POTENTIAL YIELD AND
FEMALE SPAWNING
BIOMASS GAINS FROM
REDUCED BYCATCH LEVELS
Steven Hare, Gregg Williams, Juan Valero, Bruce Leaman
“This presentation is intended to be complemented by a verbal
interpretation. As such, it is offered here solely for informational purposes,
and to allow some familiarity with the material prior to its formal
presentation.”
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
2
Overview
• NPFMC requested information on potential
benefits/implications of reducing bycatch mortality caps
• Impacts differ for U26 and O26 components
• O26 component treated same as directed removals
• U26 component modeled to estimate losses to directed fishery and
population
• Tabulate losses (potential gains) in yield (CEY) and
female spawning biomass (FSBio)
• Calculations done on 100 mt trawl/15 mt fixed gear cap
reduction increments
• Estimates of coastwide Ebio and FSBio losses for total
bycatch mortality presented at end
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Sequence of calculations
Determine size distribution of halibut bycatch
2. Compute O26 and U26 components
1.
1.
2.
O26 directly deducted from CEY
U26 modeled to estimate future lost yield and FSBio
Decompose U26 into age and sex distributions
4. Sum future “lost” yield and “missing” FSBio
3.
3
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
CEY determination process
4
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Halibut bycatch size distributions
0.04
Proportion
0.03
NMFS observercollected data from
GOA 2008 trawl and
hook-and-line
groundfish fisheries
Hook-and-Line
Trawl
0.02
26 in (66 cm)
0.01
0.00
0
50
100
Length (cm)
150
5
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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Immediate CEY gain from O26 bycatch
reduction
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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Estimating long-term Yield and FSBio Loss - 1
• Yield Loss: Cumulative amount of yield lost to the
directed fishery due to U26 bycatch or wastage
(assuming a 32 inch commercial size limit and current
target harvest rates)
• Generally listed as ratio of Yield Loss to weight of
bycatch:
YL
ratio

Wt. of Yield Loss
Wt. of Bycatch
• Requires an estimate of age and sex composition of
bycatch
8
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Estimating long-term Yield and FSBio Loss - 2
• Growth (size-at-age) models – Area 3A example
M - sd
0
5
10 15 20 25 30
0
Age
80,000
0.8
0.0
0.00
F - sd
50
100
150
200
5
3 4
67
8 9
7 8 9 11
1012
6 7 8 11
5
4
9 12
1011
16 1718
151516 17181920
16
15
141414
171819
1516
1313 14 15161718
13
5
13 14
8
3 4
1617
6 7
121212 13 1415
5
8
4
7 9
12 13 141516
6
3
12 13
10 1111
5
2
8 9 10
11
12 131415
4
67
9 1010 111111 12
3
5
11
2
0.4
Proportion
0.08
Proportion
100
50
M - length
Sex and age proportions at length
0.04
150
Distribution of sizes at age
F - length
0
Length or sd (cm)
Length and st. dev. at age
3
4
56
40 60 80
Length (cm)
120
Length (cm)
10000
30000
3A
0
20000
60000
U26 Bycatch Nos.
3A
n = 397,000
0
U26 Bycatch Nos.
• Decompose length data to sex and age composition
10
20
30
40
50
Length (in 5 cm inc.)
60
5
10
Age
15
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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Decomposition of 3A U26 bycatch
100 mt of Trawl bycatch
Area
No. of U26 hbt.
Wt. of U26 hbt (mt)
Wt. of U26 hbt (lbs)
2C
0
0
0
3A
17,999
27.809
45,981
3B
6,263
9.677
16,001
Total
24,262
37.486
61,982
15 mt of hook-and-line bycatch
Area
No. of U26 hbt
Wt. of U26 hbt (mt)
Wt. of U26 hbt (lbs)
2C
13
0.030
49
3A
620
1.375
2,274
3B
1,046
2.320
3,835
Total
1,679
3.725
6,185
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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8
Yield and FSBio Losses vary with size of catch
2
4
FSBio Loss ratio is how
much cumulative female
spawning biomass was
“missing” due to being
taken as bycatch.
0
Loss Ratio
6
Yield Loss
FSBio Loss
FSBio Replacement
@F=0.25
Yield Loss ratio is how
much commercial catch is
lost (in the future) due to
each pound of bycatch.
0
50
100
Length (cm)
150
200
FSBio Replacement is
how much commercial
catch needs to be
reduced to replace FSBio
“missing” due to being
taken as bycatch
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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Loss equations
• Simulations run over 30 years
• Straightforward age/sex structured population model
• FSBio tabulated at start of year
• Yield based on Baranov catch equation
2
30
30
Yield Loss   N g , a ,t
g 1 t 1 a t

