Stobo W.T., L.P. Fanning, B. Beck & G.M. Fowler. 2002. Abundance and maturity of three species of parasitic anisakine nematodes (Pseudoterranova decipiens, Contracaecum osculatum, Anisakis simplex) occurring in Sable Island harbour seals (Phoca vitulina). Canadian Journal of Zoology 80: 442-449.

Summary:  Stobo et al. found three species of anisakine nematodes (roundworms) co-occurring in the stomachs of harbour seals Phoca vitulina at Sable Island. The sealworm Pseudoterranova decipiens, was the most common. Anisakis simplex was found, but in much lower numbers, and none were mature, indicating that the harbour seal is not a true final host to this parasite. The third species, Contracaecum osculatum, was rare but half of worms found were mature. Abundance of P. decipiens increased with size of the seal. There was an inverse relationship between P. decipiens abundance and the age of seals of similar size, perhaps due to changes in diet. Numbers of P. decipiens may have declined over the summer, coincident with an increase in the proportion of mature worms in the seals’ stomachs. Similarities between the worm infections of grey seals Halichoerus grypus and harbour seals, suggested that A. simplex abundance may also undergo a decline in abundance. C. osculatum was only encountered during the latter half of the year. Stobo et al. estimated that the abundance of sealworm in harbour seals is roughly 2.5% of the burden carried by the grey seal population, and noted that harbour seals may represent an insignificant vector of the sealworm infecting commercial fish species in the Northwest Atlantic, provided density-dependent relationships exist between worm abundances in various host species.