RIVARn and RLEDSOE PARAMETER ESTIMATION FOR PELLA-TOMLINSON MODEL 

 2 5 



2 0- 



1 5 



Q 10 0- 



111 



>- 



5 



Figure 3. — Equilibrium stock produc- 

 tion model for yellowfin tuna data, from 

 1934 through 1967, as determined by 

 the Levenberg-Marquardt algorithm. 



EFFORT (ilO boil-liri) 



> 



overestimated in most applications of the 

 Graham-Schaefer model (note also that Ricker's 

 treatment assumes equilibrium). In contrast to 

 the yellowfin tuna data, analysis of the equilib- 

 rium model for halibut data indicates that fishing 

 effort has been concentrated slightly to the right of 

 /msy (compare Figures 3 and 4). 



In the preceding case studies, the Levenberg- 

 Marquardt algorithm gave estimates with rela- 

 tively small coefficients of variation. In both cases, 



Figure 4. — Equilibrium stock produc- 

 tion models for Pacific halibut (Interna- 

 tional Pacific Halibit Commission Area 

 2), from 1910 through 1957, as deter- 

 mined by Ricker (1975, examples 13.5 

 and 13.6, Nair-Bartlett regressions) 

 and by the Levenberg-Marquardt al- 

 gorithm (three-parameter version). 



10 11 



EFFORT (ilO ikitll) 



531 



