Brian R. MacKenzieTechnical University of Denmark
& Aarhus UniversityNational Institute for Aquatic ResourcesCharlottenlund, [email protected]
The Development of the Northern European Fishery for North Atlantic Bluefin Tuna, Thunnus thynnus, during 1900-1950
Acknowledgements
www.conwoy.ku.dk
-HMAP (www.hmapcoml.org)
-Danish climate change project
-EU Network of Excellence on Marine Biodiv. & Ecosyst. Funct.
-EU Network of Excellence on Ocean Ecosystem Dynamics Eur-oceans
Objectives
Describe development of bluefin tuna fishery in northeastern Europe.
Estimate roles of fishery developments and ecosystem conditionson catch trends up to 1950.
KattegatL. Svendsen 1932.
* = Norwegian Sea, North Sea, Skagerrak, Kattegat, Øresund
Landings of Bluefin Tuna Thunnus thynnus in Northern Europe*
Year190019101920193019401950196019701980199020002010
Land
ings
(ton
nes)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Intl.Danish
Catch Development Before 1950
Year190019101920193019401950196019701980199020002010
Land
ings
(ton
nes)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Intl.Danish
Why did landings increase in early 1900s?-fishery–related factors: increases in effort, technology, demand?-ecosystem and population factors?
-changes in temperature, food supply, etc. -series of a few exceptionally strong yearclasses
Methods
MacKenzie & Myers 2007Fish. Res.
-compile all existing data for presence of bluefin tuna inNorthern European waters since 1900
-”presence” = sightings, strandings, landings-individuals and schools-fishing industry information (effort, technology, processing)
-compile time series of relevant ecosystem variables
Data sources:
-ICES-scientific papers, reports, books-commercial statistics, museum records, ichthyofaunal descriptions-photographic and video evidence
Development of Fishery
MacKenzie & Myers 2007Fish. Res.
-many bluefin tuna were regularly seen esp. by herring fishermen
-caught as bycatch in herring fisheries-offshore/open water (when hauling herring nets onboard)-coastal traps
-some targetted fisheries with harpoons and harpoon-rifles
Development of National Fisheries (ICES data: starts in 1927)
MacKenzie & Myers 2007Fish. Res.
1904 1912 1920 1928 1936 1944 1952
Sw
edis
h la
ndin
gs (t
)
1
10
100
1000
Dut
ch la
ndin
gs (t
)
1
10
100
1904 1912 1920 1928 1936 1944 1952
Fren
ch la
ndin
gs (t
)
1
10
100
1000N
orw
egia
n la
ndin
gs (t
)
1
10
100
1000
Dan
ish
land
ings
(t)
1
10
100
1000
Ger
man
land
ings
(t)
1
10
100
1000
Norway
Germany
France
Netherlands
Sweden
Denmark
A Day at AltonaFish Auction Hall, Germany, 1910
MacKenzie & Myers 2007Fish. Res.
Photo: Brandenburg 2003; Sutton Verlag
-data not in ICES or ICCAT statistics
Development of National Fisheries pre-ICES
MacKenzie & Myers 2007Fish. Res.
Dan
ish
land
ings
at S
kage
n, D
K (t)
0.01
0.1
1
10
100
No.
can
nerie
s
0
1
2
3
4
5
Nor
weg
ian
land
ings
(nos
.)
10
100
1000
Ger
man
land
ings
in N
orth
Sea
(t)
0.1
1
10
(1910: catch in 1 day)
(1903: 1 stranding)
Swed
ish
land
ings
(t)
0
200
400
600
800
1904 1912 1920 1928 1936 1944 1952
Fren
ch la
ndin
gs in
Nor
th S
ea (t
)
0.1
1
10
100
1907: catch by 1 vessel
1904 1912 1920 1928 1936 1944 1952
Engl
ish
spor
tfish
ery
land
ings
(nos
.)
0
20
40
60
80
(1907: 1 stranding)
(1924: catch by 1 boat)
Norway
Germany
France England
Sweden
Denmark
Bluefin Tuna Sportfishery, Øresund, Denmark, 1949
© Danmarks Radio Archives
-viewable at www.dfu.dtu.min.dk/nyheder
BluefinTuna School Sightings in North Sea
Wolfe Murray 1932J. du conseil
1912 1916 1920 1924 1928 1932
Julia
n da
y
180
200
220
240
260
280
300
Schools seen regularly byobservers since 1912.
