How barriers shape freshwater fish distributions: a species distribution model approach

Barriers, from dams to culverts, continue to be built globally despite their well-known negative effects on freshwater ecosystems. While large barriers strongly influence distribution through habitat fragmentation, the effects of smaller barriers on the distribution patterns of many fish species remains poorly studied. Obstruction metrics were calculated including different types and magnitudes of barriers considering upstream, downstream or barriers within a 10 km stream network distance. These were then included in species distribution models (SDMs) of 20 fish species and compared to predictions without barriers to understand their effects on fish distributions. Barriers were important for the predictions of many fish species with the metric upstream barriers being the most relevant barrier predictor across the fish community. With the inclusion of barriers, most species saw a reduction in their predicted range and habitat suitability decreased, suggesting habitat fragmentation and indicating a higher extirpation risk. Predictions from this SDM application point out how and where barriers influence fish distributions in the studied catchment. This species-specific and spatially-explicit information is highly valuable for target-oriented river restoration measures, biodiversity conservation efforts and catchment management in general.