review of tacs · cpt: 50% abc buffer (was 20%) 1. model structure (gmacs) uncertainties lead to...
TRANSCRIPT
Review of TACsBering Sea Crab:
2020/21 Season
ADF&G presentation to BSAI crab industry, 8 Oct 2020
Join by ZOOM:https://us02web.zoom.us/j/83654596765?pwd=RzJUOE
o2TkFmZUlWSVErckpkdmlOQT09
Meeting ID: 836 5459 6765Passcode: 586393
1
2020/21 TAC Summary
2
OFL ABC TAC
(mill lb) (mill lb) (mill lb)
0.0026 0.0020 0
(total catch) (total catch) (directed fishery closed)
1.90 1.43 0
(total catch) (total catch) (directed fishery closed)
0.11 0.08 0(total male
catch) (total male catch) (directed fishery closed)
4.72 3.54 2.65
(total catch) (total catch) (retained catch)
46.58 37.26 0 (EBT), 2.35 (WBT)
(total catch) (total catch) (retained catch)
210.32 157.74 45.00
(total catch) (total catch) (retained catch)
Bering Sea Tanner crab
Bering Sea snow crab
Fishery
Pribilof blue king crab
Pribilof red king crab
St. Matthew blue king
Bristol Bay red king crab
2020
Global pandemic
Cancelled surveys = fewer tools• First missing NOAA EBS bottom trawl survey since
the start of the timeseries in 1975
2 analyses to evaluate impacts on EBS crab management
1) Retrospective analysis with and without terminal year survey
2) Sensitivity analysis with high and low proxy surveys• CPT: Take species-by-species approach to evaluate
impacts on missing survey and consider additional buffers
3
Impacts of missing survey
Some stocks more sensitive to missing 2020 survey than others
Retrospective runs Sensitivity analysis
OFL_high – OFL_low / OFL_base
4
Snow crab
5
Snow crab challenges this year
• No 2020 survey
• Change in mode structure: GMACS• Generalized Modeling for Alaskan Crab Stocks (GMACS)
• ADMB software that implements a generalized stock assessment platform for size-structured assessment
• Increase in estimated recruitment in GMACS
• SSC + Council recommended using status quo model (20.1) instead of GMACS
• Model retrospective patterns• Worse with no survey
• Mismatch between 2018 and 2019 survey• Drop in abundance
6
CPT: 50% ABC Buffer (was 20%)
1. Model structure (GMACS) uncertainties lead to increase from 20% to 25% • Retrospective patterns, 2018-2019 MMB survey
estimates, high estimates of 2015 recruitment
2. Lack of 2020 survey: +25%
• Snow crab assessment most sensitive to leaving out the most recent survey data
• “There is good evidence of strong recruitment to the stock, but, due inconsistent survey observations, there is substantial uncertainty regarding its magnitude.“
• 25% buffer approximates median of proportional change in OFL: “(no survey – survey)/survey” statistic
7
SSC recommended ABC buffer: 25%
Status quo model with 25% ABC buffer• Uncertainty related to GMACS model structure no
longer applies
• Existing 20% buffer covers model uncertainty in status quo model
• +5% due to additional uncertainty related to missing 2020 survey
• Bens thoughts: +5% buffer for the missing survey seems low given the increasingly bad retrospective bias and 2018+2019 survey data trend
8
Snow crab TAC = 45 million lbs
0%
10%
20%
30%
40%
50%
60%
2012 2013 2014 2015 2016 2017 2018 2019 2020
% o
f A
BC
TAC % of ABC
9
TAC: Annual catch target for the directed fishery, set to prevent exceeding the ABC for that stock. Limits legal sized males, but must consider all sources of mortality to ensure the ABC is not exceeded.
ABC: Level of annual catch that accounts for scientific uncertainty and is set to prevent the OFL from being exceeded.
In practice ABC limits mortality of ALLmale and female crabs regardless of size, from all sources of fishery mortality (i.e. retained catch, bycatch in directed and nondirected crab fisheries, and groundfish fisheries).
OFL: Level of fishing mortality that jeopardizes the capacity of a stock to produce the maximum sustained yield on a continuing basis.
Cat
ch
0
10-20% buffer
Overfishing Level (OFL)Federal Government
Acceptable Biological Catch (ABC)Federal Government
Total Allowable Catch (TAC)State of Alaska
Below ABC
10
1. “Model observed” estimates……. model estimates of area-swept, defining
male and female maturity within the model using maturity curves informed by
morphometric data using historic chela height data and female abdomen shape
2. “Model survey” estimates…………. interprets what the area-swept estimates
“should have been”, attempting to correct for survey sampling error
3. “Model population” estimates………the fitted line that applies a survey
selectivity curve by sex and size, attempting to correct for trawl efficiency (Q)
…….estimates of the underlying population….. “the population estimate if all
crabs in the line of the survey trawl net were caught”
• Q = proportion of animals in trawl path captured
Abundance estimates in TAC setting
11
• These estimates can differ greatly• In any given year we don’t know what estimate is closer to the true
population size• Resulting TAC can vary depending on what set of estimates is used
Snow crab: the crux of the issue
GMACS model
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
Status quo model
2020 estimates of 4 inch males (and other management quantities) fluctuate dramatically with model scenario
? ?
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Without a survey in 2020 to corroborate the survey numbers and size composition from either 2018 or 2019, additional uncertainty will exist in projections that is difficult to incorporate into assessment output directly.
Big abundance drop in 2019
What happened?
...Unknown
NOAA survey data
Snow crab: the crux of the issue
14
Down to 3.1 inches
Mostly >4.0 inches
Lots of small crab in pots
4 inch CPUE comparable to recent years
The 2018 and 2019 data points have large impacts on our understanding of the population dynamics
• Removing either data point paints a contrasting picture of the population status
Snow crab: the crux of the issue
15
• Do we believe the model estimated jump in 2020 abundances?
• Is a ~4X increase in 4 inch males plausible?
• Is there any reason to believe that the crab estimated in the model are NOT there?
16
What happened between 2018 and 2019? Why the big drop?• 2 explanations:
• high natural mortality event • the survey missed them (maybe
they moved up north?)• No 2020 survey data to inform
population dynamics• 2018+19 Environmental conditions?
