Back to the future: Investigating historical data from ...€¦ · Investigating historical data from Atlantic bluefintuna fisheries Back to the future: Exploitation since the first

Jean-Marc Fromentin

Investigating historical data from Atlantic

bluefin tuna fisheries

Back to the future:

Exploitation since the first millennium before Christ

Generalcontext

Bluefin tuna catch did not remain stable but displayed conspicuous long-term fluctuations,

possibly in relation to changes in temperature (Ravier and Fromentin 2001; 2004)

0

20000

40000

1600 1700 1800 1900

0

5000

10000

1600 1700 1800 1900

0

5000

1600 1700 1800 1900

0

5000

10000

1600 1700 1800 1900

0

4000

8000

1600 1700 1800 1900

Medo das Casas,

Portugal

1600 1700 1800 1900

0

10000

20000Zahara,

Spain

SalineSardinia

Porto ScusoSardinia

Favignana,

Sicily

FormicaSicily

Sidi Daoud,

Tunisia

0

5000

10000

1600 1700 1800 1900

70,0%

75,9%

57,8%

82,2%

74,7%

78,8%

63,4%

Skagen 1950 Bergen 1955

What’s happen to BFT in the North

Sea and Norwegian Sea?

Changes in migration patterns

Restriction of the spatial distribution

Recruitment failure/overfishing

Eradication of a sub-population

However, the leading Nordic fisheries were the most spectacular

example of Atlantic bluefin tuna fisheries collapse (Tiews 1978)

These fisheries suddenly collapsed in 1963

without any warning

Land

ings

(ton

nes)

0

5000

10000

15000

20000

1920 1930 1940 1950 1960 1970 1980 1990 2000

TheNordicfisheriescase

TheNordicfisheriescase

Nordic catch-at-size displays an unusual pattern

NordicNordicNordicNordic Fisheries

FisheriesFisheriesFisheries Collapse

CollapseCollapseCollapse

Retrospective Analysis

Italian TP(1900-00 / 1956-79)

Spanish TP(1900-00 / 1956-00)

Jap. LL (Med.)(1963-00; 1974-00)

German PS(1947-62; 1951-62)

Norwegian PS

Jap. LL (E. Atl.)(1957-00; 1974-00)

US PS(1958-00; 1963-00)

US TP(1930-73; 1955-61)

Jap. LL (W. Atl.)(1957-00; 1971-00)

Spanish BB(1940-00 / 1966-00)

BB: Bait BoatLL: Long LinePS: Purse SeineTP: Trap

French & Italian PS(1950-00; 1971-00)

(1927-79; 1956-79)

Retrospective Analysis: yeild

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

10000

20000

Yie

ld(t

) NEA-TP

Yie

ld(t

)

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

10000

20000NEA-PS

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

2000

4000

Yie

ld(t

) NEA-LL

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

2000

4000

Yie

ld(t

)

NEA-BB

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

5000

10000

Yie

ld(t

)

NWA-LL

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

1000

2000

3000

Yie

ld(t

) MED-TP

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

10000

20000

30000

Yie

ld(t

) MED-PS

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

4000

8000

Yie

ld(t

) MED-LL

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

500

1000

Yie

ld(t

)

NWA-TP

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

2000

4000

6000

Yie

ld(t

) NWA-PS

-0.5 0 0.5

-0.5

0

0.5

MED-TP

MED-PSMED-LL

NEA-TP

NEA-PS

NEA-LL

+

NEA-BB+

NWA-PS NWA-LL

axis 1 (38%)

axis

2 (

22%

)

+

++

+

+ +

++

1950 1960 1970 19800

2000

4000

6000Group 3

1950 1960 1970 19800

2000

4000

6000

8000Group 1

1950 1960 1970 19800

5000

10000Group 2

00.5

11.5

2

NE

A.T

P

ME

D.T

P

NE

A.P

S

NW

A.T

P

NE

A.B

B

ME

D.P

S

NE

A.LL

ME

D.LL

NW

A.LL

NW

A.P

S

Group 1Group 3Group 2NWA-TP

Retrospective Analysis: yeild

Median Dispersion Dispersion=f(Median)

