Transcript Slide 1

Are pelagic fisheries managed well?
A stock assessment scientists perspective
Mark Maunder and Shelton Harley
Inter-American Tropical Tuna Commission
[email protected]
http://www.iattc.org/iattc_staffMMaunder.htm
Outline
1.
2.
3.
4.
A response to Myers and Worm (2003)
Are pelagic fisheries managed well?
EPO tuna Fisheries
Summary
Myers and Worm (2003)
• “industrialized fisheries typically reduced
community biomass by 80% during the first 15
years of exploitation”
• “large predatory fish biomass today is only about
10% of pre-industrial levels”.
• Most of the data was Japanese tuna longline
catch and effort data
• I will argue that the analysis is flawed in several
respects and illustrate this will data from the
Pacific Ocean
Pacific Ocean Tuna Catch Data
3,000,000
A
Other
2,500,000
By species
Catch (t)
Skipjack
2,000,000
Yellowfin
Bigeye
1,500,000
Albacore
1,000,000
500,000
0
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
3,000,000
B
Other
By method
Catch (t)
2,500,000
Purse seine
Pole-and-line
2,000,000
Longline
1,500,000
1,000,000
500,000
0
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
3,000,000
By area
Catch (t)
2,500,000
2,000,000
C
North
Equatorial
Tropical
Subtropical
1,500,000
Temperate
1,000,000
500,000
0
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
Myers and Worm
data
40
-120 -125 -130 -135 -140 -145 -150 -155 -160 -165 -170 -175 180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70
4
35
3
30
3
25
2
20
2
15
1
10
1
5
5
0
0
-5
-
-10
-
-15
-
-20
-
-25
-
-30
-
-35
-
-40
-
-45
-
-50
-120 -125 -130 -135 -140 -145 -150 -155 -160 -165 -170 -175 180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70
YFT
BFT
Jap LL 1952-1999
20000
BET
ALB
Longhurst Areas
Spatial expansion of the longline
fishery
4
2
2
One species dominates
0
10
D
Total temperate
8
CPUE
16
Billfish
Southern bluefin
Yellowfin
Bigeye
Albacore
6
4
H
12
8
4
2
0
1950
0
1965
1980
1995
0
1950
More often than not community CPUE
declines faster than abundance
 Bi
Bi
 ri 1 
t
 Ki

