Yellowfin Tuna 1975-2005

1
Yellowfin Tuna 1975-2005
2
Major Changes

• Catch, effort, and length-frequency data for the
  surface fisheries have been updated to include
  new data for 2005 and revised data for 1975-2004.
• Catch data for the Japanese longline fisheries
  have been updated for 2000-2003 and to include
  new data for 2004.
• Catch data for the longline fisheries of Chinese
  Taipei have been updated for 2002 and new data
  added for 2003.
• Catch data fore the longline fisheries of Korea
  have been updated to include new data for 2003
• Catch data for the longline fisheries of the
  Peoples Republic of China have been updated to
  include new data for 2003 and 2004.
• Longline catch-at-length data for 2002-2003 have
  been updated and new data for 2004 added.
• Longline catch per unit effort data have been
  standardized using a delta-lognormal model,
  updated to include 2004 data.
• Growth model has been changed to fix
  length-at-age at the prior distribution of a
  Richards growth curve based on otolith data

3
Sensitivity Analyses

• Stock recruitment relationship
• Asymptotic length

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 coastal
DIS north
DIS central
DIS south
LL south
DOL south
LL north
BB
NA south
NA north
DOL north
DOL coastal
FO coastal
FO central
FO south
FO north
8
CPUE
DIS south
DIS coastal
DIS north
DIS central
LL south
LL north
DOL south
BB
NA north
NA south
DOL north
DOL coastal
FO coastal
FO south
FO central
FO north
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, (no Seasonal component)
• 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 south
FO central
FO coastal
FO north
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
NA north
FO north
NA south
FO central
FO south
FO coastal
21
Recruitment
22
Recent length-frequency data (FO)
2
3
4
1
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
31
Fishery impact
32
No Fishing and Fishery Impact
33
Biomass Comparisons
34
Reference points projections

• Assumptions
• For MSY calculations
• Average of 2002-2003 for fishing mortality
• For forward projections
• Average of 2002-2003 for catchability
• 2004 effort

35
SBR
36
SBR
37
AMSY by method
38
AMSY with method removed
39
AMSY with effort adjusted
40
Yield
41
AMSY quantities using F(y)
42
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

43
Biomass Comparison
44
Recruitment
45
Recruitment
46
SBR
47
Yield Curve
48
Sensitivity to L8proportion YFT gt given length
49
Maximum length observed by yr
50
Sensitivity to assumed L8 Biomass
51
Recruitment
52
Spawning biomass ratio
53
Selectivity
L8 170
Base case
L8 200
54
AMSY table
55
Forward Simulations

• Depletion ratio
• Surface fishery catch
• Longline catch

56
SBR
57
Catch
58
Catch with median catchability
59
Summary Main Results

• The results are similar to the previous four
  assessments, except that SBR at SBRAMSY is lower
  than in the last assessment
• The biomass is estimated to have declined
  slightly in 2005
• There is uncertainty about recent and future
  recruitment and biomass levels

60
What is robust

• The trend in biomass
• The regime shift in recruitment

61
Plausible Sensitivities and Uncertainties

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

62
Conclusions

• The biomass is estimated to have declined
  slightly in 2005
• The current SBR may be 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 the biomass
  required to produce AMSY may differ between the
  regimes

63
The END