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Doctoral thesis2020Open access

Warmer and browner waters: fish responses vary with size, sex, and species

Van Dorst, Renee


Current understanding of fish population responses to climate change is often limited to studies on the effect of temperature, ignoring potential co-occurring changes in other environmental variables. However, next to getting warmer, temperate and boreal aquatic systems are getting browner due to increased concentrations of dissolved organic carbon. Studies also generally predict mean population responses to climate change, thereby ignoring the potential for size, sex, and also species-specific responses. 

In this thesis, I aim to study the effects of warmer and browner waters on individual and population level responses in fish, and investigate if these responses vary with size, sex, and between species (Eurasian perch, Perca fluviatilis or common roach, Rutilus rutilus). To do this I used multiple methods, including space-for-time analyses, a wholeecosystem warming experiment, and aquaria and mesocosm experiments. 

I found that both warming and browning of lakes will likely decrease fish biomass production. Warming may cause a shift in size-structure towards smaller perch individuals and a lower perch population biomass, while browning will likely affect perch biomass production through lower body growth. Body growth responses to warming likely depend on body size, as small but not large individuals in my study were positively affected by high temperatures, and also sex, as males were more negatively affected by warming than females. Responses to browning may vary with body size and between species, as I found browning had a stronger negative effect on body growth of larger individuals in perch, while in roach browning only affected very small individuals. 

Overall, my findings suggest that future warming and browning will negatively affect fish individuals and populations, but that responses will vary with size, sex, and species, with potential consequences for ecological interactions and ecosystem functioning. This thesis highlights the importance of considering multiple climate stressors, integrating responses across several levels of biological organization, and acknowledging withinand between species variation, in order to understand and predict fish population responses to further climate change. 


climate change; warming; browning; lakes; body growth; biomass production; ontogeny; size-specific responses; sex-specific responses; perch; roach

Published in

Acta Universitatis Agriculturae Sueciae
2020, number: 2020:38
ISBN: 978-91-7760-594-2, eISBN: 978-91-7760-595-9
Publisher: Swedish University of Agricultural Sciences, Department of Aquatic Resources