1. Resource Ecology Group, Wageningen Univ. and Research; Droevendaalsesteeg 3a NL-6708PB Wageningen the Netherlands
2. Inst. for Marine Resources and Ecosystem Studies (IMARES); Haringkade 1 NL-1976CP Ijmuiden the Netherlands
3. Zoological Research Museum Alexander Koenig (ZFMK); Adenauerallee 160 DE-53113 Bonn Germany
4. Dutch Montagu's Harrier Foundation, Conservation Ecology Group, Groningen Inst. for Evolutionary Life Sciences (GELIFES), Groningen Univ.; PO Box 11103, NL-9700 CC Groningen the Netherlands