recommended harvest strategy for aleutian islands golden ... · 2. overfishing: probability that...
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Recommended harvest strategy for�Aleutian Islands golden king crab�
Benjamin Daly1, M.S.M. Siddeek1, Mark Stichert1, Steven Martell2, Jie Zheng1�
Alaska Board of Fisheries Meeting�
Anchorage, AK�
March 9-12, 2019�
RC 3 1 Alaska Department of Fish and Game, 2 Sea State Inc.
1
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State/Federal cooperative�management regime�
Federal process:
• NPFMC FMP: 10 BSAI crab stocks (including AIGKC)
• OFL (overfishing level): approximates MSY
• ABC (acceptable biological catch): below OFL to account for “the scientific uncertainty in the estimate of OFL and any other specified scientific uncertainty”
State process: harvest levels (TAC) and other management actions
• BOF Policy on King and Tanner Crab Resource Management, FMP, MSA national standards
• FMP Amendment 38: optimum yield ranges from 0 – <OFL�• Sum of all sources of fishing mortality <ABC
2
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Overfishing Level (OFL)�Federal Government
25% buffer
Acceptable Biological Catch (ABC)�Federal Government
Below ABC
Total Allowable Catch (TAC)�State of Alaska
OFL: Level of fishing mortality that
jeopardizes the capacity of a stock to
produce the maximum sustained yield on
a continuing basis.
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 ALL
male and female crabs regardless of size,
from all sources of fishery mortality (i.e.
retained catch, bycatch in directed and
non-directed crab fisheries, and
groundfish fisheries).
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.
Considers model uncertainty and other
factors.
Ca
tch
�
0
3
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ATTU ..
200 MILE EXCLUSIVE ECONOMIC ZONE
BOUNDARY
REGISTRATION AREA 0 ALEUTIAN ISLANDS
..,,, PRIBILOF ISLANDS
....
CAPE SARICHEF 54 °36'N
•'!-~-• AKUT, N
ISLANDS OF FOUR MOUNTAIN; ~ UNALASKA
KISKA ~.. . "'-- ,'
ATKA
ADAK_. ._J .............. "" . ~~JP~'"
0
~
:.,., , UMNAK 1-. I' I
• c., ::J Cl.
c3 s I~ u"'" I- 0
0"'" u c.o (f) "<"""I
G ,, AREA OF DETAIL
Western Aleutian Islands Eastern Aleutian Islands�
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Current Fishery Management
• Size: 6.0 inches carapace width (152.4 mm)
• Sex: Male only
• Season: August 1 to April 30
• Managed east/west of 174° W longitude
• Gear: pots (longline)
• Harvest levels (total allowable catch; TAC) fixed in regulation
• Small fleet: 5 vessels
• Rationalized fishery
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ADF&G Harvest strategy�The annual TAC is set by state regulation, 5 AAC 34.612 (Harvest Levels for Golden King Crab in Registration Area O), as approved by the BOF in March 2012:
(a) Until the Aleutian Islands golden king crab stock assessment model and a state regulatory harvest strategy are established, the harvest levels for the Registration Area O golden king crab fishery are as follows:
(1) east of 174° W long. (EAG): 3.31 million pounds; and
(2) west of 174° W long. (WAG): 2.98 million pounds;
(b) The department may modify the harvest levels based on the best scientific information available and considering the reliability of estimates and performance measures, sources of uncertainty as necessary to avoid overfishing, and any other factors necessary to be consistent with sustained yield principles.
*Prior to 2018, the word “reduce” was used
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AIGKC stock assessment model�
• In development for nearly 10 years, accepted in 2017 by NPFMC for annual OFL and ABC determination
• AIGKC considered 1 stock, managed as 2 areas: east (EAG) and west (WAG) of 174° W long.
• OFL and ABC calculated for each management area separately, then combined for a single stock OFL and ABC
• Model-based abundance estimates now available • Abundance estimates allow TAC to be scaled to stock status:
better conservation, maximizes economic and social benefits
• No fishery-independent bottom trawl survey, no area-swept abundance estimates prior to model
7
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Objective/purpose�
Objective: Develop a state harvest strategy that allows for abundance-based TAC calculations
How can we balance the tradeoff between conservation
and economic considerations?
