a1 Department of Zoology, The University, Hull
1. Ninety-six lesser black-backed gulls, Larus fuscus L., captured at about 6 weeks of age, were kept in captivity for up to 2⅛ years. At intervals some gulls were killed and examined for helminth parasites, of which 14 species were found comprising 4 species of Trematoda, 5 species of Cestoda and 5 species of Nematoda.
2. Nine of the 14 species are commonly found in Holarctic gulls and may be regarded as characteristic members of the helminth fauna of these birds. Six species are recorded from L. fuscus for the first time.
3. The life span of different species of helminth parasites in L. fuscus varied from 2 months to 2⅛ years; few specimens lived in their host for more than one year. During captivity there was a marked decline in the variety of the helminth fauna of individual gulls, as well as a general decline in the incidence and intensity of infection with individual species of parasites. There was one exception, the tape-worm Tetrabothrius cylindraceus, which increased in incidence and maintained a fairly even intensity of infection in L. fuscus over 21 months. The results are discussed in relation to the ecology of the parasite and the host.
(Accepted March 07 1973)