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What does the science say?
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Read comments in the thread……I said where the info came from. Why not ask what I see at work on the river? Someone earlier said they can’t see the the benefit of C&R because stocks and catches seem to be depleting despite it. I replied saying C&R can’t be blamed as not working due to all the other influencing factors increasing and listed them. His reply was to take the piss and offer no more argument. So, seals numbers through the roof, cormorants and goosander in huge numbers eating juvenile salmon, yet C&R is the one thing that’s claimed to not work???? 😂😂😂😂 here’s a wee bit science though, one cormorant over its 25 year average lifespan is thought to eat around 1lb (average) of fish per day, that’s over 9000lbs of fish. One bird! I’ve put over 50 off one pool on the Tweed. A smolt weighs between 0.5oz and 2.5oz. So between roughly 6 and 30 per pound. so those 50 birds I saw that day if they stayed on that one pool feeding will take 50lbs of fish, potentially between 150 and 1500 smolts. In a day. Now, I know as has the recent Tweed autopsy survey of these birds shown, they don’t just eat smolts and juvenile salmon. They had eels, brown trout, minnows in their stomachs too, hence I said potentially. But, that’s a reference to just 50 cormorants, there’s hundreds on the Tweed. Add the goosander to the mix and seals on the coast. Can you even begin to imagine the predation salmon experience? Yet, C&R is said to not show any benefit😂😂😂……..how can it possibly in amongst all that? That doesn’t mean we should not be seen to do our bit. As I said earlier, it’s the springer that needs to be protected for the benefits of dispersal the farthest through the river system.…(all I’ve said here can be sourced on a Google search)
What happens if the redd made by a pair of salmon, one or both which were released, gets washed out and all eggs are killed, meaning none hatch?
How has that “assisted with stocks”?
There are likely scores of other scenarios with differently likelihoods of happening which could result in no offspring surviving to adulthood from a released fish which goes on to spawn.
Spawning itself is not necessarily synonymous with assisting with stocks.
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If yer aunty had baws she’d be yer uncle…….seriously?
But she doesn’t, so yep, seriously. 🙂
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Well, here we’re back to the importance of distribution because it would be unusual if not impossible for EVERY redd to be washed out one season, especially in the upper reaches……where it’s more likely springers will reach. Despite what some on here have suggested. Distribution (including the early caught springers) of fish returned that continue to migrate through the upper reaches help to mitigate those risks. But hey, each to their own thoughts….😉😏
You said re released fish “lf they spawn they’ve assisted with stocks.”
I simply gave an example of where that would not be the case. I am sure there are many more.
That’s all, nothing about every redd getting washed out and certainly nothing about distribution.
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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.
Form and uncertainty in stock-recruitment relations: observations and implications for Atlantic salmon management Gurney, 2009
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
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Just glanced over your reply but I’ll read that properly later as heading out for a cast and pass it on to my freshwater fisheries scientist friend for a reply. 👍But in meantime, think about it this way. If you return two salmon and they spawn and two of their offspring return who in turn spawn, that’s helping to sustain stocks. The fact C&R standing alone can’t be shown to make an increase in returning numbers doesn’t mean we shouldn’t be doing it. All the other INCREASING pressure on the fish as I listed is continuing to erode the numbers. But, applying the argument of some suggests we just shouldn’t bother? If we argue nets should be removed we also MUST offer our own efforts up to assist, so we return fish…..I did say we need to be seen to do our bit too. The recent smolt counts on the Tweed show they are at healthy to very healthy densities. Why aren’t we seeing them return as salmon in the numbers we used to? What’s preventing that? Is returning caught springers helping to ensure the smolt numbers in the tributaries are high not assisting? Of course it is, what happens thereafter…..
Wanted to stay out of this but could not resist
One of the main reasons why spring fish are valued so much is that in times of plenty rivers with a spring run attracted anglers from all over came to fish in Scotland because most rivers in northern Europe were still closed or iced over so it was a welcome income for fisheries and the areas where they were located, so with the fall in spring fish the income has also fell.
I find it incredible to suggest that after 1000s of years of evolution that 8 out of 10 Salmon can still not reproduce successfully, I would have thought at that rate it would be a recipe for extinction (maybe it is and that is what we are seeing).
The only reason for Salmon returning to the rivers is to spawn, some might not as seen in rawners caught but they are very few compared to kelts, some might pick a better location than others. Salmon spawn in the Winter when there is more chance of floods their eggs hatch in spring when there is more water due to snow melt but they have survived since the last ice age, even storm Frank at the end of 2015 and the beginning of 2016 had less impact on fry and parr numbers than you would have thought, A lot of people think that high water washes out redds it probably does but if the gravel at a redd is displaced the gravel above a redd would replace it as it would also be moving downstream.
