1. Critical problems for migratory fish in the North Sea region from a Danish perspective By Kim Aarestrup, Anders Koed & Niels Jepsen Technical University of Denmark

2. Overview: Management setup in Denmark A fundamental aspect Overall problems Weirs How to obtain information on moving animals (you can’t see) Examples of studies and consequences of result Does recommendations work?

3. “The Management Model for Diadromous Fish populations in Denmark” Goal: Self-sustaining populations Management system - Habitat restoration - Population restoration Research and Monitoring Legislation - Ministry of Fisheries - Ministry of the Environment Stakeholders - Anglers - Fishermen

5. Gross 1987

6. Migrating Sea residence Downstream migration Spawning Hatching Spawning migration Lifecycle – a fundamental aspect

7. Causes of the decline Sewage and waste-water caused habitat loss and habitat degradation. Dredging and canalization caused habitat loss and habitat degradation. Over fishing

8. Establishment of Mill ponds (1000 – 1850), Hydropower development (1920 – 1970) and Fish farming (1894 – 1975). Caused habitat loss, habitat degradation and impaired migration.

9. A Significant problem

10. Otterstrøm (1938) and Statistic yearbooks, the Ministery of Fisheries Number of salmon caught in Ringkøbing Fjord

11. Number of rivers and streams with trout populations in Denmark - retrospective

12. Investigating the migration of fish – methods? TELEMETRY Limitations: Low numbers Tagging and handling effects Animal welfare/ethics Cost and labour intensive Advantages: Only way to get this type of information Clear results Easy to understand Easy to explain

13. Release 1 Release 2 Weir Trap Loss calculated as the relative difference in recapture. Delay Calculated as the difference in 50 % fractile Loss can be related to e.g.. Flow released for fish passage

14. Smolt loss at barriers Aarestrup et al. In prep

15. TANGE RESERVIOR

16. N=8 N=10 N=4

17. Loss is cumulative! Number of weirs to pass Survival in percent

18. River Villestrup Å, Total 22 m, app. 9 m i 6 weirs (app. 40 %) Weir A Water surface Weir B Distance from source Height above sea-level Stream bed Another serious aspect

19. ..migration barriers have been removed and habitats restored

20. Successful restoration of salmon populations is based on knowledge obtained from research and monitoring Salmon spawning-run - River Skjern

24. Population development sea trout – River Villestrup