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 2008 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 |
|
Hope |
11.62 |
13.02 |
9.94 |
6.19 |
|
Dionard |
6.19 |
12.16 |
13.22 |
8.89 |
|
Achriesgill |
7.93 |
13.12 |
3.39 |
7.65 |
|
Oldshoremore |
20.46 |
10.51 |
9.55 |
1.67 |
|
Loch na Thull |
11.29 |
14.42 |
14.66 |
5.07 |
|
Laxford |
7.26 |
7.56 |
4.05 |
0.97 |
|
Bad na Baighe |
1.77 |
7.43 |
3.48 |
4.20 |
|
Claise na Fearna |
6.19 |
12.16 |
13.22 |
8.89 |
|
Loch nam Brac |
0.00 |
0.00 |
24.01 |
13.45 |
|
Bhadaidh Daraich |
0.00 |
0.00 |
20.85 |
18.45 |
|
Duart |
1.70 |
3.02 |
7.08 |
1.94 |
|
Gleann Dhub |
0.00 |
0.00 |
0.27 |
5.71 |
|
Gleann Leireag |
0.00 |
0.36 |
2.66 |
8.95 |
|
Manse |
16.58 |
8.33 |
4.58 |
2.91 |
|
Inver |
4.60 |
7.97 |
2.89 |
3.77 |
|
Culag |
6.27 |
0.83 |
0.00 |
0.00 |
|
Badnaban |
0.00 |
0.00 |
24.24 |
10.77 |
|
Gleann an Strathan |
8.62 |
8.24 |
7.94 |
18.73 |
The West Sutherland area shows a good mix of salmonid species, with trout present in all catchments with the exception of the Culag and salmon in most . The absence of trout from the Culag is likely to be a function of the habitat surveyed, as trout have been previously sampled in the Glen Loch. Eels are also common throughout the area, occurring in all of the systems examined, with the exception of the Inver. Minnow, in contrast, occurred with varying distributions in 9 out of the 20 systems, while 3-spined stickleback and plaice were found only in the Dionard.
The results from this survey indicate that salmon and trout populations are dispersed throughout the area. With the exception of Glendhu, only rivers with restricted access to the sea did not support a salmon population, however small. These systems supported healthy trout populations. With regards to Glendhu, the poor habitat is likely to have affected this system and it is planned to remedy this in the coming year. Only in Gleann Leireag were missing year classes observed, with salmon fry absent from the sampling. This probably reflects the habitat at the survey sites, with salmon only located at one site below the falls with habitat more suited to parr. All other 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. Stocking does not form a major part in the management of systems monitored in 2007, with the exception of the Laxford and Garvie. In the Laxford the system is stocked with salmon in the Lone tributary. However this will not have affected the sites sampled during 2008. The Garvie, in contrast, is stocked with trout eggs around Loch Osgaig. Results from this stocking would be expected in the OB sites, although there was little evidence of this activity within this survey with the possible exception of OB2. 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