A POPULATION STUDY OF COD, GADUS-MORHUA L., IN NORTHERN NORWAY USING OTOLITH STRUCTURE AND PARASITE TAGS

A total of 502 cod, Gadus morhua L., was taken during spring and autum n sampling from three different localities in northern Norway: the Bar ents Sea, a silled fjord (Balsfjord) and an open fjord (Malangen). Eac h cod was allocated, according to its otolith structure, to one of two types, coastal or Arcto-Norwegian, and was then examined for infectio ns of four species of parasite: the myxosporeans Myxidium ouiforme and Zschokkella hildae, the digenean Hemiurus levinseni, and the copepod Lernaeocera branchialis. Both types of cod were present at each locali ty, with coastal cod dominating in the fjords in both seasons and in t he Barents Sea in spring, but with Arcto-Norwegian cod dominating in t he Barents Sea in autumn. Differences in the proportions of the two ty pes of cod and in parasite prevalences between seasons and localities were interpreted as indicating a migration of coastal cod from the Bar ents Sea sampling area into the fjords between March and October. We f ound no evidence that Arcto-Norwegian cod from the Barents Sea migrate into the fjords, but our results suggest that the fjords contain loca l resident populations of Arcto-Norwegian cod. It is concluded that lo cal parasite faunas are not greatly influenced by genetic differences between the two types of cod, but that their compositions are determin ed largely by variations in the abundance of intermediate hosts. (C) 1 997 Elsevier Science B.V.