not totally true
for a very short time they are protecting there young and if you take them off their bed the young will be part if the food chain
but for the rest of the out of season time the fish are in great shape and catching them doesn't hurt them....but still illegal in many places in Ontario...
so for 2 weeks of the 5 month period your statement is correct, the 4 month and 2 weeks you are not correct
and some will argue that the sunfish and others that want to eat the young of the year will consume the same amount, one here and one there till they are full or all in the nest if unguarded, but at the end of the day the numbers are about the same, and this is one of the reasons fishing during spawning doesn't hurt them in many States...