mathgeek has given all this info and fully explained it several times over in several threads (and sometimes in very scientific detail).
lower limits reduce the overall size of the fish because there are more fish consuming the finite amount of forage food sources. everywhere limits are lowered the numbers of fish increase and the size decreases accordingly.
the only exceptions to these "rules" is where the forage food sources are so plentiful as to fully absorb a doubling or tripling of fish populations feeding on them.
ask mathgeek if you need to know more about it