Halarachnidae consists of nasal mites that parasitize pinnipeds. The respiratory tracts of 22 Arctocephalus australis (South American fur seal) were examined for the presence of mites and to study their parasitological indices. Of these, 15 hosts (68.2%) were infected with Orthohalarachne attenuata, 5 of which (22.7%) were coinfected with Orthohalarachne diminuata. A moderate to severe infection by O. attenuata was observed in 27.3% of the hosts, and by O. diminuata in 9.1%. Co-infection occurred in all O. diminuata–positive hosts. No significant differences for Halarachnidae prevalence were found between male and female hosts. Mite infections of the respiratory system by Otariidae are often reported; however, further studies should be conducted to better understand host–parasite relationships and possible pathogeneses caused by these infections.