We are completing a national survey of feral rainbow trout populations in
Norway and are attempting to assess the potential for further establishment
and the dangers rainbow pose to native aquatic communities. While intensive
farming in sea pens has and continues to result in significant escapes and
numerous purposeful introductions have occurred throughout Norway, few (less
than 10) self-sustaining populations of rainbow trout have established. We
are attempting to understand why this is so. Any ideas/thoughts on this
would be of help.
 
We do know that the migratory abilities of rainbow are not responsible for
this lack of establishment. Furthermore, we know that they will spawn
successfully within Norwegain rivers. However, we almost never observe
smolts nor returning adults. There is no evidence of resident feral
populations becoming established in such rivers, the only instances of feral
populations are in landlocked lakes. The rainbow originate from a
freshwater-resident population imported from Denmark around 1902 and have
thus been captively bred for many generations.
 
Input would be appreciated, thank you.
 
Ian Fleming
 
Norwegian Institute for Nature Research
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