Dulnain salmon fry index surveys 2018

On Monday and Tuesday this week we completed all but two of the River Dulnain mainstem surveys. The remaining sites are in the upper reaches and each site entails a long drive in, these will be done as soon as an opportunity arises. Conditions were ideal, the river rose a couple inches at the weekend and the temperatures had cooled considerably from the recent highs.

The overall results were excellent with the fry counts almost double those recorded in 2015. The parr counts were much higher than in 2015, although those figures would have been affected by the ex-Hurricane Bertha spate (remember this https://www.youtube.com/watch?v=yWS6ghvapuA )

River Dulnain 2012/2015/2018 mainstem salmon fry index surveys.

Carrie and Euan processing the catch at site TSD02, which was immediately upstream of the old railway line. Habitat quality here is great; there is a big long riffle upstream, which must support many hundreds of parr.

We recorded considerable variation in the size distribution from site to site. The size distribution graphs from a selection of the sites are shown below (ordered in an upstream direction). The horizontal scale gives fish size in mm but note that the vertical scale varies according to the numbers present at each site. Bear in mind that these surveys consist of a standard 3 minute survey using a banner net to capture the fish. This methodology has been consistent since 2012.

Fry size varied a lot, and not always smaller with increasing altitude. Competition also has a big influence in this regard with the average size at the Duthil site (348 fry) being smaller than those at the Lochanhully site (85 fry). Upstream of Carrbridge the average size dropped e.g. at Feith Mhor and Dalnahaitnach. I suspect the enrichment entering the river at Carrbridge is an important factor in the increased average size, and biomass, of the juvenile stock.

The only other tributary location when the fry counts have entered the blue zone (more than 100 per minute) was in the Fiddich (in 2014 and 2017). The Dulnain, however, stands alone for a parr count in the blue zone (more than 100 in the three minute survey). The 125 parr caught in three minutes at the Lochanhully site was exceptional, the best we have recorded in the Spey catchment. Only once before have more than 100 parr been captured in one of these surveys; that was in the Spey at Aberlour in 2014. All the 2018 sites are being recorded on Gopro so check this link for an edited video of the survey Lochanhully.

Carrie releasing the catch at the Lochanhully site. This photo doesn’t do the site credit, the lower reaches comprised a superb riffle, full of small boulders providing an abundance of hiding places for fish.

Numbers are not everything when it comes to parr however. It is considered that a parr needs to be 90mm in lenght at the end of the summer to smolt the following year. From the size distributions I can see that at the lower site TSD02 90% of the 52 parr present will be large enough to smolt in 2019 (if they survive), only 16% at the Dalnahaitnach site are likely to make that threshold. This is a good thing as it spreads the smolt output from the strong 2017 cohort over more than one year.

A selection of fry and parr from TSD34. There were fry and one and two year old parr present

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A lean salmon parr of 78mm, this may need to remain until 2020 to smolt, it might not be big enough to do so in 2019.

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The low water experienced in 2018 will inevitably result in some contraction of the juvenile stock in 2018, and this will need to be factored in, but perhaps not that significantly in the Dulnain. Water levels has increased from what I would call very low to low before most of these surveys were completed. The levels did not appear too dissimilar to other low water years in the Dulnain. We also watch river temperatures closely (they are measured at each site in advance) and we do not survey if the temperature is above 20oC. Consequently we did no surveying last Thursday and Friday at all due to the high temperatures forecast.

We plan to do the same style surveys for the Nethy and Druie tomorrow, it will be interesting to see if the Dulnain high counts are repeated. Most of the Spey mainstem surveys have already been completed, but not all. These results will be published once the surveys have all been completed.

All in all these results are very encouraging.

Authored by: Brian Shaw

There are 5 comments for this article
  1. Callum Robertson at 11:03 am

    Surely we do not need more research and statistics? We need Spey Fishery Board resources allocated to projects that will provide meaningful improvement to catches. Common sense could work out that very low water will increase the density of fry and parr counts. These statistics are only relevant to that day.

    Resources should be re-allocated to the excellent work that Jimmy does at the Sandbank Hatchery.

  2. Andrew presley at 9:58 pm

    So all seems very good in river system , a very healthy river it seems.
    So my question which seems to be related to a lot of river systems in Scotland. Why don’t salmon return if good numbers are going to sea?

    • Brian Shaw Author at 8:42 am

      Hi Andrew, It is good to see that the juvenile population remains robust despite reducing numbers of adults. The numbers of adults returning from the sea has always been a function of the number of smolts leaving and marine survival. The smolt production of the Spey varies, a lot. Right now it has the potential to be very good in 2019 (no extreme spates please!). Marine survival has been declining, and possibly more unpredictable. I think that cyclical factors are one of the most important but there is also a downwards decline. Catches will improve although not likely to reach past peaks.
      Theories abound as to why marine survival is in decline; northwards movement of the plankton, sea lice from aquaculture, overfishing, underfishing, nearshore survival, too many mackerel etc. We will be involved with the AST Missing Salmon project (http://www.atlanticsalmontrust.org/missing-salmon-project-your-questions-answered/) next year which might shed some light on inshore issues.
      Anyway must go and get ready for today’s surveys, we need to get out before it warms up too much. Thanks for your interest, Brian

      • James McCaig at 8:37 am

        Hi Andrew,
        AS a riparian owner at Easter Elchies I would like to point out that your question has been answered by Brian Shaw in a form which toes the Spey Board’s line and depends on making an interpretation of the data that something can be made out of nothing. A common sense observation is that small numbers of salmon lay small numbers of eggs and that is represented by small numbers of smolts going to sea and unsurprisingly small numbers of mature fish returning to continue the cycle. However, something needs to be done to reverse the decline and the ‘wilding’ faction controlling the Spey Board refuse to address the problem.
        Regards Jim McCaig

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