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  1. #51

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    Quote Originally Posted by MCXFisher View Post
    About 3 years ago I met Salar35 on the Dee. He showed me some PowerPoint slide prints, one of which showed the return to natal stream rates. As far as I can recall they were something around or just over 30%, which led me to point out that this was far from indicative of certainty, least of all supportive of the notion that springers beget springers.
    Indeed it appears good evidence that springers do not in fact breed springers, assuming that the adults that spawn there are in fact springers! What that also suggests to me is that smolts out to adults back in those burns is a meaningless statistic. Adults in to smolts out is the important bit.

  2. #52
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    Spot on Loxie, smolt production appears to be where it's at.


    Back to the OP

    Quote Originally Posted by Walleye View Post
    This one has interested me for some years now and I think it has some relevance to the discussion on salmon stocks both at sea and in the river. It also occurs over roughly the same timeframe. Some of the available graphs are scarily similar to many I see about salmon stocks.
    Now I get it that this is a different fish in a different habitat but the lessons to be learned from the effects of exploitation and in this case the lessons to be learned about how a stock collapses and subsequently fails to recover together with the impact on communities are lessons we must learn from history before it is too late for the salmon.
    For a brief description of what happened check the following Wikipedia pages.

    Collapse of the Atlantic northwest cod fishery - Wikipedia

    Atlantic cod - Wikipedia

    Main points from my perspective....
    Removal of such a large biomass from a food chain can have massive effects on the food chain and the ability of the remaining stock to recover.
    Most thought the cod stocks in the North West would have recovered by now. Sadly, it is taking far longer than expected and some think the food chain has changed permanently and stocks may not recover.
    The fisheries were constantly mismanaged and scientists and politicians made many mistakes. Few listened to those fishermen who warned for years of impending disaster.
    In the end, the collapse benefited nobody.

    Another note relating to the theory that only a small number of returning adults are required to fill the river with parr. I don't believe this for one second. Returning adults in many rivers form a very large part of the foodchain in the river on which the parr are reliant. If fewer fish return each year, the river is able to sustain ever smaller populations of young fish with the available food resources in the river. The returning adult is not only important as a breeder and egg producer but is also necessary as a major part of the foodchain to sustain the following year's parr and smolts.
    Without this, the smolt holding capacity of the river must be affected by a reduction in returning adults.

    The main lesson here is that despite what we think we know, we don't know enough to protect the salmon from Human impact. So a risk averse policy set in this context may well be the best way forward.
    I've been thinking more and more about this OP and some of the issues it raises a bit more thoroughly than when posted, especially in light of the recent thread about the degradation of the Baltic (Sweden in this case) rivers by hydropower, daming and pollution: published data indicate the rivers produce 5% of the smolts they used to 90 years ago, before they were so impacted.

    It seems more apposite given the natural preponderance of salmon anglers to look for bogeymen outwith their environment than those within - the mythical trawlers hoovering up all the smolts, or the vagiaries of Atlantic oscillations causing massive increases in mortality sufficient to "halve stocks". I call that the "Chicken Licken Hypothesis".

    The OP above is pretty confirmatory of this view and the later posts about Girnock have hopefully demonstrated there is another view, which may appear more valid.

    The sky is not falling down, but the ability of both rivers, and the continental shelves they discharge onto, to sustain the same level of life is declining where human impacts increase.

    One aspect the Grand Banks have in common with the Baltic is pretty obvious to anyone with basic interest in demography and developmental impacts.

    The Grand Banks lie on the submerged flood plain of the mixing ground of some of the worlds greatest pollluted river systems. They sit in it's riverine discharge. Their sediments come from the erosion of the Great Lakes region and of course also include all the associated anthropogenic impacts. The rivers draining the humungous conurbation that is New York enter the Gulf Stream just downstream of the Grand Banks, adding to the pollution and eutrophication of the Banks. The Labrador Current and the Gulf Stream waters mix here, but they also mix up the polluted discharge of the St Lawrence. Over the decades this can be seen to have been a major issue.

    Now, in Ecology 101 (Carrying Capacity) when you remove a top predator, all other factors remaining the same, you cause a population explosion of that predators prey. Take away the Lynx, Wolf and Bear and hey presto, deer populations explode. Take away the peregrines and the pigeon populations explode. Kill all the turtles by chucking plastic bags into the oceans and you get a jellyfish bloom.

    Take away the Cod and well, why was the prey abundance depressed? Why did it remain so?

    Wiki may state this is a "closed system" but it cannot be. It mixes two of the biggest nutrient sources of the Atlantic! But over a vastly polluted sedimentary pile.

    Perhaps no one has looked at the problem from the other angle, and hence the dogmatic theories remain. Cause or Coincidence.

    Perhaps there are other more important factors at play than the blokes with nets? Coup de grace 's notwithstanding.

