Intestinal helminths of a landlocked ringed seal ( Phoca hispida saimensis ) population in eastern Finland

Abstract

A small, landlocked, endangered ringed seal (Phoca hispida saimensis) population lives as a postglacial relict in Lake Saimaa in eastern Finland. In this study, the intestinal metazoans were examined from a total of 61 Saimaa seals found dead from 1981 to 2001. The helminth fauna was very depauperate. Only one acanthocephalan species, Corynosoma magdaleni, has been able to survive during isolation in the freshwater environment. In addition, only two cestode species were found: Diphyllobothrium ditretum and Schistocephalus sp. However, neither of these larvae developed in the ringed seals. As the newborn pups of Saimaa seals are nursed for about 2 months only one of them was infected by C. magdaleni. At 2-5 months the pups harboured worms; however, the mean intensity did not rise distinctively until the seals were adults. C. magdaleni infection increased with increasing age and the abundances were significantly different between the age groups. There was no correlation between the number of parasites and the adult seal body weight; however, seals weighing 36 kg or more carried the majority of the worms. The distribution of the parasites was aggregated; six seals carried 65% (n=1,182) of all worms (total n=1,809) and 26 seals were uninfected. Variation in the number of worms in individual seals may indicate differences in feeding behaviour and in the diet of seals, and/or variation in the immune status of the seals.

Hookworms (Uncinaria lucasi) and acanthocephalans (Corynosoma spp. and Bolbosoma spp.) found in dead northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska in 2007

“…The three mature acanthocephalan species (C. obtuscens, C. strumosum, and C. validum) found in the present study in the northern fur seals from St. Paul Island in the Bering Sea in Alaska are common parasites in seals of neartic regions (Dailey 1975;Nickol et al 2002;Sinisalo et al 2003). Corynosoma strumosum is considered the parasite that is most widespread and abundant in seals, sea lions, and walruses.…”

Broad tapeworms (Diphyllobothriidae), parasites of wildlife and humans: Recent progress and future challenges

“…Terrestrial species of broad tapeworm genera such as Spirometra or Dibothriocephalus are not able to mature in pinnipeds or cetaceans and only plerocercoids of Dib. dendriticus and Schistocephalus solidus have been rarely found in seals from Lake Baikal and Baltic Sea, most likely representing accidental infections (Pronin and Zhaltsanova, 1999; Sinisalo et al, 2003). However, several previous checklists erroneously listed as many as eight pinnipeds and cetaceans as definitive hosts of the human broad fish tapeworm Dibo.…”

The impact of sexual selection on Corynosoma magdaleni (Acanthocephala) infrapopulations in Saimaa ringed seals (Phoca hispida saimensis)

“…Intestinal metazoan parasites were examined from 61 Saimaa ringed seals (Phoca hispida saimensis Nordquist, 1899) in Lake Saimaa in eastern Finland. The seals have been found recently dead during the years 1981-2001 (Sinisalo et al 2003). Only 35 harboured intestinal worms, all of which were C. magdaleni (Acanthocephala) (see Sinisalo et al 2003).…”

“…At present, the population consists of 220-250 individuals (Hyvärinen et al 1999 ;Kunnasranta, 2001) ; it is highly threatened, and has been protected since 1955. A single helminth species, the acanthocephlan Corynosoma magdaleni, has been able to persist in the seals of Lake Saimaa (see Sinisalo, Kunnasranta & Valtonen, 2003). We take advantage of this unusual host-parasite system to test the influence of sexual selection on the spatial distribution, female-to-male body size ratio, and female mating success of acanthocephalan infrapopulations.…”