Snow crab: the crux of the issue
EBS Bottom Temperatures and Cold Pool Extent
Kearney, Aydin, Britt, Ladd
Bering 10K ROMS hindcast
It was warm 172020 estimated as ~average temp conditions
2019 Groundfish ConditionLaman
●Groundfish condition increased in 2019 relative to 2018.
●Condition was positive for all species shown.
●Large increases were seen for pollock, N. rock sole, YF sole, ATF, and FH sole.
●These species are either predators or competitors with crab.
18
Ocean AcidificationPilcher, Cross
2020 July - Aug. 15 Bottom ΩArag Anomaly
● Anomaly plot shows 2020 compared to the 2003 - 2019 mean.
● Blue is better; red is worse.
This is an in-development model forecast product.19
20
Retrospectivepatterns: terminal year
overestimation
A retrospective pattern is a consistent directional change in assessment estimates of management quantities (e.g. MMB or OFL) in a given year when additional years of data are added to an assessment.
CPT minutes: “The CPT notes that although the existing buffer for snow crab was established in part because of the retrospective bias in the assessment, it did not take into account the additional retrospective bias due to a cancelled survey in the terminal year.”
2020 SAFE: “These retrospective patterns would have often translated to higher OFLs (i.e. overharvesting of the stock) when the terminal year of survey data was unavailable.”
21
Snow crab: the crux of the issue
22
High uncertainty:
1. Uncertainty in the population estimates• No survey
• Changes in model structure (GMACS vs status quo)
• Model retrospective patterns, exacerbated by missing 2020 survey
• Plausibility of huge abundance increases is questionable
2. Biological and environmental uncertainty• Unknown proportion of sub-industry-preferred legal males have
terminally molted
• Hypothetical recent changes in size at maturity not captured in
model
• Unknown cause of abundance drop from 2018 to 2019 survey
data: natural mortality vs survey availability
• Fluctuating environmental conditions
Snow crab: the crux of the issue
Generally agreed that 4 inch male abundance has increased in 2020:
• 2020 assessment results
• Survey information through 2019
• 2019/20 fishery data
• Observations from the fleet
Much uncertainty regarding the magnitude of 2020 increase
• No 2020 size composition data to inform increase to 4 inch size
Snow crab: the crux of the issue
23
State Harvest Strategy
1. Threshold for opening fishery: 25% BMSY
2. Exploitation on MMB:
3. Max Cap: 58% harvest rate on exploitable legal males (4-inch males: 100% new shell + 25% (or other) old shell)
24Jheng, J., Siddeek, S., Pengilly, D., Woodby, D. 2002. Overview of recommended harvest strategy for
snow crabs in the eastern Bering Sea. RIRNo.5J02-03
0.0%
2.5%
5.0%
7.5%
10.0%
12.5%
15.0%
17.5%
20.0%
22.5%
25.0%
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Exp
loit
atio
n r
ate
on
MM
B @
su
rvey
TMB/(1983-1997 Avg of TMB)
Fish
ery
clo
sed
[FMSY/3+(B-0.25*BMSY)*0.417*FMSY/(0.75*BMSY)]*100%
Where,
FMSY = 0.3
B = current year TMB
BMSY = mean TMB for 1983-1997
TMB = mature male biomass + mature female biomass
State Harvest Strategy Inputs
• Mature female biomass
• Mature male biomass
• 4 inch male abundance• Ave weight
• Shell condition proportions: oldshell vs newshell• Assumed oldshell selectivity for upcoming fishery
25
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
120%
130%
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90
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Esti
mat
e o
f O
S se
lect
ivit
y
Preseason survey year
Est'd from retained-catch samples
123% oldshell selectivity in 2019/20
• 15% OS in survey• 18% OS in
retained catch
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0
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1,600
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Bio
mas
s (m
illio
n lb
)Total mature biomass (TMB)
Observed
Model survey
Model population
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0
200
400
600
800
1,000
1,200
19
78
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Bio
mas
s (m
illio
n lb
)Mature male biomass
Observed
Model survey
Model population
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
Projected 2020 survey area-swept estimates
As a proxy, calculated model trends (mean % +/-from prior year) for prior 3 years (to capture recent trends) and applied to 2019 estimate for 2020 area-swept proxy
Example: Average MMB model increase from prior year for 2018-2020 was +72%
2020 estimate = 2019 x (1 + 0.72)
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-1
-0.5
0
0.5
1
1.5
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2.5
3
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Pro
po
rtio
nal
ch
ange
bet
wee
n Y
an
d Y
-1Model population proportional change
MMB
TMB
4 inch males
Project 2020 survey area-swept estimates
2 different projections based recent trends in the survey and model timeseries
1. “Survey-based” trends: Capture population trends in the survey timeseries via mean proportional change from Y-1 to Y for 2017-2019
• Ignores model completely
2. “Model-based” trends: Capture population trends in the model timeseries via mean proportional change from Y-1 to Y for 2018-2020
• Acknowledges biological processes such as recruitment, growth, etc., reflected in the model
• Includes 2020 model increases
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Bio
mas
s (m
illio
n lb
)
Total mature biomass (TMB)
Observed
Model survey
Model population
TMB
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“Survey-based” “Model-based”
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Bio
mas
s (m
illio
n lb
)
Total mature biomass (TMB)
Observed
Model survey
Model population
0
200
400
600
800
1,000
1,200
19
78
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Bio
mas
s (m
illio
n lb
)
Mature male biomass Observed
Model survey
Model population
0
200
400
600
800
1,000
1,200
19
78
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Bio
mas
s (m
illio
n lb
)
Mature male biomass Observed
Model survey
Model population
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MMB
“Model-based”“Survey-based”
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
34
4 inch male abundance
“Model-based”“Survey-based”
0
50
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450
500
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
TMB MMB TMB MMB TMB MMB TMB MMB
