Eighteen-year study of South Australian dolphins shows variation in lung nematodes by season, year, age class, and location

Between 1990 and 2007, carcasses of opportunistically collected short-beaked common dolphins (Delphinus delphis; n=238), Indo-Pacific bottlenose dolphins (Tursiops aduncus; n=167), and common bottlenose dolphins (Tursiops truncatus; n=15) were examined for parasites and life history data. Three species of lung nematodes (Halocercus lagenorhynchi, Stenurus ovatus, Pharurus alatus) were identified in surface nodules, subsurface lesions, or airways. Nematode burdens were light to heavy and, in many cases, would have compromised the dolphins’ health. The number of dolphins infected was related to species, year, season, age class, and geographic region. Nematodes were found in all three species but were more prevalent in short-beaked common dolphins (mean annual prevalence=26%) than in bottlenose dolphins (12%). There was a significant increase in prevalence of nematodes in short-beaked common dolphins in 2005–06 (63%) compared to 1990–2004 (14%), with a peak in April–June. More young short-beaked common dolphins were infected than subadults and adults and, during the unusual infection event, there were more dependent calves (