The River Avon rose about 1ft last night, due entirely to snow melt in the Cairngorms, and we had our first good catch of smolts this morning. The conductivity reading this morning was 32. Typically if has been 70-80 microsiemens/cm but it was reduced significantly through the influence of the lower conductivity water from the snow melt in the upper catchment. The temperature this morning was 5.1oC; it would have been higher yesterday afternoon in the warm spring weather.
According to the SEPA gauge the Avon peaked at 50cm at midnight but had dropped to about 40cm by 9 this morning. On lifting the trap lid we could see there were quite a few fish although everyone tends to understimate the number at this stage. As this was the first good catch we marked 200 of the smolts with a blue dye on the belly towards the pectoral fins. These marked fish were then released back upstream. The number recaptured over the next few days will give us the first indication of the efficiency of the trap in what is a new location.
Many of the salmon today were really still presmolts i.e. the parr marks were still visible although with signs of silvering. The average size of the smolts/presmolts was 108mm, the largest about 143mm. Also present were a few smaller parr; all with intact adipose fins.
In total we captured 295 salmon and 16 trout in the trap. The trout were up to 192mm in length.
It was good to catch a few fish today (I wasn’t quite at the “phew” stage yet, but in a new location there is always a certain anxiety as to how the trap will perform). Prior to today the highest daily total was eight. It will be interesting to see how many recaptures there are over the next few days. If we get 10-20 from the 200 released today we will be happy. As this the rise in river level was driven by snow melt (which is only now present in any quantity in the Cairngorms, i.e. – the Loch Avon area) most of these smolts to be Avon mainstem fish. There is little snow remaining in any of the tributary catchments but they will start to contribute once we get some rain.