• Conducted 30-year forecast simulations to evaluate how thirteen different harvest policies affect stock sustainability and productivity by comparing conservation and economic criteria
8
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Forecast simulations�
What the analysis is:
• A tool used to estimate relative differences in population sustainability and productivity under different harvest policies
What the analysis is not:
• A crystal ball that tells us exactly what will happen over the next 30 years
9
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Forecast simulations�• 2018 base model (scenario 18_0)
• Projected abundances for 30 years • Evaluated short term (1-8 years) and long term (1-30 years)�
results�
• 500 random replicates
• Estimated: • Mature males biomass (MMB)
• Mature male abundance (MMA)
• Legal male biomass (LMB)
• Overfishing level (OFL) Then calculated probabilities of: • Acceptable biological catch (ABC)
• Retained catch per unit effort (CPUE)
exceeding conservation • Total catch (TOTC)
thresholds, • Retained catch (RETC) meeting economic goals, etc.
• Number of annual recruits
10�
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Evaluating State HCRs�Management criteria: 2-tiered approach
Conservation
1. Overfished: probability that MMB < MSST
2. Overfishing: probability that RETC + bycatch_mort > OFL (and ABC)
3. Probability that MMB < BMSY
Economic
1. Probability of fishery closure: MMB < 0.5MSST
2. Average retained catch (RETC)
3. Annual variability in retained catch
4. Probability that retained catch < historical mean catch
5. Probability that retained catch is within desired range • EAG: 4 mill lb ± 20%; WAG: 3 mill lb ± 20%
6. Mean CPUE
7. Probability that CPUE < historical mean CPUE
8. Relative fishing effort (RETC/CPUE)
9. Stock status: Probability that MMA < MMAAVE
• Indicator of where we are on the exploitation “ramp” 11
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Harvest Control Rules�
Policy period for Exploitation rate on MMA Max Exploitation rate on MMA Exploitation rate cap on�MMAAVE MMA/MMAAVE%<100% MMA/MMAAVE%≥100% L abund�
0 1985-2017
1 1985-2017
2 1985-2017
3 1985-2017
4 1985-2017
5 1985-2017
6 1985-2017
7 1985-2017
8 1985-2017
9 1985-2017
10 1985-2017
11 1985-2017
12 1985-2017
13 1985-2017
0
MMA/MMAAVE X 0.10
MMA/MMAAVE X 0.125
MMA/MMAAVE X 0.15
MMA/MMAAVE X 0.20
MMA/MMAAVE X 0.30
MMA/MMAAVE X 0.10
MMA/MMAAVE X 0.125
MMA/MMAAVE X 0.15
MMA/MMAAVE X 0.20
MMA/MMAAVE X 0.30
MMA/MMAAVE X 0.175
MMA/MMAAVE X 0.225
EAG: 0.15, WAG: 0.23
0�
0.1�
0.125�
0.15�
0.2�
0.3�
0.1�
0.125�
0.15�
0.2�
0.3�
0.175�
0.225�
EAG: 0.15, WAG: 0.23�
0
0.25
0.25
0.25
0.25
0.25
0.3
0.3
0.3
0.3
0.3
0.25
0.25
none
12�
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Exp
loit
ati
on
ra
te o
n m
atu
re m
ale
ab
un
da
nce
(M
MA
)�
Exploitation rate on mature male abundance (MMA)
30%
25%
20%
15%
10%
5%
0%
MMA/MMAAVE
30% ramp
22.5% ramp
20% ramp
17.5% ramp
15% ramp
12.5% ramp
10% ramp
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150%�
* Includes 25% and 30% exploitation “caps” on legal male abundance 13
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30
EAG MMB (model estimates)
EAG TAC
WAG MMB (model estimates)
WAG TAC
Historical TAC and MMB model estimates
• Population abundances fluctuate
• The TAC fixed in regulation
mil
lio
n l
bs
�
25
20
15
10
5�
0�
19
96
/97
19
97
/98
19
98
/99
19
99
/00
20
00
/01
20
01
/02
20
02
/03
