I think its a good point, no doubt a good population of cod would control the carp, and take out more juvenile carp, hence shutting down the breeding. Perhaps the carp got greater headway as cod were fished to almost minimums in some areas.
I remember catching my first carp in the Condamine, in the late 80.s. I actually sat on the bank and cried! I know it was over, something had changed for ever, and we can only hope that the native fish will eventually prevail against carp.
I lived in europe for 8 years, and funnily over there they are treasured, highly sought and a readily eaten!
Bring on the Cod! Breed up boys!
Flatzie