Chen and Montgomery: Modeling the dynamics of Jasus verreauxt 



35 



U 

 O 



S 



O 1060-70 73-74 



CO 



<n 

 <0 



E 

 o 

 '3 



Case I 



1M9-70 73-74 



03-04 100B-0O 



Fishing year 



Fishing year 



Case 



Madlan 

 Lowvr S% 

 Uppef ft% 



10eO-70 73-74 



7B-7S 83-84 68-80 03-B4 1006-00 



Fishing year 



Figure 10 



The predicted median and SO^f confidence intervals of stock biomass for three sets of adjustment coefficients for the period of 

 1969-70 to 1995-96. 



artificial links among parameters (e.g. between 

 catchability coefficient and recruitment). A large num- 

 ber of built-in constraints (e.g. parameter A must have 

 a value between A j and A2) are often required to facili- 

 tate parameter estimation for such a model. This may 

 artificially result in parameters having biologically rea- 

 sonable estimates, even if the model fails. Such a fea- 

 ture also encourages the indiscriminate and uncritical 

 use of stock assessment models, which leads to the 

 misintfirpretation of results. The extra biological or fish- 

 eries information (e.g. size structure, recruitment and 

 spatial distribution) often incorporated into a dynamic 

 model will certainly increase the accuracy and reliabil- 

 ity in the estimation of parameters if the information 

 is accurate. However, in practice, extra information is 

 likely to be subject to large errors. In this case, a com- 

 plicated model assimilating extra information will prob- 

 ably fail because its validation requires that each piece 

 of information be true (Xiao^). 



It is well known that the current biomass for a 

 decreasing stock is often over-estimated when pro- 



Table 4 



Coefficients used to test the sensitivity of the stock assess- 

 ment to adjustment coefficients used to adjust reported 

 catch data in the period from 1969-70 to 1993-94. 



Adjustment coefficient 



Year 



1969-70 to 1979-80 

 1980-81 to 1989-90 

 1990-91 to 1991-92 

 1992-93 to 1993-94 



duction models are used in assessment with the least 

 squares method (e.g. Schnute, 1989; Hilborn and 



2 Xiao, Y. 1997. A theoretical consideration of subtleties in, and 

 problems with, use of production models. Commonwealth Sci- 

 entific and Industrial Research Organization (CSIRO) Marine 

 Laboratory, Hobart, Australia. Unpubl. manuscript. 



