SISSK.WV1NE: COMPARTMENTALIZED SIMULATION MODEL 



better to compare the 1963 simulated size- 

 category structure with these data, but, because 

 of a programming oversight, this information 

 was not available. The comparisons in Figures 2 

 and 3 are generally favorable and indicate that 

 the assumed linear relationships (Equations (6) 

 and (7)) describing the relative effectiveness of 

 the fishing gear and the marketability of fish as 

 a function of length were adequate. The model 

 indicates that 39.5% of the fish captured by fisher- 

 men for 1943-65 were discarded. The average 

 weights of landed and discarded fish based on 

 Figures 2 and 3 are 455 and 249 g, respectively. 

 The parameter c 13 of the recruitment function 

 (Equations (17) and (18)) was estimated by run- 

 ning the model for several values of this param- 

 eter and selecting the value that explained the 

 greatest proportion of variation in observed yield. 

 Of the values considered, c 13 equal to 60.0 x 10 6 

 and 5.8 x 10 6 for the density independent and 

 linear recruitment models were most successful 

 in explaining variation in yield. Since only a finite 

 number of values of c 13 were considered, the val- 

 ues selected are probably not the "best least 

 squares" estimates, but the results (Table 8) indi- 

 cate that the model is not very sensitive to 5-10% 

 fluctuations in this parameter. As noted earlier, 

 these values appear realistic. 



TABLE 8. — Percent of variation in yield explained by the yellow- 

 tail flounder model with various values of c\3 for 1943-65. 



The model using linear or density independent 

 recruitment explained 85.5 and 83.2% of the vari- 

 ation in yield from 1943-65, respectively. In addi- 

 tion to catch and effort data reported by Lux 

 (1969a), catch data through 1972 and effort data 

 through 1971 were available (at the time when 

 this research was in progress) for the Southern 

 New England ground (Brown and Hennemuth 

 see footnote 2; Brown see footnote 3; and Par- 

 rack see footnote 4). Both the linear and den- 

 sity independent stock-recruitment models were 

 run for 1943-72 (assuming that the level of effort 

 was unchanged from 1971 to 1972), and the 



results were compared with the available data in 

 Figures 4 and 5. Both models seem to simulate 

 catch as well since 1965 (although yield is sub- 

 stantially underestimated for 1969 and 1970) in 

 spite of the fact that they were developed indepen- 

 dently of the later data and that growth is appar- 

 ently somewhat overestimated toward the end of 

 the simulation. Since errors for any particular 



30 



25 



E 20 



TO 



c 

 o 

 u> 



o 



15 



- 10 



CO 



Q 

 < 



• PREDICTED 

 ▲ UNPUBLISHED 

 O PUBLISHED 



1945 



1950 



1955 



I960 



1965 



1970 



FIGL T RE 4. — Landings of Southern New England yellowtail 

 flounder as reported in published and unpublished reports and 

 predicted by the model with linear recruitment function (Equa- 

 tion (17)1. 



30 



£ 25 



a; 



E 



20 



CO 



o 



o 



z 

 < 



• PREDICTED 

 A UNPUBLISHED 

 O PUBLISHED 



Ol L 



1945 



1950 



1955 



I960 



1965 



1970 



FIGURE 5.— Landings of Southern New England yellowtail 

 flounder as reported in published and unpublished reports and 

 predicted by the model with a density independent recruitment 

 function (Equation (18)). 



475 



