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.
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.
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.