Blar i ICES CM documents authored by IMR scientists (1949-2011) på forfatter "Ona, Egil"

Viser treff 1-20 av 48

    • A method to reduce survey bottom trawl variability 

      Engås, Arill; Ona, Egil (ICES CM Documents;1991/B:39, Working paper, 1991)
      A technique for limiting the variability of trawl doorspread is described. In addition, modifications of trawling technique which enable the doors to stay upright and maintain constant ground contact under different ...

    • Acoustic abundance estimation of wintering Norwegian spring spawning herring, with emphasis on methodological aspects 

      Røttingen, Ingolf; Foote, Kenneth G.; Huse, Ingvar; Ona, Egil (ICES CM Documents;1994/(B+D+G+H):1, Working paper, 1994)
      The spawning component and part of the juvenile stock of Norwegian spring spawning herring have been wintering in a fjord system in northern Norway in recent years. Conditions for measuring the stock size have been ...

    • Acoustic extinction in dense herring layers, measured from a bottom-mounted transducer 

      Utne, Kjell R.; Ona, Egil (ICES CM documents, Working paper, 2006)
      Herring is often found in dense aggregations or schools, and acoustic shadowing is thus a problem in acoustic survey estimates. Knowledge of the attenuated echo intensity in herring aggregations is essential for correcting ...

    • Acoustic properties of Salpa thompsoni. 

      Wiebe, Peter H.; Chu, Dezhang; Kaartvedt, Stein; Hundt, Anna (Hölter); Melle, Webjørn; Ona, Egil; Batta-Lona, Paola (ICES CM documents;2009 / I:01, Working paper, 2009)
      Salps are common members of the world oceans planktonic community (Madin, et.al., 2006). In the southern ocean, both krill (Euphausia superba) and salps (Salpa thompsoni) can occur in dense aggregations (Loeb et al, 2009, ...

    • Angular distribution of overwintering Norwegian spring spawning herring 

      Huse, Ingvar; Foote, Kenneth G.; Ona, Egil; Røttingen, Ingolf (ICES CM documents, Working paper, 1994)
      When plankton production drops off in the fall, adult Norwegian spring spawning herring migrate to two fiords in northern Norway with stable water masses with low temperature and predation. In the wintering areas, the ...

    • Avoidance reactions of herring to a survey vessel, studied by scanning sonar 

      Ona, Egil; Toresen, Reidar (ICES CM Documents;1988/H:46, Working paper, 1988)
      The behavioural response of a shallow herring layer to a steaming vessel has been studied by the use of a high-resolution scanning sonar technique. When the vessel was completely darkened, no significant reaction important ...

    • Changes in acoustic abundance - a signal indicatior for stock dynamics for cod (Gadus morhua) 

      Godø, Olav Rune; Ona, Egil (ICES CM documents, Working paper, 1999)
      To be able to take the proper and timely management actions, it is crucial to reliably defect major changes in trends of fish stock abundance. For the assessment of Northeast Arctic cod, the Norwegian bottom trawl survey ...

    • Combined algorithms for detection of acoustic categories 

      Korneliussen, Rolf J.; Ona, Egil (ICES CM Documents;2004/R:38, Working paper, 2004)
      There is a current desire to harvest marine resources by managing total marine ecosystems rather than single species of the ecosystems. By means of algorithms applied on high-quality multi-frequency acoustic data, species, ...

    • Comparative analysis of split beam data 

      Kieser, Robert; Ona, Egil (ICES CM Documents;1988/B:44, Working paper, 1988)
      Split beam data can provide high quality, in situ, fish target strength estimates, however a careful calibration is required to realize this potential. In same cases a standard target has been used to make a large number ...

    • Correcting for avoidance in acoustic abundance estimates for herring using a generalized linear model 

      Hjellvik, Vidar; Handegard, Nils Olav; Ona, Egil (ICES CM documents, Working paper, 2006)
      When a research vessel passes over a herring school or layer, the herring may avoid the vessel by swimming downwards and horizontally. The fish may also change its orientation, which may alter its mean target strength. ...

    • Detailed in situ target strength measurements of 0-group cod 

      Ona, Egil (ICES CM Documents;1994/B:30, Working paper, 1994)
      Target strength measurements in situ of cod fry have been made using 38 and 120 kHz split beam echo sounders. Two data sets are sampled in essentially pure, evenly sized, cod concentrations, one in a Ullsfjord, Northern ...

    • Detection and counting of individual free-swimming krill using a 2MHz scanning sonar 

      Ona, Egil; Knutsen, Tor (ICES CM Documents;1992/L:18, Working paper, 1992)
      The euphausiid crustacean Meganyctiphanes norvegica (M. Sars) have been detected and counted in the scanning section of a 2 MHz scanning sonar beam up to 3 meters from the sonar head. The tests completes a pilot investigation ...

    • Detection of spatial distribution of acoustic categories 

      Korneliussen, Rolf J.; Ona, Egil (ICES CM documents, Working paper, 2005)

    • Determining the entrance position of fish in trawls 

      Ona, Egil (ICES CM documents, Working paper, 1999)
      The entrance position of a fish is defined as its two-dimensional position in a cross section of a trawl near the centre of the headline. Individual fish entering the trawl: detected by highresolution scanning sonar, ...

    • Differences in swimbladder volume between Baltic and Norwegian spring spawning herring: possible consequences for mean target strength 

      Fässler, Sascha M.M.; Gorska, Natalia; Ona, Egil (ICES CM documents;2007/H:03, Working paper, 2007)
      Volume and shape of the swimbladder of Baltic and Norwegian spring spawning herring were measured, together with individual herring fat content. Swimbladder size was found to differ significantly between the two herring ...

    • Direct measurements of equivalent beam angle on hull-mounted transducers 

      Ona, Egil; Vestnes, Gudmund (ICES CM Documents;1985/B:43, Working paper, 1985)
      Measurements for checking the equivalent beam angle on a hullmounted transducer have been made on a standard 38-29/25-E SIMRAD transducer on the Norwegian research vessel "ELDJARN". The measurements were made during a ...

    • Experiences using the constraint technique on bottom trawl doors 

      Engås, Arill; Ona, Egil (ICES CM Documents;1993/B:18, Working paper, 1993)
      The constraint technique, i.e. using a rope between the warps, has the intention of minimizing the variability in trawl geometry with depth. Experiments with the constraint technique on two different bottom trawls used ...

    • Experiences using the ES-400, split-beam echo sounder, with special reference to the single-fish recognition criterion 

      Ona, Egil; Røttingen, Ingolf (ICES CM Documents;1986/B:38, Working paper, 1986)
      Realistic estimates of in situ target strength can be made when the fish concentrations are acoustically resolved into single individuals. In the split-beam echo sounder, as in all other systems available for in situ ...

    • Fjordranching with conditioned cod 

      Midling, Kjell; Kristiansen, Tore S.; Ona, Egil; Øiestad, Victor (ICES CM Documents;1987/F:29, Working paper, 1987)
      In June 1986, 1600 pond-reared one-year old cod were released into a fjord after being conditioned with a pulsed 160 Hz sound signal to search for food at a feeding location. Echosounders, UW-video and ultrasonic ...

    • Haddock avoidance reactions during trawling 

      Ona, Egil; Chruickshank, O. (ICES CM Documents;1986/B:36, Working paper, 1986)
      Fish reaction to the whole trawling operation was studied using a stationary echo sounder-system observing the fish in front of the vessel and during trawl passage. Strong avoidance reactions were observed on haddock, ...