svigninger i de store fiskebestander, ved svein iversen
TRANSCRIPT
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SVINGNINGER I UTVALGTE FISKERIER OG BESTANDER
I NORDSJØEN-SKAGERRAK
Svein A. Iversen
WS i Økologisk historie i Nordsjøen og SkagerrakOslo 27.09.2012
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Gullestad et al 2012
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Gullestad et al 2012
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Kerby et al 2012
Fangst av bunnfisk i Nordsjøen
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Norske fangster i Nordsjøen - Skagerrak
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Norske makrellfangster
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Norske taggmakrellfangster og influks av atlantisk vann til Nordsjøen
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Norske fangster av bunnfisk i Nordsjøen - Skagerrak
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Norske fangster av industrifisk i Nordsjøen - Skagerrak
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Norske fangster av reker og pigghå i Nordsjøen - Skagerrak
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The Gadoid outburst
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GADOID OUTBURST Økning i mengden av torskefisk i Nordsjøen fra ca 1965/1970 og utover 70talletBåde torsk, hyse, sei og hvitting hadde god rekruttering og økt fangst
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Norske sild og brislingfangster i Nordsjøen
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Rekrutter (årsklassestyrke) av noen utvalgte Nordsjøbestander
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Takk for meg
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Hypotheses for the causes of the gadoid outburst (WGCCC BF4 1998)
•Changes in juvenile and adult growth, maturation and condition resulted in higher egg production per unit biomass during the GO period.
•The plankton environment during the 1960s was very conducive to growth and survival of young larvae (more food, better food, fewer predators).
• The environment during the 1960s was very conducive to survival of pelagic 0-group and settlement success.
• The demersal environment during the 1960s was very conducive to growth and survival of settled juveniles
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Mattinntak for torsk, hyse, hvitting og sei:
1974-1976: 13 mill tonn
1990-1992: 4 mill tonn
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Norske fangster av ål
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0
200
400
600
800
1000
1972 1977 1982 1987 1992 1997 2002 2007
Land
ings
in 10
00 t
Landings
0.00
0.10
0.20
0.30
0.40
0.50
1972 1977 1982 1987 1992 1997 2002 2007
F(ag
es 4
-8)
Fishing Mortality F MP FlimFpa FMSY
0
2
4
6
8
10
1972 1977 1982 1987 1992 1997 2002 2007
Recr
uitm
ent i
n bi
llions
Recruitment (age 0)
0
1000
2000
3000
4000
1972 1977 1982 1987 1992 1997 2002 2007
SSB
in 10
00 t
Spawning Stock BiomassSSB MP BlimBpa MSYBtrigger
Makrell
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Nordsjøtorsk
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Nordsjøtorsk
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Nordsjøhyse
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Nordsøsild