared-off forehead (melon). While they are born dark, adults become extensively covered in white scars and scratches caused by social interactions and battles with their primary prey, squid. Older individuals can become nearly entirely white, especially on the head, occasionally leading to confusion with Beluga whales at a distance. Notably, in 2020, three rare albino individuals were spotted north of Faial—the first records of their kind in the Atlantic.
These dolphins primarily feed on squid at night, following their prey’s vertical migration in the water column. Their social structure, extensively studied in the Azores by researchers like Karin Hartman, is unique: it is neither fission-fusion nor matrilineal. Instead, it is highly stratified, where adult males form long-term stable alliances (pods of "best friends"), while females associate based on the presence of calves. Groups are usually 6 to 12 individuals, but large summer social aggregations can reach up to 175 individuals.
Risso’s dolphins are robust, blunt-headed animals without a distinct beak. A unique feature is the vertical crease on the front of their squared-off forehead (melon). While they are born dark, adults become extensively covered in white scars and scratches caused by social interactions and battles with their primary prey, squid. Older individuals can become nearly entirely white, especially on the head, occasionally leading to confusion with Beluga whales at a distance. Notably, in 2020, three rare albino individuals were spotted north of Faial—the first records of their kind in the Atlantic.
These dolphins primarily feed on squid at night, following their prey’s vertical migration in the water column. Their social structure, extensively studied in the Azores by researchers like Karin Hartman, is unique: it is neither fission-fusion nor matrilineal. Instead, it is highly stratified, where adult males form long-term stable alliances (pods of "best friends"), while females associate based on the presence of calves. Groups are usually 6 to 12 individuals, but large summer social aggregations can reach up to 175 individuals.
observation
Risso’s dolphins are widely distributed in deep waters from tropical to cool temperate regions. They are generally easy to identify as the only medium-sized, blunt-headed dolphin with a characteristically pale, scarred appearance.
In the Azores, they are one of the most frequently sighted species because of a resident population inhabiting the south coast of Pico, where they are often found very close to shore. Pico Island is recognized as one of the world’s leading research hotspots for this species. They are present on average in 60% of Espaço Talassa’s trips, with sightings increasing towards late summer and autumn. Observations show they spend most of their daylight hours travelling (77%) and socialising (13%), while most of their feeding occurs deep underwater at night.
In the Azores, they are one of the most frequently sighted species because of a resident population inhabiting the south coast of Pico, where they are often found very close to shore. Pico Island is recognized as one of the world’s leading research hotspots for this species. They are present on average in 60% of Espaço Talassa’s trips, with sightings increasing towards late summer and autumn. Observations show they spend most of their daylight hours travelling (77%) and socialising (13%), while most of their feeding occurs deep underwater at night.
names
PT: Grampo (ou Golfinho-de-risso)
AÇORES: Moleiro
ENG: Risso’s dolphin (or Grampus)
FR: Dauphin de Risso
DE: Rundkopfdelfin
IT: Grampo (ou Delfino di Risso)
ESP: Calderón gris (ou Delfín de Risso)
NL: Grijze dolfijn (ou Gramper)
AÇORES: Moleiro
ENG: Risso’s dolphin (or Grampus)
FR: Dauphin de Risso
DE: Rundkopfdelfin
IT: Grampo (ou Delfino di Risso)
ESP: Calderón gris (ou Delfín de Risso)
NL: Grijze dolfijn (ou Gramper)
Scientific name
Grampus griseus
Discovery
Cuvier, 1812