1983-1997 Average (millions lb) 803.8 527.8 803.8 527.8 886.8 499.1 1,773.9 714.8
2020 Estimate (millions lb) 880.2 564.6 856.5 738.2 1,426.8 1,072.5 2,012.8 1,235.0
(2020 Est)/(1983-1997 Avg) 109% 107% 107% 140% 161% 215% 113% 173%
FMSY = 0.3 0.3 0.3 0.3
Exploitation Rate on MMB 0.225 0.225 0.225 0.225
Computed TAC = Exp Rate X MMB (millions lb) 127.04 166.08 241.32 277.88
Max TAC (58% cap on exploited legal males (million lb) 38.54 98.99 233.75 268.26
TAC 38.5 99.0 233.8 268.3
25% buffer 28.9 74.2 175.3 201.2
50% buffer 19.3 49.5 116.9 134.1
Survey Observed
(Survey Trend)
Survey Observed Survey Population
(Model Trend) (Model Predicted) (Model Estimated)
Assumes:
• Average weight of 4-inch ♂♂ = 1.189 lb (2019/20 FT summary)
• 15% OS proportion from 2019 survey
• 75% OS selectivity in 2020/21 fishery352019/20 TAC = 34.02 mill lb
GMACS TAC computations (not recommended by Council)
Survey Observed Survey Observed Survey Population
(Area-swept Est.) (Area-swept Est.) (Model Predicted) (Model Estimated)
Abundance of ♂♂ ≥ 4-in CW (millions) 58.1 149.2 352.3 404.3
Average wt (W; from 2019/20 fishery; lb) 1.189 1.189 1.189 1.189
% old shell (from area-swept) 15% 15% 15% 15%
Expected old shell selectivity 0.75 0.75 0.75 0.75
Exploited legal males ("ELM"; millions) 55.9 143.6 339.1 389.1
Max TAC (= 0.58xELMxW; millions lb) 38.54 98.99 233.75 268.26
TMB MMB TMB MMB TMB MMB TMB MMB
1983-1997 Average (millions lb) 803.8 527.8 803.8 527.8 768.1 475.6 1,023.9 692.3
2020 Estimate (millions lb) 880.2 564.6 846.0 641.2 871.0 586.2 1,046.2 753.5
(2020 Est)/(1983-1997 Avg) 109% 107% 105% 121% 113% 123% 102% 109%
FMSY = 0.3 0.3 0.3 0.3
Exploitation Rate on MMB 0.225 0.225 0.225 0.225
Computed TAC = Exp Rate X MMB (millions lb) 127.04 144.27 131.89 169.54
Max TAC (58% cap on exploited legal males (million lb) 38.54 82.77 128.08 163.77
TAC 38.5 82.8 128.1 163.8
25% buffer 28.9 62.1 96.1 122.8
50% buffer 19.3 41.4 64.0 81.9
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Assumes:
• Average weight of 4-inch ♂♂ = 1.189 lb (2019/20 FT summary)
• 15% OS proportion from 2019 survey
• 75% OS selectivity in 2020/21 fishery362019/20 TAC = 34.02 mill lb
Status Quo (20.1) TAC computations
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Abundance of ♂♂ ≥ 4-in CW (millions) 58.1 124.7 193.0 246.8
Average wt (W; from 2019/20 fishery; lb) 1.189 1.189 1.189 1.189
% old shell (from area-swept) 15% 15% 15% 15%
Expected old shell selectivity 0.75 0.75 0.75 0.75
Exploited legal males ("ELM"; millions) 55.9 120.1 185.8 237.6
Max TAC (= 0.58xELMxW; millions lb) 38.54 82.77 128.08 163.77
Historical Summary of Estimates Used for Setting snow crab TAC
Through 2005/06: (area-swept)
• all that was available
2006/10 − 2009/10: model survey
• Approval of snow crab assessment model by CPT/SSC in fall 2006
• Survey-predicted estimates = population estimates; Q = 1
2010/11 − 2012/13 (TAC 54, 89, 66 mil lb): model population (with Q < 1)
2013/14 (TAC 54 mil lb): model survey
• Trend in model estimates versus area-swept & very low Q
2014/15 (TAC 68 mil lb): model observed (area-swept)
• Trend in estimates of year from subsequent models (retrospective pattern)
2015/16 (TAC 41 mil lb): mid-point between model survey and model observed
• High uncertainty with model estimates
2016/17 (TAC 22 mil lb): 10% buffer on model survey
• High uncertainty with model estimates
2017/18 (TAC 19 mil lb): model observed (area-swept)
• High uncertainty with model estimates
• Fishery performance (declining trend in CPUE, reports from fishery = low performance in
historic areas)
2018/19 (TAC 27 mill lb): model observed (area-swept)
• Uncertainty with model estimates
• Confidence with estimates of MMB and 4 inch males
2019/20 (TAC 34 mill lb): model observed (area-swept)
• Uncertainty with model estimates
• Confidence with estimates of MMB and 4 inch males 37
Narrow the scope of TAC computations
• Have not used model population in recent years due to model uncertainty
• 2020 not a good year to start given missing survey and high retrospective bias
• Model uncertainty inherent in the model outputs used in harvest strategy (MMB, TMB, 4 inch male abundance)
• The 25% ABC buffer is not applied to model outputs used in harvest control rules
• Considered the application of the same 25% buffer that the CPT recommended to model-survey-based TAC
38
TMB MMB TMB MMB TMB MMB TMB MMB
1983-1997 Average (millions lb) 803.8 527.8 803.8 527.8 768.1 475.6 1,023.9 692.3
2020 Estimate (millions lb) 880.2 564.6 846.0 641.2 871.0 586.2 1,046.2 753.5
(2020 Est)/(1983-1997 Avg) 109% 107% 105% 121% 113% 123% 102% 109%
FMSY = 0.3 0.3 0.3 0.3
Exploitation Rate on MMB 0.225 0.225 0.225 0.225
Computed TAC = Exp Rate X MMB (millions lb) 127.04 144.27 131.89 169.54
Max TAC (58% cap on exploited legal males (million lb) 38.54 82.77 128.08 163.77
TAC 38.5 82.8 128.1 163.8
25% buffer 28.9 62.1 96.1 122.8
50% buffer 19.3 41.4 64.0 81.9
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Assumes:
• Average weight of 4-inch ♂♂ = 1.189 lb (2019/20 FT summary)
• 15% OS proportion from 2019 survey
• 75% OS selectivity in 2020/21 fishery392019/20 TAC = 34.02 mill lb
Status Quo (20.1) TAC computations
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Abundance of ♂♂ ≥ 4-in CW (millions) 58.1 124.7 193.0 246.8
Average wt (W; from 2019/20 fishery; lb) 1.189 1.189 1.189 1.189
% old shell (from area-swept) 15% 15% 15% 15%
Expected old shell selectivity 0.75 0.75 0.75 0.75
Exploited legal males ("ELM"; millions) 55.9 120.1 185.8 237.6
Max TAC (= 0.58xELMxW; millions lb) 38.54 82.77 128.08 163.77
Other considerations:
fishery performance, bycatch, environmental conditions
40
41
Down to 3.1 inches
Mostly >4.0 inches
Lots of small crab in pots
4 inch CPUE comparable to recent years
42
43
Predicted %SInPretained_catch =
𝑠𝑒𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑥 %𝑆𝐼𝑛𝑃𝑠𝑢𝑟𝑣𝑒𝑦(𝑠𝑒𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑥 %𝑆𝐼𝑛𝑃𝑠𝑢𝑟𝑣𝑒𝑦 + %𝐼𝑛𝑃𝑠𝑢𝑟𝑣𝑒𝑦)
Solve for “selectivity”
Sub-in-prefselectivity ~constant over time
• A little lower in last 2 seasons
High discarding in 2019/20 likely due mostly to population size structure, not shift in fishing behavior
Snow crab: observations from the fleet
• Lots of small crab (sub 4”) across the fishing grounds led to heavy sorting
throughout the season. Many skippers reported individual pots with over 1000
crab, with only a couple hundred of those being at or above industry preferred
size.