Orbit suggested that if a redd made by a released Salmon was washed out all the eggs would be killed and none would hatch TRUE?
Lets say there were two redds one made by a fish that was not caught and it got washed out eggs killed none hatch, and the other was made by a fish that was caught and released and the redd with its eggs survived and went on to hatch ???
GKs graph and explanation does not tell the whole story
Even with C&R being in place on the Dee for many years numbers of Salmon returning to many of the tributaries are still declining including the Girnock burn.
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Only three females made it back to spawn despite C&R, instead of the 49 it is thought to be required to fully stock the burn with offspring, so if there was no c&r and one of those three fish was caught and killed on the main river it would not make a difference? of course it would, and there are many spawning burns and streams across the country that are in the same situation with little or no spawning stock left to repopulate them, and then couple it with the suggestion that 8 out of 10 are unsuccessful then Salmon are in big trouble. If there were 49+ females spawning in the burn then taking any surplus would not make a difference, but there were just THREE.
As the number of adults decline so does the amount of smolts and Autumn parr all be it at a slower rate with a two year lag.
As Jamross65 says C&R is not the cause of the decline in Salmon and it does not look like C&R will increase stocks but might help slow the decline until something gets done about predation and other factores affecting Salmon.
Before the nets were taken off the North Esk it was also on the decline, which is one of the reasons the netsmen were willing to sell, since then there has been a bounce back in numbers at the logie counter which would have been expected with upto 5000 fish now not taken by the nets. This bounce back has happened on other rivers after nets have been removed but tends to fizzle out after a few years, hopefully the North Esk can carry on with the improving numbers and catches.
Someone asked Jamross65 where is the science for some of his opinions, sometimes you do not need science to see whats happening, just look a the rod catches which is all that most rivers can go by and there are not many rivers where you will find catches increasing over a 10 or 20 year average.
FMS reviews are good source of catches and 10 year averages.
One of the main reasons why spring fish are valued so much is that in times of plenty rivers with a spring run attracted anglers from all over came to fish in Scotland because most rivers in northern Europe were still closed or iced over so it was a welcome income for fisheries and the areas where they were located, so with the fall in spring fish the income has also fell.
I find it incredible to suggest that after 1000s of years of evolution that 8 out of 10 Salmon can still not reproduce successfully, I would have thought at that rate it would be a recipe for extinction (maybe it is and that is what we are seeing).
The only reason for Salmon returning to the rivers is to spawn, some might not as seen in rawners caught but they are very few compared to kelts, some might pick a better location than others. Salmon spawn in the Winter when there is more chance of floods their eggs hatch in spring when there is more water due to snow melt but they have survived since the last ice age, even storm Frank at the end of 2015 and the beginning of 2016 had less impact on fry and parr numbers than you would have thought, A lot of people think that high water washes out redds it probably does but if the gravel at a redd is displaced the gravel above a redd would replace it as it would also be moving downstream.
Orbit suggested that if a redd made by a released Salmon was washed out all the eggs would be killed and none would hatch TRUE?
Lets say there were two redds one made by a fish that was not caught and it got washed out eggs killed none hatch, and the other was made by a fish that was caught and released and the redd with its eggs survived and went on to hatch ???
GKs graph and explanation does not tell the whole story
Even with C&R being in place on the Dee for many years numbers of Salmon returning to many of the tributaries are still declining including the Girnock burn.
Only three females made it back to spawn despite C&R, instead of the 49 it is thought to be required to fully stock the burn with offspring, so if there was no c&r and one of those three fish was caught and killed on the main river it would not make a difference? of course it would, and there are many spawning burns and streams across the country that are in the same situation with little or no spawning stock left to repopulate them, and then couple it with the suggestion that 8 out of 10 are unsuccessful then Salmon are in big trouble. If there were 49+ females spawning in the burn then taking any surplus would not make a difference, but there were just THREE.
As the number of adults decline so does the amount of smolts and Autumn parr all be it at a slower rate with a two year lag.
As Jamross65 says C&R is not the cause of the decline in Salmon and it does not look like C&R will increase stocks but might help slow the decline until something gets done about predation and other factores affecting Salmon.
Before the nets were taken off the North Esk it was also on the decline, which is one of the reasons the netsmen were willing to sell, since then there has been a bounce back in numbers at the logie counter which would have been expected with upto 5000 fish now not taken by the nets. This bounce back has happened on other rivers after nets have been removed but tends to fizzle out after a few years, hopefully the North Esk can carry on with the improving numbers and catches.
