Juvenile surveys provide information on the number of young fish present in the catchment and their age ranges. This information can then be used to target areas most in need of rehabilitation, monitor improvements and determine if there has been a serious problem resulting in no recruitment for a year, or several years.
Electrofishing is used to catch the fish. By passing an electric current through the water, the fish are stunned and attracted to the electrode, where they can be netted out and examined. The fish are then returned to the survey site.
Results from the 2009 juvenile survey are as follows:
The average densities of salmon and trout per 100 m2 within each catchment surveyed
|
|
Density (100 m2) |
|||
|
Catchment |
Salmon fry |
Salmon parr |
Trout fry |
Trout parr |
|
Polla |
14.37 |
6.40 |
7.81 |
3.88 |
|
Loch Innis na Ba Buidhe |
0.00 |
3.75 |
43.64 |
12.27 |
|
Laxford |
12.47 |
9.71 |
30.10 |
11.50 |
|
Clashnessie |
0.00 |
1.56 |
6.85 |
15.30 |
The West Sutherland area shows a good mix of salmonid species, with trout and salmon present in all catchments. Eels are also common throughout the area, occurring in all of the systems examined. Minnow are also common throughout the area, with the exception of the Polla, while 3-spined stickleback were found only in the Polla.
The results from this survey indicate that salmon and trout populations are dispersed throughout the area. Missing year classes were observed in Loch Innis na Ba Buidhe and Clashnessie, with salmon fry absent from the sampling. This probably reflects the transitory nature of the salmon population within these catchments, together with the habitat at the survey sites. Trout populations in all systems had a range of age classes, with populations appearing to be healthy, if small.
When compared to the previous surveys within these systems, the fish densities did not show any discernible pattern, increasing in some systems while decreasing in others. However, they remained within the range found in previous surveys, therefore indicating that there are no current problems within these catchments. Stocking does not form a major part in the management of systems monitored in 2009, with the exception of the Laxford. In the Laxford the system is stocked with salmon in the Lone tributary. However this will not have affected the sites sampled during 2009. Other factors that may affect the results, compared to previous years, include water flow and temperature, with a wet summer affecting sampling efficiency and the ability to reach and survey many of the original sites.
The occurrence of each species in the different catchments, as a percentage of sites visited