• Higher CPUEs and cleaner fishing farther north near St. Matthew Island, but
not the kind of numbers seen in 2018/19 fishery. Sea ice covered fishing
grounds around St. Matthew Island in February.
• Sea ice on the northern fishing grounds restricted the amount of area available
for the fleet to work in. Especially high concentration of vessels fishing W/SW
of the Pribilof Islands, all sorting through the same crab over and over for few
industry preferred size males.
• Sea ice was at maximum extent in early March when it reached the northern
tip of Saint Paul Island. As sea ice retreated from northern fishing grounds in
March, most vessels saw higher CPUEs in these areas.
• Severe winter weather for much of the season – heavy freezing spray
conditions. 44
45
Based on abundance of legal (+3.1 inches) male crab
High discarding sub-industry preferred legal crab
46
Bycatch mortality rate shown here based on weight and includes females, sublegal males, and legal males
Assumes 0.3 handling mortality rate
10.3 mill lb bycatch mortality
47
Low mean wtlikely reflects high abundance of sub-industry preferred crab in population
Directed fishery discard rate revisited
• Discarding rates at timeseries high in 2019/20
• Indicates large abundance of small legal crab in population (3.1 – 4.0 inches)
• But, how many crab in 3.1 – 4.0 inch range have terminally molted? ..... Unknown
• What should we expect for 2020/21?• Model MMB doubled from 2019-2020, whereas 4 inch males quadrupled
• Proportionally more 4 inch males relative to sub-ind pref males• Could expect lower discarding rate
48
49
2019/20 discard mortality estimate: 10.3 mill lbs• ~30% of retained catch
Assuming the same rate and a TAC of 45 mill lb, thats an additional 13.5 mill lb of additional fishery mortality
Directed fishery discard rate revisited
So what's the right TAC?
50
-60%
-40%
-20%
0%
20%
40%
60%
2012 2013 2014 2015 2016 2017 2018 2019
% c
han
ge f
rom
Y t
o Y
+1
% TAC change
TAC considerations
Average % increase from 2017 to 2018 and 2018 to 2019 was ~35%
2019 TAC +35% = 45.9 mill lb51
TMB MMB TMB MMB TMB MMB TMB MMB
1983-1997 Average (millions lb) 803.8 527.8 803.8 527.8 768.1 475.6 1,023.9 692.3
2020 Estimate (millions lb) 880.2 564.6 846.0 641.2 871.0 586.2 1,046.2 753.5
(2020 Est)/(1983-1997 Avg) 109% 107% 105% 121% 113% 123% 102% 109%
FMSY = 0.3 0.3 0.3 0.3
Exploitation Rate on MMB 0.225 0.225 0.225 0.225
Computed TAC = Exp Rate X MMB (millions lb) 127.04 144.27 131.89 169.54
Max TAC (58% cap on exploited legal males (million lb) 38.54 82.77 128.08 163.77
TAC 38.5 82.8 128.1 163.8
25% buffer 28.9 62.1 96.1 122.8
50% buffer 19.3 41.4 64.0 81.9
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Assumes:
• Average weight of 4-inch ♂♂ = 1.189 lb (2019/20 FT summary)
• 15% OS proportion from 2019 survey
• 75% OS selectivity in 2020/21 fishery522019/20 TAC = 34.02 mill lb
Status Quo (20.1) TAC computations
Survey Observed Survey Observed Survey Population
(Survey Trend) (Model Trend) (Model Predicted) (Model Estimated)
Abundance of ♂♂ ≥ 4-in CW (millions) 58.1 124.7 193.0 246.8
Average wt (W; from 2019/20 fishery; lb) 1.189 1.189 1.189 1.189
% old shell (from area-swept) 15% 15% 15% 15%
Expected old shell selectivity 0.75 0.75 0.75 0.75
Exploited legal males ("ELM"; millions) 55.9 120.1 185.8 237.6
Max TAC (= 0.58xELMxW; millions lb) 38.54 82.77 128.08 163.77
0
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Ab
un
dan
ce (
mill
ion
cra
bs)
4-inch male abundance
Observed
Model survey
Model population
53
2020: “Model-based” area-swept
Plausibility of abundance increases? • In the past, we have seen big jumps from one year to the
next, but few recent examples
• Usually consider model and environmental uncertainty to inform buffers
Considerations for 2020:
• Model trends (input) for 2020
• Discard mortality
“Model-based” area-swept estimate
Option Input TAC buffer Input buffer Discard debit TAC
1 Survey observed (model 4 yr trend) 70.0
2 Survey observed (model 4 yr trend) 25% 52.5
3 Survey observed (model 3 yr trend) 25% 62.1
4 Survey observed (model 3 yr trend) 45% 45.5
5 Survey observed (model 3 yr trend) 25% 2019 rate 43.3
6 Survey observed (model 3 yr trend) 25% 17-19 ave rate 47.4
7 Survey observed (model 3 yr trend) 25% 16-19 ave rate 48.9
8 Model survey 25% 88.0
9 Survey observed (model 3 yr trend) 25% 62.1
10 2019 TAC (34 mill lb) add 35% 45.954
• Discard debits meant to acknowledge recent high grading
• 2019/20 timeseries high
Area-swept estimate (using model 3 yr trend) + TAC buffers
• 45% buffer captures uncertainty consistent with CPT thought process • Status quo 20% buffer for retrospectives, data fit• +25% buffer for missing survey
55
TAC calculation 2020 projected survey estimates using model-based trends + apply buffer to account for uncertainty in the steepness of the increasing population trajectory or to account for discard mortality
Convergence of values in the 40-50 mill lb range
2020 TAC: 45 mill lb
• Uses model-based trends that should reflect the biology and population dynamics
• Recognizes the uncertainty associated with model performance + 2020 missing survey
• Consistent with past TAC setting approaches
• Proportion of ABC is lower, but comparable to recent years
• 32% increase from 2019
• Reflects increasing abundance in stock 56
Final Thoughts
• Outlook good for stock
• Extremely challenging year to set TACs
• 2020 TAC likely precautionary
• Assessment is improving
• State harvest strategy under review
• Concerns we are wrong: forgone harvest
57
SST Projections from the
National Multi-Model Ensemble Bond
• TOP: continued warmth in Bering Sea with delayed sea ice; warmth for AI; near-normal SSTs in GOA (an end of the current MHW?).
