5.3. Questions and Tasks
97
FI SHING_MORTALITY [ LONG ] = .2
MORTALITY_O_ l[ LENGTH] = . 5 *TOTAL_ POP/ 2 0 0 0 0
MORTALITY_l _2[LENGTH] = .3* TOTAL_ POP/20000
RAND_l_2[SHORT] = RANDOM(O,l ,l)
RAND_l_2[MED] = RANDOM(0,1,2)
RAND_ l _2[LONG] = RANDOM(0 ,1 ,3)
RAND_2 _ 3[SHORT] = RANDOM(0 , 1 ,4)
RAND_2_3[ MED ] = RANDOM(0,1 , 5)
RAND_2_3[LONG] = RANDOM{O ,1,6)
SMOOTH_FRAC[SHORT] =
SMTH3{ {YEAR_O_l [SHORT ] +YEAR_l_2 [ SHORT] +YEAR_2_3 [ SHORT ] )
/ TOTAL_ POP , 2 0 )
SMOOTH_FRAC[MED] =
SMTH3({YEAR_O_l[MED]+YEAR_l_2[MED]+YEAR_2_3[MED] ) /TOTAL
_POP,20)
SMOOTH_FRAC[LONG] =
SMTH3{{YEAR_O_l[LONG]+YEAR_l_2[LONG]+YEAR_ 2_3[LONG] ) /TO
TAL_P OP, 2 °)
TOTAL_MORTALITY_ O_l[LENGTH] =
MIN{ l , MORTALITY_ O_l[LENGTH]+FI SHING_MORTALITY [LENGTH] )
TOTAL_MORTALI TY_l_2 [LENGTH] =
MIN( 1 ,MORTALI TY_ 1_2 [LENGTH]+FISHING_MORTALITY[ LENGTH] )
TOTAL_P OP = ARRAYSUM{YEAR_O_l[*]) +
ARRAYSUM(YEAR_l_2[*]) + ARRAYSUM(YEAR_2 _3[*])
5.3. Questions and Tasks
1. How wo uld the model results change if the mortality-population size relations of Equations (5) through (0) were different for each age cohort
and length of fish?
2. Investigate the sensitivity of the model results with respect to the assumptions about the distribution of births across subpopul ations made in
Equations ( 17)- 09).
3. Alter the mortality rates from those in Equation s (5.5)-(5 .10) to rates that
differ among cohorts and fish sizes such that the response of mortality
rates to changes in total population sizes are:
a) strictly convex;
b) linear;
c) strictly concave.
How do the results change qualitatively?
4. Model the system of Section 5.1 as a 2-D array.