36.2 Grass Carp Model Equations
ST1(t) ¼ ST1(t À dt) + (PSG À F1) * dt
INIT ST1 ¼ 0
INFLOWS:
PSG ¼ PLANT_STOCK_G {This section computes the max plant peak in each
year, sums those peaks over the ten-year period of the run and then divides this
sum by the sum of ten years of plant peaks which are undisturbed by grazing.}
OUTFLOWS:
F1 ¼ ST1
ST2(t) ¼ ST2(t À dt) + (F1 À F2) * dt
INIT ST2 ¼ 0
INFLOWS:
F1 ¼ ST1
OUTFLOWS:
F2 ¼ ST2
CAL_SIZE(t) ¼ CAL_SIZE(t À dt) + (INGESTION + SIZE_PULSE À EXCRETION À RESPIRATION) * dt
INIT CAL_SIZE ¼ 0
INFLOWS:
INGESTION ¼ IF CAL_SIZE > 0 THEN ACTUAL_INGEST ELSE 0 {Calories
per Fish-Week}
SIZE_PULSE ¼ PULSE(F_SIZE_CAL_1, TIME_1, 1000) + PULSE(SIZE_REAVG,
TIME_2, 1000) {This is the pulsing of the two control sizes in std. cals, into the average
calorie size state variable box.}
OUTFLOWS:
EXCRETION ¼
IF G_SIZE > 0 THEN (1-ASSIMILATION * K_1)
* K2 * INGESTION ELSE 0 {Calories per Fish–Week}
RESPIRATION ¼ IF G_SIZE > 0 THEN 7 * (STANDARD_METAB
* ACTIV_FAC)+SDA ELSE 0 {Standard Calories per Fish–Week}
CUM_DEG_DAYS(t) ¼ CUM_DEG_DAYS(t À dt) + (DD_RATE À CDD_RESET) * dt
INIT CUM_DEG_DAYS ¼ 0
INFLOWS:
DD_RATE ¼ IF WATER_TEMP >¼ 0 THEN (WATER_TEMP) * 7 ELSE 0
OUTFLOWS:
CDD_RESET ¼ IF WEEK ¼ 52 THEN CUM_DEG_DAYS ELSE 0 {This control
dumps the Cummulative Degree Days on Jan. 1st so that another accumulation
can begin. }
FRAC_AREA_LEFT(t) ¼ FRAC_AREA_LEFT(t À dt) + (FLOW_1) * dt
INIT FRAC_AREA_LEFT ¼ 0
INFLOWS:
FLOW_1 ¼ IF TIME ¼ 519 THEN PLANT_MAX/45300000 ELSE 0 {Divides
the cumulative area under the plant stock (Grams) vs. time curve by the area
under the standard curve (10 years), no variation in the avg. temp. curve}
36.2 Grass Carp Model Equations
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