Siddeek et al.: Development of harvest control rules for hard-to-age crab stocks 
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MMA (millions of crab) 
Figure 1 
Graphs of the currently implemented (A) federal and (B) state har- 
vest control rules (HCRs) for golden king crab (Lithodes aequispinus) 
in the eastern Aleutian Islands. The federal stock assessment estab- 
lishes the overfishing level on the basis of an HCR that is a function 
of instantaneous fishing mortality (F), shown in decimal form per 
year, and mature male biomass (MMB), shown in metric tons (t). The 
state HCR (HR15) determines a discrete exploitation rate, shown in 
decimal form, as a function of mature male abundance (MMA). The 
directed pot fishery closes when MMA or MMB reaches a proportion 
of 0.25 of average MMA or a proportion of 0.25 of MMB;,, which is 
35% of the unfished level of MMB (i.e., MMB given F=F,,, which is 
35% of the unfished spawning biomass per recruit), indicated by the 
vertical drops in the lines for the HCRs. The vertical drop in panel A 
does not reach zero because F attributable to bycatch can still occur in 
the groundfish fishery when the directed fishery is closed. 
The rest of this section provides a background of the 
stock of golden king crab in the eastern Aleutian Islands 
and its associated management system, which is used to 
determine which aspects are included in the operating 
model. We then outline the candidate management strate- 
gies (those currently implemented and alternative choices 
for HCRs), including some with lower and higher target 
fishing mortality rates than those previously considered 
appropriate, and compare them by using conservation and 
economic performance metrics. 
Background and fishery 
Golden king crab in the Aleutian Islands inhabit relatively 
deep water (at depths of 300-1000 m) on structurally com- 
plex habitat, such as rock and coral. They are caught by 
381 
using rectangular crab pots ranging in length 
from 1.2 to 3.0 m. Because of deep habitats, pots 
are deployed with longlines, with each string 
having 30-40 pots, each approximately 200 m 
apart from the next pot. Golden king crab in the 
Aleutian Islands compose what is considered one 
stock but are managed in 2 areas: east and west 
of the longitude 174°W. The fishery is male-only 
with a minimum size limit. The fishery has been 
managed by using a constant catch management 
strategy since the 1996-1997 fishing season. 
Rationalization of crab stocks in the Bering Sea 
and Aleutian Islands in the 2005-2006 fishing 
season resulted in dramatic changes in fishing 
practices, including those for golden king crab in 
the Aleutian Islands: most notably, reduced fleet 
size and increased average pot soak time (Fina, 
2005). Although the directed fishery accounts 
for most of the total fishery mortality, a small 
amount of bycatch occurs in other crab fisheries 
and the groundfish trawl and pot fisheries (<1% 
of the total number of removed animals; Leon 
et al., 2017). There was a belief by industry mem- 
bers that the stock could sustain higher levels of 
fishing intensity because no adverse effects to 
the population were detected through the use of 
fishery-dependent data under the constant catch 
management strategy (Siddeek et al., 2020). 
Assessment and management system 
A stock assessment provides inputs to HCRs 
(i.e., annual population abundance estimates 
and measures of productivity) and evaluates 
whether overfishing has occurred (i.e., whether 
total fishing mortality exceeds the correspond- 
ing overfishing level [OFL]) or whether the stock 
is in an overfished state (i.e., whether the stock 
size is below the minimum stock size threshold 
[MSST], which can be no lower than one half 
of the biomass [B] corresponding to maximum 
sustainable yield [MSY] or 0.5Bygy). The stock 
assessment for golden king crab in the Aleutian Islands 
has been based on a male-only, size-structured population 
dynamics model, which was adopted for management by 
the North Pacific Fishery Management Council in 2016. 
Unlike for other major crab stocks in the Bering Sea and 
Aleutian Islands, area-swept abundance estimates are 
not available for this stock because of the lack of a bottom 
trawl survey (NPFMC, 2018). Consequently, the assess- 
ment for the stock in the Aleutian Islands is based on 
fishery-dependent data (catch per unit of effort [CPUE] 
and catch size composition) and accounts for changes in 
fishing behavior due to crab fishery rationalization by fit- 
ting the operating model to separate sets of CPUE indices 
and by estimating fishery selectivity patterns for the pre- 
and post-rationalization periods (Siddeek et al., 2020). 
The North Pacific Fishery Management Council fishery 
management plan for the king and Tanner crabs in the Bering 
