Each year The Tweed Foundation carry out electro-fishing surveys to monitor the numbers of juvenile Salmon and Trout throughout the Tweed catchment. This allows us to build up a picture of how juvenile numbers vary throughout the catchment and over time, and it furthers our understanding of how both man-made and natural factors are affecting our fish stocks. With this information we can inform management decisions on the river to help ensure that we have healthy fish stocks for future years.
Electro-fishing is a common method used for sampling wild fish populations. It works by placing both an anode and cathode into a stretch of water and passing a low current between the two. Doing this immobilises fish that are within the field of current, making them susceptible to capture. Once out of the current though, fish recover within seconds and can then be processed before being released back into the river.
We carry out two types of electro-fishing: quantitative and timed.
Our quantitative surveys use a standard method. First, we isolate each site using stop nets to prevent any fish from escaping or entering during the survey. We then start to electro-fish, working methodically upstream through the site.
For our timed electro-fishing we do not isolate each site. Instead, we survey each site for up to a maximum of three minutes, this giving a good representation of the numbers of fish present.
Electro-fishing plays an important role in a number of different monitoring programmes and projects we are currently undertaking.