Mass occurrence of the physonect siphonophoreApolemia uvaria(Lesueur) in Norwegian waters

Abstract

Abstract At the end of November 1997 salmon farmers in Hordaland County on the coast of western Norway reported mass occurrence of an unknown animal that caused severe lesions and death of fishes. The organism was identified as the physonect siphonophore Apolemia uvaria. A survey of reported sightings (Fig. 1) shows that the species ranged from Gullmarsfjorden on the Swedish west coast to Finnmark in northern Norway. The first known observation from Scandinavia was from Kosterfjorden in western Sweden in early November. After news about death of farmed salmon was first made public by radio, television and newspapers in the last part of November, additional reports arrived almost concomitantly from sites all along the coast (see reports in Havbruksrevyen, internet: http:// www.intrafish.no). Based on problems reported by salmon farmers it seemed that the abundance of siphonophores along the mid-Norway coast decreased after mid December (Karl Tangen, pers. commn). In mid December we made a field survey from...