Fair enough, I asked about 'the science' because you said you listened to it; but I don't understand which aspects of science you're listening to.
Let me explain what I understand of 'the science', why I am certain 100% C&R makes no difference and why I think all C&R is probably a waste of time.
Anglers catch only a proportion of the fish running the river, let's say it's 20%; that's probably a bit high in most cases, and a bit low in some cases.
Let's assume here there are no C&R laws, as you say, most anglers now put back all the fish they catch, but for the sake of argument we'll assume the release rate is only 60%
That would give us 40% of 20% of fish being chapped - or 8% of the total run.
In very basic terms, for C&R to work; there has to be a direct
relationship between the number of eggs laid down (i.e. number of spawners) and the number of Smolts that are generated 2 or 3 years later.
This means that for X breeders you get Y Smolts. However, this is not what happens in the real world. The biological facts ('the science') tell us that the relationship between the number of eggs laid down and the number of Smolts is not straight, it's a curve. The curve looks like the one below, which shows the results of trapping and counting on the Girnock Burn on Deeside for a period between about 1972 and 2008.
View attachment 91442
Form and uncertainty in stock-recruitment relations: observations and implications for Atlantic salmon management
Each small circle shows upstream Spawner count vs the Smolt count for the corresponding year. There are lots of nuances to this, but in broad terms what this shows is that if you remove 8% of spawners it really makes little or no difference until you get down to numbers that are less than 30% of the maximum observed runs. Even then, you can double the number of of breeders and get less Smolts out, or you can keep the number of breeders the same and somehow get 3 times as many Smolts. You can get more Smolts out with 50 breeders than you do with over 100. .
This shows that survival from Fry to Smolt is density dependent
and not egg-dependent except at very low stock levels.
Remember, the Smolt is key. These wee fish are the product of the river and once they leave on their great migration, the river has done it's job. All being equal, relatively more smolts out = relatively more adults back.
Therefore, if taking away 8% of breeders makes no difference, what difference would taking 5% or 2% make? Almost certainly no difference
But what about more real life examples?
We can take a look at the North Esk. Until a couple of years ago, the nets took up to 3000 fish out of the river every year, add on the angler take and the ratio of fish killed to fish surviving had to be the highest in Scotland, especially from the year 2000 onwards. Based on the counter figures, typically somewhere around 20-35% of the total run were chapped in one way or another*. Yet stocks remained stable and varied broadly in line with other Scottish rivers. I know the nets were low down the river and probably took fish from other rivers taking a wee nosey in the Esk, but if anglers killing fish could make a difference to stocks, then how on earth could numbers have remained healthy?
I didn't ask about what you see on the river, because I don't think that what you see is any evidence for C&R 'working', in any way.
We could wrap ourselves round the axle for the next 30 pages, but I'm not sure that would be a good use of anyone's time. Make of that what you will and have a good season.
* I might have these numbers wrong, but I'm confident that the general gist is correct