Browsing Published in cooperation with others by Author "Valdemarsen, John Willy"
Now showing items 1-14 of 14
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A three level pelagic trawl for near surface sampling of juvenile fish
Godø, Olav Rune; Valdemarsen, John Willy (ICES CM Documents;1993/B:19, Working paper, 1993)In the northeast Atlantic Ocean catch rates of juvenile fish from pelagic trawls are used to calculate indices of relative abundance which are applied as a first indication of year class strength. A major constraint for ... -
Behaviour aspects of fish in relation to oil platforms in the North Sea.
Valdemarsen, John Willy (ICES CM Documents;1979/B:27, Working paper, 1979)Fish distribution around structures of the Ekofisk oil field in the central North Sea was investigated by means of gillnet fishing, longlining, jigging and echosurveying. The studies were carried out during one week in ... -
Demersal pair trawling and its operational parameters.
Dickson, W.; Valdemarsen, John Willy (ICES CM Documents;1982/B:36, Working paper, 1982) -
Fish behaviour in relation to long lines observed by TV
Fernö, Anders; Johannessen, Arne; Olsen, Kjell; Solemdal, Per; Tilseth, Snorre; Valdemarsen, John Willy (ICES CM Documents;1976/B:38, Working paper, 1976) -
Fish distribution studies around offshore installations
Olsen, Steinar; Valdemarsen, John Willy (ICES CM Documents;1977/B:41, Working paper, 1977) -
Further experiments with radial escape section (RES) as fish-shrimp separator in trawl
Valdemarsen, John Willy; Isaksen, Bjørnar (ICES CM Documents;1986/B:29, Working paper, 1986)A new approach to the bycatch problem when trawling for shrimp was initiated in Norway in 1984 utilizing the difference in swimming behaviour of fish and shrimp. A radial escape section (RES) in the aft belly of the ... -
Grid devices to select shrimp size in trawls
Valdemarsen, John Willy; Lehmann, Klaus; Riget, Frank; Boje, Jesper (ICES CM Documents;1993/B:35, Working paper, 1993)Discard of small shrimps and fish is a substantial problem in the fishery for deepwater shrimp in the Northwest Atlantic. In order to solve this problem, different grid devices are under development to sort out discard ... -
Preliminary studies on the influence of bottom obstructions and topography on the availability of demersal fish for gillnet fishing in the North Sea.
Valdemarsen, John Willy; Fernö, Anders (ICES CM Documents;1979/B:21, Working paper, 1979)Gillnet fishing experiments were carried out in the Little Fisher Bank area in the North Sea. Saithe and pollack and to some extent cod showed a patchy distribution along a gillnet string. The abundance of fish was ... -
Preliminary Tests of a Shrimp-fish Separator Section for Use in Shrimp Trawls
West, Charles W.; Valdemarsen, John Willy; Isaksen, Bjørnar (ICES CM Documents;1984/B:12, Working paper, 1984)A prototype shrimp-fish separator to be installed between the body and codend of a shrimp trawl was designed and constructed. The separator uses large square meshes to provide an escape path for fish, while funnels ... -
Reduction of fish bycatch in shrimp trawl using a solid separator grid in the aft belly
Isaksen, Bjørnar; Valdemarsen, John Willy; Larsen, Roger B. (ICES CM documents;1990/B:47, Working paper, 1990)During 1989-90 a new concept to avoid bycatch of fish in shrimp trawl has been developed in Norway. The system consists of an aluminium grid, 0.6 - 1.0 m wide and 1.3 - l.5 m long, with bars spaced 19 mm. The grid is ... -
Selectivity experiments with square mesh codends in bottom trawl
Isaksen, Bjørnar; Valdemarsen, John Willy (ICES CM Documents;1986/B:28, Working paper, 1986)During selectivity experiments with square and diamond mesh codends, an evaluation of the covered codend method and a modified trouser trawl method went in favour of the last one. Both twisted knotless- and braided ... -
Studies on the behaviour of some gadoid species in relation to traps
Valdemarsen, John Willy; Fernö, Anders; Johannessen, Arne (ICES CM Documents;1977/B:42, Working paper, 1977) -
Trawl designs and techniques used by Norwegian research vessels to sample fish in the pelagic zone
Valdemarsen, John Willy; Misund, Ole Arve (PINRO-IMR Symposium, Conference object, 1995)In resource surveys, representative identification of species and sizes of fish is of vital importance. Various designs and sizes of pelagic trawls and techniques are used in the pelagic zone by Norwegian research vessels ... -
Vertical entrance into a trawl of Barents Sea gadoids as studied with a two level fish trawl
Valdemarsen, John Willy; Engås, Arill; Isaksen, Bjørnar (ICES CM Documents;1985/B:46, Working paper, 1985)Catch figures of different demersal species(cod, haddock, saithe etc.) in the cod-ends of a two level trawl were examined using variable height of the separating panel (0.5, 0.75, 1.0 and 1.5 m). Cod enters the trawl ...