Blar i Published in cooperation with others på forfatter "Ona, Egil"
-
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 estimates of 0-group fish abundance in the Barents Sea and adjacent waters in 1992 and 1993
Nakken, Odd; Hylen, Arvid; Ona, Egil (PINRO-IMR Symposium, Conference object, 1995)Acoustic and biological data collected during the international O-group surveys in 1992 and 1993 were used to estimate the abundance of O-group fish of 4 species; cod, haddock, redfish and polar cod. The abundances of ... -
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 ... -
Comparison of the capture efficiency of 0-group fish in pelagic trawls
Hylen, Arvid; Korsbrekke, Knut; Nakken, Odd; Ona, Egil (PINRO-IMR Symposium, Conference object, 1995)In 1992 and 1993 experiments were carried out during the international 0-group fish surveys in order to study the capture efficiency of two pelagic trawls. The catches of the standard sampling trawl were compared with ... -
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 ...