The Phenomenon of Piebaldism in Sharks: A Review of Global Sightings and Patterns.

Chromatic disorders in elasmobranchs (sharks and rays) have been reported in several species, but little is known about their true abundance or consequences for survival and fitness. Piebaldism, a form of leucism characterized by partial loss of pigmentation, is among the rarest and least understood chromatic disorders reported in elasmobranchs. We conducted an extensive assessment of published and unpublished cases of piebaldism observed in sharks in the wild. Here, we report the observation of 25 incidences of this condition witnessed in 17 species of sharks from 11 families (Carcharhinidae, Dalatiidae, Galeocerdonidae, Ginglymostomatidae, Hexanchidae, Heterodontidae, Lamnidae, Odontaspidae, Scyliorhinidae, Squatinidae, and Sphyrnidae). The anatomical distribution and severity varied across shark families, with Ginglymostomatidae showing widespread aberrations on the flanks and pectoral fins, while piebaldism in Galeocerdonidae is more restricted. A single Sphyrnidae individual exhibited piebaldism across its body, while in the speciose Carcharhinidae family, piebaldism varied widely in intensity and distribution. We further discuss the taxonomic and geographical distribution of piebaldism reports, the potential fitness consequences, and uncertainty regarding the terminology used to discuss chromatic disorders in elasmobranchs. Finally, we comment on the importance of ecotourism and citizen science for improving our understanding of rare phenotypic conditions in marine megafauna such as elasmobranchs.