pelagic trawling for cod, haddock and saithe in the barents sea shale rosen, terje jörgensen and...
TRANSCRIPT
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Pelagic Trawling for Cod, Haddock and Saithe in the Barents Sea
Shale Rosen, Terje Jörgensen and Arill Engås
Insitute of Marine Research
Postboks 1870 Nordnes
N-5817 Bergen Norway
Nor-Fishing Technology Conference 2008
Trondheim, Norway 11-12 August 2008
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Overview
• Glossary• Introduction to project, objectives • 1960s-1970s pelagic trawl fishery• Why the renewed Interest?• Data collection• Catches• Comparison with demersal trawl catches• Conclusions• Next steps
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GlossaryPelagic Trawl = Midwater Trawl = Flytetrål
Demersal Trawl = Bottom Trawl = Bunntrål
Cod = Torsk = Gadus morhua
Images Northeast Fishery Science Center www.nefsc.noaa.gov
Haddock = Hyse = Melanogrammus aeglefinus
Saithe = Sei = Pollachius virens
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Introduction to Project
• Test pelagic fishery for species typically caught in demersal trawls
• Research Topics:– Availability of cod, haddock, saithe to
pelagic trawls– Selectivity of pelagic trawls– Behaviour as trawl approaches and once
inside– Development of pelagic trawl to target cod,
haddock, saithe
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1960s-1970s Pelagic Trawl Fishery
• Spring fishery for cod and haddock off northern tip of Noway, late summer fishery for haddock farther offshore
• Closed 1979 due to reports of high bycatch of juveniles (higher than in demersal trawls)
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Why the Renewed Interest?
• Impacts of demersal trawls on seabed
• Reduce bycatch of highly demersal species (eg. flatfish)
• Reduce fuel consumption
• Sorting grids and larger mesh proven successful in other trawl fisheries
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Data Collection, Net and Sensors
262 meters
40 meters
60 meters 15 meters7 meters
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Data Collection (cont.)
• Distance between doors and height relative to headrope and footrope
• Amount of towing wire and tension
• Catch in grid cover, cod end, and cod end cover
grid cover
cod end cover
cod end
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Catch Locations and Vertical Distribution, Cod
April 2008 cruise,pelagic cod area
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Catch by Time of Day, Cod
0
10
20
30
40
50
60
70
80
90
22:00-01:59
02:00-05:59
06:00-09:59
10:00-13:59
14:00-17:59
18:00-21:59
Time of day
Tota
l Cat
ch (t
ons)
Catch per Haul, Cod
0011111256
10
16
17
21
21
22
50
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1
Catch, tons
% o
f T
ota
l Ca
tch
Catches in Pelagic Trawl
Total: 175 tons
X X
50% in just 3 hauls!
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Length Distributions, Haddock
0%
5%
10%
15%
35 40 45 50 55
Fish length (cm)
% o
f fi
sh
Codend
Grid Cover
Codend Cover
Length Distributions, Cod
0%
1%
2%
3%
4%
5%
45 55 65 75 85 95 105 115
Fish length (cm)
% o
f fi
sh
Codend
Grid Cover
Codend Cover
Length Distributions of CatchFew undersized fish encountered, removed by sorting grid
47 cm, Minimum Legal Size 42 cm, Minimum Legal Size
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Length Distributions of Catch: Comparison with Demersal Trawl
Larger cod captured in cod end of pelagic trawl
mean75 cm = 4 kg
mean81 cm = 5 kg
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Comparisons With Demersal Trawls
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Image Injector Trawldoors A/S
Conclusions- Gear
• Opening of 40 m by 60 m was well-sized for the distributions and behaviour we encountered.
• Benthic trawl doors spread net adequately and made it easy to switch between pelagic and demersal trawls
• 300mm liner in belly may not be necessary (at most 9 fish meshed per haul)
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Conclusions- General
• In the right conditions, pelagic trawl is a highly effective way of catching cod (150 tons in 5 days)
• Most effective during brightest daylight hours• Sorting grid effectively removed small gadoids and pelagics
(herring and blue whiting)• Cod caught in pelagic trawl were larger than in demersal trawl • CPUE higher in pelagic trawl than demersal trawl, when
pelagic distributions were present• Fuel consumption between that of single and twin demersal
trawl• Not a replacement for demersal trawls, but pelagic trawls may
increase fleet’s flexibility and reduce seabed impact for each portion of quota caught without using demersal trawl
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Next Steps
• October cruise on R/V, focused on behaviour and selectivity studies
• Spring 2009 cruise on F/T, focused on use in commercial fishery
• Discussions with Fisheries Directorate about authorizing an experimental fishery with data collection
• We anticipate continued cooperation with net manufacturers and fishermen to refine design for selective and efficient pelagic trawls for gadoids
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Questions?