Stomach parasites and health status of short-beaked common dolphins, Delphinus delphis, stranded along the Irish coastline

Short-beaked common dolphins, Delphinus delphis, are important top predators in marine ecosystems, and inevitably they encounter a range of stressors in their environment. Parasite infections pose one such possible stressor and examining parasite prevalence and intensity of short-beaked common dolphins, and any possible impacts of infection, enables us to better understand these stressors. Here we examined the stomach parasite infection intensity of 69 stranded short-beaked common dolphins collected along the Irish coastline between 2017 and 2019. After isolating the parasites from the stomachs, all were morphologically identified as nematodes belonging to the genus Anisakis. Additional to adult nematodes, subadult and larval stages (i.e., L3 and L4) were observed. A total of 319,344 anisakid specimens were estimated from all stomach compartments of the animals both free in the lumen and attached to ulcers. Parasite prevalence was 94%, mean abundance was 4,630, and mean intensity was 4,910. A generalised linear model with negative binomial error structure revealed that dolphin body length, nutritional status and year of stranding were significantly associated with parasite intensity. The results presented highlight the high parasite intensities that may be carried by short-beaked common dolphins and their potential interaction with health parameters such as nutritional status. To gain a comprehensive overview it is important to include parasite infection investigations along with other parameters when evaluating the health status of marine mammals.