Someone asked Jamross65 where is the science for some of his opinions, sometimes you do not need science to see whats happening, just look a the rod catches which is all that most rivers can go by and there are not many rivers where you will find catches increasing over a 10 or 20 year average.
FMS reviews are good source of catches and 10 year averages.
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It does for the Dee which isnt the same for most other rivers.
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I"m still struggling to fathom how someone can put a % on how many fish are caught from the total run of any given river .
An impossible feat especially with C&R in play, unless we have someone checking the mouth for hook holes on every salmon in the river come the season end ..even then they may have been caught more than once.
As much as C&R distorts all kinds of counts and statistics, it's here for a reason and here to stay.
An impossible feat especially with C&R in play, unless we have someone checking the mouth for hook holes on every salmon in the river come the season end ..even then they may have been caught more than once.
As much as C&R distorts all kinds of counts and statistics, it's here for a reason and here to stay.
If the Logie counter for example counts 10,000 fish and the rod catch is 1000 then it is as a rule of thumb 10% then there have been studies that show the recapture rate of released fish, and also on some smaller rivers there is a redd count in comparison to captures. not exact but without counters on every river its the best we've got.
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I asked Jamross what science he was referring to, because he said he ‘listened to the science’, that’s fair enough I think.
That graph isn’t mine, it comes from the report I linked which was written by some far more eminent folk than me.
The graph already takes account of the delayed Smolt runs. Each circle shows the number of breeding hens counted up and then the number of smolts counted down in 2 or 3 years time. They can work out how many smolts are 2 or 3 years old, because they count all of them on the way down and historically they ratio is something like 20:80 in favour of 3 year old smolts.
If you read what I have written on the thread you may notice that I said that there was no direct relationship except at very low levels. 3 fish up the Girnock is definitely very low levels. Now my gut feeling is that the numbers won’t be direct and taking one fish out of the 3 left probably wouldn’t make too much of a difference to Smolt numbers. However, that’s a big call so C&R might be a reasonable measure in this case. In fact if the story is that bad everywhere, then maybe consider closing parts of the fishery? The Dee is in deep trouble and needs all the help it can get.
Take a step back and look at the underlying message of the data, (the facts) and we can see how the Dee is an example of a stopped clock telling the right time twice a day.
All those years of returning fish appear pretty pointless, they haven’t resulted in any sustainable improvement in Girnock runs. Had folk maybe engaged with ‘the science’ they would have realised that their actions were pointless and looked elsewhere much earlier. Now there’s nae fush left in the Girnock, C&R seems like the only option short of closing the fishery……
For all those rivers that are not the Dee, 100% C&R is pointless and all C&R is unlikely to make a difference. Look at the figures from the Gala on Tweed.
The idea that 2 breeding fish make 2 returners is great, but that’s just not how it works. To understand this you do need to engage with and understand the facts, common sense doesn’t apply, unless you’re a fish of course.
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The statement made on this forum that an angler chapping a fish makes NO difference is just not true.
In any river where stocks are declining each and every fish is important not only for numbers but also for genetic diversity.
Salmon are under so much pressure that we can do little about that but by returning our fish it may make a difference.
I think there is a rule that any number below 50/50 in any species is classed as in danger of inbreeding and extinction, this may not apply on the main stem of a river but would on a spawning burn, and fish that are caught on the main river there is no way of knowing where they are going to spawn.
As it stands there are many spawning burns that are in danger of becoming devoid of salmon and if we add to the problem by killing them we are contributing to the problem.
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I know what you said and what you meant
The statement made on this forum that an angler chapping a fish makes NO difference is just not true.
In any river where stocks are declining each and every fish is important not only for numbers but also for genetic diversity.
Salmon are under so much pressure that we can do little about that but by returning our fish it may make a difference.
I think there is a rule that any number below 50/50 in any species is classed as in danger of inbreeding and extinction, this may not apply on the main stem of a river but would on a spawning burn, and fish that are caught on the main river there is no way of knowing where they are going to spawn.
As it stands there are many spawning burns that are in danger of becoming devoid of salmon and if we add to the problem by killing them we are contributing to the problem.
The Dee gets all the pelters and probably is a target as they were the first to go C&R.
The Dee has been fishing for 5 days and has 4 fish. The Tay has been open since the 15th of January and has less, far north rivers from the 11th and still blank.
The truth is all rivers are struggling and there's not many of us that can truthfully think their river is healthy.
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