I’ve never fished for sea-runs in that area and I know they can be very different from one area to another but my experience has been that the fly is the least important factor. You said you knew there were fish around but that’s still where I’d start. Sea-runs are very curious, they will follow most anything so you should be seeing them behind your fly even if your not getting hits. If you see them following then adjust your retrieve till they bite, I like to start fast and will slow down if I have to, they also like an erratic retrieve rather than a steady retrieve. Still no bites but seeing fish follow, then change flies and start over experimenting with your retrieve. They travel in schools so either they are around or there not, but if you aren't seeing them behind your fly I’d be looking down the beach or waiting for the tide to change. Hope that helps