Lakes and Watercourses

TABLE 44.
CURRENT CONDITIONS: fish, lakes
Class Description No. of species 1 Species diversity 2 Biomass 3 Number 3
1 Very high number of species, etc ≥ 10 > 0.65 > 4000 > 95
2 High number of species, etc 6 – 9 0.55 – 0.65 1800 – 4000 35 – 95
3 Moderate number of species, etc 3 – 5 0.28 – 0.55 650 – 1800 13 – 35
4 Low number of species, etc 2 0.11 – 0.28 250 – 650 5 – 13
5 Very low number of species, etc ≤ 1 ≤ 0.11 ≤ 250 ≤ 5
Class Description Proportion of piscivorous fish 4
1 Very high proportion of pisc. fish > 0.82
2 High proportion of pisc. fish 0.54 – 0.82
3 Moderately high proportion of pisc. fish 0.24 – 0.54
4 Low proportion of pisc. fish 0.09 – 0.24
5 Very low proportion of pisc. fish ≤ 0.09
Class Description Overall index 5
1 Very low overall index < 2.2
2 Low overall index 2.2 – 2.6
3 Moderately high overall index 2.6 – 3.4
4 High overall index 3.4 – 4.2
5 Very high overall index ≤ 4.2
1 Only fish species native to Sweden are included (see list of species in Appendix 3).
2 Species diversity is calculated as Shannon-Wiener’s H’ = [W tot log 10 (W tot ) – Σ W i log 10 (W i )] / W tot ,
where W tot is the total weight per effort and Wi is the weight per effort for each species. An effort
constitutes one night’s fishing with a net using a standard method.
3 Biomass and number are expressed as grams and number per effort, respectively.
4 Piscivorous percids includes zander (Sander lucioperca) and perch (Perca fluviatilis) more than
150 mm in length. The parameter is only calculated for lakes where perch and/or zander are
caught.
5 The overall index is calculated as the mean of the class figures for all parameters included.
class boundaries. In most cases, this means that 50 per cent of existing
data will fall within class 3.
Class 1 in the overall index indicates that the fish fauna of the lake
consists of a large number of species with high diversity, many fish with a
high proportion of piscivorous fish, ie, a rich and diverse fish community.
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