PREVALENCE AND INTENSITY OF THE ECTOPARASITE ECHINOPHTHIRIUS-HORRIDUSON HARBOR SEALS (PHOCA-VITULINA) - EFFECTS OF HOST AGE AND INTERANNUAL VARIABILITY IN HOST FOOD AVAILABILITY

The epidemiology of the sucking lice Echinophthirius horridus was stud ied over a 4 year period in which their harbour seal hosts experienced marked inter-annual changes in food availability. Prevalence and inte nsity of infection varied in relation to host age but not sex. Burdens were highest on immature seals, but both prevalence and intensity of infection were significantly higher in years when food availability wa s low. Observed intra-population variations in ectoparasite dynamics s uggested that reported geographical differences in the prevalence of E . horridus may have resulted from methodological differences. In contr ast to previous studies of other pinnipeds, lice were also absent on w eaned pups, suggesting that E. horridus is transferred horizontally. N o significant differences were found in the haematological parameters of infected and uninfected hosts. Nevertheless, there was a significan t negative correlation between intensity of infection and several eryt hrocyte parameters, suggesting that high burdens of lice may compromis e diving ability.