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Foraging efficiency and prey selectivity in a visual predator: differential effects of turbid and humic water

  • Mikael Jönsson
  • Lynn Ranåker
  • Anders Nilsson
  • Christer Brönmark
Publishing year: 2013
Language: English
Pages: 1685-1690
Publication/Series: Canadian Journal of Fisheries and Aquatic Sciences
Volume: 70
Issue: 12
Document type: Journal article
Publisher: National Research Council Canada

Abstract english

Predators exert strong regulating forces on lower trophic levels through predation. As most fish are visual foragers, visual conditions in the water may alter the strength of this regulation. We evaluated effects of turbidity and humic water on foraging efficiency and prey-size selectivity in Northern pike (Esox lucius) feeding on roach (Rutilus rutilus). Encounter rates decreased in both turbid and humic water but were not counteracted by increased searching activity. Capture success was unaffected by turbidity but was nonlinearly affected by humic water by being high in clear and highly humic water but low in less humic water. In highly humic water, the visual range approached pike's strike distance and, together with its cryptic colours, pike may have initiated its attack before the prey detected it, limiting the possibility for prey evasive manoeuvres. Prey-size selectivity towards small prey in clear water disappeared in turbid water but was maintained in humic water. Owing to its optical properties, turbidity degrades the quality of the visual information more through scattering than humic water does through absorption. We show that the effect of visual degradation on foraging depends on the cause of visual degradation, which has not previously been acknowledged in the visual foraging literature.


  • Ecology
  • Zoology


  • ISSN: 1205-7533
Anders Nilsson
E-mail: anders [dot] nilsson [at] biol [dot] lu [dot] se


Aquatic ecology

+46 46 222 83 65

+46 70 346 25 66



Research group

Aquatic Ecology


Doctoral students and postdocs

Main supervisor

Varpu Pärssinen

Assistant supervisor

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