Louse populations of the Northern fur seal (Callorhinus ursinus)

Infestations, density, and structure of populations, distribution, and transmission of the sucking lice, Proechinophthirus fluctus (Ferris) and Antarctophthirus callorhini (Osborn), found on the northern fur seal, Callorhinus ursinus, were studied. Infestation rates, estimated by visual examination, were much smaller than those estimated by Cook’s technique, and a modified Cook’s technique is described. Of the 75 seals examined, 67 (89.3%) was infested with either P. fluctus or A. callorhini (or both) ; 50.8% of the infested seals harbored P. fluctus, and 95.8% A. callorhini. All seal pups and 71.4% of adult seals were infested with the lice. Of all the lice on the seals examined, 45.3% were P. fluctus and 54.7% were A. callorhini. All young black pups (1 to 3 months old) were infested with adults and lst-stage nymphs of P. fluctus and all different instars of A. callorhini. The adult seals collected in the spring were infested with nymphal instars of both species but not with adult lice. The mean louse population was 107.6 lice per infested host seal. The mean population of P. fluctus was similar to that of A. callorhini in black pups and adults. The mean population of the lice was at peak on the black pups and decreased as the host became older. The female seals harbored more lice than did the males. On the black pups, P. fluctus was on the pelage proper, and A. callorhini on the naked skins, viz. nostrils, eyelids, auditory canal, penile orifice, and umbilical areas. Most P. fluctus were in the fur of the head, back, and abdominal area of the silver pups(approx. 4 monthsold) and in the fur of the abdominal area of the adult seals. The sucking lice were transmitted from nursing cows to the newborn pups. Proechinophthirus fluctus was transmitted from cows to pups as adults, and A. callorhini as nymphs and adults.