Helminth parasites of sea otters (Enhydra lutris) from Prince William Sound, Alaska: Comparisons with other populations of sea otters and comments on the origin of their parasites

The helminths found in the gastrointestinal tracts and gallbladders of 68 sea otters (Enhydra lutris) from Prince William Sound, Alaska, and their prevalences were: Corynosoma enhydri (Acanthocephala), intestine, 51.5%; Orthosplanchnus fraterculus (Trematoda), gallbladder, 50%; Diplogonoporus tetrapterus (Cestoda), intestine, 12%; and Pseudoterranova decipiens (Nematoda), stomach, 1.5%. One pup examined was free of helminth parasites. Throughout its range from the Kuril and Komandorski islands in Russia, across the Aleutian Islands, Alaska, and south to California, the sea otter harbors a total of 17 or 18 species of helminths, of which 5 or 6 are incidental infections with larval (2 species of Anisakis) or juvenile worms (3 or 4 species of Polymorphus). The adult worms of sea otters (12 species) are derived primarily (9 species) from pinnipeds. One species, Microphallus pirum (Trematoda), found widely in sea otters from the Komandorski Islands to California, may be primarily a parasite of various shorebirds. Only one species, C. enhydri, is uniquely a parasite of sea otters, occurring throughout its range at prevalences greater than 50%. California populations of sea otters harbor only M. pirum, C. enhydri, and Polymorphus species, lacking any species known to be transmitted by fish; the diet of these sea otters consists almost entirely of invertebrates. Northern sea otter populations from Russia and Alaska have a more varied diet and are hosts for at least 5 fish-transmitted parasites. Among the commonly occurring parasites, the most striking difference between Russian and Alaskan populations of sea otters is the absence of O. fraterculus from Russian populations and its frequent occurrence in Alaskan populations. KEY WORDS: parasites, helminths, Orthosplanchnus fraterculus, Diplogonoporus tetrapterus, Pseudoterranova decipiens, Corynosoma enhydri, sea otters, Enhydra lutris, Alaska, North Pacific Ocean, zoogeography.