    Would be interesting to hear why prey did not recover given it's fecundity and life cycle. Not convinced that this is so black and white as the Wiki and political issue.
    Last edited by seeking; 02-10-2017 at 12:11 PM.
    "...hooking mortality is higher than you'd expect: further evidence that as a numbers game, catch-and-release fishing isn't always as straightforward as it seems"
    John Gierach


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    Unless otherwise stated, data used in any graph/figure/table are Crown copyright, used with the permission of MSS and/or EA and/or ICES. MSS / EA / ICES are not responsible for interpretation of these data by third parties

  3. #53
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    I know precious little about the humble cod, except one thing: its temperature tolerance range is remarkably narrow, perhaps no more than 4-6C wide. In contrast the salmon can tolerate water across a remarkable 23 degree range. So perhaps periodic changes in Atlantic temperatures - Keirross may advise - could have affected the cod's preferred locations.

    I read somewhere recently that the capelin fishery in the mouth of the St Lawrence is currently enjoying a boom as a result of demand from China. There is clear evidence that the quotas are being abused (Miramichi and GT0254 will have more detail). But notwithstanding the pollution they are present in vast quantities, but that has not always been the case. However, the significance of the capelin is its role as a prey species for every predator in the sea, including cod and salmon. And, if I recall correctly, like the cod it also has a rather narrow temperature tolerance range.

    So it's possible that if we wish to understand the cod population better we need to look at sea temperatures and the poor little capelin.

  4. #54

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    Quote Originally Posted by Grassy_Knollington View Post
    It is an established fact that there is no direct relationship between the number of eggs laid and the number of smolts that are produced.

    I think we need to consider how persistent the nutrients from a kelt will be and how they contribute to smolt production. I agree they could be important in the first life stages but after wards? It's a once a year bonus at a time when the parr will be in virtual hybernation. Perhaps Ness Glenn could shed some light on how significant this is.

    GK
    Hi GK,

    Regarding your first point there is actually a direct relationship, it is called the stock recruitment curve see https://www.strath.ac.uk/media/depar...appendix10.pdf Any paper with P. Bacon as an author is intense but it does mention the Girnock. Search this topic on Google for a raft of references.


    Regarding nutrients from kelts this paper gives some figures for a Norwegian river http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf . There is a net annual influx, although the point that smolt production involves a significant nutrient export is a good one. Salmon eggs themselves are also an important, albeit seasonal input. The energy boost a salmon parr experiences if it consumes a few salmon eggs must be substantial. Some of by colleagues specialise in this topic, indeed one who posts on here occasionally did his doctorate on surrogate kelt introduction. If he is not too busy with quantum physics he may contribute.

    On my local there is a corner below the Long Pool which is a regular kelt graveyard. There is always a lot of scavenger activity in the late winter but many of the carcasses become buried within the sandy sediment found at this point. This should help deliver a slow release of nutrients. Willows grow profusely on the bank at this point thereby contributing nutrients indirectly via leaf fall.

    In a more upland situation the nutrients derived from kelts is likely to be important, although how many succumb there compared to lower down? The nutrient input from eggs may be more important here as some of these will not hatch and a high proportion of the fry will die or be consumed instream. The point is marine nutrient transfer is more than just kelts.

    NG

  5. #55

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    Quote Originally Posted by Ness Glen View Post
    Hi GK,

    Regarding your first point there is actually a direct relationship, it is called the stock recruitment curve see https://www.strath.ac.uk/media/depar...appendix10.pdf Any paper with P. Bacon as an author is intense but it does mention the Girnock. Search this topic on Google for a raft of references.


    Regarding nutrients from kelts this paper gives some figures for a Norwegian river http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf . There is a net annual influx, although the point that smolt production involves a significant nutrient export is a good one. Salmon eggs themselves are also an important, albeit seasonal input. The energy boost a salmon parr experiences if it consumes a few salmon eggs must be substantial. Some of by colleagues specialise in this topic, indeed one who posts on here occasionally did his doctorate on surrogate kelt introduction. If he is not too busy with quantum physics he may contribute.

    On my local there is a corner below the Long Pool which is a regular kelt graveyard. There is always a lot of scavenger activity in the late winter but many of the carcasses become buried within the sandy sediment found at this point. This should help deliver a slow release of nutrients. Willows grow profusely on the bank at this point thereby contributing nutrients indirectly via leaf fall.

    In a more upland situation the nutrients derived from kelts is likely to be important, although how many succumb there compared to lower down? The nutrient input from eggs may be more important here as some of these will not hatch and a high proportion of the fry will die or be consumed instream. The point is marine nutrient transfer is more than just kelts.

    NG
    Interesting post, thanks.

    Iím told it used to be common practice on some highland estates to take the larder waste from deer stalking up to the top of the rivers and chuck it in to boost nutrients. Apparently illegal now.
    Last edited by Loxie; 02-10-2017 at 08:45 PM.

  6. #56

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    Not a bad idea if they did.

