Sø. Foto: Joan Holst Hansen

PhD defense about spatial ecology of lake fish

Friday 09 Mar 18


Joan Holst Hansen
PhD Student
DTU Aqua
+45 35 88 31 07

Time & Place

Friday, 16 March 2018, 10:00 am.

Building M
Vejlsøvej 51
8600 Silkeborg


A copy of the thesis "Spatial ecology of lacustrine fishes: ecological effects and applied aspects" is available for reading at DTU Aqua. Please contact Christine Hastrup, chci@aqua.dtu.dk

When animals move from one habitat to another, it may affect the stability of the entire ecosystem. PhD Student Joan Holst Hansen has investigated the migratory behavior of lake fish and the impact on the ecosystem. On 16 March she will defend her thesis

Animals move between habitats to increase foraging opportunities and reproductive success or to avoid predation and unfavorable conditions. The migratory behavior may potentially affect the stability and dynamics of entire ecosystems, e.g. by altering the density of prey fish within and between habitats. In her PhD thesis Joan Holst Hansen from DTU Aqua focus on how spatial ecology of fish in lakes influence lake ecosystems. 

One part of the thesis explores how migration of prey fish like roach and bream influences feeding and fitness of pike, which is the top predator in many lakes. Joan Holst Hansen’s studies show that if roach and bream leave a lake during winter, the density of prey in the lake may be reduced to such a low level that the pikes in the lake turn out to be in a poorer condition compared to pikes in lakes where prey do not migrate out of the lake.

Among other things, the PhD thesis also explains how the activity behavior of bream can affect water quality. While feeding, the bream disturb the soft bottom-material, so that sediment is dissolved into the water column making the water unclear. Joan Holst Hansen has studied day-to-day relationships between bream activity and water clarity and demonstrates that there are seasonal differences. She also shows that knowledge about bream movement patterns can be used to understand why some lakes sometimes abruptly switch from a clear water state to an unclear state. 

About the defense

Friday, 16 March 2018, 10:00 a.m., Joan Holst Hansen will defend her PhD thesis "Spatial ecology of lacustrine fishes: ecological effects and applied aspects". The defense takes place at Ferskvandscenteret, Building M, Vejlsøvej 51, 8600 Silkeborg.


  • Principal supervisor: Associate Professor Christian Skov, DTU Aqua
  • Co supervisor: Researcher Jakob Brodersen, Eawag, Schwizerland


  • Senior Researcher Søren Berg, DTU Aqua
  • Researcher Carolyn Rosten, Norwegian Institute for Nature Research, Norway
  • Docent Mikko Johannes Olin, University of Helsinki, Finland

Chairperson at defense

  • Deputy Director Anders Koed, DTU Aqua