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13. Nile Perch Population Dynamics in Lake Victoria :
seine_mort [Cohorts] = IF (Fishwt [Cohorts]< = 0) THEN 0
ELSE(seine_mortality[Cohorts] /Fishwt[Cohorts]) {number
of fish seined per cohort per day}
seine_mortality [Cohorts] = IF(Total_seinable_mass< = 0)
THEN 0 ELSE(IF(Fishwt[Cohorts] THEN((NP_mass[Cohorts] /Total_seinable_mass)*Total_seini
ng_intensity) ELSE 0) {number of fish seined per cohort
per day}
Tot_spawned_biomass = ARRAYSUM(Reproduction[*])
Management
Gill_net_management_regime(t)
Gill_net_management_regime(t-dt) + (new_regime) * dt
INIT Gill_net_management_regime = 0 { percent nets
deployed}
INFLOWS:
new_regime =
PULSE(((Gill_net_allowance*Total_fishable_mass)Gill_net_management_regime) ,Management-period,Managemen
t-period)
Seine_management_regime(t) = Seine_management_regime(tdt) + (new_regime_2) * dt
INIT Seine_management_regime = 0 { percent nets
deployed}
INFLOWS:
new_regime_2
PULSE(((Seine_allowance*Total_seinable_mass)Seine_management_regime),Management-period,Management-p
eriod)
env_variability =
RANDOM (Min_uncertainty, Max_uncertainty, 1)
Management-period = 1
maximum_size = max_size*env_variability {maximum size,
in grams, likely to be susceptible to a beach seine
fishery}
max_size = 1500 {maximum size of seinable fish in
grams}
Max_uncertainty = 1 { a number between one and which
denotes the maximum level of flux in the model. A max
uncertainty of two will, at most, double several of the