864 



Fishery Bulletin 101(4) 



i 

 Conduct a Stock Assessment 



i 



Select an approach for 



generating future recruitment 



(recruits or recruits / spawner) 



No C urrently under a Yes 

 Rebuilding Plan'' 



Is stock assessed to be 

 currently overfished'' 



Apply the 40-10 rule 



Yes 



 Declare stock overfished 



Has stock recovered to 

 above the t.arget level'' 



Apply the rebuilding software 



(Do not update the target rebuild 



year unless the stock has just 



been declared overfished) 



^ Apply the constraints on ^ i 



the extent of inter-annual variation 

 in harvest guidelines 



Constrain the harvest guideline 

 to fall within the maximum and minimum limits 



Figure 2 



Flowchart of the Pacific Fishery Management Council management procedure. 



puts, and the age structure at the start of the last year of 

 the assessment. 



An estimate of the pre-exploitation equilibrium spawn- 

 ing output (i.e. Bq) is obtained by multiplying the average 

 recruitment for the first ten years of the assessment period 

 by the spa-wning output-per-recruit in the absence of fish- 

 ing. This approach to estimating Sg has been used for sever- 

 al rebuilding analyses for West Coast groundfish species. If 

 the estimate of the current spawning output exceeds 0.4Sg 

 or if it exceeds 0.25 fig and the resource is not currently 

 under rebuilding (i.e. has not yet been declared to be in an 

 overfished state), a raw harvest guideline is computed us- 

 ing the 40-10 rule. On the other hand, if the estimate of the 

 current spawning output is less than 0.25 fig or the stock is 

 currently under a rebuilding plan and the spawning output 

 has not yet recovered to 0.4 fig, the raw harvest guideline 

 is based on the application of the rebuilding analysis (see 

 Appendix 1 for further details). 



It is necessary to know the maximum possible rebuilding 

 period, T^^^, when using a rebuilding analysis to calculate 

 a harvest guideline. If the stock is declared overfished in 

 the present year, T^^^ is computed as described in Appen- 

 dix 1. On the other hand, if the stock is currently under a 

 rebuilding plan, T^^^ is taken to be the value computed 

 when the stock was first declared overfished. Therefore, 

 the implementations of the rebuilding plans considered 

 in this paper are based on the assumption that the 7",,,,^,^ 

 and the probability of recovery by T^^g^ are set when the 

 first rebuilding analysis is conducted and not changed 

 thereafter. The probability of recovery by T„^^^ is taken 

 to be 0.6 in this paper because this is the probability on 

 which management of widow rockfish is currently based. 



This probability ranges between 0.55 and 0.92 among the 

 seven overfished groundfish resources for which it has been 

 selected by the PFMC. 



Calculation of a harvest guideline using the 40-10 rule 

 and application of the rebuilding analysis requires the 

 ability to generate future recruitment. For the purposes of 

 the present study (and consistent with current practice), 

 future recruitment is either generated from the estimates 

 of recruitment from the assessment or by multiplying the 

 spawning output by a generated value for the recruits-per- 

 spawning output ratio. The pool of recruitment to recruits- 

 per-spawning output is taken to be those for the last 23 

 years of the assessment period less those for the last three 

 years. The last three years are excluded because of their 

 known poor precision. The approach used to generate re- 

 cruitment therefore leads to the set of recruitments used 

 to conduct projections changing with time. Allowing the set 

 of recruitments to change with time is needed to avoid an 

 inconsistency between the recruitments used for projections 

 and the recruitments on which the estimate of Bg is based. 



Allowance is made for the raw harvest guideline to be 

 constrained so as not to change by more than a prespecified 

 percentage from that for the previous year and not to fall 

 outside of specified limits, although this option is not part 

 of the baseline simulations. 



One aspect of the actual management process that is 

 ignored in the simulation of the PFMC management pro- 

 cedure is the time-lag between the collection of data and 

 their use in assessments (for example, catch-at-age infor- 

 mation from surveys conducted in one year would usually 

 not be available for use in the assessments conducted 

 in the following year) and that between assessments 



