Soh et al.: Role of marine reserves in the management of Sebastes borealis and S. aleutianus 
175 
relatively little (Fig. 4) and was greatest during the early 
1990s. 
The estimates of posterior parameter values are shown 
in Table 3. The mean value of the posterior Q at maximum 
likelihood was about 0.78 for both species. This value of Q 
implies underestimation of the actual biomass by the sur- 
veys and is consistent with submersible observations by 
Krieger and Ito (1999), who concluded that the above-bot- 
tom distribution of shortraker and rougheye rockfish, to- 
gether with their preference for steep-slope boulder hab- 
itats, would result in a value of Q that was less than 
1.0. Natural mortality was estimated to be closer to prior 
expectations as was the shape parameter (A) in the Be- 
verton and Holt recruitment curve (Beverton and Holt, 
1957). Presumably the closeness of prior values and pos- 
terior estimates reflects the lack of information about the 
mortality and stock-recruitment relationship. 
The lower posterior value of A for shortraker rockfish 
represents more emphasis on fishery information and 
the increased value of A for rougheye rockfish represents 
more emphasis on survey information in the combination 
of the two catch histories during 1977-90. Survey catch 
data show that shortraker rockfish are found primarily 
along the continental slope, whereas rougheye rockfish 
are distributed more broadly on the continental shelf. 
Generally, survey coverage in the slope region is relative- 
ly sparse, and data are consequently acknowledged to be 
insufficient. In this regard, more emphasis on fishery in- 
formation for shortraker rockfish is desirable. The 1996 
biomass represented decreases to about 46% and 69% of 
pristine level (B 1961 ) for shortraker and rougheye rock- 
fish, respectively. 
Refugia management strategy 
The effects of refuge size on ending biomass, and differ- 
ences in fishing intensity between current management 
and refuge management were considered in the projection 
model of refuge management. Ending biomass in twenty- 
year future projections and average twenty-year fishing 
mortality rates were compared for two levels of F (“F for 
ABC” and “actual F”) and three refuge sizes. 
- - - Shortraker rockfish Rougheye rockfish 
900 
“ 700 
W 
'5 
| 600 
400 1 ‘ ‘ 1 
1940 1960 1980 2000 2020 
Year 
Figure 4 
Predicted recruitment trajectories for shortraker and 
rougheye rockfish using the Beverton and Holt model 
with shape parameter A = 0.889. 
Table 2 
Starting and ending biomasses (t) of shortraker and rough- 
eye rockfish under the current management regime, based 
on a 20-year future simulation (1997-2016). “F for ABC” 
is the fishing mortality currently used to calculate recom- 
mended ABC, and actual average fishing mortality during 
1991-96, estimated by stock reduction analysis, is denoted 
as “actual F'. 
Shortraker rockfish Rougheye rockfish 
F for ABC Actual F F for ABC Actual F 
Year (F= 0.023) (F= 0.063) (F=0.025) (F=0.015) 
1997 20,061 20,061 55,896 55,896 
2016 20,847 12,623 43,351 50,443 
Table 3 
Estimates of posterior parameter values and their standard errors. Values in parentheses are standard errors. (B 1996 =biomass 
in 1996, M=natural mortality, Q=survey catchability coefficient, A=shape parameter of Beverton and Holt recruitment curve, 
A=weighting parameter for survey information in the reconstruction of catch history, and depletion level \B i 9 g 6 IB l96l )). 
Shortraker rockfish Rougheye rockfish 
Parameter 
Prior 
Posterior 
Prior 
Posterior 
■®1996 bA 
— 
20,667 (10,260) 
— 
56,040 (30,982 
M 
0.030 (0.2) 
0.031 (0.006) 
0.025 (0.2) 
0.025 (0.005) 
Q 
1 (0.6) 
0.776 (0.325) 
1 (0.6) 
0.785 (0.407) 
A 
0.889 (0.2) 
0.889 (0.178) 
0.889 (0.2) 
0.889 (0.178) 
A 
0.5 
0.266(0.565) 
0.5 
0.554(0.707) 
^1996^1961 
- 
0.464 (0.123) 
— 
0.685 (0.120) 
