Transcript Are the apparent rapid declines in top pelagic predators real? Mark Maunder, Shelton Harley, Mike Hinton, and others IATTC.

Are the apparent rapid
declines in top pelagic
predators real?
Mark Maunder, Shelton Harley, Mike
Hinton, and others
IATTC
Outline
• Definitions and terms
• Why the declines don’t make sense
– Japanese longline catch and effort (EP0)
– Population dynamics
• Explanatory hypotheses
– Regime change
– Ecosystem
– Spatial distribution of effort
– Habitat and gear distribution
– Stupid fish hypothesis
• Summary
Definitions
•
•
•
•
CPUE = catch-per-unit-of-effort
Nominal CPUE
Fitting a model
Carrying capacity – Average abundance in
the absence of fishing
Basic assumption
C = EqA
C/E = qA
Where: C= catch, E = effort, and A = abundance
C
CPUE 
E
area
area
Albacore
Yellowfin
15
15
10
10
5
5
0
0
1950
1960
1970
1980
1990
2000
1950
1960
1970
Bigeye
1990
2000
1990
2000
1990
2000
1990
2000
Bluefin
30
0.006
20
CPUE (# per 1000 hooks)
1980
0.004
10
0.002
0
0.0
1950
1960
1970
1980
1990
2000
1950
1960
Black marlin
1970
1980
Blue marlin
0.25
8
0.20
6
0.15
4
0.10
2
0.05
0.0
0
1950
1960
1970
1980
1990
2000
1950
1960
Striped marlin
1970
1980
Swordfish
5
1.2
4
1.0
3
0.8
0.6
2
0.4
1
0.2
0
0.0
1950
1960
1970
1980
1990
2000
1950
Year
1960
1970
1980
Albacore
Catch
CPUE
15
600
10
400
5
200
0
0
1950
1960
1970
1980
Year
1990
2000
CPUE (# per 1000 hooks)
Catch (000s of fish)
800
600
15
600
10
Catch (000s of fish)
800
400
5
200
0
0
1950
1960
1970
1980
1990
2000
Bigeye
30
Catch (000s of fish)
1500
0.3
500
10
0.1
0
1970
1980
1990
10
600
5
0
0.2
1960
15
200
20
0
Catch
CPUE
400
1000
1950
Yellowfin
800
0.0
2000
0
1950
400
1960
1970
1980
1990
Bluefin
200
0.006
0.004
0.002
0
1950
0.0
1960
1950
Black marlin
1970
1960
1980
1970
Blue marlin
0.25
6
4
2000
1990
2000
1980
100
0.15
80
8
6
4
60
0.10
40
2
0.05
0
1960
1970
1980
1990
2
20
0.0
1950
0
2000
0
1950
1960
Striped marlin
5
120
4
100
3
200
100
0
1970
1980
1980
1990
2000
1990
1.2
1.0
80
0.8
60
0.6
40
0.4
1
20
0.2
0
0
2
1960
1970
Swordfish
300
1950
1990
Year
120
0.20
2000
0.0
1950
Year
1960
1970
1980
1990
2000
CPUE (# per 1000 hooks)
Albacore
20
Fit model to data
• PellaTomlinson-model with Nmsy/N0 = 30%
(based on numbers)
• Project population dynamics from an
unexploited condition using observed
catch
• Fit to CPUE data as a relative abundance
index (assume CPUE proportional to
abundance)
• Use only Japanese longline CPUE and
Catch data
Albacore
CPUE
CPUE (# per 1000 hooks)
15
10
5
0
1950
1960
1970
1980
Year
1990
2000
Albacore
Yellowfin
15
15
10
10
5
5
0
0
1950
1960
1970
1980
1990
2000
1950
1960
1970
Bigeye
1990
2000
1990
2000
1990
2000
1990
2000
Bluefin
30
0.006
20
CPUE (# per 1000 hooks)
1980
0.004
10
0.002
0
0.0
1950
1960
1970
1980
1990
2000
1950
1960
Black marlin
1970
1980
Blue marlin
0.25
8
0.20
6
0.15
4
0.10
2
0.05
0.0
0
1950
1960
1970
1980
1990
2000
1950
1960
Striped marlin
1970
1980
Swordfish
5
1.2
4
1.0
3
0.8
0.6
2
0.4
1
0.2
0
0.0
1950
1960
1970
1980
1990
2000
1950
Year
1960
1970
1980
Albacore
Yellowfin
15
15
10
10
5
5
0
0
1950
1960
1970
1980
1990
2000
1950
1960
CPUE (# per 1000 hooks)
Bluefin
1970
1980
1990
2000
1990
2000
Striped marlin
6
5
0.006
4
0.004
3
2
0.002
1
0.0
0
1950
1960
1970
1980
1990
2000
1950
1960
1970
1980
Swordfish
1.2
Remove first few
data points
1.0
0.8
0.6
0.4
0.2
0.0
1950
1960
1970
1980
1990
2000
Year
Only fit to decline
Albacore
Yellowfin
CPUE (# per 1000 hooks)
15
15
10
10
5
5
0
0
1950
1960
1970
1980
1990
2000
1950
1960
Bluefin
1970
1980
1990
2000
1990
2000
Blue marlin
8
0.006
6
0.004
4
0.002
2
0.0
0
1950
1960
1970
1980
1990
2000
1950
Year
1960
1970
1980
Regime change hypothesis
0.009
2.5
0.008
0.007
2
Productivity deviation
CPUE
Blue marlin production residuals
0.006
0.005
0.004
0.003
0.002
0.001
0
1950
1.5
1
0.5
0
-0.5
-1
1960
1970
1980
Year
1990
2000
-1.5
1950
1960
1970
1980
Year
1990
2000
2010
Change in productivity, yellowfin
example
Relative Recruitment
3
2
1
0
75
77
79
81
83
85
87
89
Year
91
Maunder 2002. IATTC Stock Assessment Report 3
93
95
97
99
01
Change in productivity, bigeye
example
Relative Recruitment
4
3
2
1
0
81
83
85
87
89
91
Year
93
95
97
99
Maunder and Harley 2002. IATTC Stock Assessment Report 3
01
Ecosystem model
High Adult Biomass
Low Adult Biomass
Proportion of production
Ecosystem model
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
Sum(N)/Sum(K)

