Talk Niels Jepsen

Hydrobiological Seminar 2021-11-25

The documentation of cormorant impact on river fish

Dr. Niels Jepsen, National Institute of Aquatic Resources, Section for Freshwater Fisheries Ecology, DTU Aqua, Silkeborg, Dänemark

In Denmark, the conflicts and problems associated with increasing predation pressure from cormorants have reached a new level during the last decade. The main reason is the fact that the birds have extended their forage areas to include rivers and even small streams. The Danish rivers have been greatly improved (restored) during the recent 25 years and the removal of dams and renaturation of rivers also gave high increase in migratory fish populations. This development has unfortunately been nullified by the cormorant predation, giving much frustration in anglers, managers and river conservation fora’s. To address the problems, documentation is necessary and DTU Aqua has carried out extensive studies of the impact of predation in rivers and lakes and the results and methods are presented here. I will also discuss with you how the documentation have influenced current cormorant management in Denmark.

Homepage of Dr. Jepsen

Additional Literature

C. Dieperink, S. Pedersen, M. I. Pedersen (2001). DieEstuarine predation on radiotagged wild and domesticated sea trout (Salmo trutta L.) smolts. Ecology of Freshwater Fish 10 (3), 177-183. https://doi.org/10.1034/j.1600-0633.2001.100307.x
C. Dieperink, B. D. Bak, L.-F. Pedersen, M. I. Pedersen, S. Pedersen (2005). Predation on Atlantic salmon and sea trout during their first days as postsmolts. Journal of Fish Biology 61 (3), 848-852. https://doi.org/10.1111/j.1095-8649.2002.tb00917.x
N. Jepsen, E. Holthe, F. Okland (2006). Observations of predation on salmon and trout smolts in a river mouth. Fisheries Managemant and Ecology 13 (5), 341-343. https://doi.org/10.1111/j.1365-2400.2006.00509.x
A. Koed, H. Baktoft, B. D. Bak (2006). Causes of mortality of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in a restored river and its estuary. River Research and Application 22 (1), 69-78. https://doi.org/10.1002/rra.894
N. Jepsen, R. Klenke, P. Sonnesen, T. Bregnballe (2010). The use of coded wire tags to estimate cormorant predation on fish stocks in an estuary. Marine and Freshwater Research 61, 320-329. https://doi.org/10.1071/MF09038
M. Boel (2012). Life history types and strategies: Case studies on brown trout (Salmo trutta) and alewives (Alosa pseudoharengus), involving physiological differences and interspecific interactions. Ph.D. thesis, National Institute of Aquatic Resources, Section for Freshwater Fisheries Ecology, https://orbit.dtu.dk/en/publications/life-history-types-and-strategies-case-studies-on-brown-trout-sal
C. Skov, N. Jepsen, H. Baktoft, T. Jansen, S. Pedersen, A. Koed (2014). Cormorant predation on PIT-tagged lake fish. Journal of Limnology 73 (1), 177-186. https://doi.org/10.4081/jlimnol.2014.715 N. Jepsen, H. D. Ravn, S. Pedersen (2018). Change of foraging behavior of cormorants and the effect on river fish. Hydrobiologia 820, 189–199. https://doi.org/10.1007/s10750-018-3656-2
S. Hansson, U. Bergström, E. Bonsdorff, T.Härkönen, N. Jepsen, L. Kautsky, K. Lundström, S.-G. Lunneryd, M. Ovegård, J. Salmi, D. Sendek, M. Vetemaa (2018). Competition for the fish – fish extraction from the Baltic Sea by humans, aquatic mammals, and birds. ICES Journal of Marine Science 75 (3), 999–1008. https://doi.org/10.1093/icesjms/fsx207
N. Jepsen, H. Flávio, A. Koed (2019). The impact of Cormorant predation on Atlantic salmon and Sea trout smolt survival. Fisheries Management and Ecology 26 (2), 183-186. https://doi.org/10.1111/fme.12329
K. Källo, H. Baktoft, N. Jepsen, K. Aarestrup (2020). Great cormorant (Phalacrocorax carbo sinensis) predation on juvenile down-migrating trout (Salmo trutta) in a lowland stream. ICES Journal of Marine Science 77 (2), 721–729. https://doi.org/10.1093/icesjms/fsz227

Talk Niels Jepsen

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