390
17. An Age-structured Model of Fish Population Enhancement
INFLOWS :
IF NET_PROFITS < 0 THEN -NET_PROFITS
NEW_DEBT_LOSSES
ELSE 0
OUTFLOWS :
ANNUAL_PAYMENT = if DEBT> 0 then (if NET_PROFITS>
DEBT then DEBT else (if NET_PROFITS> 0 then
NET_PROFITS else 0)) else 0
COST_PER_FISH = 1
INITIAL_LOAN_AMOUNT = 1000000
INTEREST_RATE = .1
NET_PROFITS = ANNUAL_REVENUE-ANNUAL_INTEREST COSTANNUAL_OP_COSTS-HATCHERY_TAXES
PRICE = 2.2{$US per KG} /1000 {convert kg to grams}
SUM_CATCH_WT = CATCH_WEIGHT[AGE_3_TO_4] +
CATCH_WEIGHT [AGE_4_TO_5] + CATCH_WEIGHT[AGE_5_TO_6] +
CATCH_WEIGHT [AGE_6_TO_7] + CATCH_WEIGHT[AGE_7_TO_8] +
CATCH_WEIGHT [AGE_8_TO_9] + CATCH_WEIGHT[AGE_9_TO_10] +
CATCH_WEIGHT [AGE_10_PLUS]
TAX_RATE = GRAPH(SUM_CATCH_#S)
(0.00, 0.00025) ,
(1.5e+06, 0.042),
(3e+06, 0 .0485),
(4 .5e+06, 0.003),
HATCHERY
(500000 , 0.0065),
(2e+06, 0 .048) ,
(le+06, 0.0163),
(2.5e+06, 0 .049),
(4e+06,
(3 .5e+06, 0.0442),
(5e+06 , 0 .001)
0 .009),
CULTURED_JUVENILES(t) = CULTURED_JUVENILES(t-dt) +
(FISH_RAISED-CULTURED_DEATHS-ENHANCEMENT) * dt
INIT CULTURED_JUVENILES = 0
INFLOWS :
FISH_RAISED = PULSE (NUMBER_FISH_RAISED,l ,l) * (IF
YEARS_ENHANCING < TIME THEN 0 ELSE 1)
OUTFLOWS:
CULTURED_DEATHS = (CULTURED_JUVENILES) *
(BEHAVIORAL_MORTALITY)
ENHANCEMENT = CULTURED_JUVENILES-CULTURED_DEATHS
BEHAVIORAL_MORTALITY = 0 .18
NUMBER_FISH_RAISED = 100000
YEARS_ENHANCING = 10
LIFE HISTORY
HAT_AGE_1(t) = HAT_AGE_1(t-dt) + (ENHANCEMENT-TO_JUV_2DIE_HAT_AGE_1) * dt
INIT HAT_AGE_1 = 0