The problem is your thermocline has setup at an unlucky depth. Wait until it changes and then go fishing again. ?
In the meantime, keep thinking it out. You see the thermocline on your depth finder. What about fish? In addition to what scaleface said, look for depth changes, small subtle ditches, channel swings, docks, brushpiles, etc. Also, depending on the forage, the fish could be positioned at less than 13 feet but out over deeper water than that chasing food. Keep trying different lures as well.