Spey Mainstem Electrofishing

Trying to quantify the juvenile fish population in a river as large as the Spey is difficult if not impossible. However one technique that can be used effectively is a time limited salmon fry survey. Using this protocol we electrofish in shallow, run/riffle habitat, for a standard period targeting salmon fry. With our new electrofishing gear we are able to set the countdown timer so that all our surveys last for a predefined period of three minutes actual fishing time.

This year we focussed almost exclusively on run/riffle habitat as this is considered to be the preferred habitat for fry. The results from this years extensive survey are shown in the graph below.

Spey Mainstem 2012 salmon fry survey

The sites are ordered from lower river on the left to upper on the right. For example the third site from the left, where 32 salmon fry/minute were recorded is at Brae Water beat 5. On the extreme right is the upper most site, located 1km downstream of Loch Spey, where no fry were found. There were only two sites where no salmon fry were found, both upstream of Spey Dam, although fry were found at 9 of the 11 sites surveyed above the dam.

The 2012 monitoring technique using the countdown timer on the electrofisher is different to that used in the past. In previous years the surveys were timed, based on total elapsed time from the start to the end of the survey. In order to calibrate the new technique with the old we also recorded the total elapsed time during each survey. The average calibrated number of salmon fry/min in 2012 was 4.04, compared with 1.9/min in 2011, despite the fact that almost a fifth of the survey sites in 2012 were upstream of Spey Dam where lower numbers of fish were expected. This is encouraging but as we were targeting run/riffle habitat higher numbers of salmon fry per minute were anticipated.

The Craigellachie sites were missed from the sequence in the survey plan but we managed to completed three sites there today. The results from these sites indicate that the increased number of salmon fry we found in 2012 is more than just an artefact of the new survey technique. At Craigellachie we did the usual sites i.e. the riffle above Telford Bridge, the glide in front of the fishing beat hut and a new site in the run between the Tunnel and Upper Slabs Pool. In 2011 19 salmon fry were found at the Telford Bridge site, today we found 110 and at the hut site we found 39 this year compared to 12 in 2011. The result from the Upper Slabs site was also good with 61 salmon fry recorded along with a few parr and many small eels.  It should be noted that the total survey time at each site this year was 7 to 8  minutes, less than the 1o minute surveys completed in the past.

All three Craigellachie sites were quite different. The Telford Bridge site is a classic riffle for fry and the results from this site were equal to the highest recorded at any of our survey sites on the Spey this year. The Upper Slabs site was bouldery and more suited to parr, whilst the site in front of the hut was what I would consider sub-optimal fry habitat, i.e. glide rather than run/riffle with limited cover. This site was surveyed at the request of the ghillie to provide a direct comparison with previous years in a different habitat type.

Sub-optimal fry habitat at site in front of Craigellachie Hut

Dougie Ross, the beat ghillie, was on hand to witness the surveys, and we were joined by one of his anglers at the Telford Bridge site. I would consider that all three sites were well populated with salmon fry, each supporting a density according to the habitat present. The results indicate a significant improvement in the numbers of salmon fry present in the river this year.

In conclusion we found that salmon fry are present from the bottom of the river almost to the very top, with only 2 sites from a total of 61 surveyed yielding no fry, although parr were recorded at these sites. The numbers varied from site to site but even with a new survey technique the calibration exercise carried out indicates that salmon fry numbers are significantly greater in real terms than those recorded in recent years.

There are 6 comments for this article
  1. Jock Royan at 4:13 pm

    Hi Brian,

    I agree with Mel that it’s very encouraging to view your recent fry survey data. I do however recognise that you have a great deal of experience in this field therefore I will simply use your figures as a starting point rather than comparing them with past survey results.

    What I’d be much more interested in and feel that would give us a better idea of survival through the fry stage is future surveys of 1+ parr. I personally find the fry surveys pretty meaningless.

    Great blog do keep the information flowing.

    Best regards,

    Jock Royan

    • Brian Shaw at 8:03 pm

      Hi Jock,
      I agree that it would be ideal to quantify the 1+ density in the main stem but that is not possible using electrofishing. The Spey is far too wide to survey using any quantitative electrofishing technique especially in typical parr habitat which is bouldery and fast flowing.
      However I can say that parr were captured at 46 of the 61 mainstem fry sites with the highest number recorded at the site upstream of Pollwick Pool at Castle Grant beat 3. Here 30 parr were recorded during the 3 minute fry survey. Big wide run/riffle areas such as that are the boilerhouses of the Spey smolt production so it was good to see an abundance there.

      I can’t agree however that salmon fry surveys are meaningless. Fry are at the bottom of the production pyramid and without a broad base there will be limited parr and ultimately smolt production. In fact in the lower river there is likely to be a significant S1 smolt output so if we don’t survey the fry we will never see these quick maturing fish.

