Now to walking you through what succeeding at a 2-6 percent SAR rate would mean for one population of fish, the South Fork of the Salmon natural origin Chinook.
I want to stress again that these exercises are not science, I will try to go through them with the best information I have available to me, but this is not scientific. I started out my college career majoring as a fisheries biologist. That didn't last long. I changed to journalism which I knew would allow me to experience fisheries biology throughout my career as an observer, which meant I could go where I wanted to go and observe the parts that interested me and I have done that in Kentucky, Missouri and Idaho. When I was out of journalism for about six years and in PR, I started a chapter of Trout Unlimited to keep observing and also to help improve habitat in various hands-on projects. This exercise will not be scientific.
Enough of the preamble, there are going to be important factors that I will be able to bring into this exercise. We know the range of returning natural origin Chinook to the SF Salmon River between 1982-2009, which is 100-2380 fish. Sex ratios over the span are still a number that eludes me, but I do have year specific sex ratios and year specific natural origin Chinook returns and I have some fecundity data (this is the part where this is less scientific) because the fecundity data is hatchery fish from the McCall Fish Hatchery and I'm going to throw it out for the easier number of 5,000 (so if the model breaks down, it is here). I don't know if our McCall Hatchery salmon that return to the same river have a higher number of eggs than the naturals do. I am sure there is some difference between the two, but I am not sure that it makes a huge difference as I am going to use 5,000 for simplicity sake. I do know that McCall Hatchery smolts when released are some two and a half times bigger than the same age natural origin smolts, but the naturals obviously catch up by the time they return. Sorry, for rambling.
This exercise will take the number of female natural origin Chinook from a given year, assume a fecundity of 5,000 eggs and in the SFSR it's normally something like 4,300-4,800 and in some other rivers in Idaho I have seen it as low as 2,300, assume that of those 5,000 fertilized eggs that 8 percent survive to the smolt stage and then extrapolate the smolt to adult return (SAR) numbers if we were somehow able to achieve a 2-6 percent SAR.
And before we start, we haven't done that. The McCall Fish Hatchery was over the 2 percent bar in one year, the magical year of 2001 (which was a year that I personally believe breathed life back into the four lower Snake River dams as the returns from that one year dwarfed everything before and since in the lower Snake dam age 1975-present). This SAR number is the calculation of how many of the smolts who at the time they leave for sea return to spawn in one, two or three years as an adult. That's the real number that matters in recovery, not just some smolt to adult number that would only track the number to the sea. Returns are what matters.
OK, in 2006 the SF Salmon River had 92 natural origin female Chinook return and 170 natural origin males return or 65 percent of the run that year was male and 35 percent was female. The total run of natural origin fish that year was 262, not a great number, not a recovery goal for sure. On the hatchery side, the split was 54 percent male and 46 percent female. There are a myriad of factors that can influence these sex ratios, from there being just more of one sex dying at various places like dams, estuary, salmon shark's mouth, Orca's mouth and also how many are produced from the brood year. If you want to read something that will blow your mind and scare you a little bit and perhaps will be a future subject here read this (High Incidence of a Male-Specific Genetic Marker in Phenotypic Female Chinook Salmon from the Columbia River).
We have 92 females, and here is another part that will not be scientific as some of these 92 females that went sliding down the tube on the upstream side of the weir only to later die full of eggs they never released will not be subtracted from the total. So there are some prespawn mortality numbers I am not adding in here, as well.
From our 92 females we would get 460,000 eggs. From those, 8 percent we assume would survive to the smolt stage, or 36,800 smolts and now we will ignore all those downstream survival rates because this is a SAR exercise where we assume we are successful and have 2-6 percent SAR and from those 36,800 smolts we would get back 736 adult spawners at 2 percent and 2,208 adult spawners from the 6 percent rate. You can see that either the 2 percent of the 6 percent SAR rate increases the run and if thus maintained over eight successive brood years we would eventually have a self-sustaining population of natural origin fish in the river. Here we have increased the run from 262 fish to a range of 736-2,208.
An easier way to look at this is from one redd under the 2-6 SAR return rate you get back 8 adults at 2 percent and 24 adults at 6 percent if there are 5,000 fertilized eggs in that redd. Even if there are only 2,000 fertilized eggs in that redd you would get back 3.2 adults at 2 percent and 9.6 adults at 6 percent. That tells me if we could ever achieve a 2-6 percent range in SAR over a string of eight years that we would begin having some self-sustaining populations in the Snake River basin tributaries.
Another interesting exercise that I will not go into here is that from this ever-increasing expansion rate from a 2-6 percent SAR we would eventually get to a point where the returning fish would outnumber the habitat available for them in their natal stream and there would greater expansion of the range to other suitable habitats in connected streams on the good side of this possibility and likely higher prespawn mortality rates or at least an ever-increasing number of fish that died before they spawned in the river. You can do this on your own at home by taking the 736-2,208 fish, use a similar sex ratio, and extrapolate the next generation and it will increase and then do it again. Eventually, we would get to a very large population of returning fish. This would be a shot in the arm to commercial fishing industry as well as the sport fishing industry. More importantly, it would be a huge shot in the arm to the stream's other fish and organisms that rely on the nutrients dead and decaying salmon provide to a stream and to the surrounding forest as well as bears and wolves and other mammals that eat salmon would transport those Pacific Ocean nutrients higher up the watershed and back into the flora and fauna.
There is one thing we can do that would greatly increase the survival of smolts to the sea and that is remove the four lower Snake River dams. The habitat for these fish is plentiful in Idaho's streams like the SF Salmon River and the Middle Fork Salmon River and Secesh River, Big Creek, and various other absolutely fantastic streams. It's the route they take to the sea that is unnatural and thus what has to change if we are ever to achieve these rates that would allow these fish to recover themselves.