Water level regulation affects niche use of a lake top predator, Arctic charr ( Salvelinus alpinus)

• Published in: Ecohydrology
• Main Authors: Eloranta, Antti P., Sánchez‐Hernández, Javier, Amundsen, Per‐Arne, Skoglund, Sigrid, Brush, Jaclyn M., Henriksen, Eirik H., Power, Michael
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Arctic; Arctic charr; Salvelinus alpinus
• Online Access: http://dx.doi.org/10.1002/eco.1766; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Feco.1766; https://onlinelibrary.wiley.com/doi/pdf/10.1002/eco.1766; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/eco.1766

Abstract Water level fluctuations are expected to deteriorate the littoral zone in heavily regulated hydropower reservoirs, but there is limited empirical evidence of how food webs and fish populations are affected. We contrasted the size, growth, condition, niche use (i.e., habitat and diet), and parasite infection of allopatric Arctic charr ( Salvelinus alpinus ) populations in two neighboring and comparable Norwegian mountain lakes. We hypothesized that the presumed abiotic and biotic deterioration of the littoral zone would lead to reduced abundance and growth as well as to increased pelagic niche use and reduced niche width of the charr in the heavily regulated Govdajavri (maximum regulation amplitude 24 m) as compared with the unregulated Cazajavri. Our stable isotope and parasite data showed that charr had a slightly narrower and more pelagic feeding niche in the regulated than in the unregulated lake. The relative abundance of charr was lower in the regulated lake, but no between‐lake differences were observed in charr condition, and the charr grew slightly faster in the regulated than in the unregulated lake. Our study suggests that impaired littoral production can alter food webs in alpine hydropower reservoirs and induce a pelagic niche shift by top predators. These results argue for further investigations of hydropower impacts on lake food webs along with other factors that influence the abundance and niche use of fish, such as intraspecific interactions and compensatory growth, which may partly mask the potential impacts.