Were there more parr back then……

“If the burn was capable of holding that many fish then, what has changed that means that it can’t physically hold that many fish now? Yet another example of where the hatchery would be useful to bring a burn back to its previous levels of productivity? I’m afraid I don’t buy this tale of salmon / sea trout parr densities being sufficient – I’m convinced there must have been a whole heap more back in the day…..” Henry Taylor 2013.

Above is a quote from Henry’s comment on the recent Chabet Burn post on this blog. I responded at the time that I would provide a full reply once I’d gathered my thoughts.

First a few details about the Chabet Water (to use its proper name). The length from Glenconglass Farm to the Avon confluence is 6200m, with an estimated mean width of 3.5m the wetted area is 21,700m2, most of which is high quality habitat. We have no information on fish densities other than a paper record from 1991 when lots of trout and a few salmon were found in a quick presence/absence survey upstream of the culvert. We don’t know the upper limit of salmon penetration but experience elsewhere in the catchment shows that below 3m width trout tend to dominate over salmon. Nearby and similar quality burns such as the Blye/Lochy/Conglass support high densities of juvenile salmonids (based on our current and relatively recent standards), with salmon dominating in the lower reaches and trout in the upper.

I want to look at a few issues here, namely:

1) smolt production

2) marine survival and number of returning adults

3) number of spawners and smolt production

4) current juvenile densities

5) hatchery supplementation

1) What is the potential smolt output from the Chabet Water? We know from our smolt trapping in tthe Truim and Tromie, and research on other rivers that smolt production in highland Scotland is typically around 5/100m2, with fluctuation from year to year and from river to river. The Truim and Tromie produced about 7 salmon smolts/100m2 in 2012, a good figure but I’d suggest that a burn like the Chabet Water would be potentially capable of producing more (assumption based on the habitat quality, the presence of limestone in the catchment and fish densities from adjacent burns).  For the sake of this illustration I’m going to assume that the smolt output from the Chabet is 9.2/100m2, only because that would result in a nice round smolt output of 2000 from this small burn. That seems a lot but combining salmon and sea trout smolts it is not unrealistic. Larger streams such as the Truim are dominated by salmon but a more even mix of salmon and trout smolts could be expected from a smaller burn such as the Chabet.

2) If we assume for a minute that all the smolts were salmon then at 30% marine survival the number of adults returning to the river would be 600. Back in the 1940s that number would have been hit hard by netting and angling, but there may still have been 3-400 adults returning to the burn, a number that could have produced the 100 foul hooked fish in a spate noted by the bailiff at the time.

In recent years the marine survival of salmon has generally been lower, ranging from 20-4% between 1981 and 2009. At 5% marine survival and the same smolt production we would only have 100 adult returning to the river. Current in river exploitation is very low so we might expect about 80-150 adults to return to the burn across the range of recent marine survival figures. We counted 35 redds in the Rothes Burn last December, a much smaller burn,  so I wouldn’t be surprised to count 40-80 redds in the Chabet Water (job for December 2013).

Marine survival of sea trout is harder to track down but figures I’d seen in the past showed survival to be as high as 25% for those returning as finnock but consideraby lower for fish staying at sea for longer.

So if smolt production had remained stable then marine survival alone could explain the apparent big reduction in numbers of returning spawning fish. Of course the bailiffs report from 1941 may have been from an exceptionally good year?

3) Henry’s argument, and the same argument is made by many others, is that parr densities, and subsequent smolt production are nowhere near as high as they used to be, or potentially could be. So what actually happens when numbers of returning adults decline? Monitoring on the Girnock Burn, River Dee, provides one of the best long term data sets relevant to this question. In four decades from the mid 60s to the mid noughties the number of returning adults to the Girnock Burn decreased by 70%, from a mean of 84  down to 25. Over the same period the smolt output decreased by 35%, a much smaller decline, although still highly significant in fishery terms (figures from a paper by Gurney et al. published in 2008). As juvenile salmonids populations are controlled by density dependent factors the declines in numbers of spawning fish can be compensated for by improved survival rates of the remaining eggs/fry, and in the opposite case increases in adult numbers doesn’t necessarily mean more parr .  Hopefully the figures from the Girnock above show that in actual fact parr densities are much more stable than many perceive them to be.

