River Dulnain salmon fry surveys – interim results

The 2015 electrofishing survey programme includes the River Dulnain amongst the tributaries due for assessment. In 2012 we introduced the three year rotational system so this year sees the first of the repeat visits to locations surveyed in year one of the rota. A few weeks ago we managed to completed most of the Dulnain mainstem salmon fry index surveys reaching as far upstream as river section 55 (27.5km from the confluence with the Spey). Three more Dulnain mainstem salmon fry surveys are still to be completed. This blog summarises the findings so far.

In order to enable direct, and statistical, comparisons to be made the same sites surveys in 2012 were all revisited, although one or two had changed somewhat. In addition two new sites were added to provide better geographical coverage (they will be excluded from the 2012/2015 comparisons).

The first new site was in the lower reaches just upstream of the railway line (soon to be operational again hopefully).

New site in the lower reaches about 1km upstream from the spey confluence. The site produced quite good fish numbers with 46 fry and 22 salmon parr.

New site in the lower reaches about 1km upstream from the Spey confluence. The site produced quite good fish numbers with 46 fry and 22 salmon parr.

 

The site at Duthil was one of the most productive in 2012 and it remained so this year with 224 fry captured in the three minute survey. The habitat here is ideal for fry and they were found in every sweep of the probe all the way across the riffle.

The site at Duthil was one of the most productive in 2012 and it remained so this year with 224 fry captured in the three minute survey. The habitat here is ideal for fry and they were found in every sweep of the probe all the way across the riffle.

The catch from the Duthil survey site.

The catch from the Duthil survey site.

The Dulnain was severely affected by the Bertha spate last August with the hump backed bridge at Carrbridge featuring the national news. In 2012 the survey site in section 34 is now dry riverbed with the flow switching to the other side of the channel.

The Dulnain was severely affected by the Bertha spate last August with the impressive flow through the hump backed bridge at Carrbridge featuring the national news. As a result of the gravel movements during the spate the 2012 survey site in section 34 is now dry riverbed with the flow switching to the opposite side of the channel.

2015 survey site in section 34. Not exactly a direct comparison with with 2012 but in mobile sectiosn such as this there is no option but to follow the habitat. Salnon fry numbers at this site were about one third of the 2012 catch.

2015 survey site in section 34. Not exactly a direct comparison with 2012 but in mobile sections such as this there is no option but to follow the habitat. Salnon fry numbers at this site were down at about one third of the 2012 catch.

At Dailnahaitnach the river had become braided with several channels present. We spent half the survey time in each of the channels in the foreground of the photo.

At Dalnahaitnach the river had become braided with several channels present. We spent half the survey time in each of the channels in the foreground of the photo. Good fry habitat here and the survey produced 43 fry.

As we progressed upstream the catches of fry declined in comparison to the lower sites, similar to the pattern found in 2012. The last survey section surveyed so far was in section 55.

The run riffle habitat in the left side of the channel was surveyed in section 55. Not many fry and no parr were found here this year.

The run riffle habitat in the left side of the channel was surveyed in section 55. Not many fry and no parr were found here this year. There weren’t many fry and parr in 2012  either but more than we found this year.

There are there more sites upstream still to do but now the grouse season is nigh access will be a little more problematic. However the estates are usually very accommodating with our requests.

The comparative results so far are shown in the graphs below.

Dulnain salmon fry counts per minute in 2012/2015. The average per minute in 2012 was 16.2 compared to 22.7 this year.

Dulnain salmon fry counts per minute in 2012/2015. The average fry count per minute in 2012 was 16.2 compared to 22.7 this year (although somewhat distorted by the much higher counts in site TSD21). Fry counts in all the sites below Carrbridge (section 30) were higher in 2015 than in 2012 but upstream the results were more mixed. Once of the results are available we will do a statistical comparison to see if there are any significant differences.

For parr

These surveys are targetted at fry but parr are also caught. The average parr count from the same sites surveyed in both years was 2.5 per minute this year compeared to 1.8 in 2012. The two new sites, TSD02 and TSD26 both produced above average parr counts but those results were excluded from the above comparison.

It will be interesting to see what we find in the remaining sites and to see if there have been any statistically valid differences between the two survey years. The overall pattern of higher fry counts downstream of Carrbridge was consistent and is likely to be a stable feature due to factors such as habitat suitability, altitude, distance from the sea and general instream productivity. These results from the Dulnain were quite encouraging but the the results from other sites across the catchment have been mixed. More soon once the remaining surveys have been completed.

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