Abstract
The early life cycle of sealworm in Icelandic waters is not known. Various fish serve as transport hosts but benthic coastal fish, especially bull rout (Myoxocephalus scorpius), probably have a major role in transmission of larvae to the final hosts, seals. Grey seals (Halichoerus grypus) are more heavily infected with sealworm than common seals (Phoca vitulina) and the grey seal population, estimated at 6,000, probably plays a larger role in the dynamics of the worm than the estimated 15,000 common seals. Other seals seem to play a small or insignificant role in sealworm dynamics in the area. Sealworm abundances in fish and final hosts are higher off the west coast than in other areas in Iceland. A combination of shallow, temperate waters, large numbers of small islands inhabited by numerous seals and grey seals’ consumption of heavily infected bull rout during the breeding season in autumn are important factors responsible for maintaining an abundance of sealworm in this area. Future research on sealworm in Iceland should focus on long term monitoring of worm abundance in all potential hosts in order to observe, interpret and predict possible changes, the dynamics of infections in fish frequently consumed by seals and on seasonal and spatial variations in worm fecundity.
Highlights
Sealworm (Pseudoterranova decipiens) is abundant in commercial fish species in Icelandic waters and the fishing industry spends considerable time and effort searching for and removing larvae from the fillets
Sealworm were found in 3 of 16 harp and 2 of 7 hooded seals examined (Hauksson MS 1996). It is not known which invertebrates serve as intermediate hosts for sealworm in Icelandic waters
Large piscivorous fish are often heavily infected with sealworm, but fish of this size are seldom consumed by seals and are not likely to play an essential role in the life cycle of the worm
Summary
Sealworm (Pseudoterranova decipiens) is abundant in commercial fish species in Icelandic waters and the fishing industry spends considerable time and effort searching for and removing larvae from the fillets. Genetic studies on sealworms from the north Atlantic have shown that sealworms in Icelandic common and grey seals consist of two morphologically similar but reproductively isolated species, P. decipiens krabbei and P. decipiens (sensu stricto) (Paggi et al 2000) This has, not been taken into consideration in other studies on sealworm in Icelandic waters. Comparisons of cod from Icelandic waters and those from Greenland (Platt, 1975, 1976), northern Norway (Kahl 1939, Platt 1976), the Norwegian coast, North Sea and the Baltic (Kahl 1939) have shown that sealworm was most abundant in Icelandic fish. Worm abundance in cod varies within Icelandic waters being highest off the west coast (Pálsson MS 1975, Platt 1975, Hauksson 1984, 1992a). Between 1992 and 1996 numbers of common seals fell from 1200 to 600, and grey seals, from 140 to 10 (Hauksson, pers. comm.)
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