Viability of Photo-Identification as a Tool to Examine the Prevalence of Lesions on Free-Ranging Common Dolphins (Delphinus sp.)

Lesions on cetacea can be useful to assess the natural and anthropogenic pressures faced by a population. The aim of this study was to assess the viability of photo-identification (photo-IL)) as a tool to examine potential pressures affecting gregarious, free-ranging common dolphins (Delphinus sp.). Photo-ID was collected between 2010 and 2013 in the Hauraki Gulf (HG), New Zealand. From 1,411 independent encounters, 2,083 individuals were identified from permanent nicks and notches on their dorsal fins. Of these individuals, the number of lesions on 12 body sectors was assessed. Prevalence was determined by weighting the number of lesions by the cumulative number of images for each body sector. Of the 2,083 individuals identified, 77.9% (n = 1,622) exhibited lesions. Of all body segments examined, the anterior peduncle exhibited the highest percentage of lesions (91.1%). Most lesions observed were represented by indentations and impressions (84.2%, n = 1,368), followed by cut-like indentations (54.1%, n = 878), hyper-pigmented lesions (43.1%, n = 700), and hypo-pigmented lesions (37.4%, n = 607). A significant difference in the prevalence of lesions between the leading and trailing edges of dorsal fins was evident. Possible causes of lesions are discussed, including intra-or interspecific interactions, environmental conditions, infectious origins, fisheries and vessel interactions, and/or human-induced environmental stressors. Findings suggest that despite limitations, photo-ID can he used as an opportunistic, non-invasive research tool to examine lesions on free-ranging delphinids.