A to Z at the smolt trap

We have had a busy few days at the Avon smolt trap with catches increasing further following a small rise in river levels earlier in the week. On Wednesday the river height increased by a couple inches but not until the early hours of the morning, possibly too late to stimulate an increase in the smolt run that night. The catch was still over 400 fish in total with more in the 6 foot diameter trap as usual.  That was despite there being a log of about 4′ in length and  6″ in diameter lodged in the cone. The trap was turning like a battery powered clock running out of charge – struggling to get the needle past twenty to the hour!

The offending log jammed in the 6 foot trap cone. It was still turning but only just.

The offending log jammed in the 6 foot trap cone. It was still turning but only just.

 

Wednesday mornings catch in the 6 foot trap. Few would guess there were 220 fish in the box.

Wednesday mornings catch in the 6 foot trap. Few would think there were 220 fish in the box.

Thursday was a big day with over 800 fish but todays catch was higher at over 1000. I don’t think we have seen the biggest daily catch yet; I hope for the other guys sanity that doesn’t happen this weekend as I would feel really guilty for having the weekend off.

Both recapture trials this week have produced trap efficiency estimates of 15-17%, higher than the earlier trials but we are stll only catching 1 in every 6 or 7 fish passing. An overall smolt production estimate will be provided at the end of the trapping period when trap efficiencies at a variety of flows have been calculated.

So far we have caught 4400 salmon in the traps, at least 95% of which have been smolts or presmolts; the rest mainly one year old parr. 39% of the salmon have been caught in the 4 foot, outer trap with 61% in the 6 foot trap – almost a direct correlation with trap size? However for the trout the situation is reversed with 54% caught in the 4 foot trap. We have caught 147 trout to date, 3.2% of the total fish caught but that will increase later when the trout smolt migration picks up. Todays catch of 33 trout was the highest so far.

Three trout, more than likely three different age classes. The larger fish at the top was more advanced in smolting but the middle fish is also likely to smolt this year. The darker trailing edge to the tail is a sure sign of smolting. The early signs of a black edge on the tail of the middle fish can be seen.

Three trout, more than likely three different age classes. The larger fish at the top was more advanced in smolting but the middle fish is also likely to smolt this year. The darker trailing edge to the tail, which can be seen clearly on the top fish, is a sure sign of smolting. The development of a black edge on the tail of the middle fish can be seen. The only theory that I have read regarding the dark trailing edge on smolts tails (found on salmon smolts also) was presented by Dick Shelton in his book “To Sea and Back”. His theory was that the black pigmentation of the fins, especially the tail, showed up prominently under water and may help the smolts to maintain contact with each other whilst migrating in shoals. The wee parr at the bottom is unlikely to smolt this spring, indeed it may never, perhaps it is destined to remain as a river trout which might not be a bad strategy at the moment.

The A to Z? Well today I marked the record sheets in alphabetical order so that we could match the scale packets to the correct sheet. We were on sheet Z when we finished so we knew we had over 1000 fish for the day. I think I will just number the sheets from now on.

 

 

There are 4 comments for this article
  1. Niall Cook at 11:53 am

    Hi,

    On our 8′ diameter trap we found it tricky to remove objects like that and bigger (especially at night on a rising river!!) so we installed a couple of hatches into the drum where it narrows towards the neck – i can send you pics if you like? Niall.

  2. craig mackay at 11:03 pm

    …fascinating stuff and a great read!…keep the updates coming and well done for all the unseen hard work!

  3. Anthony Tinsley at 4:00 pm

    With catches this high you will have a very accurate estimate of the smolt population in the Avon this year. We’ve come a long way since our first screw trap deployment on the Brae Water. Well done, all.

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