4) I spoke at length with a ghillie the other day including this subject and he stated that juvenile densities must have been 4-5 times higher in the past than they are now. I have looked at the long term trends (1997 to 2011) in parr densities from our own electrofishing surveys and with the proviso that the data weren’t collected for this specific purpose, nor has any statistical analysis been carried out, there does appears to have been a decline in mean salmon parr densities but it is in the order of 20%. That is a significant decline but it is not a collapse in the stock and we still have a well distributed and healthy salmon population throughout the entire accessible area of the Spey catchment. All the information and experience I can access indicates that that maximum parr densities nowadays are little different from those that would have existed at the peak of the salmon population. However, it is likely that more of the catchment now supports a lower parr density than existed when salmon runs were more abundant but that is not the same as saying parr densities must have been much higher.

5) It seems so obvous doesn’t it? Catches are going down, juvenile densities don’t look that good so lets put some hatchery reared on top of the wild ones. However, lots of recent research shows a negative impact of stocked fish on existing native stock with a further, more significant, negative impact on breeding success when they return to breed. Some of the papers I’ve read on this subject were on steelheads in the US but their ecology is similiar to our salmon. If the findings of those papers can be transferred to our situation we run the risk of making the situation worse by stocking. The ultimate scenario would be a downward spiral in fish numbers with an eventually total reliance on stocked fish. Hatcheries have a role in fisheries management but I’d argue that trying to enhance a reasonably healthy and robust fish population in an accessible part of the catchment is not an appropriate use.

One key question is what drives smolt output, the number of juveniles or the number of spawners? That depends on where you are on the stock recruitment curve:

Stock recruitment curve

Stock recruitment curve

With adult numbers to the right of the red line juvenile numbers are at maximum and more adults won’t result in increased production. Adult numbers to the left of the red line means there are not enough to fish to fully populate the available habitat and lack of juveniles will limit smolt production. Understanding where you are on this curve is important but difficult to ascertain. Knowing input and output figures would help but large flucuations in fry and parr densities can indicate that numbers of spawning fish are not consistently to the right of the red line. My guess is that with the early running fish we are likely to be around the red line, later running fish numbers may be better but we still have years when they are likely to be close to the red line. This is why in these days of relatively low marine survival, in a historical context, conservation of the stock is so essential.

To summarise:

the Chabet Water is potentially a very productive burn

marine survival alone explains most of the decline in adult numbers

its a myth that maximum parr densities were formerly much higher

salmon have a good strategy to cope with changes in population numbers

the fishery board employs a biologist to help formulate a coherent management policy on amongst other things, the hatchery operation

we need to really focus on understanding, managing and conserving the stock during a period of relatively low marine survival

We will survey the Chabet Water this summer and I’m sure that as in other burns in the area we will find a high density of juvenile fish. There will be a mixture of salmon and trout but then again I think the use of the term “of the salmon kind” in the 1940s bailiffs report hints that there were sea trout involved in the foul hooking incident.

To finish on a positive note the excellent smolt numbers from the Truim and Tromie last year suggest that these rivers are functioning well as “smolt factories”, maybe not at maximum output but producing very respectable smolt numbers nevertheless.

 

 

 

There are 22 comments for this article
  1. Tony Andrews at 8:32 am

    A most interesting discussion. The point about damage from spates came from a SEPA official who is a member of the South Esk Catchment Management Partnership, which I chair. The point made by SEPA is that average peak flood events have increased by more than 30% in the last thirty years. These bigger events are accelerating the morphology of the main stem as well as the substrata and benthos.

    During the 30 years we have recorded a change from sea trout abundance declining sharply and salmon and grilse at least holding their own. It is possible that higher energy spates have changed the size of gravels, pebbles and cobbles, larger diameters suiting spawning salmon rather than sea trout.

    At present these are pretty much unsubstantiated theories, except the SEPA data which I think are sound. I have also observed that bigger flood events are expanding the channel of the main stem and producing massive movement of silt and gravels. My view therefore is that the South Esk main stem is having some problems in containing peak flows. The result affects the biology of the river as much as it does the riparian morphology.