Nt

 species
f  Nt   1 
K


species

K = carrying capacity
N = numbers





f(N) is the single species production
Ecosystem results
• Fits the data significantly better
• Nearly all improvement from fit to bluefin
tuna data
• Also improves fit to blue marlin data
Single Species
CPUE
Bluefin tuna
1950
1960
1970
1980
1990
2000
Ecosystem
CPUE
Year
1950
1960
1970
1980
Year
1990
2000
Single Species
CPUE
Blue marlin
1950
1960
1970
1980
1990
2000
1980
1990
2000
Ecosystem
CPUE
Year
1950
1960
1970
Year
Spatial expansion of the longline
fishery
Spatial hypotheses
Time
Highest CPUE
Highest Profit
Equal distribution
Simulation of effort expansion
• Effort increases by 100 units every 5 years
• Movement of effort only occurs every five
years
• No movement of fish among areas
• In highest profit hypothesis, new effort goes
into new area and old effort stays in the
same area
• In highest CPUE hypothesis, all effort goes
into new area
Relative CPUE
CPUE trends
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
10
20
30
40
50
Time
Highest CPUE (smoothed)
Highest Profits (smoothed)
Equal Effort (Abundance)
Expansion of the fishery
1.2
1
0.8
0.6
0.4
0.2
0
1950
1960
1970
1980
Year
Hooks
Squares
1990
2000
30% of striped marlin catch
% catch in coastal area
Limited stock distribution: striped marlin
45
40
35
30
25
20
15
10
5
0
1950
1960
1970
1980
1990
2000
1980
1990
2000
Year
1.2
1
CPUE
0.8
0.6
0.4
0.2
0
1950
1960
1970
Year
Habitat, gear, and fish behavior
• Fish have habitats that they prefer
• Habitat changes with the environment
• Fishermen’s behavior determines where
the gear fishes
• Gear, habitat, and fish behavior have to
match for fishing to be successful
• Gear, habitat, and fish behavior have to be
taken into consideration when interpreting
CPUE
Bigelow et al. 2000
Environment
Thermocline
Depth of gear
50-400
50-150
Current
Current
Measure of depth (HPB)
Increasing depth of longlines
1970
1975
1980
1985
Year
1990
1995
2000
Bigeye tuna
Year
EPO examples
1960
1970
1980
1990
2000
CPUE
Yellowfin tuna
Abundance
CPUE
Nominal CPUE
1960
1970
1980
1990
Year
From Keith Bigelow
Nominal CPUE
Abundance
2000
Habitat standardization
• Used to remove the changes of gear depth and
the environment from the relative index of
abundance
• Method developed by Hinton and Nakano 1996
• Applied to bigeye and yellowfin tuna by Bigelow
et al. 2002
• Used in the assessments of yellowfin tuna,
bigeye tuna, blue marlin, striped marlin, and
swordfish in the EPO
The “stupid” fish hypothesis
The stupid fish hypothesis under
historic effort
1950
1960
1970
1980
Year
CPUE
Catch
1990
2000
CPUE vs abundance
Abundance or CPUE
1
0.8
0.6
0.4
0.2
0
1950
1960
1970
1980
Time
Abundance
CPUE
1990
2000
The big “stupid” fish hypothesis
(size-specific vulnerability)
Size-specific vulnerability
The size specific vulnerable
hypothesis under historic effort
1950
1960
1970
1980
Year
CPUE
catch
1990
2000
Blue marlin example
Vulnerability
1
0.8
0.6
0.4
0.2
0
0
2
4
6
8
10
Age
Big stupid fish
CPUE
Constant vulnerability
1950
1960
1970
1980
1990
Year
Big stupid fish
Constant vulnerability
2000
Historic yellowfin length frequency
data
Purse seine
60 cm
Size at 50% maturity
