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Fishery Bulletin 118(4) 
Sea and Aleutian Islands established a state and federal 
cooperative management regime that defers crab manage- 
ment to the state of Alaska with federal oversight (NPFMC?). 
As part of the federal process, status determination criteria, 
including OF Ls and acceptable biological catches (ABCs), are 
calculated annually for crab stocks on the basis of a 5-tier 
system that accommodates varying levels of uncertainty, in 
which stocks with more biological information and greater 
assessment richness fall into lower tiers (NPFMC’). Annual 
catch levels (i.e., total allowable catches [TACs]) are deter- 
mined by the state of Alaska according to fishery regulations 
established by the Alaska Board of Fisheries, but catch levels 
and management actions need to be consistent with the pro- 
visions of the fishery management plan of the North Pacific 
Fishery Management Council, the national standards of the 
Magnuson-Stevens Conservation and Management Act, and 
other applicable federal regulations (NPFMC’). As such, it 
is necessary to consider the federal and state HCRs to ade- 
quately represent the management system. 
The federal stock assessment establishes the OFL on 
the basis of an HCR (Fig. 1A) that is a function of instanta- 
neous fishing mortality and mature male biomass (MMB), 
includes a proxy for Fyysy (F'35, the fishing mortality rate 
corresponding to 35% of the unfished spawning biomass 
per recruit; Clark, 1991, 2002) and a proxy of Bygy (B35, 
the spawning biomass corresponding to F3;). The ABC is 
then computed as 75% of the OFL. The directed fishery 
closes when MMB is <0.25Bygy. 
The state HCR (Fig. 1B, Suppl. Fig. 1B [online only]) deter- 
mines a (discrete) exploitation rate as a function of mature 
male abundance (MMA), involves a target level of average 
MMA (MMA,,,.), a threshold for opening and closing the 
directed fishery (0.25MMA,,,.), and a maximum exploita- 
tion rate on MMA (Daly et al., 2019). The outcomes from 
this HCR may be constrained by a maximum number of 
legal-sized males that are allowed to be removed, or they 
may be unconstrained. 
The final TAC is the minimum of the outcomes of the 
state HCR (when expressed as a catch) and the ABC. We 
investigated only options for the state HCR in this study 
but simulated both federal and state HCRs because, for 
example, increasing the target exploitation rate in the 
state HCR may have no effect on stock dynamics if the 
resulting catch is less than the federal ABC (i.e., is a 
lower level to prevent catch exceeding OFL). Historically, 
the outcome of the state HCR has been substantially 
lower than that of the ABC (Suppl. Fig. 2) (online only). 
Materials and methods 
The recently developed stock assessment model for golden 
king crab in the Aleutian Islands provides the input required 
' NPFMC (North Pacific Fishery Management Council). 2008. 
Final environmental assessment for Amendment 24 to the fish- 
ery management plan for Bering Sea/Aleutian Islands king and 
Tanner crabs to revise overfishing definitions, 177 p. [Available 
from website.] 
to support a state HCR that scales the target exploitation 
rate by using population abundance. However, the shift to 
abundance-based management needs to be evaluated by 
using analyses tailored to the management framework 
for golden king crab in the Aleutian Islands. We evaluated 
5 HCRs (Table 1) for the stock of gold king crab in the eastern 
portion (i.e., east of 174°W) of the Aleutian Islands by project- 
ing the population (in the operating model) forward in time 
with catches determined by the state HCRs (constrained by 
the federal ABCs). For the initial year of 2018, stock abun- 
dance by size class and operating model parameter val- 
ues were estimated by using an integrated size-structured 
assessment model based on data for 1981—2018 (Siddeek 
et al., 2020; Suppl. Materials [online only]). The 30-year pro- 
jections were replicated 1000 times. The fishing mortality 
rate for the groundfish fishery was set to the average during 
1999-2018. We chose a 30-year period for the projections 
because survival for animals in the population in 2018 would 
be <1% by 30 years, assuming an instantaneous natural 
mortality rate of 0.21/year. The trajectories of selected per- 
formance metrics appear to stabilize within ~20 years (for 
example, for trends in MMB and MMA, see Figure 2). 
Selection of uncertainties 
It is computationally impossible to consider all possible 
sources of uncertainty associated with a stock and fishery. 
Rather, the sources of uncertainty considered in analyses 
were selected because they were thought to be those most 
likely to substantially affect performance of management 
strategies (following table 3 in Punt et al., 2016): 
e Uncertainty in stock productivity and recruitment 
variability: captured with alternative values for the 
steepness (h) of the stock—recruitment relationship in 
the Ricker model (Ricker, 1954) and with the extent 
of variation and autocorrelation in recruitment in 
the stock—recruitment relationship; 
e Estimation uncertainty: captured with the extent of 
variation and autocorrelation in estimates of biomass 
and abundance and with linear and nonlinear rela- 
tionships between CPUE and stock abundance; 
e Initial stock size uncertainty: captured with alterna- 
tive specifications for initial stock abundance by size 
class and with the extent of variation and correlations 
in initial stock abundance among size classes; and 
e Implementation uncertainty: accounted for with 
the extent of variation in realized catch with regard 
to TAC. 
There are many other possible uncertainties that could 
have been but were not included in the simplified MSE, 
owing to a lack of evidence for such factors based on his- 
torical data and a lack of data with which to parameterize 
them in the operating model: 
e Process error: depensation in the stock—recruitment 
relationship and occasional catastrophic mortality 
or recruitment events; 
