Skin conditions, epizoa, ectoparasites and emaciation in cetaceans in the Strait of Gibraltar: An update for the period 2016-2020

Cetacean populations in the Strait of Gibraltar are heavily impacted by human activities. Photographs are a valuable tool to monitor the external health of cetaceans. We visually screened 27,866 pictures taken during whale watching operations in the years 2016-2020 for abnormal conditions, such as emaciation, dermal diseases and epizoic infestations. Prevalence levels could not be calculated as data were obtained opportunistically. Dermal diseases were detected in 566 sightings and occurred in all species. Bottlenose dolphins were most strongly affected (n = 192). Hypopigmented skin lesions were most common in all species (n = 291). Tattoo skin disease‐like lesions affected 16 animals ( T. truncatus : n = 12; G. melas : n = 3; D. delphis : n = 1). Other observed conditions include expansive annular lesions in three juvenile pilot whales. Furthermore, we report the presence of open wounds in 28 animals ( G. melas : n = 23; T. truncatus : n = 2; P. macrocephalus : n = 3). In three pilot whales, these wounds did not heal over a period of several years. Epizoic and ectoparasitic infestations include the observation of Xenobalanus spp. and Pennella balaenopterae . Multiple fin whales were sighted with very high numbers of Pennella balaenopterae , ranging up to 84 parasites per host. Emaciation was mainly detected in bottlenose dolphins (n = 36) and seemed to affect these animals more severely during specific years, potentially indicating fluctuations in prey availability.