Wild leucistic Risso’s dolphins (Grampus griseus) in the Azores

Abstract

Leucism has been reported in at least 14 cetacean species, including Risso’s dolphin (Grampus griseus). Risso’s dolphins with abnormal pigmentation were sighted and photographed north of Faial Island, Azores Archipelago, in 6 separate events between 2020 and 2023. In 2020, a calf and a juvenile/subadult were observed within a group of over 100 individuals. A leucistic calf with pale skin and dark eyes was observed in 2021, 2022, and 2023 in the same area followed by the same adult within a pod of about 12 individuals, including 3 juveniles, all with normal coloration. This is the first report of wild leucistic Risso’s dolphins in the Atlantic, which could be of interest in future local population and hypopigmentation studies on a dolphin species known to become completely white with age.