Punt: Managing West Coast groundfish resources through simulations 



861 



for industry of the implementation of a rebuilding plan 

 can be substantial (e.g. a reduction in the catch of canary 

 rockfish from 883 metric tons (t) in 1999 to only 90 t in 

 2001), although there are also indirect consequences in the 

 form of reductions in the harvest of nonoverfished species 

 to prevent overharvesting of overfished species through 

 technical interactions. 



The performance of the method commonly used for as- 

 sessments of West Coast species has been evaluated to 

 some extent (e.g. Sampson and Yin, 1998; lanelli, 2002). 

 However, the performance of this assessment method in 

 combination with the rules used to determine harvest 

 guidelines has not been evaluated. 



Management procedures'* are combinations of stock as- 

 sessment methods and catch control laws that have been 

 evaluated by means of Monte Carlo simulation to assess 

 the extent to which they are able to satisfy the manage- 

 ment objectives for a fishery. Evaluation of management 

 procedures by means of Monte Carlo simulation has been 

 argued to be essential because "if a management procedure 

 is unable to perform adequately in the ideal world repre- 

 sented on a computer, what basis is there to assume that 

 it will perform adequately in the real world?" (Sainsbury^). 

 One caveat to this argument is that it is only possible to 

 evaluate a management procedure if it is fully specified and 

 if it will be followed for several years in reality. 



Management procedures have been adopted by the In- 

 ternational Whaling Commission for managing commer- 

 cial and aboriginal whaling (e.g. IWC, 1992, 2001) and by 

 southern African nations for managing a variety of pelagic 

 and demersal resources (Butterworth and Bergh, 1993; Co- 

 chrane et al., 1998; Geromont et al., 1999). Management 

 procedures are under consideration in Australia (Punt et 

 al., 2001) and New Zealand (Starr et al., 1997). If it can 

 be assumed that the same rules will be applied to modify 

 rebuilding plans each time new information on abundance 

 and year-class strength becomes available, it is possible to 

 consider the combination of the assessment method, the 

 default 40-10 rule, and rebuilding plans as a "manage- 

 ment procedure" and evaluate it by means of Monte Carlo 

 simulation. This study therefore involves determining from 

 past practice the "management procedure" being applied 

 by the PFMC. However, this "management procedure" has 

 not been formally adopted in any way and the approach to 

 managing West Coast groundfish could change in time. 



This paper first outlines a simulation framework (a 

 management procedure evaluation, MPE, framework) 

 within which the expected performance of the approach 

 used by the PFMC to determine harvest guidelines can 

 be evaluated. It then evaluates variants of this approach 

 for scenarios similar to that of managing the fishery for 

 widow rockfish. 



'' Also referred to as "harvest strategies" ( Punt et al ., 200 1 ), "man- 

 agement decision rules" (Starr et al., 1997 ), "fisheries control sys- 

 tems" ( Hilborn, 1979 ), and "operational management procedures" 

 (Barnes, 1999). 



^ Sainsbury, K. G. 2001. Personal commun. CSIRO Marine 

 Research, Castray Esplanade, Hobart, TAS 7000, Australia. 



Materials and methods 



The steps in evaluating management procedures are as 

 follows: 



1 Identification of the management objectives and rep- 

 resentation of these by using a set of quantitative 

 performance statistics. 



2 Identification of a range of alternative management 

 procedures. 



3 Development and parameterization of a set of alterna- 

 tive structural models (called operating models) of the 

 system. 



4 Simulation of the future use of each management 

 procedure to manage the system (as represented by 

 each operating model). For each year of the projection 

 period, the simulations involve the following steps; 



a Generation of the data available for assessment 

 purposes. 



b Application of a method of stock assessment to 

 the generated data to determine key assessment- 

 related quantities (e.g. current age-structure, 

 spawning output in relation to target and limit 

 levels, historical trends in recruitment) and any 

 inputs to the catch control law. 



c Application of the catch control law element of the 

 management procedure to determine a harvest 

 guideline. 



d Determination of the biological implications of 

 this harvest guideline by setting the catch for 

 the "true" population represented in the operat- 

 ing model based on it. The step can potentially 

 include "implementation uncertainty" (Rosenberg 

 and Brault, 1993). 



The harvest guideline is not updated every year in the 

 simulations described in this article, but rather every 

 third year (co-incident with the results from each new 

 survey) and thus reflects the intended frequency with 

 which assessments for West Coast groundfish species are 

 conducted. Each simulation trial (i.e. each combination of 

 an operating model variant and candidate management 

 procedure) involves 100 simulations of an 80-year manage- 

 ment period. The four steps listed above are discussed in 

 detail below. 



Note that for the application considered in this paper 

 then, there are three "models": 1) the operating model that 

 represents "reality" for the simulations, 2) an assessment 

 model (a stock synthesis-like approach), and 3) a model to 

 calculate the harvest guidelines. The data available to the 

 last two models are generated from the first model. 



The operating model 



The operating model has been taken to be virtually iden- 

 tical to that on which the population assessments and 

 rebuilding analysis calculations are based (Appendix 1), 

 with two exceptions: 1) the approach used to generate 

 recruitment and 2) the allowance for variability over time 

 in commercial selectivity. Commercial selectivity is given 



