Punt: Managing West Coast groundfish resources through simulations 



869 



in which the rebuilding analysis indicates recovery will 

 occur and the year at or before which it actually occurs; 

 and 3) the probability of being below the overfished level 

 after 20 and 60 years. 



The first variant of the baseline management procedure 

 ("with constraints" in Table 4) involves imposing maximum 

 and minimum catch limits of 30 and 8000 t and constrain- 

 ing changes in harvest guideline not to exceed 25% from 

 one year to the next, except in the first year when reduc- 

 tions of up to 99% are allowed. This variant leads to much 

 lower interannual variation in catches when a 60-year pe- 

 riod is considered ( 17% compared with 25% ) but the AAV 

 is actually higher for the first 20 years. This variant also 

 leads to higher probabilities of recovery. However, there is 

 still a large discrepancy between the actual year of recov- 

 ery to 0.4Sg and the year that underlies the management 

 procedure (the value of F^^^ in Table 4 is only 0.27 for the 

 "with constraints" variant). 



The second variant considered ("no 10 year and esti- 

 mated ^msy" see Table 4) drops the requirement that T^^^ 

 be defined as 10 years if the resource can be recovered in 10 

 years and instead always sets T^^^ to T^^^^ plus one mean 

 generation. It also allows the Fj^gy proxy used when apply- 

 ing the 40-10 rule to differ from the default value of Fgg^^ 

 by setting it to F (Jakobsen, 1993) ii^ F is lower than 

 ^MSY- Estimating (rather than fixing) F^^gy is consistent 

 with the recommendation of Brodziak (2002). The major 

 performance difference between this variant and the base- 

 line management procedure is the increased value of F^.^^. 



The "preferred" variant in Table 4 combines the features 

 of the "with constraints" and "no 10 years and estimated 

 ^msy" variants. Compared with the baseline management 

 procedure, it leads to a markedly increased value for F^^^ 

 (remarkably close, in fact, to the desired value of 0.6), 

 slightly lower catch variability, a less than 5% chance of 

 being overfished after 20 years, and higher probabilities of 

 being recovered to 0.4Bg after 20 and 60 years of manage- 

 ment. The major disadvantage of this variant is the lower 

 catches and that it leaves the spawning output well above 

 40% of Bg after 60 years (see row "preferred" in Table 4). 



Prior to the adoption of Amendment 11 of its Groundfish 

 Management Plan, the PFMC set harvest guidelines using 

 only the 40-10 rule.^ Table 4 therefore also lists results for 

 management procedures based on the 40-10 rule. When 

 the 40-10 rule is applied without any constraints ("PFMC 

 (baseline)" in Table 4), the probability of recovery and the 

 values for the "50%'D" statistic are lower (particularly 

 the former) than for the "preferred" variant. In contrast, 

 application of the 40-10 rule with constraints ("PFMC 

 (preferred)" in Table 4) leads, arguably, to no more than a 

 slight difference in cateh (the 40-10 rule achieves higher 

 catches) and probability of recovery (the "preferred" vari- 

 ant achieves a higher probability of recovery ). The remain- 

 ing analyses of this paper focus on the "preferred" variant. 

 Future consideration of management procedures for West 

 Coast groundfish resources should consider a management 

 procedure that is based simply on the 40-10 rule and has 

 no associated rebuilding analysis component, at least for 



' Albeit with different target fishing mortality levels. 



comparative purposes. At present, however, such a man- 

 agement procedure would be inconsistent with the SFA 

 because it would not specify the time to recover to the proxy 

 for 5^,gY 'even if the results of this paper suggest that there 

 is considerable uncertainty associated with the estimation 

 of this particular quantity). 



Sensitivity to alternative operating model specifications 



The values assumed for h and a^ in the baseline operating 

 model are somewhat arbitrary. Table 5 therefore examines 

 the sensitivity of the results for the "preferred" manage- 

 ment procedure to varying the values assumed for these 

 parameters, as well as that of the size of spawning output 

 at the start of the first projection year to fig. 



The results are, as expected, sensitive to all three of the 

 factors considered. Increasing a^ from 0.4 through 0.6 to 1 

 leads to lower and more variable catches, a slightly higher 

 probability of recovery in the first 20 years and a markedly 

 higher value of 50%D after 60 years (0.74 for <7;j=l com- 

 pared to 0.46 for cr^=0.4). The ability to detect an overfished 

 stock declines slightly as the extent of variation in recruit- 

 ment increases. The management procedure behaves as 

 expected as steepness is increased from 0.25 through 0.4 to 

 0.7; the probability of recovery is markedly higher for high 

 values of steepness even though the management proce- 

 dure does identify cases with low steepness, and accordingly 

 sets very low harvest guidelines in such cases. However, 

 it is perhaps noteworthy that the probability of correctly 

 identifying that the resource is overfished is lowest for the 

 least productive scenario. The catches for the scenario in 

 which the spawning output is 10% of Bg at the start of the 

 first projection year are much lower than for the baseline 

 scenario, particularly over the first 20 years. However, these 

 lower catches are necessary to achieve recovery (the median 

 value of the statistic 50%I> after 60 years is 0.52 and there 

 is a 0.93 probability of the spawning output having recov- 

 ered to 0.4Bg after 60 years for this scenario). 



The behavior of the management procedure can be evalu- 

 ated in terms of whether it eventually allows the stock to 

 recover to 0.4Bg and whether it keeps the stock away from 

 the overfished level of 0.25Bq. The "preferred" management 

 procedure can be argued to satisfy this criterion, except 

 possibly for the scenario with the lowest steepness but, 

 even in this case, the probability of recovery is 0.6 after 

 60 years. 



The value for the F^^^ statistic varies markedly depend- 

 ing on steepness and the ratio of the spawning output at 

 the start of the first projection year to Bg. Although the 

 "preferred" management procedure performs well for the 

 baseline scenario in terms of recovering the resource by the 

 predicted value for T^^^, this good performance is clearly a 

 fortunate anomaly. However, it does help to highlight that 

 predictions of the year-to-recovery from rebuilding analy- 

 ses should be interpreted with considerable caution. 



Sensitivity to data quality 



The data-related specifications for the baseline trial 

 (Table 2) could be considered to be data-rich. It is therefore 



