Appendix A. A description of the input parameters needed to create an ECOPATH mass balance, their units, and empirical relations necessary to calculate them, following the ECOPATH user guide (Christensen et al. 2005).
TABLE A1. Input parameters needed to create an ECOPATH mass-balance.
| Parameter | Description | Unit |
| Biomass (B) | Average biomass per unit area in the habitat area where the group occurs | t/km2 |
|
Production to biomass ratio (P / B) |
Equivalent to the instantaneous rate of total mortality (Z) | y-1 |
|
Consumption to biomass (Q / B) |
Rate of intake of food by a group over time | y-1 |
|
Ecotrophic efficiency (EE) |
Fraction of production that is further used in the system | |
|
Production over consumption (P / Q) |
Ratio between production and consumption, corresponds to gross food conversion efficiency |
|
|
Unassimilated consumption |
Fecal fraction, part of consumption that returns to detritus | |
| Detritus import | Rate of entry of detritus into the system | t/km2/y |
| Fishing landings | Represent the non-discarded part of the catch, expressed as flows | t/km2/y |
| Diets | Expressed as the fraction each prey contributes to the overall diet of a group |
TABLE A2. Empirical equations used to calculate productivity and consumption (Christensen et al. 2005), as well as quantifying Caridina nilotica* stocks (Goudswaard et al. 2006).
| Productivity |
P / B = Z = M + F P / B = K × (L∞ - L) / (L - L') |
| Consumption | Q / B = 10C1 - W∞-C2 × 10-C3 × 10A × C4 |
| Natural mortality | M = KC5 × L∞-C6 × C7 |
| Fishing mortality | F = Y / B |
| Length | L∞ = Lt / (1 - e(t - t0)) |
| Weight-length | W = a × Lb |
|
Shrimp weight-length relationship* |
FW = LC8 × e-C9 / C10 |
TABLE A3. Parameters needed for the empirical equations.
| P | Production | t/km2/y |
| B | Biomass | t/km2 |
| Z | Total mortality rate | y-1 |
| M | Natural mortality rate | y-1 |
| F | Fishing mortality rate | y-1 |
| K |
von Bertalanffy growth function parameter expressing rate at which asymptotic length is approached |
y-1 |
| L8 | Asymptotic length | cm |
| L | Mean length | cm |
| L’ | Length at entrance into fishery | cm |
| Y | Yield | t/km2 |
| Q | Consumption | t/km2/y |
| W8 | Asymptotic weight | G |
| A | Tail aspect ratio parameter | |
| Lt | Length at age t | Cm |
| t | Age | y |
| t0 |
von Bertalanffy growth function parameter expressing hypothetical age of a fish of length 0 |
y |
| W | Weight | g |
| L | Length | cm |
| a | Scaling factor in W-L relationship | |
| b | Exponent in W-L relationship | |
| DW | Dry weight | G |
| FW | Fresh weight | g |
TABLE A4. Constants used in empirical relations (Christensen et al. 2005).
| C1= 7.964 | C6= 0.279 |
| C2= 0.204 | C7= 4.439 |
| C3= 6.583 | C8= 2.7 |
| C4= 0.083 | C9= 4.876 |
| C5= 0.65 | C10=0.2 |
LITERATURE CITED
Christensen, V., C. Walters, and D. Pauly. 2005. ECOPATH with ECOSIM: a user's guide. Fisheries Centre, University of British Columbia, Vancouver.
Goudswaard, K. P. C., F. Witte, and J. H. Wanink. 2006. The shrimp Caridina nilotica in Lake Victoria (East africa), before and after the Nile perch increase. Hydrobiologia 563:31–44.