Vertical distribution of Atlantic salmon (Salmo solar L.) in net pens: trade-off between surface light avoidance and food attraction

Abstract The vertical distribution of Atlantic salmon (Salmo salar L.) reared in marine net pens of 7 m depth was studied by means of an echo integration system in relation to temporal and environmental factors. Great variations in local densities were found. In summer up to 80% of the fish could be localized within a 1-m depth interval, whereas in winter the fish were more evenly spread out in the pen. High light levels resulted in deeper fish distribution. The fish usually descended at dawn and ascended at dusk and swam deeper in summer than winter, and there was a negative correlation between light level and fish density at the surface in summer. Feeding also influenced fish distribution most strongly in summer, with rapid upwards swimming when feeding started and a gradual descent during the course of feeding. The fish stayed generally deeper in a feeding regime with infrequent (twice daily) than frequent (every 10 min) feeding. The vertical distribution could largely be explained by a trade-off between light-induced surface avoidance and food attraction. Avoidance of the pen bottom and excessively high densities also seemed to play a role. The implications of the findings regarding choice of pen size, selection of feeding regimes and development of automatic feeding systems are discussed.

[1]  R. G. Randall,et al.  Atlantic Salmon: Planning for the Future , 1989 .

[2]  S. H. Jákupsstovu.  Exploitation and Migration of Salmon in Faroese Waters , 1988 .

[3]  Åsmund Bjordal,et al.  Surface activity of Atlantic salmon (Salmo salar L.) in net pens , 1993 .

[4]  Jon-Erik Juell,et al.  An ultrasonic telemetric system for automatic positioning of individual fish used to track Atlantic salmon (Salmo salar L.) in a sea cage , 1993 .

[5]  Jan Tore Øvredal,et al.  PC-based echo integration system for fish behaviour studies , 1988 .

[6]  Bjørn Totland,et al.  Monitoring Biological and Environmental Parameters in Aquaculture , 1987 .

[7]  Felicity A. Huntingford,et al.  Daily feeding rhythms in Atlantic salmon in sea cages , 1991 .

[8]  D. A. Levy.  Acoustic Analysis of Diel Vertical Migration Behavior of Mysis relicta and Kokanee (Oncorhynchus nerka) within Okanagan Lake, British Columbia , 1991 .

[9]  D. Levy,et al.  Sensory Mechanism and Selective Advantage for Diel Vertical Migration in Juvenile Sockeye Salmon, Oncorhynchus nerka , 1990 .

[10]  Anders Fernö,et al.  Influence of hunger level and food availability on the spatial distribution of Atlantic salmon, Salmo salar L., in sea cages , 1994 .

[11]  M. Phillips.  Behaviour of rainbow trout, Salmo gairdneri Richardson, in marine cages , 1985 .

[12]  C. Clark,et al.  Diel Vertical Migrations by Juvenile Sockeye Salmon and the Antipredation Window , 1988, The American Naturalist.

[13]  A. Sutterlin,et al.  Thermal behaviour of rainbow trout and Arctic char in cages moored in stratified water , 1992 .

[14]  A. Johannessen.  Early stages of Lepeophtheirus salmonis (Copepoda, Caligidae) , 1977 .

[15]  J. Muir,et al.  Recent Advances in Aquaculture , 1982, Springer Netherlands.

[16]  S. L. Lima,et al.  Behavioral decisions made under the risk of predation: a review and prospectus , 1990 .

[17]  Åsmund Bjordal,et al.  A multiple approach to behaviour studies of salmon reared in marine net pens , 1988 .

[18]  A. Fernö.  Aggression and growth of Atlantic salmon parr. I. Different stocking densities and size groups , 1986 .

[19]  John D. Neilson,et al.  Diel vertical migrations of marine fishes: an obligate or facultative process? , 1990 .

[20]  A. Fernö,et al.  The effect of shading in pen rearing of Atlantic salmon (Salmo salar) , 1990 .