Fall vs Spring Steelhead on the Huron

I am not understanding why fishable numbers of steelhead (few and limited locations) end up over the ladder in the springtime, yet no information is found anywhere of them passing the ladder in the fall. The Grand gets fall steelhead all the way to Lansing, so what gives on the Huron? Has anyone ever targeted fall run fish above Flat Rock? I remember reading net statistics from when the ladder was first installed. I do recall fish DID pass then. Perhaps not having boat access in this stretch...

Fall vs Spring Steelhead on the Huron

Fall vs Spring Steelhead on the Huron