1 Wildlife Estonia, Veski 4, Tartu 51005, Estonia.
2 Estonian Marine Institute, University of Tartu, Vanemuise 46, Tartu 51014, Estonia.
3 Chair of Hydrobiology and Fishery, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 5, Tartu 51006, Estonia.
4 Norwegian Institute for Nature Research NINA, PO Box 5685, Trondheim No-7485, Norway.
5 Technical University of Denmark, National Institute for Aquatic Resources, Silkeborg 8600, Denmark.