    This presentation from Wester Ross Fisheries Trust covers the issue, ehh, shall we say quite comprehensively! http://www.wrft.org.uk/files/Referti...2016forweb.pdf Some references to salmon carcasses are included. 106 pages but you can scroll through it quickly.
    Last edited by Ness Glen; 02-10-2017 at 07:59 PM.

  7. #57

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    Quote Originally Posted by Ness Glen View Post
    Not a bad idea if they did.

    This presentation from Wester Ross Fisheries Trust covers the issue, ehh, shall we say quite comprehensively! http://www.wrft.org.uk/files/Referti...2016forweb.pdf Some references to salmon carcasses are included. 106 pages but you can scroll through it quickly.
    I do know one keeper who takes the view that SG are wrong and he will continue to do what he believes is right!

    Thinking a little outside the box is there not a substantial cost for the disposal of frames from the the seafish processing industry? Could fisheries boards not get large quantities of these for the cost of haulage and use them to fertilise the upper reaches or other nutrient poor areas of their catchments?

  8. #58

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    Quote Originally Posted by Ness Glen View Post
    Hi GK,

    Regarding your first point there is actually a direct relationship, it is called the stock recruitment curve see https://www.strath.ac.uk/media/depar...appendix10.pdf Any paper with P. Bacon as an author is intense but it does mention the Girnock. Search this topic on Google for a raft of references.

    NG
    Thanks NG

    It is quite hard going, specially for somebody like me who thinks that least mean squares are a kind of crisp. Without (re) reading it in detail this is my take on the findings and explains in more detail why I think what I think.

    I should have caveated my statement (as I usually do) that there is no direct relationship 'except at very low levels'. You are correct that the paper finds proposes a relationship between overall egg deposition and overall smolt production, but it is not a direct one.

    This, and the availability of measurements may be why the paper breaks down survival into 2 separate processes: One is ova > fry, the other is fry > smolt. The resultant stock recruitment curve is the combination of both observations and of course generated with a series of statistical techniques to filter out the 'noise' of environmental conditions - which are assumed to be essentially random for the purpose of the study.

    The techniques are powerful and they remove the noise but not in such a way as to suggest a direct relationship. The proposed recruitment curve is recognizably different from river to river (Girnock, Bush, N Esk, Nepisguit), suggesting there is something, (or more accurately some things) in the 'random' noise that help to moderate smolt production. Finally when examined at the river level the actual data points fall outside the expected confidence limits on a number of occasions.

    It is worth mentioning one basic (and sound) principle used paper yet frequently decried on here. Namely that randomness generally cancels itself out over time, leaving a relevant trend from a messy dataset. As MCX says 'If you can't be accurate, be consistent.'

    Of course where the changes are not random that principle is no longer sound. As an example, the assumed randomness in the Girnock environment may not be quite as clear as suggested and the baseline may be shifting.

    Gurney observed (in a separate paper) that the measured temperature of Girnock has clearly changed over time. Colder Winters, Warmer Summers and this has clear implications for smolt production, earlier activation times, poorer winter feeding, faster maturation, increased maturation and resultant decline in smolting . . . . This linear trend is assumed to be random noise in this latter paper.

    Rgds

    GK

  9. #59

    Default No cod

    Quote Originally Posted by MCXFisher View Post
    I know precious little about the humble cod, except one thing: its temperature tolerance range is remarkably narrow, perhaps no more than 4-6C wide. In contrast the salmon can tolerate water across a remarkable 23 degree range. So perhaps periodic changes in Atlantic temperatures - Keirross may advise - could have affected the cod's preferred locations.

    I read somewhere recently that the capelin fishery in the mouth of the St Lawrence is currently enjoying a boom as a result of demand from China. There is clear evidence that the quotas are being abused (Miramichi and GT0254 will have more detail). But notwithstanding the pollution they are present in vast quantities, but that has not always been the case. However, the significance of the capelin is its role as a prey species for every predator in the sea, including cod and salmon. And, if I recall correctly, like the cod it also has a rather narrow temperature tolerance range.

    So it's possible that if we wish to understand the cod population better we need to look at sea temperatures and the poor little capelin.

    The cod were overfished and the quota set for capelin was based upon no cod predation so they are overfished, Particularly females for roe to China. Salmon have toe at algae off the stones now.

    The EU sold most of their capelin quota to Norway. Very smart !!

  10. #60
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    Quote Originally Posted by Dave Wilkinson View Post
    The cod were overfished and the quota set for capelin was based upon no cod predation so they are overfished, Particularly females for roe to China. Salmon have toe at algae off the stones now.

    The EU sold most of their capelin quota to Norway. Very smart !!


    In what waters did the E U have capelin quota to sell ?
    To my knowledge there is no capelin resource within the EU's EEZ and possibly never has been.
    Last edited by acercon3; 14-10-2017 at 11:36 PM.

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