1955 1960 1965 1970 1975 1980180

220

260

1955 1960 1965 1970 1975 1980

40

80

180 200 220 240 260

40

80

1955 1960 1965 1970 1975 1980

200

240

1955 1960 1965 1970 1975 198050

100

170 180 190 200 210 220 230 24050

100

1955 1960 1965 1970 1975 1980 1985150

200

1955 1960 1965 1970 1975 1980 1985

50

100

160 180 200 220 240

50

100

1965 1970 1975 198050

100

150

1965 1970 1975 1980

40

80

120

50 100 150

40

80

120

1970 1975 1980 1985 1990

100

150

200

1970 1975 1980 1985 1990

100

150

100 150 200

100

150

1970 1975 1980 1985 1990160

200

240

1970 1975 1980 1985 1990

60

100

140

160 180 200 220 240

60

100

140

through time…

NEA PS

NEA TP

MED TP

NWA LL

NWA PS

NEA BB

Retrospective Analysis: Size

Retrospective Analysis: Size

Yield vs Median size

NEA-PS

NEA-TP

MED-TP

NWA-PS

Yield vs Dispersion size

0 2000 4000 6000 8000 10000180

220

260 p < 0.001

0 2000 4000 6000 8000 1000020

40

60

80

p < 0.001

0 4000 8000 12000 16000150

200

250p < 0.001

0 4000 8000 12000 1600040

80

120

p > 0.1

0 500 1000 1500 2000 2500 3000

160

200

240p < 0.001

0 500 1000 1500 2000 2500 3000

60

80

100p < 0.001

0 1000 2000 3000 4000 5000 600050

100

150p > 0.1

0 1000 2000 3000 4000 5000 6000

40

80

120p > 0.1

Yield (ton) Yield (ton)

Med

ian

leng

th(c

m)

Inte

r-qu

artil

e-ra

nge

(cm

)

-7 -6 -5 -4 -3 -2 -1 0 1-3

-2

-1

0

1

2

19361937193819391940194119421943

1944

1945194619471948

1949

1950

1951

1952 1953

1954195519561957195819591960196119621963196419651966196719681969197019711972197319741975197619771978

NEA-PS (1956-1979)

axis1, 76%

axis

2, 1

0%

Year-class 1954-1974

Retrospective Analysis: Cohort

PCA…

Same strong year-classes in both fisheries

Include several continuous strong year-classes (here 1945 to 1952)

There is no sudden stop, but a kind of “ebb and flow”

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1-2

-1

0

1

2

3

193619371938193919401941194219431944

1945

1946

1947

1948

1949

1950

19511952

1953

1954

19551956 1957195819591960196119621963196419651966196719681969197019711972197319741975197619771978

axis 1, 63%

axis

2, 2

1%

NEA-TP (1956-1979)

axis 1, 32%-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5-2

-1.5

-1

-0.5

0

0.5193619371938193919401941

19421943

1944

1945

1946

1947

1948

1949

1950

1951

1952

1953

1954

195519561957

1958

1959

1960

1961

19621963

19641965196619671968196919701971197219731974197519761977197819791980198119821983

MED-TP (1956-1979)

axis

2, 2

0%

axis

2, 1

3%Other fisheries display different patterns, but also some similarities

Also include several continuous key year-classes

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2-4

-2

0

2

4

6

193519361937193819391940194119421943194419451946194719481949

1950

1951

19521953

1954

1955

1956

1957195819591960

NWA-TP (1955-1961)

axis 1, 74%

PCA…


clustering…


NE

A-B

B

NW

A-P

S

ME

D-T

P

NE

A-T

P

NE

A-P

S

1966-1979

The strong link between Norway PS and Spain trap vanished during the 1970s

ME

D-T

P

NE

A-T

P

NE

A-LL

NE

A-P

S

NW

A-LL

NW

A-P

S

NE

A-B

B

1971-1981

Strong connection between Gibraltar

and the Northeast Atlantic fisheries

during the 1950s and 1960s

Possible connections between the

Mediterranean Sea / Northwest

Atlantic and the Northeast Atlantic

Discussion –Part 1

Key feeding ground in the Northeast Atlantic

Main migration routes of Atlantic bluefin

tuna were from the Mediterranean

spawning grounds and from the West

Atlantic coasts to the North Sea

In agreement with conventional tagging experiments from the 1950s and 1960s (Aloncle et al. 1974; Tiews 1978; Mather et al. 1995)

Bluefin tuna primarily fed on juveniles

herring (up to 400,000 tons/year, Tiews 1978)

