It's January, it's cold, that can only mean one thing - salmonid redd counting!
We've been out and about on the River Allen this week, along with the Wild Trout Trust, undertaking our annual salmonid redd count survey to assess salmon (and trout) spawning and distribution. This is part of an ongoing large-scale ecological monitoring programme on the River Allen and lower River Stour, commissioned by South West Water.
Salmon lay their eggs in 'nests' in clean gravel, called redds. Female salmon will find a suitable spot and dig a depression in the gravel using their tail. This also cleans silt out of the gravel, which is important to maintain water flow and oxygen for egg development.
The resulting redd will typically comprise a depression in the gravel with a mound of displaced gravel immediately downstream, where the eggs will be deposited. The action of cleaning the gravel and removing silt means that redds are visible as clean patches in contrast to the surrounding river bed.
The same 12 km stretch is walked each year and all redds are recorded, including details such as size, location and whether or not any fish were present. All the data are mapped in GIS and raw data stored to assess trends over time.
Comments