• MIDDLE: similar spatial pattern, but decreased magnitude of anomalies.
• BOTTOM: near-normal temps along coast, moderate warmth in EBS, slight warmth in C&W AI.
• Possible La Niña; weakens by Spring 2021.
58
Bristol Bay Red King Crab
59
Bristol Bay Red King Crab
Federal 2020/21 ABC/ACL, OFL Determination
ABC/ACL= 3.54 mill lb total catch
• including bycatch mortality of males and females in all fisheries
• based on a 25% buffer on OFL
OFL = 4.72 mill lb total catch
Stock estimated at 75% of BMSY in 2019/20
Stock projected to be at 59% of BMSY in 2020/21
60From 2020 SAFE
25% Buffer on ABC
ABC buffer was 20% in 2019 assessment• Uncertainty associated with: 1) poor fit to 2018 + 2019 survey
data, 2) retrospective patterns, 3) recent environmental conditions (warm bottom temps, lack of cold pool)
• Ignoring lack of 2020 survey, model uncertainty has not changed from 2019
Cancelled 2020 survey• Retrospective + sensitivity analyses: uncertainty = +5%
• No 2020 info to inform declining trend• May be approaching overfished status (2020 assessment: 59% B/Bmsy)
• Avoiding overfished is important as king crab stocks do not rebuild easily
61
62
63
BBRKC weighted centers of catch
64
2019/20 BBRKC: observations from the fleet
• Severe weather on the RKC grounds kept most of the fleet tied up
in port until 10/17.
• Seemed to be only one small school of crab that produced decent
CPUEs for the few vessels that were on it, and that got cleaned up
early in the fishery. Opposed to 2017/18 and 2018/19 fisheries,
where there were larger schools of crab that produced high CPUEs
for the duration of the fishery.
• Low CPUE (scratch fishing) for most vessels throughout the
fishery.
• Many vessels were moving gear around trying to get on a school
of crab, which never materialized.
• Very large crab, with few recruits, in general.
65
Bristol Bay Red King Crab Harvest Strategy
Stock threshold for opening fishery:•8.4-million mature-sized females (females ≥ 90 mm CL), and
•14.5-mill lb of effective spawning biomass (ESB)
Exploitation rate on mature-sized (≥120-mm CL) male abundance:•10%, when ESB <34.75-mill lb
•12.5%, when ESB is between 34.75-mill lb and 55.0-mill lb
•15%, when ESB ≥55.0-mill lb
Harvest capped at 50% of legal male abundance
•ESB = effective spawning biomass•F = mature-sized female (females ≥ 90 mm CL) abundance•M = mature-sized male (males ≥ 120 mm CL) abundance •L = legal male (males ≥ 135 mm CL) abundance•W = expected average weight of landed legal males 66
Avg wt 2019/20 Fishery = 7.136
Parameter Estimate 95% CI
ESB (millions of lb) 25.120 (-)
F (millions of crab) 9.668 (7.725 - 27.304)
M (millions of crab) 5.151 (4.346 - 6.033)
L (millions of crab) 3.718 (2.934 - 4.484)
2020 LBA
0
0.05
0.1
0.15
0.2
0 10 20 30 40 50 60 70 80Exp
loit
atio
n r
ate
on
MM
A
ESB (mill lb)
BBRKC Harvest Strategy
Harvest Strategy Closure Thresholds
2 thresholds, both based on mature females
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Mill
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ab
Mature Females
2020 model Area-swept closure threshold
8.4 mill mature females
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ion
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f lb
Effective Spawning Biomass (ESB)
2020 model closure threshold
14.5 mill lb ESB
2019 area-swept: 8.6 mill67
1. Stock above threshold for opening fishery
• F = 9.668 million > 8.4-million
• ESB = 25.120-mill lb > 14.5-mill lb
2. Exploitation rate on mature-sized male abundance (M)
• ESB between 14.50 mill lb and 34.75-mill lb →
•10% exploitation rate on MMA
3. TAC computation according to state harvest strategy:
10% exploitation rate applied to estimated mature-sized male abundance
•5.151 million MMA
•(0.10) x (5.151) = 0.515 million crabs
Check: 50% cap on harvest of legal males
•3.718 million legal males
•(0.5) x (3.718) = 1.859 million crabs > 0.515-million crabs
→Compute TAC on harvest of 0.515-million legal males
→Assume 2019/20 fishery ave wt: 7.136 lb
TAC computation
68Computed TAC = 3.676 mill lb
TAC: Annual catch target for the directed fishery, set to prevent exceeding the ABC for that stock. Limits legal sized males, but must consider all sources of mortality to ensure the ABC is not exceeded.
ABC: Level of annual catch that accounts for scientific uncertainty and is set to prevent the OFL from being exceeded.
