On the occurrence of Corynosoma spp. (Acanthocephala) in ringed seals (Pusa hispida) in the Bothnian Bay, Finland

Abstract

The occurrence, location, sex ratio, growth, and development of Corynosoma strumosum and Corynosoma semerme were studied in 29 Baltic ringed seals, Pusa hispida botnica, in October–November 1977. The prevalence of infection was 96.5% for both species, the intensity of infection being 68(1 to 324) per infected seal in C. strumosum and 140 (1 to 1230) in C. semerme. Of the C. strumosum, 99% were in the small intestine; the remainder, together with 97% of the C. semerme, were distributed from the caecum to the rectum. The numbers of C. strumosum increased along the small intestine, and although the sex ratio remained constant, young females were more numerous in the anterior part of the intestine and gravid females more numerous distally. Factors affecting the numbers and proportions of the Corynosoma species are discussed with reference to their development and the progress of infection in the intestine of the ringed seal.