First decent catch in the smolt trap

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.

The Avon smolt trap from downstream. The relative size of the trap in rleation to the channel width was be seen from this angle. We haven't measrued the channel width yet but it is around 20m. The trap is only 1.8m wide so we are sampling only a small part of the total flow, although the deepest part.

The Avon smolt trap from downstream. The relative size of the trap in relation to the channel width can be seen from this angle. We haven’t measured the channel width yet but it is around 20m. The trap is only 1.8m wide and is only sampling a small part of the total flow, although the deepest part.

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.

Steve "tattooing" with blue dye to provide a temporary identification mark.

Steve “tattooing” with blue dye to provide a temporary identification mark.

Two presmolts awaiting marking.

Two fish awaiting marking.

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.

Size distribution of the salmon caught in the trap today. There were many in the high 90s but they will all smolts this year. Once they enter the Spey the rations available will be much richer than in the upper Avon.

Size distribution of the salmon caught in the trap today. There were many in the high 90s but they will smolt this year. Once they enter the Spey the rations available will be much richer than the sparse feeding they have been accustomed to in the upper Avon. We took scale samples from every 10th fish today. Of those read previously all have been 3 or 4 year old, much as expected as the older smolts generally run first.

In total we captured 295 salmon and 16 trout in the trap. The trout were up to 192mm in length.

Sea trout smolt of nearly 8".

Sea trout smolt of nearly 8″.

 

The back of the pickup makes a good workstation

The back of the pickup makes a good workstation.

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.

 

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