20
03
/04
20
04
/05
20
05
/06
20
06
/07
20
07
/08
20
08
/09
20
09
/10
20
10
/11
20
11
/12
20
12
/13
20
13
/14
20
14
/15
20
15
/16
20
16
/17
20
17
/18
20
18
/19
14
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Estimates of historical exploitation rates�
0.35
Exp
lota
tio
n r
ate
(G
HL/
MM
B)
usi
ng
20
18
mo
de
l e
stim
ate
s o
f M
MB
0.3
0.25
0.2
0.15
0.1
0.05
0
19
96
/97
19
97
/98
19
98
/99
19
99
/00
20
00
/01
20
01
/02
20
02
/03
20
03
/04
20
04
/05
20
05
/06
20
06
/07
20
07
/08
20
08
/09
20
09
/10
20
10
/11
20
11
/12
20
12
/13
20
13
/14
20
14
/15
20
15
/16
20
16
/17
20
17
/18
20
18
/19
EAG
EAG 10 yr mean
WAG
WAG 10 yr mean
23%
15%
• Exploitation rates have changed
over time within the EAG and WAG
• Exploitation rates have been
consistently higher in the WAG vs
the EAG
15
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1
EAG�P
rob
ab
ilit
y�
Probability of exceeding OFL
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Short term (yr 1-8)
Long term (yr 1-30)
Policy HR "ramp" Legal cap
0 0% 0%
1 10% 25%
2 12.5% 25%
3 15% 25%
4 20% 25%
5 30% 25%
6 10% 30%
7 12.5% 30%
8 15% 30%
9 20% 30%
10 30% 30%
11 17.5% 25%
12 22.5% 25%
13 15% fixed 0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13�Policy�
0
16
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WAG�P
rob
ab
ilit
y�
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0�
Probability of exceeding OFL�
Short term (yr 1-8)
Long term (yr 1-30)
Policy HR "ramp" Legal cap
0 0% 0%
1 10% 25%
2 12.5% 25%
3 15% 25%
4 20% 25%
5 30% 25%
6 10% 30%
7 12.5% 30%
8 15% 30%
9 20% 30%
10 30% 30%
11 17.5% 25%
12 22.5% 25%
13 23% fixed 0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13�Policy�
17
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EAG�P
rob
ab
ilit
y�
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0�
Probability of exceeding ABC�
Short term (yr 1-8)
Long term (yr 1-30)
Policy HR "ramp" Legal cap
0 0% 0%
1 10% 25%
2 12.5% 25%
3 15% 25%
4 20% 25%
5 30% 25%
6 10% 30%
7 12.5% 30%
8 15% 30%
9 20% 30%
10 30% 30%
11 17.5% 25%
12 22.5% 25%
13 15% fixed 0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13�Policy�
18
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WAG�P
rob
ab
ilit
y�
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0�
Probability of exceeding ABC�
Short term (yr 1-8)
Long term (yr 1-30)
Policy HR "ramp" Legal cap
0 0% 0%
1 10% 25%
2 12.5% 25%
3 15% 25%
4 20% 25%
5 30% 25%
6 10% 30%
7 12.5% 30%
8 15% 30%
9 20% 30%
10 30% 30%
11 17.5% 25%
12 22.5% 25%
13 23% fixed 0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 Policy 19
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Policy HR "ramp" Legal cap
0 0% 0%
EAG�R
ET
C (
mil
lio
n l
bs)
�
5.5
5.0
4.5
4.0
3.5
3.0
2.5
0
Short term (yr 1-8)
Long term (yr 1-30)
7 12.5%
8 15%
9 20%
10 30%
11 17.5%
12 22.5%
13 15% fixed
1 10% 25%
2 12.5% 25%
3 15% 25%
4 20% 25%
Average Retained Catch 5 30% 25%
6 10% 30%
30%
30%
30%
30%
25%
25%
0%
1 2 3 4 5 6 7 8 9 10 11 12 13�Policy�
20�
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EAG�
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Re
tain
ed
ca
tch
(m
illio
n l
b)
25% L cap
30% L cap
Fixed 15%, No L cap
0% 5% 10% 15% 20% 25% 30% 35%�Exploitation rate on MMA�
21
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Policy HR "ramp" Legal cap
0 0% 0%
1 10% 25%
2 12.5% 25% WAG 3 15% 25%
4 20% 25% Average Retained Catch� 5 30% 25%
RE
TC
(m
illio
n l
bs)
�
6 10% 30% 3.5
3.0
