My understanding is that the state uses redd counts to estimate run size. They take the redd count from the parents of this year's returning fish, and then take into consideration the conditions and events that may have influenced survival. Redd counts are done on foot, by boat, and by plane, depending on the stream. That's just what I've picked up from reading this, and other, internet boards. There are a few guys on this board who know a lot about fisheries management and can answer your questions in a lot more detail than I have. Maybe one of them will add something here.