First record of atypical pigmentation pattern in fin whale Balaenoptera physalus in the Atlantic Ocean.

Atypical pigmentation, which is rarely observed in the wild, may influence social interactions between animals and can be detrimental for survival. Hypopigmentation, which is the lack of pigment in a part or on the entire body, is a type of atypical pigmentation pattern that can be either acquired (e.g. vitiligo) or congenital resulting from the inheritance of mutations in pigment-related genes (e.g. albinism, leucism and piebaldism). This study documents atypical pigmentation in a fin whale Balaenoptera physalus off the northwestern coast of the Iberian Peninsula (Atlantic Ocean). Photographic and video data collected between 2016 and 2017 on 30 individual fin whales were examined. One fully-grown fin whale exhibited hypopigmentation. Several white patches of different shapes and sizes were present across the body of the fin whale including on the head, body, dorsal fin, flippers, and flukes. The position, shape, and lack of inflammation of the white patches on the whale observed, along with its body length and condition, might indicate that the depigmentation pattern is due to vitiligo. To our knowledge, this is the first case of atypical pigmentation pattern in fin whales described with photographs and video records. As these observations are rare, especially in highly migratory, long-lived, marine mammal species, this study provides valuable information to better understand the occurrence of this phenomenon. Further studies are needed to determine the ecological and physiological implications of atypical colourations, which might have a significant influence on the animal's survival.