In practice ABC limits mortality of ALLmale and female crabs regardless of size, from all sources of fishery mortality (i.e. retained catch, bycatch in directed and nondirected crab fisheries, and groundfish fisheries).
OFL: Level of fishing mortality that jeopardizes the capacity of a stock to produce the maximum sustained yield on a continuing basis.
Cat
ch
0
10-20% buffer
Overfishing Level (OFL)Federal Government
Acceptable Biological Catch (ABC)Federal Government
Total Allowable Catch (TAC)State of Alaska
Below ABC
69
Computed TAC and ABC
ABC = 3.54 mill lbs
Computed TAC = 3.676 mill lbs
ABC limiting TAC...why this year?
• Reductions in OFL due to changes in model structure
• Additional ABC buffer (25%)
...........................................Must look at bycatch
70
High discard
rate in past 2
seasons
71
Steady increase in retained catch mean weight
72
Suggests low recruitment to legal size
2019/20 estimated
oldshell selectivity
comparable to recent
years
So, what's up with
the discard mortality
rate?
73
Ratio of sublegal crabs
up in 2018/19 + 2019/20
relative to recent years,
but comparable to the
long-term trends
Vessels were seeing
more sublegal male
crabs than they have
since 2011-ish
High discard mortality
rate in last 2 seasons
likely related to : 1) more
sublegal crabs in pots,
and 2) higher proportion
of legal crabs in old shell
condition0.0
0.2
0.4
0.6
0.8
1.0
BBRKC Observer pots: subL_male/total male
su
bL
_M
/To
tal_
M
19
90
19
91
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92
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74
Bycatch in groundfish fisheries
0
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0.15
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0.25
0.3
0.35
0.4
0.45
Byc
atch
mo
rtal
ity
(mill
lb)
Assumed prior 3-yr average groundfish fishery discard mortality
75
76
Assumed prior 3 yr directed fishery discard rate
TAC = ABC reduced for anticipated bycatch
77
ABC = 3.54 mill lbs
Average mortality in GF fisheries 2017-2019 = 0.353 mill lb
2020 BBRKC test fishery = 0.1235 mill lb
3.54 – (0.353 + 0.124) = 3.064 mill lbs
Average discard mortality rate in directed fishery 2017-2019 = 0.157
TAC + (TAC*disc rate) = 3.30
TAC * (1 + disc rate) = 3.30
TAC = 3.30/(1 + disc rate)
TAC = 3.064/(1+0.157) = 2.648 mill lbs
0
5
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25
30
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
AB
C (
mill
ion
lb)
ABC components
BBRKC TAC BBRKC Test fishery
Directed discard Tanner bycatch
Groundfish mortality ABC- total fish mort.78
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30
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
AB
C (
mill
ion
lb)
TAC vs ABC
TAC ABC-TAC79
0%
10%
20%
30%
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70%
80%
90%
100%
20
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% o
f A
BC
ABC - TAC ABC - total fishery mort.
• Space between TAC and ABC among lowest its been• Space between ABC and total fishery mortality
lowest its ever been
80
81
BBRKC Ecosystem Indicator Time Series
82
Stage 1 Indicator Analysis: Traffic Light Test for Ecosystem Indicators
Title Description Recent
Juvenile sockeye
salmon abundance
Estimated September juvenile sockeye salmon biomass
from the Bering Arctic Subarctic Integrated Surveys in the
EBS +
Pacific cod biomass Biomass (1,000t) of Pacific cod within the BBRKC
management boundary on the EBS bottom trawl survey -
Benthic invertebrate
biomass
Combined biomass (1,000t) of benthic invertebrates within
the BBRKC management boundary on the EBS bottom
trawl survey •
BBRKC recruit
biomass
Biomass of male red king crab (110-134 mm CL) from the
EBS bottom trawl survey that will likely enter the fishery
the following year. -
BBRKC Catch
Distance from Shore
Mean distance (km) legal male Bristol Bay red king crab
were caught from shore in the autumn fishery (starting Oct.
15th) using observer data.
+
BBRKC mature male
area occupied
The minimum area containing 95% of the cumulative
CPUE for BBRKC mature males from the EBS bottom
trawl survey +
BBRKC mature
female area occupied
The minimum area containing 95% of the cumulative
CPUE for BBRKC mature females from the EBS bottom
trawl survey +
Title Description Recent
Cold Pool Index
Fraction of the EBS BT survey area with bottom water less
than 2°C on 1 July of each year from Bering10K ROMS model
output hindcasts
•
Summer Bottom
Temperature
Average of June-July bottom temperatures (° C) within the
BBRKC management boundary from the Bering 10K ROMS
model output hindcasts •
Arctic Oscillation
Average of Jan-March Arctic Oscillation Index estimates;
constructed by projecting daily 1000mb height anomalies
poleward of 20°N onto the loading pattern of the Arctic
Oscillation
+
Corrosivity Index
Percent of the BBRKC management area containing an
average bottom aragonite saturation state of < 1 from Feb-
April +
Spring Bottom
Temperature
Average of Feb-March bottom temperatures (° C) within the
BBRKC management boundary from the Bering 10K ROMS
model output hindcasts •
Wind Stress June ocean surface wind stress within the BBRKC
management boundary. Product of NOAA blended winds and
MetOp ASCAP sensors from multiple satellites •
Chlorophyll-a
Biomass
April-June average chlorophyll-a biomass within the Southern
Inner Shelf of the Bering Sea; calculated with 8-day composite
data from MODIS satellites •
Ecosystem Considerations: • Available physical indicators for 2020 show a return to near-average conditions in
Bristol Bay• A relatively high positive Arctic Oscillation index in winter 2020 may suggest
favorable conditions for BBRKC productivity• Current-year increases in corrosive bottom waters in Bristol Bay have the
potential to impact shell formation, growth and survival of BBRKC83
Ocean AcidificationPilcher, Cross
2020 July - Aug. 15 Bottom ΩArag Anomaly
● Anomaly plot shows 2020 compared to the 2003 - 2019 mean.
● Blue is better; red is worse.
This is an in-development model forecast product.84
SST Projections from the
National Multi-Model Ensemble Bond
• TOP: continued warmth in Bering Sea with delayed sea ice; warmth for AI; near-normal SSTs in GOA (an end of the current MHW?).
