Ice cover affects the growth of a stream-dwelling fish
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Protection provided by shelter is important for survival and affects the time and energy budgets of animals. It has been suggested that in fresh waters at high latitudes and altitudes, surface ice during winter functions as overhead cover for fish, reducing the predation risk from terrestrial piscivores. We simulated ice cover by suspending plastic sheeting over five 30-m-long stream sections in a boreal forest stream and examined its effects on the growth and habitat use of brown trout (Salmo trutta) during winter. Trout that spent the winter under the artificial ice cover grew more than those in the control (uncovered) sections. Moreover, tracking of trout tagged with passive integrated transponders showed that in the absence of the artificial ice cover, habitat use during the day was restricted to the stream edges, often under undercut banks, whereas under the simulated ice cover condition, trout used the entire width of the stream. These results indicate that the presence of surface ice cover may improve the energetic status and broaden habitat use of stream fish during winter. It is therefore likely that reductions in the duration and extent of ice cover due to climate change will alter time and energy budgets, with potentially negative effects on fish production.
KeywordsClimate change Energy budget Global warming Salmonid Winter
We deeply thank Oscar Askling, Teemu Collin and Lena Watz for their much appreciated help with the field work. We are also grateful to Anders Andersson, Lisette Carlsson, Åsa Enefalk, Anna Hagelin, David Höök, Simon Jonsson, Fredrik Laaksonen, Adam Lewenhaupt, Pia Larsson, Emmy Norrman, Raimo Neergard, Johnny Norrgård, Daniel Nyqvist and Anna Watz for assistance in the field. Karlskoga fiskevårdsförening, Sveaskog, Karlstad stift and the County Board of Örebro län generously let us work in their stream. We especially thank Jim Hellquist at Sveaskog, Martin Engström at the County Board of Örebro län and Peter Randén at Kedjeåsen Uteliv, who were all very supportive throughout the study.
Author contribution statement
JW formulated the idea, had a leading role in the study design, collected and analysed the data and wrote the paper. EB, JJP and LG contributed to the idea and to the study design and provided editorial advice.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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