Avon mainstem results: classified information

We have updated the mainstem timed classification based on all the results from 2012 and 2103. The classification is produced by ranking the results, split in five bands, then identifying the breakpoints between each band. The results from the Avon mainstem surveys are shown in the table below. Each of the bands has been colour coded with dark green used for the top 20% or top fifth of the results, then light green, yellow, amber and red for the bottom 20% of results, just like a glorified traffic light system.

Avon mainstem results, colour coded based on results collected form the Spey catchment over the last two years.

Avon mainstem results, colour coded based on results collected form the Spey catchment over the last two years. The results are in almost perfect order except from site TA84L1 where some very nice habitat yielded a better number of fish.

I commented last week on the small size of parr in the upper Avon. Subsequently I have had a quick look at the mean size of the one year old parr, although this was based only on an assessment of the sizes by eye. Scale reading will be required to establish the breakpoints between one and two, older parr.

Mean size of the Avon one year old parr (with health warning, scale reading is required to establish the age of the parr).

Mean size of the Avon one year old parr (with health warning, scale reading is required to establish for certain the age of the parr). The fry in the middle reaches of the Spey mainstem are now larger on average than the one year old parr in the upper reaches.

For comparison the mean size of the one year old salmon parr in the lower Livet site was 94.1mm, 10mm larger than the highest mean of any site on the Avon. The Livet is a far richer river than the Avon and high densities of good size fry and parr can be supported there.

There are 2 comments for this article
  1. Charlie Herd at 6:06 pm

    Brian,

    Do these results not suggest that we should be stocking the parts of the Spey mainstem which appear to be capable of supporting many more and healthier juveniles than many of the other areas surveyed.?

    Charlie.

    • Brian Shaw Author at 1:44 pm

      Hi Charlie,
      The mainstem results indicate that the salmon fry numbers have improved on last year and are generally good throughout the mainstem with the exception of above Spey Dam. There are areas where fry numbers are lower than others but that will always be the case, indeed there will be variation from year to year as we have seen this year with much higher numbers in the lower mainstem than 2012. The distribution of the fry we counted in July will become less localised over the course of the forthcoming year as they disperse away from the spawning areas. Parr numbers exceeded fry at 7 sites out of 63 surveyed in the Spey mainstem, these were generally sites where the habitat was more suitable for parr. Therefore some of the differences in fry numbers are as much due to the suitability of the survey sites as anything else.
      The 2013 Spey mainstem salmon fry index survey highlights an encouraging situation.
      Brian Shaw

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