• MIDDLE: similar spatial pattern, but decreased magnitude of anomalies.
• BOTTOM: near-normal temps along coast, moderate warmth in EBS, slight warmth in C&W AI.
• Possible La Niña; weakens by Spring 2021.
85
Overall Outlook
• Continued downward trajectory• Troubling population trends: approaching “overfished” status
(MSST = 50% Bmsy)
• B/Bmsy=59%
• King crab populations in general show little resilience
• Low estimated recruitment
• Females nearing harvest strategy closure thresholds
• Length frequencies discouraging, no strong pulses of small crabs in system
• Fluctuating environmental conditions• Projected warming for near future
86
Tanner crab
87
Tanner crab challenges this year
• No 2020 survey
• New harvest strategy: 2 control rules• 1. Exploitation on MMB via “female dimmer”• 2. 50% ELM CAP
• Model challenges • Outputs are for entire EBS, not E/W 166° W• Tendency to overestimate +5-inch males
88
89
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9
Mill
ion
lbs
Historical TACsEast and west combined
90
912019 NOAA survey
Some recruitment Low abundance
EAST
2019: 93% oldshell
EAST
0
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201
2
201
3
201
4
201
5
201
6
201
7
201
8
201
9
Per
cen
t o
ldsh
ell
Ab
un
dan
ce (
mill
ion
cra
b)
5-inch males EAST of 166
Abundance Percent oldshell
2019: lowest abundance
in past ~20 yrs
92
932019 NOAA survey
WEST
Strong recruitmentLow abundance
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
5
10
15
20
25
30
200
5
200
6
200
7
200
8
200
9
201
0
201
1
201
2
201
3
201
4
201
5
201
6
201
7
201
8
201
9
Perc
en
t o
ldsh
ell
Ab
un
dan
ce (
mill
ion
cra
b)
5-inch males WEST of 166
Abundance Percent oldshell
94
2019: 96%
oldshellWEST
Hope for the future
0
2
4
6
8
10
12
newshell oldshell
Bio
mas
s (m
ill lb
)
5 inch males WEST of 166
0.45 mill lb
10.58 mill lb
952019 NOAA survey
Tanner crab all EBS (female)
Carapace length (mm)
Ab
un
da
nce
(m
illio
ns)
10
20
30
40
50
0 510
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
20160 5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
2019
2015
10
20
30
40
50
2018
10
20
30
40
50
2014 2017
Shell condition
Soft & molting New - hard Old Very old
1975-2014 2015-2019
Tanner crab MMB
• Overall shift of MMB to the west in recent years
96
97
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1975
1976
197
719
7819
7919
8019
8119
8219
8319
8419
8519
8619
8719
8819
89
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
200
120
0220
0320
0420
0520
0620
0720
0820
0920
1020
1120
1220
13
2014
2015
2016
2017
2018
2019
2020
Pro
po
rtio
n w
est
16
6 W
Proportion west of 166 W
5 inch male abundance
MMB
Implications for mean stock-wide size-at-maturity?• Likely smaller than historical
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
5%
10%
15%
20%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150%
Fem
ale
bio
mas
s (c
urr
en
t ye
ar/l
on
g te
rm a
vera
ge)
Exp
loit
atio
n ra
te o
n m
atu
re m
ale
bio
mas
s (M
MB
)
MMB/MMBAVE
Exploitation rate on mature male biomass (MMB)
Upper bound
Lower bound
Floating HCR
Females (B/Bave)
Harvest strategy: “Female dimmer”
98
No female “off switch”
MMB “off switch” is 25% of long-term average
Harvest strategy: 50% ELM Cap
ELM= “exploitable legal males”• 5 inch males: 100% newshell + 40% oldshell
• Considers selectivity of oldshell crabs: industry generally prefers “clean” (mostly newshell) crab
• Mean OS selectivity = ~40%
• Sensitive to industry preferred size
• TAC capped at 50% of ELM: 0.5 * ELM * ave wt
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
"Est
imat
e"
of
OS
sele
ctiv
ity
Preseason survey year
Est'd from retained-catch samples
Est'd from retained-catch samples
99
Harvest strategy inputs needed
• MFB for entire EBS
• MMB east and west of 166 W
• 5 inch male abundance east and west of 166 W
• 5 inch male ave wt east and west of 166 W
• Proportion 5 inch male oldshell-newshell east and west of 166 W
100
Because no 2020 survey, there are key assumptions in implementing
the harvest strategy in 2020
• MMB and 5 inch male abundance proportions east-west
• Used 2017-2019 survey mean for 2020
• 5 inch male % in oldshell condition • Used 2019 proportion
• Ave wt of 5 inch males • Calculated as Biomass/Abundance
101
102
Model estimates
Challenges for setting TAC
• EBS wide• 2020
estimates
Status quo 20% ABC Buffer
Model performance: similar to prior years
• No change from status quo 20% buffer
Missing survey: No additional buffer • Retrospective + sensitivity analyses did
not indicate high sensitivity to OFL
103
Model Challenge #1
Apportioning model estimates east-west of 166 W
Approach: Calculate survey proportions east-west for each harvest strategy input (MFB, MMB, 5 inch male abund) apply those proportions to the model output.