Suda and Schaefer 1965
Longline
150 cm
Other Hypotheses
• Multiple stocks (e.g. northern and southern
albacore)
• Fraction of stock (bluefin)
• Stock distribution limited (e.g. Striped Marlin,
Swordfish, sailfish, shortbill spearfish)
• Gear saturation/interference
• Increase in fishing power
• Targeting (swordfish, bait, setting at night)
• Age specific natural mortality
• Fishing regulations (e.g. EEZ)
Myers Dalhousie Group
• Soak time – increases current CPUE
– Has slightly increased
– Increased soak time increases CPUE
• Shark damage – increases current CPUE
– 25% in early data and about 4% in recent data
– Lower shark damage increases CPUE
• Hook saturation - increases current CPUE
– Bait loss due to catching other species has decreased
– More bait available increases CPUE
•
•
•
•
Depth of gear
Ecosystem
Also looking at non-pelagic species and dada from trawl
World wide patterns similar
Summary
– Regime change
• Same for all species?
• Implies that the stocks are depleted
• New management values for new regime
– Ecosystem
• Implies that the stocks are depleted
• Does not explain all increase in production
– Spatial distribution of effort
• Spatial expansion occurred when the rapid
declines occurred
• CPUE declines faster than abundance
• Final depletion level is the same
Summary continued
– Habitat and gear distribution
• Did not change during period of depletion
• Current abundance may be underestimated for
most species explaining current catches
– Stupid fish hypothesis
• Both stupid fish and age-specific vulnerability could
explain some of the decline
• Indicates stocks are less depleted
– Limited distribution of stock
• Probably explains increase in CPUE for striped
marlin, swordfish, sailfish, and spearfish
Conclusions
• Regime change, ecosystem, and spatial
distribution result in high depletion levels
• Longline depth, stupid fish hypothesis, and
age-specific vulnerability result in lower
depletion levels
• Ecosystem, spatial distribution, longline
gear depth, and age-specific vulnerability
most likely
Hypothesis
Regime change
Ecosystem
Spatial distribution
Gear depth
Stupid fish
Size-specific vulnerability
Multiple stocks
Fraction of stock
Interference
Increased power
Targeting
Age-specific M
Fishing regulations
Soaktime
Shark damage
Hook saturation
More
Current depletion level
Same
Less
Unknown
x
x
x
x (most)
x
x
x
x
x
x
Depends
x
x
x
x
x
4
Yellowfin and Bigeye selectivity
2
0
40
4
8
12
16
20
24
28
4
8
12
16
20
24
Yellowfin
Bigeye
A 8FISHERY
FISHERY
-- PESQUERIA 911
-- PESQUERIA
FISHERY -- PESQUERIA
10 -FISHERY
15
1.5
PESQUERIA 12
1.4
1.2
10
1.0
1.0
0.8
0.6
5
0.5
0.4
0.2
0.0
40 4
A 3
0
8
4 812
16 16 24
2032
40
24
28
Age in quarters
FISHERY
-- PESQUERIA 4
0.0
4 8
16
24
4
32 8
40 12
Age in quarters
FISHERY -- PESQUERIA
5
5
FISHERY
-- PESQUERIA 7
16
20
24
FISHERY -- PESQUERIA 8
5
5
Current yellowfin length frequency data
FISHERY -- PES
QUERIA
125
cm
60 cm
Size at 50% maturity
8
150 cm
FISHERY -- PESQUERIA
4
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
1950
1960
1970
1980
1990
2000
Year
1
0.5
ln(residual)
CPUE
Age-specific selectivity and recruitment
residuals
0
-0.5
-1
-1.5
1950
1960
1970
1980
Year
1990
2000