Cormorant Predation Effects on Fish Populations

Cormorants are highly effective piscivorous birds whose expanding populations in freshwater and coastal habitats have prompted extensive research into their effects on fish stocks. Predation pressure by cormorants can alter fish abundance, size structure and community composition, with potential consequences for commercial and recreational fisheries. Studies employ diverse approaches—diet analyses, population modelling, bioenergetic assessments and meta‐analyses—to quantify consumption rates and resultant mortality in both temperate and boreal systems. In many regions, cormorant predation coincides with human exploitation of shared fish resources, giving rise to conflict and debate over sustainable harvest levels. Ecologically, intense predation may reduce recruitment of vulnerable age classes, shift predator–prey dynamics and cascade through food webs, affecting ‟keystone” and bycatch species. Conversely, some research highlights compensatory increases in fish growth and reproduction following partial predation losses. Understanding the context‐dependence of these interactions is critical: factors such as prey availability, habitat complexity and seasonal movements of both cormorants and fish regulate the net impact on fish populations. Global analyses underscore taxon‐specific responses and variable effect sizes, while regional case studies demonstrate how ecological, social and economic dimensions must be integrated in management. Insights into cormorant foraging ecology, their spatial use of foraging grounds and the finescale origins of prey have informed ecosystem‐based fisheries management and non‐lethal mitigation strategies, including habitat modification and targeted deterrents. Overall, research reveals that cormorant predation effects are complex, context‐dependent and of global significance for biodiversity conservation and fisheries sustainability.

Research from Nature Portfolio

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Cormorant Predation Effects on Fish Populations publication trend

The graph below shows the total number of articles in cormorant predation effects on fish populations across all publications each year (not limited to Nature Index journals).

Technical terms

Piscivorous: Feeding primarily on fish.

Biomass: The total mass of a given population of organisms in a particular area.

Predation mortality: The proportion of a prey population removed by predators over a specified period.

Effect size: A quantitative measure of the magnitude of a phenomenon, such as the impact of predation on fish numbers or biomass.

Meta‐analysis: A statistical method that combines results from multiple studies to identify overall patterns and effect estimates.

References

1. Knowledge co-production around the cormorant-fishing conflict using a joint fact-finding approach. Environmental Science & Policy (2024).
2. Estimation of Fishery Losses from Great Cormorants during the Wintering Period in Greek Lagoons (Ionian Sea, W. Greece). Sustainability (2023).
3. Cormorant predation effects on fish populations: A global meta‐analysis. Fish and Fisheries (2021).
4. Microchemical provenancing of prey remains in cormorant pellets reveals the use of diverse foraging grounds. Journal of Wildlife Management (2022).