Remember that with steelhead they are just part of the O. mykiss complex. When I was growing up they were considered separate subspecies in that steelhead were a separate genetic group that went to sea.

Recent work shows that to be wrong. A steelhead is a rainbow that goes to sea and a resident is a steelhead that stays home. Apparently, the juveniles respond to cues in freshwater such as flows, temperature, productivity (available food) to decide which switch to flip.

Further, there are indications that on streams with dams, where minimum spawning flows are set for the fall that the increased cool water flows help the salmon spawn and the mykiss decide to be resident.

Further, lots of bad stuff seems to be occurring in PS and the ocean. For decades, rearing and older smolts that left from out of the Narrows had sucky survival. Marine survivals overall seem way dawn.

As every teenaged male knows, the primary purpose in life is to reproduce. Same with fish. If going to the ocean is a poor decision (survival-wise) those that stay will be more successful.

There are a lot of things holding down the number of steelhead; some we can fix (like delivery of MDNs and flow regimes) and some are much harder (AK hatcheries and climate change).