1 e

m
Fg , a ,t selg , a
Fg , a ,t selg , a
 Fg ,a ,t sel g ,a  m
Wg ,a  0.00000692 L3.24
30
30
FSBio Loss    N g , a ,tWg ,a Mata
g  f t 1 a t
FSBio Replacement 
FSBio/(lb of bycatch)
FSBio/(lb of commercial catch)

W
g ,a
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Time component of losses
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NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Delayed CEY gains (losses)
13
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Total CEY gains (losses)
14
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
Total FSBio gains (losses)
15
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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Summary of potential gains
Gains per pound of bycatch
mortality reduction (all sizes)
Gear
CEY
O26
U26
FSBio
Total
Total
Trawl
0.625 0.427
1.052 2.155
Hook-and-Line
0.752 0.226
0.978 1.208
• Migration is not factored into this analysis
• Impacts would be spread to the east relative to impacts listed in paper
• Previous reports provided estimates of downstream impacts from total
coastwide bycatch, but results are sensitive to migration assumptions
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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SUMMARY OF 2011 BYCATCH
MORTALITY, YIELD AND
FEMALE SPAWNING
BIOMASS LOSSES
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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2C
n = 12,000
1000
1500
40
50
60
20
30
40
50
60
3B
n = 116,000
60
20
30
40
50
60
4CDE
n = 710,000
10
20
30
40
50
60
50
60
40
50
60
40
50
60
4A
n = 258,000
10
20
30
ALL
n = 1,576,000
0
0
5000
50000
15000
100000
4B
n = 76,000
10
300000
50
40
200000
40
30
100000
30
20
0
10000
20
150000
0
20000
0
10
10
20000
20000
60000
30000
3A
n = 397,000
10
60000
30
40000
20
0
0 500
300
0 100
10
0
U26 Bycatch Numbers
2B
n = 6,000
3000
3500
2500
2A
n = 1,000
500
700
2011 U26 Bycatch Totals – by length
10
20
30
40
50
60
Length (in 5 cm increments)
10
20
30
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
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2011 U26 Bycatch Totals – by age
1000
500
15
3B
10
15
5
10
Females
Males
10
15
15
4A
5
10
15
ALL
50000
0
0
2000
20000
6000
15
4CDE
60000
10000
4B
5
10
0
5000
0
10000
0
5
5
10000 20000 30000
10
10000
30000
3A
5
150000
15
0
0
10
15000
5
0
U26 Bycatch Numbers
0
200
50
400
100
2C
1500
800
2B
600
150
2A
5
10
Age
15
5
10
15
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
0.30
0.20
YL ratio: 1.23 lb/lb
2010
2000
3B
0.0 0.5 1.0 1.5 2.0 2.5
2005
0.5
0.0
0.5
0.0
2005
2010
2000
2005
2010
3
2005
2010
YL ratio: 1.59 lb/lb
4A
2010
ALL
M lbs
4
2
0
2
1
0
2000
2005
2010
8
4
4CDE
0.2
0.1
0.0
M (lbs)
YL ratio: 1.83 lb/lb
10
4B
0.3
YL ratio: 1.56 lb/lb
2005
YL ratio: 1.66 lb/lb
2000
5
2000
2C
0.10
0.00
1.5
3A
2000
1.0
YL ratio: 1.23 lb/lb
2010
YL ratio: 1.95 lb/lb
0.00
0.02
0.2
0.0
2005
1.0
1.5
2000
M (lbs)
2B
0.04
Lost commercial yield
U26 bycatch
YL ratio: 1.44 lb/lb
6
2A
0.1
M (lbs)
0.3
YL ratio: 1.44 lb/lb
0.06
2011 U26 Yield Loss by area
2000
2005
2010
2000
2005
2010
20
NPFMC/IPHC Bycatch Workshop - 24/25 April 2012
0.8
2B
FSBio ratio: 5.75 lb/lb
2C
0.4
0.10
0.2
2000
2005
2000
3B
2005
FSBio ratio: 5.31 lb/lb
2010
4A
2005
4B
2000
2005
2010
2000
FSBio ratio: 5.85 lb/lb 4CDE
2005
FSBio ratio: 5.57 lb/lb
2010
ALL
2005
2010
0
5 10
5
0
2000
20
M lbs
10
0.8
0.4
0.0
M (lbs)
30
FSBio ratio: 4.99 lb/lb
2010
15
1.2
2000
0
0
0
1
2
2
2
4
3
4
4
6
5
FSBio ratio: 5.27 lb/lb
2010
8
3A
6
FSBio ratio: 5.55 lb/lb
2010
0.0
0.00
2005
6
2000
M (lbs)
FSBio ratio: 5.01 lb/lb
0.6
Lost FSBio
U26 bycatch
0.20
2A
0.4
0.8
FSBio ratio: 4.89 lb/lb
0.0
M (lbs)
1.2
2011 U26 FSBio by area
2000
2005
2010
2000
2005
2010
21