A dolphin of warm and temperate seas worldwide that feeds mainly on squid.
Its head is rounded without a distinct beak. Colour lightens with age, and adults often show many pale scars.
How do Risso’s dolphins stay in contact while hunting deep below the surface? Researchers analysed nine tag records from eight dolphins off Terceira, Azores, collected in 2013–2019. Burst-pulse calls changed in length and timing across dives. Short calls were common near the surface around dives; longer ones appeared early in deep daytime descents, before echolocation clicks began.
The researchers distinguished these social calls from “buzzes,” rapid click sequences linked to prey-capture attempts. They proposed that shorter calls may reach companions near the surface, while longer ones may carry to dolphins at depth. Their message is unknown; they may share location or feeding information. Different calls may help dolphins stay connected while searching for food at different depths.
IUCN Red List · Least Concern (LC) · Global species-level assessment (Grampus griseus)
The IUCN global assessment lists Risso’s dolphin as Least Concern (LC). It was assessed on 21 February 2018 and published in 2018. A separate regional assessment lists the Mediterranean subpopulation as Endangered (EN), showing that risk differs among regions. NOAA says U.S. Risso’s dolphins are not listed as threatened or endangered under the Endangered Species Act, while they are protected by the Marine Mammal Protection Act. NOAA identifies entanglement in fishing gear, hunting, underwater noise and contaminants as threats. U.S. measures include plans to reduce fishery interactions and efforts to limit vessel disturbance and noise.