...With the seymour... It seems to be getting better habitat and food wise, but you still need the stock to seed the river, and as that has been so low over the years there's only so much the fish can catch up...
Habitat restoration and nutrient enrichment IS
improving freshwater conditions, without a doubt. Steelhead have the intrinsic ability to increase fecundity when numbers are low and the habitat is available. "Seeding" the river will not ensure improved quantities and especially not stock quality.
Well Ribolovac, it seems this is an impossible question to answer with just one point or a clear definition of one or even several reasons for low returns. There were many contributors to the decline, and just as many, if not more impeding their rehabilitation. There are some good points here made by several, but I'd like to reiterate one or two as they are likely the biggest players here.
Harps, if you realize I used the term "seed" loosely, you will understand I am referring to that stocks ability to replenish itself and increase the population size on its own, not some typical plea to have our hatcheries try and do it for them.
Regardless of which method were employed, I still don't feel those fish will ever "catch up", ie: ever getting close to numbers we could be happy with, or near maximum yield for the system.
Your point about poor ocean survival, is a very pertinent one in this regard.
Despite the expected higher "realized fecundity" that should
occur with habitat and nutrient improvements, that ocean mortality still limits the number of viable offspring returning to get the job done. I am sure that as someone who sounds like he has some population ecology background, you will concede that an increase in fecundity is not intrinsic to just steelhead. Most populations, regardless of species, be they fish, bird, insect or any other, will show an increased fecundity once factors like competition, habitat, predation, food sources, etc are improved in their favor. It's pretty much intrinsic for almost every population you could study on the planet, but we're talking about steelhead, and they fit within one of the many broad exceptions to simple models for population growth ...
Many migratory species populations don't follow these models closely at all, salmon and steelhead being no exception. Thus despite much of the good work that has been done to restore habitat, and increase nutrient content on rivers like the Seymour and others, population sizes remain low with seemingly no improvment.
It's that can of worms, "ocean mortality". So many contributing factors with many seemingly beyond our immediate control, and then there's the ones we haven't even noticed yet. It's an even more complex question than just the freshwater side of the steelhead lifecycle.
So Ribolovac, although it seems perfectly reasonable to expect some of these nice little rivers of ours should have more fish, even if those in charge take proper care of them, it doesn't mean we are going to see any obvious results. What Harps mentioned about ocean survival is probably one of the most important factors to look at. So you look at each individual river, and take care of the freshwater side of things, and likely there's still no obvious change in population sizes, what then? Well, steelhead spend a majority of their life cycle in the ocean.
Try and put a few fingers on the many reasons they don't make it back from there and then you're getting somewhere...
If some breakthroughs regarding our impacts on the saltwater portion of the steelhead lifecycle were achieved, than I might be optimistic about some of our stocks. In my opinion, we certainly won't see any significant mean increase in population sizes in our lifetime, and unfortunately not likely ever, and I am an optimist.