Long-term host parasite dynamics in eight odontocete species from south-eastern South Africa

Although investigations of stranded and bycaught cetaceans have been conducted since the 1970s, little is known about parasites infecting the 25 species found in the South African subregion. For this study, we retrospectively identified parasites from eight bycaught and stranded odontocete species along the south-eastern coast of South Africa between 1970 and 2015 to produce a list of parasite species affecting southern African odontocetes and examine patterns of infection in host species with regards to age, sex, time intervals and collection method. Parasites were identified in 192 out of the 2599 individuals examined. Previously unreported parasite species were found for several southern African odontocete species, underscoring the importance of museum collections for biological research. Offshore and stranded odontocetes generally had a higher prevalence of parasites, although there were a few exceptions. Binomial logistic regression models showed significantly higher probability of parasitic presence (p < 0.05) in stranded Delphinus delphis than bycaught individuals, and significantly lower probability of parasitic presence (p < 0.05) in neonates and calves of stranded Tursiops aduncus and Stenella coeruleoalba than adult animals. No significant difference (p > 0.05) was detected between the sexes of all odontocete species investigated (p > 0.05). Parasitic prevalence was highest during the most recent years (2000–2015) for half of the odontocete species investigated, in agreement with the models. Accurate morphological identification of parasites affecting marine mammals is essential for comprehending disease epidemiology, assessing the health of cetacean populations, and developing effective conservation and management strategies.