Yes, these are different cod stocks. There is, as far as I know, no intermixture between the Icelandic areas and the Norwegian and Russian areas in the eastern part of the North Atlantic.
The northeast Arctic cod between Norway and Russia do not migrate outside Norwegian and Russian waters, except for a small area in the Barents Sea in international waters. Over the years, we have had some problems with third countries fishing outside the quotas in that international area in the loophole, as it's called. I am looking at my Icelandic friends who have a bit of history there.
Today Norway and Russia have bilateral agreements with our neighbours in the North Atlantic and eastern Atlantic so that there is no fishing outside the fixed total quota by countries in the northeast Atlantic. Now and then we have vessels from other third countries in the loophole area in the Barents Sea, but it's not a problem anymore. There are very few; it happens once in a while but not more than that.