Back in the late 70s we had a few sturgeon come up the two creeks I was working on. Thought was that they were following the summer chum for eggs and carcasses. A couple years after I left there were more than 200 that came up one creek a bit, apparently to feed. These guys may be coming up, following the spawners (or hoping there will be some) and this may be a response to the fresh/salt change. I would guess, that if it is a response to that interface, that low flows may make for a very small mixing zone.