• What about 2020? Used 2017-2019 mean
104
105
0
50
100
150
200
250
300
350
400
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Bio
mas
s (m
ill lb
)Mature males EAST of 166 W
Survey area-swept
Model survey
106
0
20
40
60
80
100
120
140
160
180
200
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Bio
mas
s (m
ill lb
)Mature males WEST of 166 W
Survey area-swept
Model survey
107
0
20
40
60
80
100
120
140
160
180
200
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Bio
mas
s (m
ill lb
)5 inch males EAST of 166 W
Survey area-swept
Model survey
108
0
20
40
60
80
100
120
140
160
180
200
19
75
19
76
19
77
19
78
1979
19
80
19
81
19
82
19
83
19
84
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
2001
20
02
20
03
20
04
20
05
2006
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
20
20
Bio
mas
s (m
ill lb
)5 inch males WEST of 166 W
Survey area-swept
Model survey
109
0
50
100
150
200
2501
97
51
97
61
97
71
97
81
97
91
98
01
98
11
98
21
98
31
98
41
98
51
98
61
98
71
98
81
98
91
99
01
99
11
99
21
99
31
99
41
99
51
99
61
99
71
99
81
99
92
00
02
00
12
00
22
00
32
00
42
00
52
00
62
00
72
00
82
00
92
01
02
01
12
01
22
01
32
01
42
01
52
01
62
01
72
01
82
01
92
02
0
Bio
mas
s (m
illio
n lb
)Mature female biomass
Survey area-swept
Model survey
Entire EBS
Model Challenge #2: Model Fit
• 2019: Possible overestimates in 2019 for all harvest strategy inputs
• 2020: Difficult to interpret 2020 estimate without survey to inform
Approach: 4 TAC calculations for comparison
1.Model based TAC: use model outputs as is (after apportioning east-west)
2.Survey based TAC 1: Calculate 2020 survey area-swept estimates by projecting 2019 survey estimate using model-based trend for 2018-2020 (mean proportional change from Y-1 to Y)
3.Survey based TAC 2: Calculate 2020 survey area-swept estimates by projecting 2019 survey estimate using survey-based trend for 2017-2019 (mean proportional change from Y-1 to Y)
4.Buffered TAC: Apply 30% buffer on model-based TAC to reflect model uncertainty ....details on 30% to follow
110
MMB survey projections: EAST
111
0
50
100
150
200
250
300
350
400
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Bio
mas
s (m
ill lb
)
Mature males EAST of 166 W
Survey area-swept
Model survey
2020 survey projection
“Model-based”
0
50
100
150
200
250
300
350
400
19
75
19
76
19
77
19
78
19
79
19
80
19
81
19
82
19
83
19
84
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
1997
1998
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
20
20
Bio
mas
s (m
ill lb
)
Mature males EAST of 166 W
Survey area-swept
Model survey
2020 survey projection
“Survey-based”
112
0
5
10
15
20
25
30
35
40
45
50
20
15
2016
20
17
20
18
20
19
20
20
Bio
mas
s (m
ill lb
)Mature males EAST of 166 W
MMB
25% average
Model-based projection
Survey-based projection
Closure threshold
MMB survey projections: WEST
113
0
20
40
60
80
100
120
140
160
180
200
19
75
19
76
19
77
19
78
19
79
19
80
19
81
19
82
19
83
1984
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
2013
20
14
20
15
20
16
20
17
20
18
20
19
20
20
Bio
mas
s (m
ill lb
)
Mature males WEST of 166 W
Survey area-swept
Model survey
2020 survey projection
0
20
40
60
80
100
120
140
160
180
200
19
75
19
76
19
77
19
78
19
79
19
80
19
81
19
82
19
83
1984
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
2013
20
14
20
15
20
16
20
17
20
18
20
19
20
20
Bio
mas
s (m
ill lb
)
Mature males WEST of 166 W
Survey area-swept
Model survey
2020 survey projection
“Model-based” “Survey-based”
Model
114
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
5%
10%
15%
20%
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
120%
130%
140%
150%
FMB
/FM
BA
VE
Exp
loit
atio
n r
ate
on
MM
B
MMB/MMBAVE
Exploitation rate on mature male biomass (MMB)
East
West
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
5%
10%
15%
20%
0%
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
11
0%
12
0%
13
0%
14
0%
15
0%
FMB
/FM
BA
VE
Exp
loit
atio
n r
ate
on
MM
B
MMB/MMBAVE
Exploitation rate on mature male biomass (MMB)
EastWest
Model-based survey projection
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
5%
10%
15%
20%
0%
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
11
0%
12
0%
13
0%
14
0%
15
0%
FMB
/FM
BA
VE
Exp
loit
ati
on
ra
te o
n M
MB
MMB/MMBAVE
Exploitation rate on mature male biomass (MMB)
EastWest
Survey-based survey projection
Performance of the female dimmer varies with population estimates
TAC calculation 4: 30% buffer on model-based TAC
115
0
20
40
60
80
100
120
140
160
20
00
20
02
20
04
20
06
20
08
20
10
20
12
20
14
20
16
20
18
20
20
Mill
ion
po
un
ds
5-inch male biomass
Survey area-swept
2020 model survey Model consistently overestimates 5 inch males
2019 model estimate ~double that of survey
30% buffer is coarse-level approximation of mean overestimation of 5-inch males for 2000-2019
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
Pro
po
rtio
nal
dif
fere
cne
Proportional difference between area-swept and model survey
Mean = 0.32
TAC Options (mill lbs)
116
EAST WEST
Model-based TAC 2.29 3.92
Model-based survey TAC 0.62 1.10
Survey-based survey TAC 0.00 0.78
30% buffer on model-based TAC 1.60 2.74
Old Harvest strategy 0.00 0.00
117
0
20
40
60
80
100
120
140
160
180
200
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Bio
mas
s (m
ill lb
)5 inch males EAST of 166 W
Survey area-swept
Model survey
Declared “overfished”
Closed
2019 at similar levels, model projected decline in 2020
EAST TAC = 0
• Both model-based and survey-based 2020 projections VERY close to 25% closure threshold
• Survey-based projection below closure threshold
• Model trends for MMB + 5 inch males decreased from 2019
• 5 inch males likely >90% oldshell
• Concerns about BBRKC bycatch
• Uncertainty due to missing 2020 survey• 2019 MMB model estimate ~2x survey estimate
118
WEST TAC = 2.35 mill lb
• Mid-point between model-TAC (3.92) and survey-based TAC (0.78)
• Model-based likely overestimate, survey based likely underestimate
• Uncertainty about missing 2020 survey
• Brand new harvest strategy: leaning more into model estimates
• Model trends for MMB + 5 inch males decreased from 2019
• 5 inch males likely >90% oldshell
119
Tanner crab outlook
• Likely continued decline of 5 inch males in 2020• 2020 model estimate + 2019 survey size comps
• Mature females: 2020 model estimate increasing• Hope for the future: female population trend tends to
lead that of males by 1 or 2 years • Early signs of strong juvenile cohort form 2017-2019
reaching maturity?
• East: portion of large male crab is senescing but weak sign of recruits in the 75-100 mm size class from 2019 survey
• West: portion of large male crab is senescing but strong sign of recruits across juvenile cohorts
• Years from reaching legal size• Hope for the future
120