BFT collapse

Norwegian spring-spawning herring (Torensen & Ostved 2000)The Nordic bluefin tuna fisheries collapse

might be due to the failure of the major

Northeast Atlantic herring stocks

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

-0.4

-0.2

0

0.2

0.4

-0.6

0.6

Cooling Warming Cooling Warming

SS

T a

nom

alie

s (°C

)

SST anomalies from the Northeast AtlanticA significant cooling rapidly took place in the

Northeast Atlantic in the early 1960s

Atlantic herring stocks displayed large

temporal and spatial variations being related

to climate changes (Hjort 1914; 1926; Alheit & Hagen

1997; Corten 2001…)


Norwegian spring-spawning herring (Torensen & Ostved 2000)

The rapid cooling of the Northeast Atlantic could

have affected herring recruitment that has

indeed dropped since the mid-1950s and more

obviously after 1962, so that this area could not

support the voracious appetite of bluefin tuna

BFT collapse

The Nordic bluefin tuna fisheries collapse



The persistence of a high fishing capacity on

herring has induced a huge increase in the

fishing mortality and the crash of these

populations (another example of synergistic

effects of climate and overfishing)


Conclusions –Part 1

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

-0.4

-0.2

0

0.2

0.4

-0.6

0.6

Cooling Warming Cooling Warming

SS

T a

nom

alie

s (°C

)

BUT the close match between the

cooling and the Nordic fisheries

collapse may indicate that

changes in temperature might

have also affected BFT behaviour

Nordic fisheries

Yie

lds

(t)

0

10000

20000

1920 1930 1940 1950 1960 1970 1980 1990 2000

The Nordic bluefin tuna fisheries collapse



Why the strong connection between the Nordic fisheries and the Spanish traps did not

vanish before the mid-1970s???

No changes in BFT condition before and after the crash (Tiews 1978)

No indication of recruitment failure in the French and Spanish bait boat fisheries

The Nordic fisheries collapse fisheries might result from changes in BFT migration

patterns in relation to the collapse of the herring stocks and the cooling of the

Northeast Atlantic during the early 1960s

BFT could have stayed in the Northwest

Atlantic, as the high catches offshore of

Brazil and along the US Northeast coasts

during the 1960s could advocate for it

1960-1969 1970-1979

1980-1989 1990-1999


Changes in migration patterns from decade-

to-decade is consistent with past & current

knowledge as well as past & present tagging

information (conventional and electronic)

Would there be a nowadays a new key feeding

ground in the Northwest Atlantic??


Strong differences in yields,

size and year-classes between

the Northeast Atlantic and

Mediterranean traps

This can hardly be explained by changes in migration solely and underlying

processes of collapse/decline of these two fisheries are likely to be different

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

50000

100000

Cat

ch (

nb)

NEA-TP

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 20000

50000

100000

Cat

ch (

nb)

MED-TPDifferences in catches all over

the 20th century


21

3

During the 1950-1960s, sub-

population (1) would have been

dominant and could have spatially

mixed with the 2 others

Atlantic BFT could be constituted by 3 sub-populations : (1) a highly migratory one over

all the North Atlantic and Mediterranean, (2) a resident one in the Mediterranean and (3) a

resident one in the West Atlantic


2

1

3

Since the 1980s, the sub-population (2) would be dominant while sub-

populations (1) and (3) would have

strongly declined

The declining catch in the North Atlantic and the increasing catch in the Mediterranean

since the early 1980s may be interpreted as a change in sub-population size in response

to environmental modifications and possibly overexploitation

Overexploitation in the Western

Mediterranean Sea would prevent therebuilding of sub-population(1) and

could explain why bluefin tuna did not

come back massively in theNortheast Atlantic since the 1990s


Conclusion

The history of BFT fisheries is likely to reflect interactions between these

biological, trophic, environmental and fishing processes

Bluefin tuna migration patterns have probably changed through time (in relation to

abiotic and trophic factors)

Fisheries are also dynamics in both time AND space (mostly increasing/expanding)

Bluefin tuna population structure that remains largely unknown is probably more

complex than currently thought

Abiotic factors (e.g. SST) that affect fish population dynamics and structure are

also varying through time and space

Thanks for your attention

Bluefin tuna fisheries have a tremendous history, but

what about their future???

Documents

Back to the future: Investigating historical data from ...€¦ · Investigating historical data from Atlantic bluefintuna fisheries Back to the future: Exploitation since the first