For our last day electrofishing we headed for the mainstem to collect some semi-quantitative (no stop nets and only one run through with the electrofisher) data on fish densities. Mostly we do timed salmon fry index electrofishing surveys on the mainstem but that techique doesn’t produce data on fish densities. It is impossible to fish the entire width of the Spey mainstem (even in these very low water conditions) so we restricted ourselves to surveying defined areas along the margins, a technique that had been used before and should be repeatable in the future.
This area of the river at Aberlour has in the last couple years produced high salmon and parr counts so it was no surprise to find that densities of both were excellent. The density of salmon fry was 134/100m2 and for parr 62/100m2. Over 60% of the parr were larger than 90mm, a size threshold considered to indicate it would be ready for smoltification the following spring.
The next site had been surveyed before in 2002 and 2003, although the river had changed a little making exact replication difficult.
The density this year was 98 fry and 33 parr per 100m2 respectively. The salmon fry density was similar compared to 2002 (114/100m2) and 2003 (79/100m2) whilst the parr density was higher than found in 2002 (20.2/100m2) but less than the 50/100m2 recorded in 2003. Still there appears to have been little overall change in fish densities now compared to that snapshot from over a decade ago.
The next site was upstream of Advie Bridge where the habitat looked good but fish densities were lower than anticipated. I don’t have a good photo showing the entire site but the picture below shows the type of habitat present.
Unfortunately two thirds of the way through the site Steve slipped on the slimy rocks, landing on the anode which ceased to function. Thankfully he was okay and it was the the last electrofishing day rather than in the middle of our survey programme. We missed out on the last planned site at Grantown but we had at least gathered some interesting semi-quantitative data from the mainstem, the most important part of the Spey catchment in terms of smolt production.