are pelagic fisheries managed well? a stock assessment scientists perspective

Are pelagic fisheries managed well?

A stock assessment scientists perspective

Mark Maunder and Shelton HarleyInter-American Tropical Tuna Commission

mmaunder@iattc.orghttp://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

qq

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)