      Thanks for the feedback.
      Brian

      • Jock Royan at 6:45 pm

        Thanks Brian,

        Perhaps the term meaningless was badly chosen. What I was trying to say was that since 90%+ fry don’t actually make it to the parr stage, it’s hard to quantify the smolt output based upon fry density. You know my worry regarding the juvenile population of the middle & upper river – by juvenile population, I mean parr & ultimately smolts, not fry.

        My fear was also that we are close to the stage where we haven’t enough returning adults to populate the middle & upper tributaries. Let’s hope the encouraging fry survey figured can be converted into an increased smolt output.

        Thanks again,

        Jock

        • Brian Shaw Author at 7:33 pm

          Lets hope so Jock.

          What we noticed at the two upper Dulnain sites the other day was that fry were present across the width of the channel. I observed the guys surveying from the bank and I could see that small fish were caught most sweeps of the probe. The guys were surprised to be finding consistent fry numbers in what would be considered optimum parr habitat, i.e. knee deep, bouldery, moderate flow.

          At the start of the summer the fry are found in the margins, shallows etc, but as they mature they start to populate the entire stream width. Of course this accelerates in the following spring when the smolts migrate leaving lots of prime juvenile habitat for the 1+ parr. It is marvellous the way nature has it worked out!

          This year at least it looks as if there were sufficient adults to populate the entire upper reaches. It should, and needs to be that way every year of course.

  2. Mel McDonald at 8:15 pm

    Hello Brian,

    Your regular and frequent blog updates are proving interesting.

    Your blogs are very interesting indeed and provide a great insight into the work going on in the river and help anglers to understand the issues on the river.

    A few observations if I may ? The results of the mainstem 2012 juvenile surveys are most encouraging. Certainly as far as I am concerned I have seen much more evidence of juvenile fish in the river this season than for several years.

    Would you put this down to the reduction in the introduction of fed fry from the hatchery in 2011 increasing the available food supply from natural spawning fish thus allowing more fry/parr to survive ? Do you think that a decreased incidence of damaging large gravel moving spates at critical spawning times may have helped survival rates since 2009 ? Is it possible to mitigate against these potentially damaging spates in any way ?

    It is good to know that at least some breeding fish are making it to the high headwaters despite the long standing water abstraction issues at Spey Dam and in the high tributaries. Clearly some salmon are able to successfully negotiate the river despite the apparent barriers to migration.

    Do you think that juvenile numbers are running at anywhere near optimum capacity for the Spey and if not how would you see an optimum capacity being restored. Will increased habitat areas make a significant difference without an increase in breeding fish numbers ?

    I know you are relatively new to the river but your thoughts on these matters would be interesting to hear.

    • Brian Shaw at 9:08 am

      Hi Mel,

      Thanks for your comments, it is gratifying to know that someone is reading my rambles!

      Regarding the number of fry present in the river this year the one thing I am sure of is that it has nothing to do with the reduction in the numbers of fish from the hatchery. Historically most of the stocking was done in the tributaries. Fry don’t move much in the first summer so the mainstem fry would have been spawned within a few hundred metres of where we found them at most.

      Competition for food supply is unlikely to limit fry production in the mainstem of the lower Spey, unless fish are present at high densities. There is a suggestion in our data that the mean size of the fry at the sites supporting the highest numbers of fish were lower than at neighbouring sites with lower fish numbers. Most of the food a fry consumes will be sourced in its immediate vicinity. At the Craigellachie Bridge site the fry were present at approx 2/m2 so there is little chance of an emerging nymph or a fly caught in the surface film travelling far before it is intercepted.
      I found some interesting differences in the size of the fry at the three Craigellachie sites surveyed last week which provides an insight into the factors controlling growth. I’ll put up a post on this later today.

      Mega spates and gravel movements may or may not be a significant factor affecting salmon output on the Spey. In the past I have seen good fry numbers in other rivers following big spates, I would have thought any impacts are likely to be local rather than widespread, although I may be wrong for the Spey. However the stable flows present this winter are probably ideal for survival of fry and summer growth. Iain Tennant, Brae Water Senior Ghillie, refers to the “black riverbed”, i.e. algae covered rocks, which only occurs in his beats during periods of stable low flows. Such conditions should be good fry survival/invertebrate production.

      What we have seen this year regarding juvenile numbers on the Spey is that there is a reasonably broad base to the pyramid. Mortality occurs throughout their lives so in a healthy river system you want large numbers of fry at the base with ultimate smolt output dependent on subsequent survival through the parr and smolt stages. To be honest I would expect to see similar numbers or greater each year in the mainstem!

      Regarding increased habitat availability, salmon are great colonisers and they will soon utilise any new suitable habitat. Their strategy of producing a lot of low maintenence eggs means that survival rates in good vacant habitat can be high from only a few colonisers.

      More later……

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