Allt Cuaich: trickle resistant salmon

The Allt Cuaich will be familiar to many as the almost dry river bed under the A9 just to the north of Dalwhinnie. I use the term almost dry as over the last few years there has been a small residual flow, although I think that prior to that there were periods when with no visible flow.

The Allt Cuaich starts at Loch Cuaich, which lies on the hills above the A9. Loch Cuaich was utilised by the hydro electric companies in the 1930s/40s with the construction of a dam at the outlet exerting complete control over the flow from the loch and other surrounding catchments.

Loch Cuaich photographed from the dam

Loch Cuaich photographed from the dam.

Below the dam there is a further weir across the Cuaich to ensure that water from two significant tributaries is not lost to the hydro system.

The long concrete weir across the Cuaich at the power station

The long concrete weir across the Cuaich at the power station. The weir diverts the flow from at least two burns into the aqueduct that transfers water from the Spey into Loch Ericht and the Tay catchment.

There are four sluices on the Cuaich weir each of which is leaking to a certain. Cumulatively the water from each of these leaks forms the entire flow down the Cuaich below the weir.

One of several sluices in the Allt Cuaich weir

One of several “leaking” sluices in the Allt Cuaich weir.

Last year SEPA completed two electrofishing surveys in the Cuaich, one above and one below the weir. The results from the survey below the weir (midway between A9 and the weir) revealed the presence of  three year classes of salmon ; fry, one and two year old salmon parr. This shows that salmon were able to access the Cuaich and spawn in each of the last three years, and possibly earlier, although three year old parr are not encountered often enough to be classed as common anywhere in the upper Spey. These results caused great excitement within the agency and other organisations – obviously all that salmon needed to survive, and apparently thrive was a mere trickle of water.

The finding that salmon were present in the Cuaich was indeed a surprise as the system had been engineered to ensure that salmon couldn’t get into the burn. There is a “heck” across the lower Cuaich which is supposed to stop salmon running the burn during periods of high flow, e.g. when the dam is spilling, so that they don’t get stranded once the flow subsides.

The non-functioning Cuaich heck. It looks good on a day like this but if the dam spills it is easy to envisage how a rock could become lodged below one of the gates leaving an opening for salmon to run.

The non-functioning Cuaich heck. It looks good on a day like this but if the dam spills it is not hard to envisage how a rock could become lodged below one of the gates leaving an opening for salmon to run.

As we were surveying the Truim catchment in detail this summer we included two sites on the Cuaich. We had never surveyed the Cuaich before so two new sites were established, one close to the area where SEPA had found salmon and the other just upstream of the A9.

We found salmon in both sites, although there were no fry in the upper site (same location where SEPA had found fry last year). The densities of parr in both sites were in the moderate categories so they were present in reasonable densities.

Survey site in the Cuaich midway between A9 and weir.

Survey site in the Cuaich midway between A9 and weir. No salmon fry at this this site suggesting that no adult salmon made it this far upstream last winter.

Two parr from the upper Cuaich site

Two parr from the upper Cuaich site

At the lower site (nice tranquil site just above the A9) we did find salmon fry as well as parr: maybe only a few spawning salmon made it past the heck last winter.

Survey site just upstream of the A9.

Survey site just upstream of the A9; moderate density of salmon here along with quite a lot of trout.

It is clear from these surveys that salmon are great survivors and colonisers. Conditions must have testing for these fish during the hot dry summer when water temperatures would have been high with all those exposed rocks; although being north west facing would have limited the exposure to the sun.  The salmon density may be moderate but the wetted width of the Cuaich is currently a fraction of what it would be naturally. The old Spey spawning records show that up to 96 redds were counted in the Allt Cuaich before the hydro was built. It was probably an important spawning tributary for spring fish which may have spent the summer in the loch before dropping down to spawn.

SSE are proposing introducing a formal compensation flow as part of the Tummel hydro review but it is likely to amount to little more that the current leakage from the weir. The absence of fry in the upper site suggests that much more will need to be done to produce a truly sustainable and viable salmon population in the Allt Cuaich.

Authored by: Brian Shaw

There are 7 comments for this article
  1. Gary Neal at 7:56 pm

    I used to fish around Etteridge about twenty years ago and caught my one and only Salmon on a fly on the Spey across the A9 below Loch Cuaich. I have wonderful memories and now want to take my Son up to experience the beauty. My gamekeeper friend has long since moved to a different estate.
    Please can you tell me if I can still fish the Loch and where we could stay. Thank you

  2. Max Allan at 12:37 am

    When the water in the allt na sluidhe was diverted to loch ericht hundreds of parr died between the dam &the truim in the late 50’s I onc counted 180 salmon killed by otters and left on the riverside …I’d be prepared to bet there are no runs of nearly that magnitude in the whole river now

    • Brian Shaw Author at 6:45 am

      Very interesting Max, that is the first information I have heard about the fish in the Sluidhe, It looks like a nice burn which I’m sure salmon would have used for spawning. An otter harvest of that magnitude in the Truim suggests a run of thousands of fish, unfortunately that doesn’t happen nowadays but they were catching 4000 fish to the rod before the end of April then, now it is under a quarter of that, Changed days but the big spring runs may return.
      Thank you for the comment.
      Brian Shaw

      • Max allan at 11:21 pm

        Sorry did not find your response until today. Last saw 2 salmon stranded in spill pool below the dam diverting water to loch ericht in 1958 late autumn, the fish in the burn were never more than 18-24 inches long. We saw many parr & a few silvery smolts until 1958 after that there were only occasional flash floods so guess no salmon got up to spawn &even if they did I suppose the fry would have ended up in loch ericht. There were only
        2 pools above the a9 bridge one at the bridge and one below the railway bridge so any larger fish were easy to find. We used to carry parr & occasional smelt down to the river. Mostly around Easter, in 1956 we moved 96…great things childhood diaries.
        Regards,
        Max Allan

        • Brian Shaw Author at 7:39 am

          Very interesting Max, and I am very impressed by your powers of recall, although I know who how a St Kildain felt waiting for a reply to a mailboat letter that they had cast into the ocean months before!
          Maybe the 2 salmon you found stranded at the dam were from the smolts you rescued in 1956? I like your observation that only grilse/small salmon use these smaller burns. As part of the review of the hydro scheme flow will be restored into the Cuaich and also into the Allt Bhran, a Tromie tributary. Hopefully it won’t be long before we see the return of naturally spawning salmon in the Bhran. Restoration of flows and fish passage were discussed for the Sluidhe in the early days of the water framework direcive but was excluded at that stage. It may be possible to consider it again and your observations are very useful in that regards.
          Grateful for your comments, it is invaluable to hear observations relating to the pre-hydro days.
          Best regards
          Brian Shaw

          • Max allan at 10:13 pm

            Glad that my childhood notes were of some use. Nice to hear that at least some streams will have at least some chance of regaining some of their former glory.
            Regards,
            Max Allan

  3. Ross. at 2:56 pm

    What a surprising outcome! Surprising, encouraging but sad at the same time.

    Anything we (general public reading these blogs) can do to restore the situation to years gone by? (also in reference to water abstraction in Truim).

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