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Fishery Bulletin 101(4) 



because they are conditioned on knowing the age-structure 

 of the population at the start of the projection period and 

 are based on fixed levels of fishing mortality during the 

 rebuilding period. 



The impact of estimation uncertainty is also evident 

 in Figure 4. The following are three examples of this: 1) 

 management based on the rebuilding plan only starts in 

 year 53 in simulation 1 because, prior to this year, the stock 

 assessment indicates (erroneously) that the stock is above 

 rather than below 0.25Bq; 2) the resource is predicted to 

 have recovered to 0.4Bg in year 71 in simulation 1 (and 

 hence management is based on the 40-10 rule thereaf- 

 ter) — however, the spawning output is really only slightly 

 larger than O.Sfiy at this time; and 3) in simulation 3 the 

 assessment model indicates that the spawning output has 

 recovered to above 0.4Bg in year 65 when, in fact, it recov- 

 ered to 0.4Bq three years earlier. 



The results of all 100 simulations are summarized by 

 the time-trajectories in Figure 5. The trajectories of catch 

 in Figure 5 are notably less variable that the individual 



trajectories in Figure 4 because, for instance, the 5"^, 

 median, and 95'^ intervals for the catch in year 80 are 

 obtained by sorting all 100 year-80 catches and taking the 

 appropriate percentiles. Unlike the individual trajectories, 

 the median trajectories of catch and spawning output show 

 quite smooth changes over time. This result highlights the 

 importance of the AAV statistic that captures interannual 

 variation in catches within individual simulations. 



Overall, there is a high probability (0.82) that the as- 

 sessment model identifies that the spawning output is less 

 than 0.25Bq at the start of the projection period (Table 4). 

 However, the probability that recovery occurs at or before 

 the Tjjjax y6ar predicted from the rebuilding analysis con- 

 ducted in projection year 1 is rather low (0.22) and 50% 

 of simulations exceed 0.4Sq only in year 72 (i.e. after 30 

 years). The probability of being below the overfished level 

 of 0.25Bq still exceeds 5% after 60 years of management 

 with this management procedure although there is an 80% 

 probability that the spawning output recovers to 0.4B„ 

 sometime during the first 60 years of management with 

 the management procedure. 



It should be noted that the impact of recruitment vari- 

 ability and assessment errors following recovery to OABq 

 can be consequential. For example, the probability of hav- 

 ing reached 0.45q after 60 years of management by using 

 the management procedure exceeds 0.8 but the median 

 value of the ratio of the spawning output in year 60 to Bq 

 is nevertheless still less than 0.4 (Table 4, Fig. 5). One rea- 

 son for the spawning output not stabilizing at 0.4 Bg is a dis- 

 crepancy between the fishing mortality rate that stabilizes 

 the population at Bq (deterministically) and Fgg,. For the 

 baseline steepness of 0.4, the fishing mortality required to 

 stabilize the spawning output at 0.4 Bq actually corresponds 

 to a lower fishing mortality than ^50% (closer to J^63%^- 



Sensitivity to alternative management procedures 



Table 4 includes results for a range of variants of the 

 baseline management procedure designed to improve its 

 performance. The following are areas where improved 

 performance is desirable: 1) the extent of interannual 

 variability in catches; 2) the similarity between the year 



