Fulfilling spawning flow requirements for potamodromous cyprinids in a restored river segment

Area of Science:

• River ecology and restoration science.
• Ichthyology and fish migration studies.
• Hydroelectric impact assessment and mitigation.

Background:

• The Baixo Sabor hydroelectric scheme (operational since 2015) has blocked fish migration, causing loss of spawning habitats for the Iberian barbel (Luciobarbus bocagei).
• The Vilariça River, downstream of the dam, was selected for habitat rehabilitation to compensate for the lost spawning grounds.

Purpose of the Study:

• To assess the effectiveness of habitat restoration in the Vilariça River as a compensatory measure for Iberian barbel spawning.
• To identify and model suitable spawning habitats for Luciobarbus bocagei.

Main Methods:

• Restoration involved constructing submerged weirs with fish ramps, bank reinforcement, boulder placement, and increasing river water flow via reservoir water diversion.
• A 1D hydrodynamic model coupled with CASiMiR software was used to determine the weighted usable area for barbel spawners.
• Field observations documented fish migration timing, water conditions, and habitat preferences of different life stages.

Main Results:

• Nine suitable spawning grounds were identified in the rehabilitated Vilariça River.
• Iberian barbel migration initiated in mid-April, coinciding with increased water temperature (approx. 16°C) and decreased water flow.
• Spawning occurred in coarse substrates with shallow water and moderate currents; juveniles and females exhibited distinct habitat preferences, with maximum suitability at ~1.5 m³/s.

Conclusions:

• The habitat restoration successfully created functional spawning grounds for Iberian barbel.
• The habitat suitability model proved accurate in predicting spawning site occurrence, serving as a valuable tool for river managers.
• Ecological flow management and habitat engineering can effectively mitigate impacts of hydroelectric dams on potamodromous fish populations.