Weir count accuracy?
I'm just curious; how accurate is fish identification at certain weirs? Is it 100% at all weirs? 75 at some, 95% at others? The reason I ask is based on yesterday's visit to Fish Creek. The clear water was full of fish, but the majority were pinks. There were some reds, and some silvers. It was very difficult to determine which was which until they were in the net, as all were the same size, and ocean bright. If these fish are getting to the weir within a day or two of entering the creek, how do the techs differentiate all species passing through?
I suspect the weir count is less than 100% accurate; 705 pinks july 24, 2898 sockeye, 65 silvers. My catch in the clear water was 2 silvers, 1 red, and 20 some odd pinks. That does not say that's what the stock composition was: I had a poor net for the job, pinks swim slower and go up instead of down and around, and some of the reds were so small they passed right through. Still, though, most of the fish I saw were pinks, and the fact I caught a two to one ratio of silvers to reds leads me to wonder if 68 silvers and 700 pinks to nearly 3000 sockeye is a skewed figure.
A small system with a weir is pretty good - the fish are channeled through a counting area and are easily seen. So while mistakes can be made if the techs are sloppy it should be fairly close.
Originally Posted by willphish4food
On larger systems that have flow or dirty water the error can be much higher, especially if the weir erodes and a hole develops under the bottom plate or pickets.