    TA

  2. John Carmichael at 12:15 am

    Having read the preceding Blogs, three points are worth mentioning: Though Peter Gray’s restocking on the North Tyne no doubt helped following the loss of spawning area due to the construction of Keilder dam between 1975 -1981, at the same time the sea trout stocks improved at a similar rate but without stocking. b) Though I have only fished the Aberdeenshire Dee in March for the last 34 years it has never been “closed”, even during the ‘foot & mouth’ crisis. c) A quick check of the daily heights at Boat O’Brig over the last 60 years (1952-2011) does not show main stem spates being larger now. Of the last 32 spates above say 400 m3/s sixteen were before 1981 and sixteen since, the largest by far of 1089 m3/s was on 17/08/1970.

  3. Anthony Tinsley at 2:17 pm

    Apologies for the lateness of my comment as away fishing.

    ”If the burn was capable of holding that many fish then, what has changed that means that it can’t physically hold that many fish now?”

    Nothing significant because it’s not the carrying capacity in the summer when it all looks good and anglers are about that matters. It is the carrying capacity in the winter that matters and is the major limiting factor to the production of any spawning tributary. Principally a lack of food, but also shelter and extremes of flows. Historically before marine survival rates started to drop, there undoubtedly were more parr about in the summer and autumn but no more by February/March, and fortunately by and large we still have enough in February/March to fully exploit the available food etc. These are still able to produce us a biological and harvestable surplus but regrettably it is rather smaller than before because of the lower marine survival rate.

    There is no earthly point in putting in more juveniles if they are not going to survive the next winter and worse still displace wild juveniles.

    ‘We have nothing to lose.’

    I am afraid I do not regard £125,000 a year as ‘Nothing’!

    Anthony Tinsley
    Former Chairman Spey Research Trust.

  4. Henry Taylor at 11:55 am

    Hi Brian,

    I would just like to thank you for the full reply you have given to my comment on your previous post relating to the Chabet Burn.

    I do appreciate the stock recruitment curve you provided above and accept that if we have returning fish hitting above the curve then planting out more fry / parr will do more harm than good. I still wonder whether we have reached this point accross the catchment though (I certainly dont catch as many parr as previously in the main stem) – you yourself, mention above the Spey Dam as an area where there may be a lower distribution than there should be.

    On a slight tangent, I must admit that I have never visited this dam – is there a similar fish pass to Pitlochry (which I have visited on the way to the Spey)?
    What have the operators of the dam (is it Scottish Hydro?) done to contribute to the restoration of the habitat affected by its construction? I see from a previos post that a fish counter was being established.
    Also, what are they doing (presumably the same company)to compensate the Spey valley for the impact of the water obstraction to other Hydro schemes?

    Kind regards,
    Henry

    • Brian Shaw Author at 5:01 pm

      Hi Henry,
      Above Spey Dam is definitely an area where Bob’s stocking monitoring showed that the natural stock levels were well below the flat portion of the recruitment curve, I’m sure there are other areas also.
      Spey Dam does have a fish pass, but no visitor centre, I doubt it would provide the same spectacle as the Pitlchry Fish pass! Spey Dam is operated by Rio Tinto. The answers to your last questions: little and nothing unfortunately.
      Brian

      • Henry Taylor at 5:43 pm

        What lobbying has the SFB carried out to rectify this to date?

        • Brian Shaw Author at 6:37 pm

          Henry,
          Have a read of the SFB annual reports, you will find them in the publication section of the website. This issue has received a lot of attention over the last few years!
          Brian

