My retrievers could give a rats a** about gophers, rock chucks, rabbits, etc.
More often than not, the decline in these rodents is in the form of disease, NOT predidation by hunting dogs.
I wonder at times where some of the state biologists studyed. When asked this question they often reply with the lame answer, "and where did your degree in wildlife management come from? Answer, the U. of common sense.