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8.1.2. Principles
8.1.2. Principles
This model is based on two major equations
a. Describes the production term
b. Energy balance of each group
The model is computed from the equation
Pi = Yi + Bi . M2i + Ei + BAi + Pi . (1-E Ei)
Pi = Total production rate (i)
Yi = Total fishery catch rate of (i)
M2i = Total predation rate for group
Bi = Biomass of the group.
Ei = Net migration rate which includes emigration – immigration
BAi is the biomass accumulation rate for (i) while MOi = Pi (1-EEi) is the other mortality rate for (i).
The above equation can be expressed as
Bi . (P/B)i . EEi $$\sum_ {J=1} ^ {n}$$Bj $$\cdot{Q \over B}$$; DCji - YA - Ei -BAi = 0
Where, P/Bi is the production / biomass ratio
Q/Bi is the Consumption / biomass ratio
DCji, the fraction of prey (i) in the average diet of predator (j).
The production rate, Pi could be calculated as the product of Bi. the biomass of (i), while the Pi/Bi is production / biomass ratios for group (i). The Pi/Bi rate mostly corresponds to total mortality Z.
The other mortality includes mortality due to decrease of old age and could be computed from
Moi = Pi . (1 – EEi)
Where, EEi is called ecotrophical efficiency of (i).
The ecotrophic efficiency is described as the production that is utilized in the system.
M2 is the production term that links production and prey as
M2i =$$\sum_{J=1}^n$$ . DCji
The summation includes all (n) predator groups (j) feeding on group (i),
Qj is the total consumption rate for group (j)
DCji is the fraction of predator (j) diet contributed by prey (i).
Qj is calculated as the product of Bj, the biomass of group (i) and Qj / Bj the consumption / biomass ratio for group (j).
Ecopath model sets up a system with many linear equations for parameterization. This model usually solves the set of one of the following parameters for catch group in a system. The parameters are biomass, production / biomass ratio, consumption / biomass ratio or ecotrophic efficiency.