Are pelagic fisheries managed well?
A stock assessment scientists perspective
Mark Maunder and Shelton HarleyInter-American Tropical Tuna Commission
[email protected]://www.iattc.org/iattc_staffMMaunder.htm
Outline
1. A response to Myers and Worm (2003)2. Are pelagic fisheries managed well?3. EPO tuna Fisheries4. 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
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002Ca
tch
(t)
Other
SkipjackYellowfin
Bigeye
Albacore
A
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
Catc
h (t)
OtherPurse seine
Pole-and-line
Longline
B
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
Catc
h (t)
North
EquatorialTropical
SubtropicalTemperate
C
Pacific Ocean Tuna Catch Data
By species
By method
By area
Myers and Wormdata
- 50
- 45
- 40
- 35
- 30
- 25
- 20- 15- 10- 505101520
25
30
35
40707580859095100105110115120125130135140145150155160165170175180- 175- 170- 165- 160- 155- 150- 145- 140- 135- 130- 125- 120
707580859095100105110115120125130135140145150155160165170175180- 175- 170- 165- 160- 155- 150- 145- 140- 135- 130- 125- 120- 50
- 45
- 40
- 35
- 30
- 25
- 20- 15- 10- 505101520
25
30
35
40
Jap LL 1952-1999 20000YFTBET
BFTALB
Longhurst Areas
Spatial expansion of the longline fishery
One species dominates
0
2
4
6
8
10
1950 1965 1980 1995
BillfishSouthern bluefinYellowfinBigeyeAlbacore
Total temperateD
CP
UE
More often than not community CPUE declines faster than abundance
1i ii i i i
i
B Br B q EBt K
0iBt
SS SS
i i ii i
B CPUEK q K
2i i
i ii ii i
i i ii i
q qK Kr rK q K
2 2 2 2 2 22i i i j i j i i i j i ji i j i i j
q K q q K K q K q q K K
1 , pairs Biomass declines faster than CPUEi i
j j
r qi j
r q
1i
j
22
i i i i ii i i
q K K q K
Abundance of tunas in the Pacific Ocean
Integrated models
0
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
6,000,000
7,000,000
1952
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
Adu
lt bi
omas
s (t)
YellowfinBigeyeAlbacore
Japanese longline CPUE
0
10
20
30
40
50
60
70
1952
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
CPU
E (k
g pe
r 100
hoo
ks)
YellowfinBigeyeAlbacore
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1940 1950 1960 1970 1980 1990 2000 2010
F/Fmsy
Adult biomass
0.00E+00
2.00E+05
4.00E+05
6.00E+05
8.00E+05
1.00E+06
1.20E+06
1.40E+06
1.60E+06
1940 1950 1960 1970 1980 1990 2000 2010
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
Current depletion levelHypothesis More Same Less UnknownRegime change xEcosystem xSpatial distribution xGear depth x (most)Stupid fish xSize-specific vulnerability xMultiple stocks xFraction of stock xInterference xIncreased power xTargeting DependsAge-specific M xFishing regulations xSoaktime xShark damage xHook saturation x
Single Species
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 MortalityBigeye 5-21 quarters old
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1975 1980 1985 1990 1995 2000
Ann
ual f
ishi
ng m
orta
lity
Fishery Impact on EPO bigeye tuna
Year
75 77 79 81 83 85 87 89 91 93 95 97 99 01 03
0.0
0.2
0.4
0.6
0.8
1.0
Fish
ery
impa
ct
LonglineFloating objectSmall discards
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 spawner-recruitment relationship, fishing mortality should be kept at 1999 levels.
No recommendation for bigeyeCatch quota for yellowfin
Three month closure of the floating-object fishery
Fishing mortality increased 54% from 1999 levels.
2001 Assuming a moderate spawner-recruitment 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 spawner-recruitment 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)
