Preliminary results on the assessment of Danube River fish species migration behavior in relation to Iron Gate I and II dam using acoustic telemetry equipment

Abstract

The dam’s construction without fish passes had a major impact, obstructing migratory fish populations from moving between different parts of the river systems and utilizing their key habitats. Fish species and fish populations are depending on long migrations are most seriously affected by river fragmentation. Building well-functioning fish passage systems for migratory fish species at Iron Gate I (rkm 943) and Iron Gate II (rkm 863), is crucial for strengthening and re-establishing Danube’s River migratory fish populations. Between March and May 2021, 112 fish specimens were captured downstream Iron Gate II dam. All the fish was previously tagged with 69 KHz ultrasonic transmitters and released upstream Iron Gate II dam reservoir (53 fish) and downstream Iron Gate II dam (59 fish). Some of the acoustic transmitters are equipped with depth sensors, which provide information of water depths used by fish. Fish movements were recorded by a network of 18 ultrasonic automatic Vemco VR2w receivers (10 downstream the Iron Gate II dam and Gogosu branch, 6 in the IG II lake and 2 receivers at the Iron Gate I dam) with a 15 month battery life, positioned in Danube River. Downloading and interpreting recorded data by these receivers will be an important starting point for "We Pass 2" project that will begin in fall of 2021, when will be realized high resolution recordings of 3D fish movements, for finding the best technical solution for their passing upstream or downstream of dams.