cruising reds

Took advantage of my day off and tried a new spot today. I was rewarded by finding three schools of reds, 15-20 fish in each, ranging 24-30 inches. I managed three on a grub and then followed the schools around after that to see what they would do. One of the schools stayed around some oyster rakes. The other two cruised up and down the grass line at the top of a small mud flat at the mid to high tide. They were clumped together as thick as mullet and paced back and forth along a roughly 60ft length of bank. Never saw them feed. Never stopped and milled around. Just back and forth, pretty fast, too. I don’t think they were spooked cause I crept up on them pretty slow and staked off at a distance. Any idea what they were doing? How do you target these? Are they waiting for something? I tried several different grubs and even threw a fly or two, all of which they ignored.