Date Published: February 5, 2019
Publisher: Public Library of Science
Author(s): Andrea Benedetto Leone, Giusy Bonanno Ferraro, Luigi Boitani, Monica Francesca Blasi, Athanassios C. Tsikliras.
Skin marks occur frequently in many cetacean species across the globe revealing a broad spectrum of causes, including social interactions, infectious diseases and injuries produced by anthropogenic factors. The current study used photo-id data from 2005–2014 to estimate the skin mark pattern on resident bottlenose dolphins (Tursiops truncatus) from the Aeolian Archipelago (Italy). Thirteen skin mark types were identified and their origin, prevalence and permanence time were examined. The pattern of skin marks was assessed for the abundance, richness, distribution and severity in six body regions and compared among age classes, sex and degree of dolphins’ interaction with trammel nets (DIN). Our results showed higher prevalence, abundance, richness and distribution of skin marks in adults than in the younger age classes, with the exception of black marks and white ring lesions. The prevalence and abundance of skin marks were higher in males than females, with the exception of scratches and white patches. Moreover, gunshot wounds, mutilations and irregular dorsal fin edges were found only on adult males. Since males showed higher DIN than females and, in dolphins with higher DIN, skin marks were more abundant and frequently distributed in different body regions, the skin mark pattern in regard to DIN seems to be sex-related. The more severe marks were observed on adults, males and dolphins with higher DIN, namely skin disorder, tooth rake marks, small shallow indentations, deep indentations and mutilations. On the contrary, the severity of scratches, white patches and dark ring lesions was higher in females than males, but not significantly related to DIN and age of the individuals. Our results showed that photo-id data provide an efficient and cost-effective approach to document the occurrence of skin marks in free-ranging bottlenose dolphin populations, a critical step toward understanding the cause and supporting the conservation strategies.
Cetacean skin marks have been widely reported [1–3] and revealed a broad spectrum of causes, including infectious diseases (poxvirus and herpesvirus) [4–15] as well as environmental causes (solar radiation and water salinity) [16–19], injuries produced by sharks or parasitic copepods/diatoms, traumatic scarring [16, 20–25] and scars caused by propellers [16, 17, 19, 26, 27] or fishing gears [13, 28–31]. Biological and chemical contaminants may contribute to skin mark development in cetaceans [17, 19].
Four hundred surveys were carried out over 564 hours for a total of 6.204 km surveyed from 2005 to 2014. A total of 185 sightings were recorded, corresponding to 120.55 hours spent with the dolphins (mean ± St. Dev. sighting time = 35.8 ± 33.4 minutes, range 10–194 minutes). The dolphin groups covered 1.320 km at an average (± St. Dev.) speed of 10.74 ± 2.45 km/h.
Epidermal marks are common in all bottlenose dolphin populations [13, 16, 19, 32, 62, 68] and other cetacean species across the globe [7, 29, 62, 69–75], but both their prevalence and severity may vary among populations as a result of environmental and anthropogenic factors and/or individual behaviour and metabolism [17, 19, 32, 63, 76–78].