FISH REMOVAL IN LJUBLJANSKO BARJE: PROTECTING AMPHIBIANS FROM INVASIVE SPECIES

As part of ongoing amphibian monitoring in newly excavated ponds in Ljubljansko barje, we discovered an unwelcome resident – the invasive pumpkinseed sunfish (Lepomis gibbosus). These ponds were created to serve as habitats for amphibians, but the presence of fish, particularly invasive species, can significantly disrupt this delicate ecosystem.

Why Do Fish Pose a Threat in Amphibian Habitats?

Fish, especially invasive species, pose a serious threat to amphibians. Some of them prey on amphibian eggs, larvae, and even adult amphibians. Herbivorous species feed on aquatic plants that amphibians use for attaching their eggs and as hiding spaces. As a result, many amphibian species tend to avoid waters inhabited by fish, causing a decrease in reproduction site availability.

Invasive species like the pumpkinseed sunfish are particularly harmful because they outcompete native species and threaten biodiversity. In September, after confirming the presence of this invasive species in some of our ponds, electrofishing was conducted to remove them from the ponds.

Amphibians need fish-free environments to reproduce. Regular removal of invasive species is crucial to creating and maintaining safe breeding habitats. This not only helps preserve biodiversity of these ecosystems and ensures the long-term survival of amphibian populations.

The Pumpkinseed Sunfish: An Invasive Threat

Native to North America, the pumpkinseed sunfish was originally introduced to Europe as an ornamental fish for ponds and as food for larger predatory fish. This species is highly adaptable and can rapidly populate new environments. Its predatory nature makes it a serious threat to local biodiversity. We believe that recent floodwaters likely carried these fish into the ponds.

What is Electrofishing?

Electrofishing is a safe and efficient method that can be used to control invasive species. By using electric current, fish are temporarily stunned, allowing for their safe removal or relocation. This technique enables the targeted removal of harmful species like the pumpkinseed sunfish, helping to restore balance to the ecosystem without harming other species.