-schools observed near Dogger Bank during herring fishing
Prey Escape from Schools of Feeding Bluefin Tuna
Svendsen, L. 1949
-garfish being attacked from below and jumping above water to escape
Commercial Bluefin Tuna Fishery, Kattegat, Denmark, 1949
MacKenzie & Myers 2007Fish. Res.
© Danmarks RadioArchives
Tuna Presence and Multi-decadal Scale Temperature Variability
MacKenzie & Schiedek 2007Glob. Ch. Biol.
Bluefin tuna were present and abundant during:-cold periods (1900-1925)-warm periods (1930-1960).
North Sea SST during Summer
1880 1900 1920 1940 1960 1980 2000
Sur
face
Tem
pera
ture
(N
orth
Sea
)
13
14
15
16
17
MacKenzie & Myers 2007Fish. Res.
School Sightings & Temperature 1923-31
MacKenzie & Myers 2007Fish. Res.
13.5 14.0 14.5 15.0 15.5Firs
t day
of s
ight
ing
of tu
na s
choo
ls
(Jul
ian
day)
196
198
200
202
204
206
208
210
212
214
North Sea SST, Hadley Ctr.
13.5 14.0 14.5 15.0 15.5Dur
atio
n of
sig
htin
gs o
f tun
a sc
hool
s (d
ays)
60
65
70
75
80
85
90
95
13.5 14.0 14.5 15.0 15.5Last
day
of s
ight
ing
of tu
na s
choo
ls
(Jul
ian
day)
260
265
270
275
280
285
290
295
First day
Last day
Duration
-presence/absence notrelated to interannual varationsin regional SST
1900 1910 1920 1930 1940 1950
Sum
mer
SST
13
14
15
16North Sea SST during July-Aug-Sept.
Tuna Presence and Multi-decadal Food Variability
Torsten & Østvedt 2000; ICES 2007
Bluefin tuna were present and abundant during:-low-food periods (1900-1925)-high-food periods (1930-1960).
1880 1900 1920 1940 1960 1980 2000Spaw
ner b
iom
ass
(100
0s t)
o
f Arc
t.-N
orw
. Her
ring
0
7500
15000
22500
Spaw
ner b
iom
ass
(100
0s t)
o
f Nor
th S
ea H
errin
g
0
2000
4000
6000
Norweg.North Sea
-herring were main prey of bluefin tuna in North and Norwegian Seas(Tiews 1964; 1978)
Industrialisation of Northern European Bluefin Tuna Fisheries (1)
-huge increase in effort (boats, gears, fishing skill)
Norwegian tuna fishing effort
0
100
200
300
400
500
1945 1950 1955 1960 1965
No.
of b
oats
Hamre et al. 1966
Development of Fishing Methods
L. Svendsen 1932So. Kattegat, DK
M. Tangen, 1999Norway
Hanson, B. 1927Norway
L. Svendsen 1932So. Kattegat, DK
Industrialisation of Northern European Bluefin Tuna Fisheries (2)
-huge increase in technology and skill
-increase in demand and canneries (e. g., first Danish cannery built in 1920s; others followed in DK and Norway)
-harpoons, harpoon-rifles, rod-reel, handlines, hydraulically-operated purse seines
-all these fishery-related changes lead to large increases in landings
Presence Before 1900
Tuna bonesduring Medieval(Enghoff 1999)
183 tuna caught in 1548 (Rørdam 1887)
1 fish caught 1545
Bluefin Tuna Fishing in Norway in 1760s
Strøm, Hans. 1766.
Physical and EconomicDescription of Søndmør Tax District, Bergen Parish,Norway. Part 2
Bluefin Tuna Fishing in Norway in 1760s
Every summer a large amount of tuna comes with the herring.
One man could catch 15-20 tuna per summer using a harpoon in the 1760sin Jørgenfjord, Norway.
-H. Strøm 1766
H. Strøm 1788
Bluefin Tuna in Northern Europe Before 1900
MacKenzie, in prep.
All No. Europe
1500 1600 1700 1800 1900
Pre
senc
e -based on fish faunalists, fishery records,archaeological remains,etc.
