The Tweed Foundation

THE TWEED FOUNDATION

Ettrick Fish Counter Camera

On September 22nd, the new, improved version of the counter was installed. This has a camera which is triggered by the scanner to take 5 photos of each fish it registers. It was hoped that this would allow at least 10% of the fish that pass to be identified as either Salmon or Trout. In fact, it appears that an actual majority of fish can be identified directly from their photographs, using the tail as the main feature for identification. Those that cannot be visually identified will be separated by their lengths, as before, using information from those that can be identified as to what proportions of fish are trout or are salmon in each length category. This will give much better estimates of relative proportions than those previously used, which were based on trapping in the fish ladder during 1998, so previous years' data will be re-analysed once there is photo information from a whole year. It is already clear that the number of large Sea-trout running the Ettrick has been underestimated.

Two examples of the sort of photographs that are now being taken are attached, one of a Salmon and one of a Trout. There is an infra-red light source at the scanner, which allows photos to be taken at night without alarming the fish.

From the September 22nd to the 30th, the totals for those fish that could be directly identified are -

774 Salmon

236 Trout

(+182 uncertain)

The new model of counter will also make checking its overall efficiency easier. Previously, an underwater TV camera was positioned over the upstream exit of the scanner so that fish coming out could be seen on screen and a check made as to whether they had been registered or not. This sort of check could only be carried out when water levels were sufficiently low for the TV cable to be strung over the river to the fish ladder. With the new model, the camera that takes the still photos of the fish is actually on all of the time, though photos are only taken when the scanner triggers it as a fish is registered. This continuous picture can now be used to see what proportion of fish passing through is actually registered by the counter and will allow many more efficiency checks to be made and at higher water levels than previously.

Sea Trout

Sea Trout tail

Salmon

Salmon tail

Video clip are also records and these can be seen at fish counter results

 

[Home] [About] [Management] [News] [Contact] [Site map] [Join]