http://www.fishbase.org/Summary/Species ... php?id=258
I think we can assume from this reasonably reliable source that the pike is indeed a freshwater fish with certain strains (i.e. Baltic) able to tolerate brackish waters, i.e. estuaries. I'd imagine that if fjords had a good sized river entering them, the water might be sufficiently diluted to a point where pike might be able to hack it for a time.Occurs in clear vegetated lakes, quiet pools and backwaters of creeks and small to large rivers (Ref. 5723). Usually solitary and highly territorial. Enters brackish water in the Baltic.
As regards Lumpy's source
Err, did it mention if they caught any?Saltwater Flyfishing: Britain and Northern Europe. in it its says that they regurally fish for pike in the fjords in Norway.