Observations on the infectivity of parasitic third-stage larvae of Uncinaria lucasi Stiles 1901 (Nematoda: Ancylostomatidae) of Northern fur seals, Callorhinus ursinus Linn., on St. Paul Island, Alaska.

Twelve fur seal pups, which had not nursed their mothers, were used in an infectivity experiment. Pups were exposed to parasitic 3rd-stage larvae of Uncinaria lucasi from belly tissues of fur seal bulls, bachelors, and pregnant cows, to determine maturation capability of the larvae. Hookworms were not recovered from the intestines of 3 pups receiving larvae from belly blubber of bulls, 6 pups receiving larvae from belly blubber of bachelors, and 1 nonexposed pup. Maturation of hookworms did occur in 2 pups exposed to larvae from a mixture of belly blubber, mammary tissue, and milk of pregnant cows. Parasitic 3rd-stage hookworm larvae from belly tissues of pregnant and "non-pregnant" fur seal cows averaged 938.1 and 802.1 micron long, and 34.1 and 31.5 micron wide, respectively; however, larvae from belly tissues of a fur seal bull, bachelors, 2-year-old males, male and female yearlings and pups, and Steller Sea Lion subadults averaged 640.5-732.0 micron long and 20.9-24.9 micron wide.