A global checklist of the parasites of the harbor porpoise , a critically-endangered species, including new findings from the Baltic Sea.

The common harbor porpoise is a widely-distributed marine mammal with three known subspecies, including , with a clearly distinct and critically endangered (CR) subpopulation from the Baltic Sea (Baltic Proper). As part of an assessment of the condition and health threats of these mammals, it is important to conduct parasitological monitoring. The aim of the study was therefore to compare the data on porpoise parasitofauna from this subpopulation with those on porpoises from other areas. The study included 37 individuals from 1995 to 2019; eight species of parasites were found (prevalence 83.8%, mean intensity 724.2, range 2-3940), with a predominance of lung nematodes - (94.7%), (69.4%), (63.8%), (22.2%); the highest intensity was recorded for (989, 53-2928). Two species of Anisakidae ( - 33.3%, sp. - 20.0%) were found in the digestive tracts, which were a new record for this population. The fluke was found in the livers of 31.3% of porpoises. The tapeworm was also recorded in the intestine of one individual; this is typical for these hosts, but previously undetected in the Baltic subpopulation. Parasites coexisted in numerous hosts, constituting a heavy burden for them. The obtained data were compared with those from the parasitofauna from other regions, based on a compiled checklist (1809-2021) including all species of porpoise parasites (55 taxa). Compared to the worldwide porpoise parasitofauna checklist, the number of parasites found in the nominative subspecies (Baltic Proper subpopulation) is small: including only 10 taxa (eight in the current study). These species are typical of porpoises and usually the most common; however, the level of infection of Baltic porpoises (intensity and total parasite load) is very high, which can undoubtedly have a negative impact on their condition and overall health.