2.5
2.0
1.5
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Short term (yr 1-8)
Long term (yr 1-30)
7 12.5% 30%
8 15% 30%
9 20% 30%
10 30% 30%
11 17.5% 25%
12 22.5% 25%
13 23% fixed 0%
Policy 22
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WAG�
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 R
eta
ine
d c
atc
h (
millio
n l
b)
25% L cap
30% L cap
Fixed 23%, No L cap
0% 5% 10% 15% 20% 25% 30% 35%
Exploitation rate on MMA� 23
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5
EAG�R
eta
ine
d c
atc
h (
mil
l lb
)� 4
Legal cap
Policy 1
Policy 2
Policy 3
Policy 4
Policy 5
Policy 6
Policy 7
Policy 8
Policy 9
Policy 10
Policy 11
Policy 12
Policy 13
Relative fishing effort
Policy
0
1
2
3
4
5
6
7
8
9
10
11
12
13
HR "ramp"
0%
10%
12.5%
15%
20%
30%
10%
12.5%
15%
20%
30%
17.5%
22.5%
15% fixed
0% 3 25%
25%
25%
25%
25%
2 30%
30%
30%
30%
30%
25% 1 25%
0%
0.00 0.05 0.10 0.15 0.20 0.25
Relative effort (RETC/CPUE)�
0
24
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WAG�R
eta
ine
d c
atc
h (
mil
l lb
)�
3.5
3
2.5 Legal cap
Relative fishing effort
Policy 1
Policy 2
Policy 3
Policy 4
Policy 5
Policy 6
Policy 7
Policy 8
Policy 9
Policy 10
Policy 11
Policy 12
Policy 13
Policy
0
1
2
3
4
5
6
7
8
9
10
11
12
13
HR "ramp"
0%
10%
12.5%
15%
20%
30%
10%
12.5%
15%
20%
30%
17.5%
22.5%
23% fixed
0%
25%
2 25%
25%
25%
25% 1.5 30%
30%
30% 1 30%
30%
25% 0.5
25%
0%
0.00 0.05 0.10 0.15 0.20 0.25
Relative effort (RETC/CPUE)�
0
25
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Decision Matrix
Distill the conservation and economic risk metrics into a single decision table based
on policy ranks
Conservation Catch Catch Stability Metric Unit
Overfished Probability
Severely overfished Probability
Overfishing (OFL) Probability
Overfishing (ABC) Probability
Below BMSY Probability
Metric
Retained catch
Unit
Mill lb
Metric
Fishery closures
Annual catch var
Relative TAC (1)
Relative TAC (2)
CPUE (1)
Unit
Probability
Proportion
Probability
Probability -1
crab pot
CPUE (2)
Relative effort
Stock status
Probability -1
RETC CPUE
Probability
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EAG: Decision Matrix�SHORT TERM (year 1-8)
Conservation Catch Catch Stability Policy Description HR "ramp" L cap
0 No fishing 0% 0%
1 10% ramp, 25% L cap 10% 25% 1 13 1
2 12.5% ramp, 25% L cap 12.5% 25% 3 11 2
3 15% ramp, 25% L cap 15% 25% 5 9 6
4 20% ramp, 25% L cap 20% 25% 9 5 9
5 30% ramp, 25% L cap 30% 25% 12 2 12
6 10% ramp, 30% L cap 10% 30% 2 12 3
7 12.5% ramp, 30% L cap 12.5% 30% 4 10 4
8 15% ramp, 30% L cap 15% 30% 6 8 7
9 20% ramp, 30% L cap 20% 30% 10 4 10
10 30% ramp, 30% L cap 30% 30% 13 1 13
11 17.5% ramp, 25% L cap 17.5% 25% 8 6 8
12 22.5% ramp, 25% L cap 22.5% 25% 11 3 11
13 15% fixed, No L cap 15% 0% 7 7 5
LONG TERM (year 1-30) Conservation Catch Catch Stability
Policy Description HR "ramp" L cap
0 No fishing 0% 0%
1 10% ramp, 25% L cap 10% 25% 1 13 1
2 12.5% ramp, 25% L cap 12.5% 25% 3 11 2
3 15% ramp, 25% L cap 15% 25% 5 9 6
4 20% ramp, 25% L cap 20% 25% 9 5 9
5 30% ramp, 25% L cap 30% 25% 12 2 12
6 10% ramp, 30% L cap 10% 30% 2 12 3
7 12.5% ramp, 30% L cap 12.5% 30% 4 10 5
8 15% ramp, 30% L cap 15% 30% 6 8 7
9 20% ramp, 30% L cap 20% 30% 10 4 10
10 30% ramp, 30% L cap 30% 30% 13 1 13
11 17.5% ramp, 25% L cap 17.5% 25% 8 6 8
12 22.5% ramp, 25% L cap 22.5% 25% 11 3 11
13 15% fixed, No L cap 15% 0% 7 7 4 27
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WAG: Decision Matrix�SHORT TERM (year 1-8)
