In his book "Lifeline of the Confederacy: Blockade Running During the Civil War" Stephen Wise shows that it wasn't the blockade that halted the flow of supplies to the confederacy, it was the loss of ports to the advancing Union armies.
Interesting point. Fort Pulaski (Savannah) was taken by Union forces. The forts at the mouth and along the Mississippi were taken. The fort or forts of Port Royal Roads (SC) were taken. Galveston was taken for a short while, then the Federals and their six-ship fleet were thrown out by a couple of Texas ships stacked with cotton bales on their decks to block the Federal sharpshooters. Brazos Santiago was taken at the mouth of the Rio Grande. I think Fort Marion in San Augustine, Florida, must have been taken. I don't know about Fort Morgan at Mobile.