Yellowfin Tuna 19752006

1
Yellowfin Tuna 1975-2006
2
Major Changes

• Catch, effort, and length-frequency data for the
  surface fisheries have been updated to include
  new data for 2006 and revised data for 2000-2005.
• New or updated longline catch data are available
  for Chinese Taipei (2002-2005), China
  (2001-2005), and the Republic of Korea
  (2003-2005).

3
Sensitivity Analyses

• Stock recruitment relationship

4
Data

• Fishery definitions
• Catch
• Effort
• Length frequency

5
Yellowfin Fishery Definitions
6
Catch
DIS south
DIS north
DIS coastal
DIS central
DOL south
LL south
LL north
BB
DOL coastal
DOL north
NA north
NA south
FO south
FO central
FO coastal
FO north
7
Effort
DIS north
DIS coastal
DIS central
DIS south
LL south
DOL south
LL north
BB
DOL north
NA north
DOL coastal
NA south
FO central
FO coastal
FO south
FO north
8
CPUE
DIS south
DIS coastal
DIS north
DIS central
LL south
LL north
DOL south
BB
NA south
NA north
DOL coastal
DOL north
FO coastal
FO central
FO north
FO south
9
Fixed Parameters

• Natural Mortality
• Fecundity at age
• Sex ratio at age
• Selectivity curves for the discard fisheries
• The steepness of the stock recruitment
  relationship 1 (no relationship)

10
Natural Mortality
11
Sex Ratio
12
Relative Fecundity
13
Estimated parameters

• Recruitment
• Temporal anomalies
• Catchability
• Temporal anomalies
• Selectivity
• Initial population size and age-structure
• Mean length at age
• Variation of length at age

14
Results

• Fit to the length frequency
• Growth
• Fishing mortality
• Selectivity
• Recruitment
• Biomass
• Catchability

15
Fit to the length-frequency
LL south
LL north
BB
DOL south
NA north
DOL north
NA south
DOL coastal
FO coastal
FO north
FO south
FO central
16
Growth
17
Fishing mortality
18
Age Specific Fishing Mortality
19
Selectivity
DIS central
DIS south
DIS north
DIS coastal
LL north
BB
DOL south
LL south
DOL north
DOL coastal
FO north
FO south
FO central
FO coastal
20
Catchability
LL north
BB
LL south
DOL north
DOL south
DOL coastal
FO north
NA north
NA south
FO south
FO coastal
FO central
21
Recruitment
22
Recent length-frequency data (FO)
FO south
FO central
FO coastal
FO north
23
Recent length-frequency data (Unassociated)
NA north
NA south
24
Recent length-frequency data (Dolphin associated)
DOL north
DOL south
DOL coastal
25
Recent length-frequency data (longline)
LL south
LL north
26
Stock - recruitment
27
Biomass
28
Spawning Biomass
29
Average weight
Surface
Longline
LL south
LL north
DOL coastal
DOL north
NA south
BB
DOL south
FO south
FO central
FO coastal
FO north
NA north
30
No Fishing and Fishery Impact
31
Biomass Comparisons
32
Reference points projections

• Assumptions
• For MSY calculations
• Average of 2004-2005 for fishing mortality
• For forward projections
• Average of 2004-2005 for catchability
• 2006 effort

33
SBR
34
SBR
35
AMSY by method
36
AMSY with method removed
37
Yield
38
AMSY quantities using F(y)
39
Phase plot
Regime dependent
40
Sensitivity h 0.75

• When the spawning population is 20 of its
  unexploited level the recruitment is 75 of its
  unexploited level
• Biomass
• Recruitment
• SBR
• Yield Curve
• AMSY

41
Biomass Comparison
42
Recruitment
43
Recruitment
44
SBR
45
Yield Curve
46
AMSY table
47
Forward Simulations

• SBR
• Surface fishery catch
• Longline catch

48
SBR
49
Catch
50
Updated Japanese data

• New data for 2005
• Catch
• CPUE
• Length frequency

51
Updated Japanese data Biomass
52
Updated Japanese data Recruitment
53
Updated Japanese data SBR
54
Summary Main Results

• The results are similar to the previous
  assessment
• The biomass is estimated to have declined to
  levels substantially lower than recent years
• There is uncertainty about recent and future
  recruitment and biomass levels

55
What is robust

• The trend in biomass
• The regime shift in recruitment

56
Plausible Sensitivities and Uncertainties

• The stock recruitment relationship
• Uncertainty in current biomass and recruitment

57
Conclusions

• The biomass is estimated to have declined to
  levels substantially lower than recent years
• The current SBR is close to the SBR required to
  produce AMSY
• The current fishing mortality rates are close to
  those required to produce AMSY
• The average weight of a yellowfin in the catch is
  much less than the critical weight and increasing
  the average weight could increase AMSY
• There have been two different productivity
  regimes and the levels of AMSY, and possibly
  three, and the biomass required to produce AMSY
  may differ between the regimes

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The END