Conservation Catch Catch Stability Policy Description HR "ramp" L cap
0 No fishing 0% 0%
1 10% ramp, 25% L cap 10% 25% 1.5 13 1
2 12.5% ramp, 25% L cap 12.5% 25% 3.5 11 3.5
3 15% ramp, 25% L cap 15% 25% 5 9 5
4 20% ramp, 25% L cap 20% 25% 8 6 8
5 30% ramp, 25% L cap 30% 25% 12.5 1 13
6 10% ramp, 30% L cap 10% 30% 1.5 12 2
7 12.5% ramp, 30% L cap 12.5% 30% 3.5 10 3.5
8 15% ramp, 30% L cap 15% 30% 6 8 6
9 20% ramp, 30% L cap 20% 30% 9 5 9
10 30% ramp, 30% L cap 30% 30% 12.5 2 12
11 17.5% ramp, 25% L cap 17.5% 25% 7 7 7
12 22.5% ramp, 25% L cap 22.5% 25% 10 4 10.5
13 23% fixed, No L cap 23% 0% 11 3 10.5
LONG TERM (year 1-30) Conservation Catch Catch Stability
Policy Description HR "ramp" L cap
0 No fishing 0% 0%
1 10% ramp, 25% L cap 10% 25% 1.5 13 1
2 12.5% ramp, 25% L cap 12.5% 25% 3 11 3
3 15% ramp, 25% L cap 15% 25% 5 9 5
4 20% ramp, 25% L cap 20% 25% 8 6 6
5 30% ramp, 25% L cap 30% 25% 13 2 12
6 10% ramp, 30% L cap 10% 30% 1.5 12 2
7 12.5% ramp, 30% L cap 12.5% 30% 4 10 7
8 15% ramp, 30% L cap 15% 30% 6 8 8
9 20% ramp, 30% L cap 20% 30% 9 5 10
10 30% ramp, 30% L cap 30% 30% 12 1 13
11 17.5% ramp, 25% L cap 17.5% 25% 7 7 4
12 22.5% ramp, 25% L cap 22.5% 25% 10 4 11
13 23% fixed, No L cap 23% 0% 11 3 9 28
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Summary: EAG • The 30% and 22.5% ramps (both L caps) are aggressive with
moderate/high probability of exceeding OFL • Moderate probability to being overfished (i.e., MMB<MSST) under
some recruitment scenarios
• The 17.5% and 20% ramps (25% L cap) and 15% fixed (No L cap) have moderate/high probability of exceeding ABC
• The 10% and 12.5% ramps are “safe” (low probability of exceeding conservation thresholds) but may not optimize yield
• The 15% ramp (with either the 25% or 30% legal cap) is likely the best trade-off between meeting conservation objectives and optimizing yield
• Moderate levels of conservation risk • Simulations predict TACs around 3.7 mill lbs with moderate annual
variability (~10-12%) without high increases in fishery effort relative to the 10% and 12.5% ramps
• Approximates historic exploitations rates
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Summary: WAG�• The 30% and 22.5% ramps (both L caps) and the 23% fixed rate is
aggressive with moderate/high probability of exceeding OFL • Moderate probability to being overfished (i.e., MMB<MSST) under some
recruitment scenarios
• All policies with 15% ramps or higher have high probabilities of exceeding the ABC
• The 10% and 12.5% ramps are “safe” but may not optimize yield�• The 15%, 17.5%, and 20% ramps (with either legal cap) likely
the best trade-off between meeting conservation objectives and optimizing yield
• Increasing conservation risk within the 15%-20% range
• Predicted TACs are similar (2.6-2.7 mill lb)
• Annual catch variation is similar
• TACs will likely flirt with area-specific ABC • Simulation results are sensitive to how bycatch mortality is estimated
• Relative fishing effort has to increase dramatically for modest catch increase
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Recommendation�
EAG: 15% ramp with a 25% legal cap
WAG: 15%, 17.5%, or 20% ramp with a 25% legal cap
Combined EAG policy 3 + WAG policy 4�
0
2
4
6
8
10
12
Milli
on
lb
s
OFL
ABC
RETC+Bycatch
RETC
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30�
Projection year 31
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Thank you�
32