Diel variation in the vertical distribution and schooling behaviour of sardine (Sardina pilchardus) off Portugal

Juan Zwolinski, Alexandre Morais, Vitor Marques, Yorgos Stratoudakis, Paul George Fernandes

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35 Citations (Scopus)


Diel patterns in the schooling behaviour and vertical distribution of pelagic fish schools were studied by examining their echotraces from repeated acoustic survey transects at three inshore sites off the Portuguese coast. At two sites, sardine was the dominant pelagic species, and echotrace characteristics of fish schools were similar to those reported in the literature. At the third site, where there was a multispecies pelagic assemblage that included sardine, there was more variability in several of the school descriptors. At all sites, fish schools expanded after sunset, enlarging their cross-sectional area along the horizontal plane and reducing their mean internal acoustic density, while maintaining their overall mean abundance. Downward migration was rapid (within 1 h) after sunset and simultaneous with school expansion. School-like aggregations with total backscattering similar to daytime schools were present throughout the night, although the proportion of small schools and scattered fish appeared to increase at that time. At dawn, sardine rose back up the water column and rapidly reformed into the typical daytime schools. This pattern of diel vertical migration is opposite to that described for most clupeoids worldwide. The implications of this behaviour on abundance estimation by acoustic monitoring surveys for small pelagic fish are discussed.

Original languageEnglish
Pages (from-to)963-972
Number of pages10
JournalICES Journal of Marine Science
Issue number5
Early online date11 Jun 2007
Publication statusPublished - Jul 2007


  • acoustic surveys
  • clupeoids
  • diel cycles
  • schools
  • vertical migrations
  • Herring Clupea-Harengus
  • capelin mallotus-villosus
  • sprat sprattus-sprattus
  • pelagic fish schools
  • spatial-distribution
  • Mediterranean Sea
  • target-strength
  • Baltic Sea
  • patterns
  • density


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