caa a22 4500 39755060X CHVBK 20180308164749.0 cr unu---uuuuu 161202e199610 xx s 000 0 eng 10.1006/jmsc.1996.9999 doi (NATIONALLICENCE)oxford-10.1006/jmsc.1996.9999 Tilt angle distribution and swimming speed of overwintering Norwegian spring spawning herring [Elektronische Daten] [Ingvar Huse, Egil Ona] When plankton production in the feeding areas decreases in the fall, adult Norwegian spring-spawning herring migrate into two fjords in northern Norway. In these wintering areas the herring occupy deeper water. Lacking the ability to refill the swimbladder they are constantly negatively buoyant. This leads to different adaptive behaviour during the day and at night, behaviour which is reflected in swimming angle. Split-beam tracking methods and still-frame photography have been used to study the herring behaviour inside the dense wintering schools. Negative buoyancy seems to be controlled through constant swimming at speeds between 0.25-0.42 ms−1 because these are sufficiently high to generate lift when the pectoral fins are used as spoilers. During the day, when the layers aggregate, the average swimming angle is close to horizontal while positive average swimming angles of up to 40° were recorded at night. A bimodal distribution of tilt angles, with one positive and one negative component, indicating a "rise and glide” swimming strategy was also observed at night. Vertically undulating split beam tracks confirmed this particular type of swimming behaviour. As adult herring are directional targets at the echo-sounder frequency used for acoustic assessment of the stock, the possible impact of the observed tilt angles on average acoustic target strength is discussed. © 1996 International council for the Exploration of the Sea Articles nationallicence herring nationallicence acoustics nationallicence tilt angle nationallicence swimming speed nationallicence Huse Ingvar Institute of Marine Research, P.O. Box 1870, N-5024, Bergen, Norway aut Ona Egil Institute of Marine Research, P.O. Box 1870, N-5024, Bergen, Norway aut ICES Journal of Marine Science Oxford University Press 53/5(1996-10), 863-873 1054-3139 53:5<863 1996 53 icesjms https://doi.org/10.1006/jmsc.1996.9999 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1006/jmsc.1996.9999 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Huse Ingvar Institute of Marine Research, P.O. Box 1870, N-5024, Bergen, Norway aut NATIONALLICENCE 700 1- Ona Egil Institute of Marine Research, P.O. Box 1870, N-5024, Bergen, Norway aut NATIONALLICENCE 773 0- ICES Journal of Marine Science Oxford University Press 53/5(1996-10), 863-873 1054-3139 53:5<863 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