  5. GRAHAM SALISBURY (SRG) at 8:56 am

    Brian, I am sorry to disappoint you in that my views remain unchanged, the problem I and many others have is that we are hearing nothing to different from the past 20 years of science and surveys, yes I fully appreciate the level of detail you go into and your genuine desire for the river to do well but what I would like to see is someone thinking outside the box! On the Dee they took radical steps to enhance stocks ahead of the times, with the river closed completely for a number of years in the spring, and a major programme of fencing off burns and improving habitat coupled with total catch and release.
    I believe we need to use all the tools at our disposal Science, Habitat, and Hatcheries to put the river back on course. Over the past twenty-thirty years I am reliably informed the habitat on some estates has been significantly improved already, with miles of spawning burns being fenced off etc.; I want to see/hear your proposals in detail with a time table which will make a change from the general statement of ‘Science and Habitat Improvement’. We could I am sure apply for EU funding due to the special status of the Spey, to provide set-a-side corridors for farmers along the main stem and our burns, creating spray free zones to boost the invertebrate supply and have more fenced off, I feel frustrated in your belief Salmo-Salar is so good at recolonizing the system it will take place naturally, between the same goal posts, if this were the case the past twenty years should have been long enough in my opinion!
    We have the fastest flowing river in the UK with global warming creating large damaging spates our juvenile stock could be fine for six-twelve months and then be decimated within days after a large spate, an intelligently run hatchery can mitigate against such natural disasters and make use of areas inaccessible which we understand Tulchan Estate alone has miles of such pristine habitat. Also on a final point, The Board only implemented the ‘token’ autumn parr programme recommended by Gray within the last two seasons after pressure from SRG. I urge you to come up with a radical proposal which may not please everyone but will have the chance of making a break from the past twenty-thirty years of stagnation or decline, Tulchan have offered to fund the reopening of their hatchery what have you got to lose?
    GRAHAM SALISBURY (SRG)

    • Brian Shaw Author at 10:45 am

      Graham, You are ignoring history. Over the last decade many other rivers have taken different routes to that of the Spey, where a great deal of effort and energy was expended on a large hatchery operation, one of the biggest in Scotland, and all the associated activities that the operation of such a hatchery entails. The genetic study and the most basic investigation of stocking and anticipated returns shows that the strategy didn’t worked. I tried to get all this across at the Aberlour meeting. The large hatchery expansion in 2003 involved stocking all inaccessible areas plus widespread stocking in top of existing stock in accessible areas. I would have thought that anyone looking at the information available in an analytical way is quite likely to arrive at the conclusion that the hatchery operation was actually part of the problem rather than the solution.

      Not only are you ignoring history but you have a very short or selective memory. Over your selected 25 year period of “stagnation or decline” rod catches have actually been quite stable and in the three years from 2006 to 2008 the rod catch was above 10,000. You have to go back to 1993 to 1995 to find a similar three year period when the rod catch was above 10,000.

      Let me assure you that we are working on many fronts to improve the habitat on the river, investigating invertebrate productivity, water quality, although I do admit that we could be a lot better at putting that across. We wil be a lot more proactive in publicising this sort of works this year. We are working on easing the remaining obstacles to fish passage, delivering and developing habitat improvements, trying to minimise exploitation, working with SEPA to improve the management of the abstractions at the top of the river, riparian tree planting, removing channel modifications, a list of proactive activities although there could be much more done. There is nothing fundamantally wrong with the Spey as a salmon river. The only thing on your list we are not doing is stocking above impassable waterfalls. As I have discussed before this is controversial, not SFB policy, likely to become an offence under the WANE act. Unless there is a significant reversion in SFB policy I can’t see that policy changing. The SFB has moved on and is now concentrating its resources on the huge area of accessible habitat where sustainable improvements can be delivered.

      In my view what is needed at present is a steady hand; not thinking out of the box, we have suffered from that enough already. There have been a couple poor seasons of catches, although in 2011 from all the accounts I heard there was no shortage of fish in the river that year; there is every reason to be positive about the future although you consistently chose to ignore these findings.

      Let me assure you we are working very hard on a wide range of activities and in due course it would be good to draft and consult on a detailed action plan but that is still under development. In the meantime I have some invertbrates to count and identify. Keep an eye on the blog later as the findings will be interesting.

      Brian

      • henry spence at 12:09 pm

        Hi Brian,

        Is there a scientific basis to the 10,000 number that seems to be the acceptable number for a successfull Spey Season.

        • Brian Shaw Author at 1:12 pm

          No Henry, just a number that signifies an above average season, I think we’d all be more than happy if 15,000 were caught
          Brian

          • henry spence at 4:14 pm

            Hasn’t that number recently only signified that parts of the Spey have fished well.

            The trend over the last 10 years seems to be that 10,000 fish reflect an excellent season for the lower Spey beats while on the Middle and Upper Spey the catches have been declining.

            Believe it or not I have met some Lower Spey fishers who don’t really get what all the fuss is about as their weekly catches have tendended to increase eg Rothes in the Spring as you mentioned.

            There does seem to be a real lack of parr in the middle stretches compared to what used to be, as evidenced by the fact that when I was a youngster watching my father fish I could rise a parr just about every timer I cast a size 20 dry fly out, when I try and do the same for my kids now it’s almost as hard to catch one as it is their mothers/fathers!

          • Brian Shaw Author at 4:54 pm

            Hi Henry,

            Since 1952 10,000 has been beaten in the reported catch 25 times and below that on 36 occasions. But as you point out since 1989 there have only been 6 years when the rod catch was greater than 10,000. If there were 10,000 fish caught this year there would I’m sure be many happy faces, assuming an even distribution of catches of course. The trend for the dowmstream movement in catches is really hurting the middle and upper beats.

            I am very conscious of the reports about the lack of parr in the middle mainstem, and I’m sure these reports have a lot of validity. When we do our electrofishing in the mainstem it is good to see lots of fry, you want a wide base to the population pyrmid in these areas; there is a lot of good habitat in the mainstem and in the lower river at least no shortage of invertebrates. Last year we found reasonable numbers of fry so it will be interesting to see if we can figure out how many parr there are this year.

            Once I have recovered from sorting and counting the Brae Water samples I will collect a couple invertbrate samples from the middle river for comparison.

      • GRAHAM SALISBURY (SRG) at 12:15 pm

        Brian, the historical hatchery procedures on the Spey we know involved planting out huge numbers of unfed fry at periods when there was either no food in the system, and/or when the river was in a feeding frenzy, coupled with the fact that many were planted out in far too high a density’s in areas where there were probably already healthy wild stocks. The Hatchery didn’t fail the management system did! Unfed fry were effectively cannon fodder and I would be very surprised if any survived, I believe an intelligently run and targeted autumn parr programme as advocated by (SRG) is completely different from the historical procedures carried out on the Spey and P Gray has confirmed this, he is also happy to advise/oversee the reopening of Tulchan’s Hatchery.
        We could exchange on this subject endlessly but to save this, what I think we can both agree on is that we want what is best for the river. I maintain my view the agenda needs changing or the goal posts shifting to make a difference and I agree not recklessly but in a controlled and measured way, otherwise in 10 years we may both be contemplating retirement with a missed opportunity having passed us by. I am here with an open mind to be convinced, but as yet have heard or seen nothing that sways my opinion.
        Yours, GRAHAM SALISBURY (SRG)

        • Brian Shaw Author at 10:48 pm

          Good to see we have found some common ground Graham. Here a few final thoughts:

          1) There has been very little stocking with unfed fry, the vast majority were fed on before stocking even in the early days.

          2) I note that Tony Andrews in his Finavon, South Esk blog reckons that his river suffers far worse from damaging floods than larger rivers; interesting how opinions can vary so much on this issue. However it is a human trait to fear the worst for your own. If the opportunity arises I intend to try and assess the impacts of really big spates on the ecology of the Spey, I’m sure we won’t have to wait for long.

          3) If you were to run a hatchery operation intended to offset damage caused by large spates you would have to be prepared to stock and run the hatchery every year on the off-chance of a damaging spate otherwise you would never be in a position to react. And if there were no spates to mitigate against what would you do with the insurance stock kept in the hatchery? Which stocks would you keep? To make a meaningful difference large numbers would have to be held, thats a lot of wasted stock if not required and landfill costs are high. Salmon have evolved a very effective strategy to re-populate vacant habitat and experince elsewhere generally shows that full recoveries within one year are the norm following extreme events.

          4) As it is one of our best marketing strategies I won’t question whether the Spey is the fastest flowing river in Scotland or not. And as it was one of the earliest things I remember from school in Grantown it must be right.

          Best regards

          Brian

  6. Ian Gordon at 9:58 pm

    “The factors influencing where the fish stop and become catchable are not understood and obviously vary greatly over from year to year and over time”

    Might be worth a word with Throstor Ellidason Brian. My feeling is, he knows more about the above than most, which may or may not help with your future decision making.

