caa a22 4500 397550871 CHVBK 20180308164749.0 cr unu---uuuuu 161202e199604 xx s 000 0 eng 10.1006/jmsc.1996.0054 doi (NATIONALLICENCE)oxford-10.1006/jmsc.1996.0054 Diel variation in the catchability of gadoids and its influence on the reliability of abundance indices [Elektronische Daten] [Kathrine Michalsen, Olav Rune Godø, Anders Fernö] Present management of the north-east Arctic cod and haddock stocks is based on scientific assessments of stock abundance. The assessment procedures apply acoustic and bottom-trawl survey indices of abundance for tuning of the VPA (virtual population analysis). The reliability of the survey indices is strongly dependent on the precision and accuracy of the fish sampling conducted with trawls. Variation in bottom trawl catches and vertical distribution of cod and haddock from a small area were studied with the aim of finding environmental factors of explanatory importance for the observed variation. Data were obtained over a period of three days from two vessels trawling in parallel, one of which simultaneously collected acoustic information on vertical distribution. Variation in catch size and length composition was analysed and related to the observed vertical distribution. The results show that tidal currents affect the vertical distribution of cod and haddock and, hence, the availability to the bottom trawl. On the other hand, light intensity apparently affects the catch efficiency of the sampling trawl. Consequently, the abundance estimates from acoustic and bottom-trawl surveys are affected by the interaction of diel rhythms in tidal current and light intensity. This illustrates the importance of monitoring the environmental factors that influence fish behaviour in order to increase the reliability of the abundance estimates. © 1996 International Council for the Exploration of the Sea Regular Articles nationallicence catch efficiency nationallicence diel variation nationallicence fish distribution nationallicence gadoids nationallicence light intensity nationallicence tidal currents nationallicence Michalsen Kathrine Institute of Marine Research PO Box 1870 Nordnes, N-5024 Bergen, Norway aut Godø Olav Rune Institute of Marine Research PO Box 1870 Nordnes, N-5024 Bergen, Norway aut Fernö Anders Department of Fisheries and Marine Biology, University of Bergen Bergen High Technology Centre, N-5020 Bergen, Norway aut ICES Journal of Marine Science Oxford University Press 53/2(1996-04), 389-395 1054-3139 53:2<389 1996 53 icesjms https://doi.org/10.1006/jmsc.1996.0054 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1006/jmsc.1996.0054 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Michalsen Kathrine Institute of Marine Research PO Box 1870 Nordnes, N-5024 Bergen, Norway aut NATIONALLICENCE 700 1- Godø Olav Rune Institute of Marine Research PO Box 1870 Nordnes, N-5024 Bergen, Norway aut NATIONALLICENCE 700 1- Fernö Anders Department of Fisheries and Marine Biology, University of Bergen Bergen High Technology Centre, N-5020 Bergen, Norway aut NATIONALLICENCE 773 0- ICES Journal of Marine Science Oxford University Press 53/2(1996-04), 389-395 1054-3139 53:2<389 1996 53 icesjms Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford