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Table 2

Fish-based metrics comprising the Balaton fish index (BFI) assessing the ecological quality ratio (EQR) of Lake Balaton, their categories and scoring by categories. eNPUE (ind. 100 m−1), catch per unit effort by number in electric fishing samples; gNPUE (ind. standard gillnetting effort−1) and gBPUE (g standard gillnetting effort−1), catch per unit effort by number and biomass in gillnetting samples; standard gillnetting effort represents one hour of fishing with a standard gillnet setup − 14 mesh sizes, 2.5 m long each − covering the whole water column. Native, native phytophilous (phyt.), native key species and non-native species are listed in Appendix 1.

Metrics Metric categories Scoring by category


  1 2 3 4   1 2 3 4
Electric fishing samples                  
1. nnative with eNPUE ≥ 0.1 ind. 100 m−1 <8 8–10 11–12 13≤   0 3 7 10
2. eNPUEphyt. eNPUEtotal −1 <0.05 0.05–0.15 0.15–0.25 0.25≤   0 3 7 10
3. eNPUEnon-native eNPUEtotal −1 <0.01 0.01–0.1 0.1–0.25 0.25≤   10 7 3 0
                   
Gillnetting samples                  
4. nnative with gNPUE ≥ 0.2 ind. standard gillnetting effort−1 <4 4–6 7–8 9≤   0 3 7 10
5. gNPUEnon-native gNPUEtotal −1 <0.01 0.01–0.1 0.1–0.25 0.25≤   5 3 1 0
6. gBPUEnon-native gBPUEtotal −1 <0.01 0.01–0.1 0.1–0.25 0.25≤   10 7 3 0
7. gBPUEcarp gBPUEtotal −1 <0.001 0.001–0.01 0.01≤     0 5 0  
8. gBPUErazor fish <20 20–200 200–1000 1000≤   0 5 10 5
9. gBPUEpikeperch gBPUEtotal −1 <0.01 0.01–0.04 0.04–0.08 0.08≤   0 5 10 5
10. gBPUEbream <300 300–1200 1200≤     0 5 0  
11. gBPUEtotal <1000 1000–4000 4000≤     0 5 0  
                   
Electric fishing and gillnetting samples                  
12. Age structure (balanced: balanced in all native key species and in all other native species with exception of no more than two; partly unbalanced: unbalanced in one key species or at least in three other native species; unbalanced: unbalanced at least in two native key species) Balanced Partly unbalanced Unbalanced     5 3 0  
13. Health status (good: <5% of individuals show any sign of diseases, heavy infection by parasites, malformations and hybridisation; 5–20% of individuals show some signs of these abnormalities; bad: >20% of individuals are affected). Good Moderate Bad     5 3 0