    I’m sure he would be delighted to share is experience with you.

    ellidason@strengir.is

  7. Olivier Devictor at 5:03 pm

    Has the Fishery Board considered a hatchery approach which would follow Peter Gray’s methods ?

    • Brian Shaw Author at 7:46 pm

      Hi Olivier, yes the hatchery policy has been closely aligned with the Peter Gray approach for the last few years. You will find further details regarding the stocking monitoring in the 2012 Annual Report or in the 2012 Electrofishing report both of which can be found in earlier blog posts (7th Feb 2013 and 21st Nov 2012 respectively).
      Best regards
      Brian Shaw

  8. GRAHAM SALISBURY (SRG) at 11:03 am

    Hello Brian, there is no doubt in my mind and that of many seasoned Spey Rods & Ghillies that the runs are declining despite 80% plus catch & release. However we dress up the stats; there are less fish returning in the current cycle. Rivers tend to die off from the top down; it would be very interesting to analyse past season’s results from Craigellachie Bridge upstream. What is the Boards latest’s state of play with stocking above impassable obstructions, or in areas with low juvenile counts with the carrying capacity? Have we a five year-ten year plan yet to improve returns or are we going to let history repeat itself. In tha past prior to your arrival annual surveys where carried out the usual jargon published at the end of each season over a twenty year period, culminating in the Chair at the autumn Aberlour meeting openly suggesting we sweep the past 20 years under the table hailing a new beginning with yourself as our new savour.
    Brian, SRG have had detailed discussions with Tulchan estate and they have confirmed they are happy to fund the reopening of their hatchery at no cost to the board, are you able to work with them and support the targeted stocking of an autumn parr programme above impassable obstructions, or in areas with low juvenile counts and the carrying capacity?
    Yours, GRAHAM SALISBURY (SRG).

    • Brian Shaw Author at 9:01 pm

      Dear Graham, No one would try to claim that the returns of fish last year were good, grilse numbers in particular were well down, although the same situation prevailed on many other rivers.
      It is true that in recent seasons an increasing proportion of the catch has been taken in the lower river but twenty years ago the opposite prevailed. Mike Ewan, Rothes and Aitkenway senior ghillie, recently told me that when he started on the river they rarely caught a fish before April, although they saw plenty; now it is one of the top spring beats. The factors influencing where the fish stop and become catchable are not understood and obviously vary greatly over from year to year and over time.

      The statement that “rivers tend to die from the top down” is in my view without foundation. Indeed there are many examples of rivers suffering from pressures such as diffuse pollution where the opposite is the case; where only the upper reaches provide suitable spawning and nursery habitat. On the Spey last year there were at least as many fish spawning in the upper reaches as in the lower, a fact that I highlighted in the blog post made on the 19th December following a visit to Delfur, the premier Spey fishing beat, which even last year held a large stock of fish until the end of the fishing season. I also keep highlighting the excellent smolt production figures from the Truim and Tromie, two major upper river tributaries. These results are hardly indicative of a river dying from the top down?

      The Foundation and Board have a well established procedure for reviewing the stocking policy; considering a wide range of information to assess the contribution that could be made by the hatchery including juvenile surveys, post stocking monitoring and genetic studies. Indeed the Chairman of SRG is a Spey Fishery Board member and is able to participate in these reviews. The current hatchery policy, which has evolved over a number of years, is published in the annual report and there is no need for me to go into any more detail here. Regarding the Tulchan hatchery Roger Knight has made it clear on many occasions that the board has more than sufficient in-house capacity and expertise to fulfill its current stocking requirement.

      In my first year here I have found no justification for any expansion of the hatchery operation (exception – above Spey Dam). Juvenile fish are present throughout all accessible areas of the catchment, including positive results from the mainstem. Our efforts should be focussed on protection and enhancement of habitat and conservation; and they are, we are just not that good at publicising it although that is improving.

      I really have only one aim here and that is to be trusted by those concerned with the health of the river and the fishery to provide good advice based on scientific understanding, best practice and personal experience. Whilst that ambition is unlikely to be completely fulfilled it really is quite disappointing to me to see that you do not appear to have altered your views on this issue in any way.

      Brian Shaw

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.