Journal article
Vertical migration and dispersion of sprat ( Sprattus sprattus ) and herring ( Clupea harengus ) schools at dusk in the Baltic Sea
Department of Informatics and Mathematical Modeling, Technical University of Denmark1
Section for Population- and Ecosystem Dynamics, National Institute of Aquatic Resources, Technical University of Denmark2
National Institute of Aquatic Resources, Technical University of Denmark3
Section for Fisheries- and Monitoring Technology, National Institute of Aquatic Resources, Technical University of Denmark4
Section for Management Systems, National Institute of Aquatic Resources, Technical University of Denmark5
In populations of herring (Clupea harengus) or sprat (Sprattus sprattus), one typically observes a pattern of schools forming at dawn and dispersing at dusk, usually combined with vertical migration. This behaviour influences interactions with other species; hence a better understanding of the processes could contribute to deeper insight into ecosystem dynamics.
This paper reports field measurements of the dispersal at dusk and examines two hypotheses through statistical modelling: that the vertical migration and the dissolution of schools is determined by decrease in light intensity, and that the dissolution of schools can be modelled by diffusion, i.e. active repulsion is not required.
The field measurements were obtained during 3 days in March at one location in the Baltic Sea and included continuous hydroacoustical monitoring, trawl samples, and hydrographical CTD data. Echogram patterns were analysed using the school detection module in Echoview® and local light intensities were calculated using a model for surface illuminance.
The data and the analysis support that schools migrate upwards during dusk, possibly trying to remain aggregated by keeping the local light intensities above a critical threshold, that schools initiate their dissolution when ambient light intensity drops below this critical threshold, and that fish subsequently swim in an uncorrelated random walk pattern.
Language: | English |
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Year: | 2003 |
Pages: | 317-324 |
ISSN: | 17652952 and 09907440 |
Types: | Journal article |
DOI: | 10.1016/S0990-7440(03)00039-1 |
ORCIDs: | Thygesen, Uffe Høgsbro , Lundgren, Bo , Nielsen, Bo Friis , Nielsen, J. Rasmus and Beyer, Jan |