Population dynamics of sealworm, Pseudoterranova decipienssensu lato, in sculpins, Myoxocephalus scorpius, from two areas in Norway between 1990 and 1996

The abundance of sealworms (Pseudoterranova decipienss.l.) in sculpins (Myoxocephalus scorpius) was studied at Torbjørnskjaer, southeast Norway, and Vega, northern Norway, in samples from 1990 to 1996. The harbour seal ( Phoca vitulina) population at Torbjørnskjaer declined by 70% during the phocine distemper virus epizootic in 1988, and has increased during the 1990s. The abundance of sealworms in sculpins was relatively stable from 1992 to 1996 and any effect of the reduction in the number of harbour seals on the abundance of sealworms has been short-term. When correcting for size differences, young sculpins (2-4 years) from Torbjørnskjaer had higher abundances than those from Vega, while in old sculpins (5-7 years) the abundances seemed similar and stabilised. This happened at a younger age among the more heavily infected sculpins at Torbjørnskjaer than at Vega, and we interpret this as density dependence in the fish host.