92
5. Impact of Fishing Pressure on Mean Length of Fish
you to sum the elements within a given array. Choose the individual age cohorts as the arguments of the ARRAYSUM function:
TOTAL POP = ARRAYSUM(YEAR_O_l[*J)
+ ARRAYSUM(YEAR_1_2[*J) + ARRAYSUM(YEAR_2_3[*J).
(22)
The asterisk indicates that we sum across all elements.
Next , specify the natural mortality rates for each cohort, as we did in Section 5.1. Again, leave the "Apply to All" button clicked on as the specifications are assumed to be the same across all length classes. Create a converter for FISHING MORTALITY and unclick the "Apply to All" button,
since now the fishing-induced mortality for the zero- to one-year-olds is always 0, whereas that for the other age cohorts may be larger than 0. When
you unclick the "Ap ply to All" button, you can navigate among the elements of an array to specify them individually. For now, specify all fishing
mortality rates as 0, and change the values for the two older age cohorts
later when we introduce fishing.
With the natural and fishing-induced mortality rates defined, we can
specify total mortality analogous to the way we have done this before in
equation (20). Now, our equations apply to all length classes, but differ between age cohorts:
TOTAL MORTALITY 01 = MINO,MORTALITY_O_l[LENGTH]
+FISHING_MORTALITY[LENGTHJ);
(23)
TOTAL MORTALITY 1 2 =MINO,MORTALITY_C2[LENGTH]
+FISHING_MORTALITY[LENGTHJ).
(24)
Your model should now be as in Figure 5.16.
Let us next introduce the random numbers and birth rates required to
specify the number of births. Each of those are arrays, and their values differ among the length classes of fish. To ensure that the random numbers
can differ among length classes, give each of them a different seed. Then
specify the flow of births, one length class at a time . For example, the first
element in the BIRTHS array is
BIRTHS[SHORT] =
BIRTH_RATE_1_2[SHORT]*RAND_1_2[SHORT]*YEAR_1_2[SHORT]+
BIRTH_RATE_2_3[SHORT]*RAND_2_3[SHORT]*YEAR_2_3[SHORT]+
BIRTH_RATE_l_2[MED]*.5*0-RAND_C2[MEDJ)*YEAR_l_2[MED]+
BIRTH_RATE_2_3[MED]*.5*0-RAND_2_3[MEDJ)*YEAR_2_3[MED]+
BIRTH_RATE_C2[LONG]*0 /3)*0-RAND_C2[LONGJ)*YEAR_l_2[LONG]+
BIRTH_RATE_2_3[LONG]*0/3)*0-RAND_2_3[LONGJ)*YEAR_2_3[LONG].
(25)
5. Impact of Fishing Pressure on Mean Length of Fish
you to sum the elements within a given array. Choose the individual age cohorts as the arguments of the ARRAYSUM function:
TOTAL POP = ARRAYSUM(YEAR_O_l[*J)
+ ARRAYSUM(YEAR_1_2[*J) + ARRAYSUM(YEAR_2_3[*J).
(22)
The asterisk indicates that we sum across all elements.
Next , specify the natural mortality rates for each cohort, as we did in Section 5.1. Again, leave the "Apply to All" button clicked on as the specifications are assumed to be the same across all length classes. Create a converter for FISHING MORTALITY and unclick the "Apply to All" button,
since now the fishing-induced mortality for the zero- to one-year-olds is always 0, whereas that for the other age cohorts may be larger than 0. When
you unclick the "Ap ply to All" button, you can navigate among the elements of an array to specify them individually. For now, specify all fishing
mortality rates as 0, and change the values for the two older age cohorts
later when we introduce fishing.
With the natural and fishing-induced mortality rates defined, we can
specify total mortality analogous to the way we have done this before in
equation (20). Now, our equations apply to all length classes, but differ between age cohorts:
TOTAL MORTALITY 01 = MINO,MORTALITY_O_l[LENGTH]
+FISHING_MORTALITY[LENGTHJ);
(23)
TOTAL MORTALITY 1 2 =MINO,MORTALITY_C2[LENGTH]
+FISHING_MORTALITY[LENGTHJ).
(24)
Your model should now be as in Figure 5.16.
Let us next introduce the random numbers and birth rates required to
specify the number of births. Each of those are arrays, and their values differ among the length classes of fish. To ensure that the random numbers
can differ among length classes, give each of them a different seed. Then
specify the flow of births, one length class at a time . For example, the first
element in the BIRTHS array is
BIRTHS[SHORT] =
BIRTH_RATE_1_2[SHORT]*RAND_1_2[SHORT]*YEAR_1_2[SHORT]+
BIRTH_RATE_2_3[SHORT]*RAND_2_3[SHORT]*YEAR_2_3[SHORT]+
BIRTH_RATE_l_2[MED]*.5*0-RAND_C2[MEDJ)*YEAR_l_2[MED]+
BIRTH_RATE_2_3[MED]*.5*0-RAND_2_3[MEDJ)*YEAR_2_3[MED]+
BIRTH_RATE_C2[LONG]*0 /3)*0-RAND_C2[LONGJ)*YEAR_l_2[LONG]+
BIRTH_RATE_2_3[LONG]*0/3)*0-RAND_2_3[LONGJ)*YEAR_2_3[LONG].
(25)