Salmon smolt run picking up nicely now

Over the last few days the smolt descent on the River Avon has picked up. On Thursday we trapped about 39 fish, Friday 80, Saturday 120 and over 320 this morning. The river level is dropping all the time but despite this the number of smolts running has increased. This increase is driven by the maturation of the smolts; fewer are classed as presmolts now, and higher temperatures. Yesterday morning the temperature was 7.6oC, it would have been higher during the lovely daytime sunshine but this morning it had dropped to 6oC following a sharp overnight frost.

What a lovely walk we have in the morning up to the smolt trap.

What a lovely walk we have in the morning up to the smolt trap.

On Friday we marked approximately 75 smolts and released them 1.2km upstream. On Saturday we had 5 recaptures of marked fish with a further 2 this morning giving a trap efficiency of 9%. The last few mark recapture trials have produced results of between 5-10%; exactly the sort of the consistency we were looking for. This tells us that we are only catching between  1 in 20 to 1 in 10 of all the smolts running past the trap at present. Further trials are planned this week.

The smolts have been coming in a range of sizes, generally between 90 to 140mm. The largest smolt of the season so far was caught this morning.

A big salmon smolt of 168mm. Scales were taken of this fish for aging purposes.

A “jumbo” salmon smolt of 168mm. Scales were taken of this fish for aging purposes.

This little video clip shows the fish retention box at the back of the 6ft smolts trap. There were about 70 smolts in the box yesterday morning. The constant flow of fresh water through the box keeps the fish in a lively condition. Click here to view the video.



There are 3 comments for this article
  1. Euan Reid at 7:20 pm

    Thank you Brian I would like to do that. Will drop you a text and organise.

  2. Euan Reid at 10:21 pm

    The smolt trap information is very interesting Brian and I take an interest because i was on the upper beat on gordon castle when the rotary screw trap was working on the left bank of the Rock Pool. The trap was checked and counted twice every day and a very high percentage of the smolts were captured overnight rather than through the day. Does this mean that the smolts move mainly at night or is it possible that during daylight hours they are more aware of the rotating drum of the trap and avoid it?

    • Brian Shaw Author at 1:24 pm

      Hi Euan,
      It is generally accepted that the smolts migrate mainly at night and that is my opinion also, certainly in burns and smaller rivers. I have checked the Avon trap a lot in the evening, and other traps, just prior to darkness and there has never been more than the occasional fish in the trap during daylight hours.
      The Avon is dropping all the time and we have had to lift the drum almost daily to keep clear of the river bottom. With less of the flukes in the water the rotation speed of the 6′ trap is lower (3.5 revs/minute today) but it still seems to be fishing okay; we had 400 in total today with 231 in the 6′ trap and 170 in the 4′. 200 were marked and released back upstream today so we should get a few recaptures tomorrow. You are more than welcome to come up and see the trap if you have time?

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