In the months of April and May 2020, as part of the monitoring of the fish passes on the Drawa and Korytnica rivers, field tests were carried out within which it was checked whether the flowing smolt of migratory fish will use the fish pass to overcome the water barrage and also whether other species of fish can find the entrance to the fish pass and whether they are able to overcome it by swimming against the current. They were carried out on the fish passes on the Drawa (near EW Kamienna in Głusk and at MEW Koleśno in Drawsko Pomorskie) and on the Korytnica (in the towns of Sówka and Jaźwiny).
The research used the RFID (radio frequency identification) system. It includes marking fish with PIT (passive integrated transponder) stamps, which, when passing through an electromagnetic field, emit radio signals containing unique stamp codes. The field is produced by the so-called loop aerias that alternately generate an electromagnetic field and are aerials that receive a signal and transmit it to a decoding and recording receiver. These aerials were placed in fish passes.
In the study of smolt flow, 500 specimens of salmon smolt at the age of 2+ were marked. Apart from that, additionally from 183 to 414 other fish belonging to over 20 species were also marked in those places.
The study of the smolt flow (the fish pass at EW Kamienna) showed that only some of them flow down through the fish pass, and the vast majority of them flow with the mainstream and probably flow through turbines. The low percentage of smolts finding the fish pass during downward migration confirms the need for an installation directing the fish to the fish pass, the design of which is also being completed under the LIFEDrawaPL Project.
According to the research on the migration of tagged fish, fish of all the more numerous species, appearing both below and above the steps, were able to use the fish passes. There were also nonreophilic species and small specimens among them. This means restoring connection between the ichthyofauna above and below the investigated partitions, increasing the effective population size of post-modromous fish and the range of migratory fish.
Detailed results of the monitoring are available in the final report on the monitoring of the functioning of fish passes available in the Download section