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Research article - Peer-reviewed, 2021

Cormorant predation effects on fish populations: A global meta-analysis

Ovegard, Maria K.; Jepsen, Niels; Nord, Mikaela Bergenius; Petersson, Erik


This paper provides the results from the first meta-analysis to examine the impact of cormorant (Phalacrocoracidae) predation on fish. It is based on a systematic search of literature, covering studies using significance-based hypotheses tests on the relation between fish parameters and cormorant abundance. The results show that extensive research on cormorant diet exists, but few studies use statistical hypotheses testing to examine the effect on fish populations. In total, 603 publications were identified from titles and abstracts, to include the interaction between cormorants and fish. From these, 27 articles tested fish population parameters against cormorant predation, whereof 22 could be included in analyses. The effect size was defined negative in cases when cormorant numbers or presence reduced fish numbers or biomasses, or when individual fish sizes decreased, and vice versa for a positive effect. In a hierarchical dependence model, the combined effect of cormorant predation on fish was negative, but the overall effect was not significant at the 95% confidence level (-0.169, 95% C.L. -0.505 to 0.167, p = .256, df = 5.26). A covariate analysis revealed a difference in predatory effects between fish prey taxa (p = .006, df = 5.73), but no difference in effect sizes between study type, foraging habitat, or response variable measured. The meta-analysis reveals a complex interaction between cormorants and fish, but adds to the consensus on the importance of considering cormorant predatory effects in research, conservation actions, ecosystem-based management, and environmental monitoring.


cormorant; effect; management; meta‐analysis; Phalacrocorax; predation; wildlife‐conflict

Published in

Fish and Fisheries
2021, volume: 22, number: 3, pages: 605-622
Publisher: WILEY

Authors' information

Swedish University of Agricultural Sciences, Department of Aquatic Resources
Jepsen, Niels
Technical University of Denmark
Bergenius, Mikaela (Bergenius Nord, Mikaela)
Swedish University of Agricultural Sciences, Department of Aquatic Resources
Swedish University of Agricultural Sciences, Department of Aquatic Resources

Associated SLU-program


Sustainable Development Goals

SDG14 Life below water

UKÄ Subject classification

Fish and Aquacultural Science

Publication Identifiers


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