-present several decades and centuries in past
Bluefin Tuna Near Copenhagen During the Stone Age (ca. 7000-3900 BC)
Amager Beach, Copenhagen (5800 BC)
Landskrona, Sweden (4000 BC; Eriksson & Magnell 2001)
Enghoff et al. 2007Fish. Res.
Conclusions (Pre 1950)
-bluefin tuna have been present in large numbers in northern European waters before onset of heavy fishing in 1950s-1960s
-landings increased because of huge increases in effort & tech.-bluefin tuna are now extremely rare
-gone from many people’s memories (and expectationsof which species comprise local fish community!)
Next steps:
-understand why collapse occurred in 1960s-understand why they have not (yet) returned
Brian R. MacKenzieTechnical University of Denmark & Aarhus UniversityNational Institute for Aquatic ResourcesDK-2920 Charlottenlund, [email protected]
Ecological and Fishing Influences on Presence of Bluefin Tuna in Northern European Waters
Talk Outline
1. Development of fisheries – catch, effort, environmentaldata pre-1950s (MacKenzie and Myers 2007: Fish. Res.)
2. Current state – why a decline and disappearance in 1960s-hypotheses
3. Prospects for recovery and reappearance
Hypotheses for Decline
Change in numbers of recruits migrating to region, due to -overexploitation of spawners and/or recruits-env. effects on recruitment processes
Change in migration pattern
Food abundance – not enough?
Temperature (too cold?)
Hypothesis
-need to understand processes over large areas
Tuna Presence and Multi-decadal Scale Temperature Variability
MacKenzie & Schiedek 2007Glob. Ch. Biol.
SST during most of 1960s similar to earlier decadeswhen BFT were also present-BFT also are good thermal-regulators and are usually seasonally present until SST < ~11-12 C-decline not likely due to low temperature
North Sea SST during Summer
1880 1900 1920 1940 1960 1980 2000
Sur
face
Tem
pera
ture
(N
orth
Sea
)
13
14
15
16
17
MacKenzie & Myers 2007Fish. Res.
Was Disappearance Related to Loss of Key Prey Species (Herring)?
Torsten & Østvedt 2000; ICES 20071880 1900 1920 1940 1960 1980 2000Sp
awne
r bio
mas
s (1
000s
t)
of A
rct.-
Nor
w. H
errin
g
0
7500
15000
22500
Spaw
ner b
iom
ass
(100
0s t)
o
f Nor
th S
ea H
errin
g
0
2000
4000
6000
Norweg.North Sea
-bluefin tuna may have altered migration pattern since main food supplywas nearly eliminated
-herring collapsed in both Norwegian and North Seas in 1960s (mainly due to overfishing; Fiksen & Slotte 2002; Cushing 1995):
MacKenzie et al., in prep.
Increase in Size
Despite loss of prey, some big tuna still migrated here during 1960s-1980s.
Decline accompanied by increase in size and age in Norwegian catches:
Fromentin & Powers 2005
-similar aging seen in Spanish catches (Pusineri et al. 2002)
Why Did Medium-Sized Tuna Stop Migrating to Northern Europe?
Possible reasons:
-young tuna changed their migration pattern (e. g., went somewhere else,stayed in Mediterranean, etc.)
-reduced production of young tuna (low recruitment) due to fewer adults
-lower survival of young tuna as juvenile exploitation increased (e. g.,juvenile landings were 450,000/year in B. Biscay and Morocco during 1949-62; Cort & Nøttestad 2007)
Cause of DeclineMain reason probably exploitation.
Disappearance followed increasing and heavy exploitation of bluefin tuna and its prey in several areas:
Juv. + adultsNorth SeaHerringJuv. + adultsNorwegian SeaHerring
Mainly juvenilesBay of BiscayBFTMainly adultsNorth SeaBFTMainly adultsNorwegian SeaBFTLH StageAreaSpecies
MacKenzie et al., in prep.
Tuna Presence and Ecosystem Properties
1880 1900 1920 1940 1960 1980 2000Spaw
ner b
iom
ass
(100
0s t)
o
f Arc
t.-N
orw
. Her
ring
0
7500
15000
22500
Spaw
ner b
iom
ass
(100
0s t)
o
f Nor
th S
ea H
errin
g
0
2000
4000
6000
Norweg.North Sea
MacKenzie et al. n prep.
