Populations, microhabitat preference and effects of infestation of two species of Orthohalarachne (Halarachnidae: Acarina) in the northern fur seal.

All of 116 northern fur seals examined, except black pups (up to 3 monts old), had nasal mites, Orthohalarachne attenuata and O. diminuata, with the mean density of 1,808 mites per subadult male, 435 per adult female, 251 per silver pup, and 21.5 per black pup. Only 63% of black pups examined were infested with both mites. Larvae represented as much as 99% of the total mite population (total samples), and the females of both species of Orthohalarachne accounted for more than 90% of the total population of adult mites. The O. attenuata adults inhabited the nasopharynx and O. diminuata adults were found primarily in the lungs. Larvae of both species occupied the mucus-filled turbinates. The heavy infestation with these mites appeared to result in impairment of respiration in fur seals, and could also cause lesions in the lungs and secondary alveolar emphysems, predispose to more serious diseases, or even kill the host animal.

Variable activity of disophenol against hookworms and lice of northern fur seal pups on St. Paul Island, Alaska.

Six critical tests with disophenol were conducted in July, 1978, in fur seal pups (Callorhinus ursinus) naturally-infected with adult hookworms, Uncinaria lucasi, and infested with various stages of two species of sucking lice, Proechinopthirus fluctus (Ferris) and Antarctophthirus callorhini (Osborn). Disophenol at a dose rate of 12.5 mg/kg was administered subcutaneously to each of six pups. Each pup was contained in an individual cage for 60 h posttreatment at which time pups were exmained at necropsy. Efficacy against hookworms ranged from 2% to 88% and of both species of lice ranged from 26% to 90% for the six pups. Disophenol removed approximately 90% of all adult lice but only slightly more than 60% of all nymphs. The only sign of toxicosis was a probable drug related fluid-like feces for four pups from 12 to 60 h posttreatment.

Newborn northern fur seals (Callorhinus ursinus)--do they suffer from cold?

Several hundred thousand northern fur seals (C. ursinus) are born each summer during July at St. Paul Island in the Bering Sea. The weather in the area is usually cold, wet, and windy during the breeding season. At birth the pups are small (5--6 kg) and insulated only by a partly wettable pelt and a 2- to 4-mm layer of blubber. In air, the pups' lower critical temperature appears to be below the 6 degrees C 50-yr record low July temperature for the islands. During rainy weather much of the insulative value of the pelt is lost, and the pups, which already have a high resting metabolic rate of 3.5 W.kg-1, must increase heat production by shivering and/or nonshivering thermogenesis to maintain deep body temperature. The high level of metabolism (up to 18 W.kg-1) is supported by a very rich milk. The pups will, nevertheless, become hypothermic if their insulation is not improved through peripheral vasoconstriction and shedding of water from the pelt by periodic shudder. Even with these protections the newborn and very young pups are brought close to their limit of tolerance during rainy and windy days. Unfit pups are likely to succumb under such circumstances.

Activities of dichlorvos or disophenol against the hookworm (Uncinaria lucasi) and sucking lice of northern fur seal pups (Callorhinus ursinus) on St. Paul Island, Alaska.

One controlled and six critical tests were conducted in July, 1977 with northern fur seal pups (Callorhinus ursinus) to determine the efficacies of a single dose of dichlorvos capsules at 29.3 to 32.8 mg/kg, tablets at 10.5 to 11.5 mg/kg, or disophenol at 9.9 mg/kg given subcutaneously against natural infections of adult Uncinaria lucasi. In the controlled test, 20 pups were treated and 10 pups were nontreated. Removal of hookworms in this test was 99% for five pups receiving dichlorvos capsules, 99% for five pups receiving dichlorvos tablets, and 77% for 10 pups receiving disophenol. Also, both formulations of dichlorvos and the formulation of disophenol were highly active against natural infestations of two species of sucking lice (Proechinophthirus fluctus and Antarctopthirus callorhini). In critical tests with four pups treated with dichlorvos capsules at 28.6 to 30.6 mg/kg, removal of hookworms was uniformly 100%. Disophenol at 9.9 mg/kg removed 100% and less than 1% of hookworms in two pups, respectively, in critical tests.

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.

Lymphosarcoma in an infant northern fur seal (Callorhinus ursinus).

An infant northern fur seal (Callhorinus ursinus) died in a rookery on St. Paul Island, Pribilof Islands, Alaska. Grossly, slight enlargement of the mesenteric lymph nodes was seen. Microscopically, a lymphosarcoma composed of sheets of monomorphic lymphoid cells in sections of lymph node and tonsil was seen. Electron microscopy of formalin-fixed tissues revealed several structures that were possible of viral origin in the cytoplasm of the neoplastic cells.

Naturally-occurring leptospirosis in northern fur seals (Callorhinus ursinus).

A 4-year study of Northern fur seal (Callorhinus ursinus) leptospirosis in the Bering Sea has shown that in newborn pups Leptospira pomona is associated with a multiple hemorrhage syndrome. Adults may develop an interstitial nephritis and shed organisms in the urine. The hed prevalence, based on microscopic slide agglutination tests, ranged between 7.0% and 15.4% for adult females and 3-4 year old bachelor bulls, whereas nursing pups averaging 4 months of age had a prevalence of 2%. These results are used to conclude that leptospirosis is not acquired primarily on the breeding rookeries but rather is more frequently acquired subsequent to the purps leaving the rookeries, presumably through the food chain during their first pelagic cycle.

Lesions associated with Orthohalarachne attenuata (Halarachnidae) in the northern fur seal (Callorhinus ursinus).

In northern fur seals (Callorhinus ursinus) up to at least 4 years of age there is virtually 100% prevalence of infestation with the nasal mite Orthohalarachne attenuata. Although clinical observations and gross examination indicate that the condition is not serious, some erosion and inflammation of the nasal turbinates and nasopharynx were seen associated with mites in histological sections.

Renal fibrosarcoma in the northern fur seal.

A 2-week-old northern fur seal female pup (Callorhinus ursinus) found dead in the Pribilof Islands had an irregular mass at the anterior pole of the right kidney. Histopathological examination revealed a fibrosarcoma.