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RESEARCH PRODUCT

Host‐parasite relationships between two seal populations and two species of Corynosoma (Acanthocephala) in Finland

subject

description

Ringed seals (Phoea hispida botnica), from the Bothnian Bay, north-eastern Baltic Sea were examined for acanthocephalan parasites in 1977-1982, and specimens from Lake Saimaa in south-eastern Finland (P. h. saimensis) were examined in 1980-1981. The two seal stocks have been isolated from Arctic stock for 11,000 years and from each other for 8,000 years. Corynosoma strumosum and C. semerme were found in the Baltic seals, but only C. strumosurn in those from the lake. Eighty two of the ringed seals caught in the Bothruan Bay were infected with both Corynosoma species, one with a single infection of C. strumosum and one with C. semerme inautumn. The total number of C. semerme increased in relation to the nurnber of C. strumosum in each set of seals both in autumn and spring. Corynosoma setnerrne was dominant in most seals in spring, but in only an average of 60% in autumn. The predominance of C. strumosum in 400/n of the autumn material (range 33-80%) is of interest because species ratio favouring C. strumosum is not found in any more heavily infected paratenic fish host of Corynosoma in the Bothnian Bay. The change in the Corynosoma species ratio of seals in autumn may be explained by their exceptional feeding behaviour at this time of the year (total or partial fasting) and the suggested longevity of C. strumosum as compared with C. semerme. The stability of the acanthocephalan populations in ringed seals is documented.Page • 362 • 362 • 363 363 364 365 • 365 368 • 368 • 369 • 370 • 370 Introduction Materials and methods Results Prevalence of infection . Sex ratio and developmental stages of female