1880 1900 1920 1940 1960 1980 2000
Surfa
ce T
empe
ratu
re
(
Nor
th S
ea)
13
14
15
16
17
If presence depends on warm temperatures and high food abundance,then there should be lots of tuna in these waters:
Immigration of “Southern” Species to Northern European Waters
-ocean warming is allowing many fish species to expand habitatsto North and Norwegian Seas…
Science 308: 1912-1915 (2005)
“Southern” Species Moving North
Swordfish Xiphias gladius; 66 kgLittle BeltSeptember, 2006
Gilthead seabream Sparus aurataGuldborgsund, western BalticJuly 2007
Anchovy, survey data, 1925-2004
Beare et al. 2005
Bluefin Tuna Reappearance?
Bluefin tuna still very rare
-1 caught as bycatch in Skagerrak in 2004
-must consider other explanations related to population and fishing
Bluefin Tuna Catch Development
Year1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Land
ings
(ton
nes)
0
10000
20000
30000
40000
50000
60000
Total East. Atl. + Medit. Northern Europe (SD IIA, IIIA, IV)Danish (IIIA + IV)
ICCAT 2006
-large increase in reported landings in recent decades
Spawner – Recruit Temporal Development
1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008
Rec
ruitm
ent (
age
1; 1
000s
)
0
1000
2000
3000
4000
5000
Spa
wne
r bio
mas
s (1
000s
t)0
50
100
150
200
250
Rec.SSB
MacKenzie et al. in prep.
-decrease of spawner biomass is now limiting recruitment
Spawner biomass (t)0 50000 100000 150000 200000 250000
Rec
ruits
(age
1; 1
000s
)
0
1000000
2000000
3000000
4000000
5000000
6000000
93
9495
969798
99
100
101
102
103
Reproductive Potential
In other fish species and populations:
-older, larger females and repeat spawners produce
-more eggs/g, -better quality eggs-eggs over larger areas-eggs over longer periods of the year
(Kjesbu, Marshall, Marteinsdottir, papers…)
How has age structure of bluefin tuna changed relative to reproductive potential?
Population Demographics
1968 1972 1976 1980 1984 1988 1992 1996 2000 2004Prop
ortio
n of
age
8+
in s
tock
0.0
0.1
0.2
0.3
1968 1972 1976 1980 1984 1988 1992 1996 2000 2004
Rep
eat s
paw
ners
as
prop
ortio
n of
to
tal s
paw
ners
in s
tock
0.6
0.7
0.8
0.9
1.0
-proportion of old tuna in stockhas declined, even from 1970
-proportion of repeat spawnershas decreased
Trends in Population Demographics
Reproductive potential of bluefin tuna has probably been reduced,for reasons in addition to the decrease in biomass of spawners.
-quality of reproductive output may have decreased(assuming that BFT respond like other fish species?)
-this will make recovery difficult and slower.
Landings of Juvenile Bluefin Tuna
ICCAT 2006 (1970-2004);Cort & Nøttestad 2007 (1949-62)
Large numbers of 0-groups are also caught in E. Atl. and Med. but landingsare unknown (ICCAT 2003, 2006).
1968 1972 1976 1980 1984 1988 1992 1996 2000 2004Pro
p. o
f age
s 1-
3 in
tota
l cat
ch
0.0
0.2
0.4
0.6
0.8
1.0
E. Atl + Med.W. Atl.
1952 1960 1968 1976 1984 1992 2000Cat
ch o
f age
s 1-
3 (1
000s
)
0
400
800
1200
1600
E. Atl + Med.B. Biscay & Atl. MoroccoW. Atl.
-landings in Eastern Atlantic and Mediterranean dominated by immature fish
-effects on past and future population dynamics needs to be investigated and quantified.
-existing studies suggest exploitation of juveniles and adultsis not sustainable (Fromentin & Fonteneau 2001)
-many bluefin tuna not being given opportunity to reproduce
Fishing Pattern in Eastern Atlantic
Conclusions (post 1950)Disappearance in 1960s not due to low temperatures.
Disappearance mainly due to direct effects of fishing on -adult and juvenile bluefin tuna-prey (herring).
Bluefin tuna has been present in these waters during cold and warm periods, and during food-rich and food-poor periods.
If abundance associated with warm, food rich waters, there should now be lots of bluefin tuna in northern European waters.
Recovery failure mainly due to continued high fishing on tuna adults and juveniles.
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