Our annual fish surveys in the River Derwent catchment look for juvenile Atlantic Salmon and Brown Trout to determine the health and state of the catchment and monitor the species’ spawning success. Survey results also help us identify areas that are under-performing and secure funding for projects to improve habitat and water quality, and aid fish passage.
Trout fry - about 5-6 months old and salmon fry slightly older.
Surveys take place across the River Derwent catchment. The River Derwent arises out of Styhead Tarn, above the village of Seathwaite (the wettest place in England), and flows through the towns of Keswick and Cockermouth before reaching the sea at Workington.
As it flows through Cumbria it is joined by several large tributaries such as the River Greta, River Cocker and the River Marron, as well as many smaller tributaries.
We have survey sites on most tributaries of the River Derwent. Sites are selected based on a number of factors which are discussed in the reports. The main rivers are only surveyed if conditions are appropriate, due to the deep and fast flowing nature of these watercourses.
We first surveyed in 2015 when we looked at 89 sites. The number of sites surveyed had risen to 157 sites by the 2018 season.
We use the semi quantitative electrofishing method to conduct the surveys. Electrofishing is a common method used to survey fish populations. It involves creating an electric field in the water to draw the fish out, temporarily immobilising them and therefore making them easier to catch with a hand net. Prior to surveying, temperature and conductivity readings are taken to help the user to determine the settings the equipment should be on. The semi quantitative survey method requires fishing for a set length of time, usually a standard 5 minutes. The 5-minute time period is programmed into the kit which only times when the electric pulse is being used. The river is then fished in a zig zag pattern, working upstream against the flow, until the time runs out. The diagram below taken from the equipment manual shows the zig zag pattern and direction of travel.
Figure 2 is a diagram from the e fish manual, the only difference is we don’t use an upstream stop net. The following photos are examples of the method in action.
All fish caught are identified and recorded. Only the salmonids (collective name for both salmon and trout) are measured. In order to measure the salmonids, they are placed on a board which has an inbuilt ruler, mouths at zero and the value is taken from where the fork in their tail falls and rounded to the nearest 5mm. In the results you will see terms such as fry and parr. A fry is a juvenile salmonid less than a year old, a parr is a young salmonid, which is over a year old.
Photographs of fish being processed and measured, all fish are returned to the river after this has occurred.
We couldn’t conduct the surveys if it wasn’t for our wonderful volunteers.
Just some photos of the many volunteers who have helped conduct fish surveys in the past.
If you would like to join us please email email@example.com
This project is generously funded by the following organisations:
Some photographs used on this page were taken by our volunteers, including Martin Pullan and Hannah Marshall.