All of the numbers I made up for the River Zip were hypothetical, but were meant to be representative of an ailing chinook run much like the one being discussed in this thread.

I chose 500 fish because that sounds pretty depressed, but yet still enough of a critical mass that some potential recovery is still possible. Reasonable?

I chose a recruit ratio of 0.8 for wild spawning because we are talking about habitat that is so unproductive that it does not even allow what few returning spawners left to even replace themselves in the next generation. That means a number less than one. I did not want to choose a number less than 0.5 or else folks would accuse me of being far too pessimistic. Halfway between 0.5 and 1.0 is 0.75, but I wanted to be just a wee bit more optimistic than middle of the road, so I chose 0.8. Still reasonable?

I gave the rationale for the recruit ratio of 0.68 for hatchery-born spawners... they spawn with less success than wild-born fish. The Hood River project shows that naturally spawning (one-generation-from-wild) hatchery steelhead show only 85% of the reproductive fitness as their wild-born siblings. No data like that is available for salmon, but it seemed reasonable to apply that same percentage of reduced productivity... 0.85 x 0.8 = 0.68. Are you still with me?

I chose 100 fish (50 pairs) for the hatchery broodstock because that's sort of a minimum critical mass to make a hatchery project worthwhile... it would yield about 175,000 eggs (3500 per female). Moreover, I did not think it wise to risk more than 20% of the available wild run to a potential hatchery SNAFU. Sound reasonable?

I assigned the hatchery project a recruit ratio of 2:1 in the first scenario, and then for kicks, a ratio of 3:1 in the second scenario. I thought I was being pretty damned generous. To give you an idea of chinook recruit ratios in a healthy drainage with near-pristine habitat and no directed commercial harvest, recruit ratios for Alaska's early run Kenai kings have ranged from 0.53 to 3.89. For the past 21 years, escapements have averaged 11.4K while returns have averaged 15.9K.... that's a recruit ratio of 1.39.

I gave the returning progeny of hatchery-born parents the benefit of the doubt by assigning them with reproductive fitness equal to wild. In essence, I conveniently erased any negative hatchery-induced effects in the second generation. The recruit ratio of 0.68 was applied only to the fresh crop of hatchery-raised spawners... 200 fish each generation in the first scenario and 300 fish each in the second scenario. All of the naturally-produced spawners were assigned a recruit ratio of 0.8 even though a significant number of them had hatchery-raised parents. Still with me?

So in each of the scenarios I painted, the return from each generation was the total of three components:

1) Hatchery production resulting from 100 wild brood fish. The hatchery production was always constant, either 200 or 300.

2) Production from hatchery-born spawners. This was also constant, either 136 (200 x 0.68) or 204 (300 x 0.68).

3) Production from wild-born spawners. This figure would change with each generation depending on the number of naturally-produced spawners available.

In the first scenario, the combined production from all three components promptly resulted in a net loss that got progressively smaller with each passing generation until hitting a near-steady state at a total return of 485 fish after 10 generations. At that point the run was effectively losing a fish per generation.

In the second scenario, the result was a net gain that got progressively smaller with each passing generation until hitting a near-steady state at a total return of 915 fish in the 20th generation. At that point the run was only gaining one fish per generation.