Punt: Managing West Coast groundfish resources through simulations 



871 



stock has recovered to 0.4fig. In terms of the last option, 

 one of the issues considered an early rebuilding analysis for 

 widow rockfish involved fishing mortality increasing to its 

 target level as the stock approaches 0.4BQ(MacCall^). 



The values for the F^^^ statistic highlight that the predic- 

 tions of the time to recovery (even in a probabilistic sense) 

 from rebuilding analyses are highly uncertain. The uncer- 

 tainty of this estimate of the time to recovery is due to the 

 uncertainty about current stock size and that associated 

 with making long-term predictions based on a short time- 

 series of spawning output and recruitment data. 



Although the performance of the management proce- 

 dures is less than ideal, the results are almost certainly 

 optimistic because the operating model is extremely simple 

 and considers no major structural uncertainties (except for 

 variability in selectivity over time). In contrast, Punt et al. 

 (2002) found that including spatial structure in an oper- 

 ating model and assessing the stock by using a spatially 

 aggregated assessment approach led to assessments that 

 were markedly in error. However, the simulations con- 

 ducted by Punt et al. (2002) were developed for a far more 

 data-poor situation than that for West Coast groundfish, 

 although there is also clearly spatial structure in the West 

 Coast groundfish fishery. Another source of uncertainty not 

 considered in this paper but that may be of critical impor- 

 tance to the management of West Coast groundfish species 

 is the impact of environmental regime shifts, which have 

 been argued to impact long-term trends in recruitment (e.g. 

 Francis et al., 1998). 



An important aspect of this study is the ability to focus on 

 the relationship between the overall performance of a man- 

 agement procedure and the performance of its constituent 

 parts. For example, the results for the "deterministic data" 

 scenario in Table 4 show that given the approach used to 

 conduct the future projections, even perfect information 

 from surveys and very large age-composition samples are 

 unlikely to lead to marked improvements over the current 

 situation if that situation is adequately modeled by the 

 baseline operating model. Identification of the key sources 

 of uncertainty could be used to focus future management- 

 related research activities. 



The computational requirements of the calculations out- 

 lined above are substantial. In particular, the need to apply 

 a fairly complicated method of stock assessment once every 

 three years means that rapid evaluation of management 

 procedures is (currently) computationally not feasible. 

 It is possible, in principle, to simplify the management 

 procedure considerably by assuming that the results from 

 a stock assessment can be mimicked by generating a bio- 

 mass estimate based on the "true" biomass but with some 

 random error (e.g. Hilborn et al., 2002). However, although 

 such an approach may be satisfactory for some manage- 

 ment procedures (e.g. those that set the harvest guideline 

 equal to some fraction of the current biomass), this is not 

 the case for PFMC-type management procedures that de- 

 pend on the (assessed) age-structure of the population. 



9 MacCall, A. D. 2002. Personal commun. NMFS Santa Cruz 

 Laboratory, 110 Shaffer Rd, Santa Cruz, CA 95060. 



It needs to be recognized that any simulation study is by 

 design case-specific. However, the conclusions of this study 

 may be relevant to a fairly broad set of West Coast rock- 

 fish species owing to their similar biology and exploitation 

 history — the two factors most likely to impact the relative 

 performance of different management procedures. 



Acknowledgments 



Discussions with Alec MacCall, John DeVore, and Richard 

 Methot are gratefully acknowledged as are the comments 

 on an earlier version of this paper by Pamela Mace and 

 two anonymous reviewers. This work was funded through 

 NMFS grant NA07FE0473. 



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