Grade 
Description 
Interpretation 
A 
Excellent 
In the top 20% for a fishery of this type 
B 
Good 
In the top 40% for a fishery of this type 
C 
Fair 
In the middle 20% for a fishery of this type 
D 
Fair 
In the bottom 40% for a fishery of this type 
E 
Poor 
In the bottom 20% for a fishery of this type 
F 
Fishless 
No fish of this type present 
How is fish density on the Avon graded?
 From 2002 to 2006 inclusive the site on the Avon at Avonwick Mill (now named Turtley Corn Mill) was fished between stop nets and each survey consisted of 3 runs
 From 2007 onwards the site has been fished using no stop nets and only one run (The Environment Agency National Fish Population Database (NFPD) automatically adjusts the figures for the onerun surveys and produces the results as if they had fished the site using 3 runs between stop nets)
 The same site is fished every year and is fished in an upstream direction using electric fishing kit producing a Pulsed Direct Current of approximately 0.3amps
The number of fish caught is expressed as the density of fish per 100 square meters 100m. This value is then converted into a grade using the following conversion table:


A 
B 
C 
D 
E 

Age 
Density of fish per 100 square meters 100m 
Brown/Sea Trout 
0+ 
>38 
17 to 37 
8 to 16 
3 to 7 
<3 
Brown/Sea Trout 
>0+ 
>21 
12 to 20 
5 to 11 
2 to 4 
<2 
Salmon 
0+ 
>86 
45 to 85 
23 to 44 
9 to 22 
<9 
Salmon 
>0+ 
>19 
10 to 18 
5 to 9 
3 to 4 
<3 
 In the next set of tables, population density is expressed in two ways:
 Density of fish per 100 square meters 100m
 and as the corresponding National Fishery Classification Scheme grade – from A through F
 The data from three local rivers – the Avon, Erme and Yealm is presented below for comparison
 EA data kindly supplied by Mike Cooper and Stuart Watts, Aune Conservation Association
Avon – Glazebrook Avonwick Mill 
Year 
Trout Fry density 
Grade 
Trout Parr density 
Grade 
Salmon Fry density 
Grade 
Salmon Parr density 
Grade 
2002 
5.68 
D 
4.39 
D 
8.51 
E 
5.93 
C 
2003 
11.87 
C 
12.84 
B 
40.12 
C 
8.99 
C 
2004 
12.02 
C 
18.35 
B 
27.2 
C 
9.81 
C 
2005 
8.52 
C 
16.19 
B 
10.51 
D 
6 
C 
2006 
18.62 
B 
19.3 
B 
33.18 
C 
6.77 
C 
2007 
11.13 
C 
12.11 
B 
33.38 
C 
8.51 
C 
2008 
9.58 
C 
9.3 
C 
27.63 
C 
11.56 
B 
2009 
10.27 
C 
10.61 
C 
78.03 
B 
11.98 
B 

Erme – Lower Piles 
Year 
Trout Fry density 
Grade 
Trout Parr density 
Grade 
Salmon Fry density 
Grade 
Salmon Parr density 
Grade 
2002 
15.59 
C 
15.02 
B 
3.69 
E 
0.85 
E 
2003 
13.93 
C 
8.47 
C 
1.09 
E 
2.73 
E 
2004 
29.61 
B 
12.21 
B 
18.32 
D 
3.05 
D 
2005 
30.63 
B 
12.25 
B 
16.44 
D 
6.13 
C 
2006 
25.97 
B 
9.74 
C 
8.99 
E 
4.25 
D 
2007 
20.53 
B 
21.38 
A 
4.5 
E 
6.75 
C 
2008 
11.88 
C 
4.99 
D 
0.48 
E 
3.09 
D 
2009 
14.20 
C 
13.74 
B 
0.93 
E 
4.19 
D 

Yealm – Potson’s Wood (SX6027056630) 
Year 
Trout Fry density 
Grade 
Trout Parr density 
Grade 
Salmon Fry density 
Grade 
Salmon Parr density 
Grade 
2002 
5.8 
D 
7.1 
C 
6.2 
E 
2.1 
E 
2003 
8.1 
C 
14.9 
B 
16.9 
D 
3.7 
D 
2004 
5.2 
D 
12.2 
B 
27.0 
C 
5.2 
C 
2005 
2.1 
E 
9.8 
C 
32.0 
C 
8.5 
C 
2006 
12.9 
C 
11 
C 
39.2 
C 
8.2 
C 
2007 
1.0 
E 
4.1 
D 
40.6 
C 
3.7 
D 
2008 
6.5 
D 
5.9 
C 
7.5 
E 
3.6 
D 
