Salmonid spawning takes place in the late autumn and winter. Migratory salmonids such as salmon and sea trout, migrate upstream to spawn in their favoured locations in rivers and streams, and bury their eggs in depressions in the gravel created by kicking the gravel up with their tails. These areas are called redds and are fairly easy to spot when river conditions allow.
Redd counting has been taking place on the Wessex rivers for many years and has proved to be a very useful fishery management tool for both River Keepers/riparian owners and regulatory bodies.
Casterbridge Fisheries have been redd counting for many years now and has developed a consistent and reliable programme for collecting this valuable data in line with those employed by the Environment Agency on the other Wessex rivers.
Aims & objectives
Redd counting provides the following information:- A record of the spawning range in each year under specific flow conditions
- A comparison between years, allowing trends to be identified over time
- Identifies obstructions to fish passage
- Identifies areas of clustered spawning
- Identifies under-utilised spawning habitat
- The identification and later assessment of gravel cleaning sites
- Provides spawning data for the interpretation of fish population surveys
Ideally redd count data is collected every winter. However, river conditions can be unfavourable for long periods and monitoring windows missed, or the redds are flattened out and confidence in the accuracy of a count is too low. For this reason every effort is made to collect reliable data when river conditions allow.
In addition to the above, redd count data is of great importance when used to monitor the success of recently constructed fish passes, hydro electric schemes and in river enhancement projects.
Overall redd counting gives fishery owners, managers and other interested bodies a detailed indication of salmonid spawning abundance within the river catchment. The collection of this information is an important tool for the future research of our changing rivers and will continue to drive enhancements leading to the protection and promotion of our migratory salmonid stocks.
Methodology
The following methodology is used to collect the Redd count data and has been developed in conjunction with the Environment Agency (EA) to retain a high level of comparability with historical data collected by the EA and its predecessors.
- Redd counting takes place in late December and early January when the Salmon and sea trout have only just finished spawning
- Water conditions must be suitable for full observation of redds and any fish in the immediate area
- Individual salmon redds are mapped using GPS, the length and width of each redd is recorded and whether the redd has been cut on a gravel cleaned site
- Redds >1.1m wide are recorded as Salmon, <1.1m as sea trout
- Surveyors are experienced operatives who are competent at redd counting and work in pairs in line with our redd counting work instruction and risk assessment
- Information on the numbers recorded, measurements taken and, if possible, photographs, are then compiled and submitted in a detailed report
With experience it is possible to differentiate between salmon and sea trout redds by recording the timing of the spawning, gravel size and the size and shape of the redds excavated. The monitoring team should always consist of at least one person involved in the previous surveys to maintain a high level of consistency.
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