Prevalence, intensity and numbers of parasites in the gastrointestinal tract of ringed seals (Pusa hispida)

Complete gastrointestinal tracts from 257 ringed seals (Pusa hispida) from Svalbard, Norway, were examined for helminth parasites. Three different helminth groups were recorded (acanthocephalans 61.1%; nematodes 38%; cestodes 0.9%). Acanthocephalans (Polymorphidae) and cestodes (Anophryocephalus and Diphyllobothrium sp(p)., as well as unidentified species, were confined to the intestines. The anisakid nematodes Phocascaris phocae, Pseudoterranova sp(p)., Anisakis sp(p)., and Phocascaris/Contracaecum sp(p). were recorded in both stomachs and the anterior part of the small intestines. The abundance of nematodes and acanthocephalans varied significantly with sampling location of the seal hosts. This is likely due to the relative prevalence of Arctic versus Atlantic water in the different fjord systems, which strongly influences the age class and species of fish available as prey for the seals. Adult male ringed seals had significantly higher abundances of nematodes than did adult females or juveniles. Adult males also had significantly higher abundances of acanthocephalans than did adult females, but were not significantly different from juveniles in this regard. Nematode abundance increased significantly with age of male hosts, but this trend was lacking in female seals. Infection parameters appeared to be related to differences in the age of polar cod (Boreogadus saida) exploited by male, female, and juvenile seals.

对来自挪威斯瓦尔巴群岛的257只环斑海豹（Pusa hispida）的完整胃肠道开展了寄生蠕虫检测。本次研究共记录到三类寄生蠕虫：棘头动物（acanthocephalans）占比61.1%，线虫（nematodes）占比38%，绦虫（cestodes）占比0.9%。其中，Polymorphidae科棘头动物以及Anophryocephalus属、Diphyllobothrium sp(p).及未定种绦虫仅寄生于肠道内。异尖科线虫包括Phocascaris phocae、Pseudoterranova sp(p).、Anisakis sp(p).以及Phocascaris/Contracaecum sp(p).，均寄生于胃与小肠前段。线虫与棘头动物的感染丰度随宿主海豹的采样地点存在显著差异，该现象可能与不同峡湾系统中北极水与大西洋水的相对占比有关——该因素会显著影响海豹可捕食鱼类的年龄组与物种组成。成年雄性环斑海豹的线虫感染丰度显著高于成年雌性与亚成体海豹；其棘头动物感染丰度也显著高于成年雌性，但与亚成体海豹无显著差异。雄性宿主的线虫感染丰度随年龄增长显著升高，而雌性海豹未呈现该趋势。感染参数似乎与不同性别及年龄组海豹所捕食的极地鳕（Boreogadus saida）的年龄差异存在关联。