 Bi  qi EBi

BSS
CPUESS

 K i  q iK i
i
qi
i r Ki
i

 Ki
2


2
q
K

K
q
Ki



i
i
i
i


 i

i
i
qi
1
qj
Bi
0
t
q K
2
i
i
2
i
i
i
qi2
i r Ki
i
 qi Ki
i
 2 qi qj Ki K j   qi Ki    qi  qj  Ki Kj
2
i j
2
i
ri qi
  1i, j pairs  Biomass declines faster than CPUE
rj q j
2
i j
2
Abundance of tunas in the Pacific
Ocean
Integrated models
1
0.9
7,000,000
5,000,000
0.6
Yellowfin
4,000,000
Year
0.7
Bigeye
3,000,000
0.5
0.4
Albacore
0.3
2,000,000
0.2
1,000,000
0.1
0
1940
1950
1960
1
19
52
19
55
19
58
19
61
19
64
19
67
19
70
19
73
19
76
19
79
19
82
19
85
19
88
19
91
19
94
19
97
20
00
0
70
1.60E+06
60
1.40E+06
50
Yellowfin
1.20E+06
Bigeye
1.00E+06
40
30
Albacore
Biomass (t)
CPUE (kg per 100 hooks)
Japanese longline CPUE
Estimated biomass
Biomass - no fishin
Biomass - no longl
8.00E+05
6.00E+05
20
4.00E+05
10
2.00E+05
0
19
52
19
55
19
58
19
61
19
64
19
67
19
70
19
73
19
76
19
79
19
82
19
85
19
88
19
91
19
94
19
97
20
00
Adult biomass (t)
0.8
6,000,000
0.00E+00
1940
1950
1960
CPUE is inconsistent with catch and population
dynamics
Blue is total catch, red is CPUE
Change in targeting: from albacore to bigeye
Blue is total catch, green is Taiwan CPUE, red is Japan CPUE
Single Species
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
Are pelagic fisheries managed
well?
1. What are the management objectives?
2. Are the management objectives
reasonable?
3. Can we determine if the management
objectives have been achieved?
What are the management
objectives? Don’t really know
• International commissions
• Individual country jurisdictions
• Over-arching objective
– Maintain stocks at levels capable of producing
MSY
– Modified by other factors
– Precautionary approach
• Most specific objectives vary by
user/country and are unrecorded
Are the management objectives
reasonable? Yes, but too vague to be useful
• Stated management objectives are vague
– Need to have something that covers the diverse goals of users
– Are the specific interpretations reasonable?
• MSY
– Reasonable given difficulty determining other factors
– More useful as an indicator than an objective
– Negative aspects of MSY covered by “modifying factors” and
precautionary approach
– Depletion to around 30% of unexploited
• But these are not the real objectives
– Social, economic, cultural, ….
– Bycatch only important if causes a penalty
Considerations
• Multiple species
– Can’t get MSY for each simultaneously
– Sustainable overexploitation of some species may be
required
• Different gears
– Yield
– Economics
– Bycatch
• Different countries
– Economic and social dependence
• Different users have different objectives
Can we determine if the management
objectives have been achieved? Depends
• Estimate MSY quantity e.g BMSY or FMSY
–
–
–
–
Age-specific F
Age-specific Natural mortality
Steepness of the stock-recruitment relationship
What years to average recruitment
• Comparison quantity Bcur or Fcur
– Most recent B and F uncertain
• Ratios (e.g. F/FMSY) are more precisely estimated and
should be estimated inside the assessment model
• Problems with estimating unexploited biomass (Myers
and Worm debate, shifting baselines)
EPO Tuna Stocks
• Inter-American Tropical Tuna Commission - governing body
• Yellowfin, skipjack, bigeye
• Longline
– Distant water nations
– Large bigeye
– Sharks, Turtles
• Purse seine on floating objects
– Ecuador, EU
– Skipjack, small bigeye
– Sharks and other fish
• Purse seine on unassociated schools
– Opportunistic
– Skipjack, small yellowfin
– Similar but less than Floating objects
• Purse seine on dolphin associated schools
– Mexico, Venezuela
– Large yellowfin
– Dolphins
Yellowfin Tuna Spawning Biomass
Ratio (S/S0)
Skipjack Tuna Spawning Biomass
Ratio (S/S0)
Bigeye tuna Spawning Biomass
Ratio (S/S0)
Bigeye Fishing Mortality
Bigeye 5-21 quarters old
0.7
Annual fishing mortality
0.6
0.5
0.4
0.3
0.2
0.1
0
1975
1980
1985
1990
1995
2000
Fishery Impact on EPO bigeye tuna
1.0
Longline
Floating object
Small discards
Fishery impact
0.8
0.6
0.4
0.2
0.0
75
77
79
81
83
85
87
89
Year
91
93
95
97
99
01
03
Year of
assessment
Stock assessment conclusion
Staff recommendation (includes
actions for all species)
Adopted conservation
measures
Change in fishing
mortality from
comparison year
2000
Assuming a moderate spawnerrecruitment relationship, fishing
mortality should be kept at 1999
levels.
No recommendation for bigeye
Catch quota for yellowfin
Three month closure of the
floating-object fishery
Fishing mortality
increased 54%
from 1999 levels.
2001
Assuming a moderate spawnerrecruitment relationship, fishing
mortality should be reduced (10%)
from 2000 levels.
Fishing effort should not be
allowed to increase beyond current
levels.
Closure of floating-object
fishing if catches of small
bigeye reach 1999 levels,
but not before November
2001. No closure occurred.
Fishing mortality
increased 11%
from 2000 levels.
2002
Assuming a moderate spawnerrecruitment relationship, fishing
mortality should be kept at 2001
levels.
Close the floating-object fishery if
small bigeye catches reach 1999
levels and a complete EPO closure
for December 2002.
Complete closure of the
EPO for December 2002
Fishing mortality
increased 55%
from 2001 levels.
2003
Fishing mortality needs to be
reduced substantially (20-50%)
from levels observed in 2000 and
2001.
Complete EPO closure for two
months plus two month closure of
an area of high bigeye catches.
Longline catches reduced to 2000
levels
Closure of a smaller region
(than proposed) for
December 2003. Longline
catches reduced to 2001
levels
Fishing mortality
increased 60%
from 2000-2001
levels.
2004
Fishing mortality needs to be
reduced substantially (30-60%)
from levels observed in 2001 and
2002
Complete EPO closure for two
months plus either a six month
closure of a area of high bigeye
catches or a six month closure of
an area for floating-object sets or
500t individual vessel catch limits.
Longline catches to be reduced to
levels of 2000
Complete closure of the
EPO for six weeks (This
resolution was agreed upon
in October 2003). Longline
catches reduced to 2001
levels.
Bycatch research in the EPO
• IATTC bycatch database 100% observers
on large purse seine vessels
• IATTC resolution to collect data on turtles
• IATTC collaboration with WWF to reduce
turtle mortality
• The reduction in dolphin mortality in the
EPO purse seine fisheries
• IATTC protected species modeling
Summary
• Myers and Worm (2003) analysis
– Flawed
– Should not be used to determine the status of large predatory
fish biomass
• Are pelagic fisheries managed well?
–
–
–
–
Difficult to answer
We don’t know what the management objectives are
We don’t know what the management objectives should be
Even if we did, we might not be able to determine if they have
been met
• Tuna stocks
– Some stocks appear to be poorly managed (e.g. bigeye tuna in
the EPO)
– Some stocks appear to be healthy, but the associated fisheries
have management problems (e.g. skipjack tuna in the EPO)
– Some stocks appear to be well managed, but with other issues
(e.g. yellowfin tuna in the EPO)
– The status of many stocks are uncertain (e.g. billfish in the EPO)