SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL 

 30 



1965 



FIGURE 6. — Simulated landings of yellowtail flounder with 



-'gmm 



= 250 mm and 300 mm. Landings greater than 30,000 



metric tons are not shown. 



than 300 mm, these fish have a higher probability 

 of surviving until they are recruited and spawn. 

 The result was from a 207c to a severalfold in- 

 crease in landings. 



Using the Beverton and Holt yield per recruit 

 (YPR) function, Brown and Hennemuth (see foot- 

 note 2) found less than a 40% increase in yield 

 by delaying the age at first capture from 1.75 yr 

 (or 245 mm) to 2.5 yr (or 302 mm) for F less than 

 1.1. This was the highest simulated fishing mor- 

 tality rate during 1943-65. The substantially 

 greater increase in yield from the simulation 

 reported in Figure 6 results from increased re- 

 cruitment which is not considered in the Beverton 

 and Holt YPR function. 



The benefit of increasing mesh size to eliminate 

 discard mortality is clearly demonstrated (for the 

 linear recruitment model), but this analysis ig- 

 nores financial and technological difficulties 

 which may be involved (Gates and Norton 1974). 



The effect of the seasonality of fishing mortality 

 was explored by varying seasonal effort adjust- 

 ment factors (c 3 , c 4 , c 5 , and c 6 ). Situations where 

 effort was applied uniformly throughout the year 

 and where all effort was applied during a single 

 quarter were considered. These cases are com- 

 pared with the results reported earlier (c^ = 1.26, 



25 



o C 3 =I26,C 4 = 037, C 5 = 88, C 6 = I 49 



± 



_L 



± 



1945 



1950 



1955 



I960 



1965 



FIGURE 7. — Simulated landings of yellowtail flounder with fish- 

 ing effort applied uniformly and with c 3 -c 6 as assumed for 

 1943-65. 



30 



£ 25 

 o 



I 20 



en 

 ■o 



c 

 o 

 in 



o 



en 



Q 



-z. 

 < 



10 



5 - 



O C 3 = 1.26, C 4 =0 37, C 5 

 • C 3 =4 0, C 4 = C 5 = C 6 = 

 AC 4 =4 0, C 3 = C 5 = C 6 =0 



965 



FIGURE 8. — Simulated landings of yellowtail flounder with all 

 fishing effort in the first or second quarter of the year and with 

 c 3 -c 6 as assumed to have occurred for 1943-65. 



c 4 = 0.37, c 5 = 0.88, and c 6 = 1.49) in Figures 7-9 

 and Table 9. 



The simulations reported in Figures 7-9 indi- 

 cated that the seasonal aspect of the expenditure 

 of effort and resulting fishing mortality could 



477 



