In October 2020, the Inland Fisheries Institute from Olsztyn presented the final results of the fish pass’ monitoring at the Kamienna EWC carried out with the use of “a scanner”.
The task was carried out with the Riverwatcher fish counter (scanner) produced by the Icelandic company VAKI Aquaculture Systems Ltd., placed in the outlet slot of the fish pass. The Riverwatcher fish counter uses the infrared scanning method. It consists of two plates, 20 by 60 cm, fixed in a frame 40 cm apart. On one plate there are diodes emitting infrared light beams received on the other plate. A flowing object (fish) cuts this net and on this basis its silhouette is created; since there are two parallel rows of LEDs and receivers, there are also two silhouettes for each object. The extension of this counter is a steel tunnel 1.05 m long. In it there is a camera and “day” or infrared lighting. The recording device records each moving object with the exact time of the event, the direction and speed of movement and the height of the object; its length is calculated from the height and the length to height ratio set by the user. A short film is attached to each record. According to the manufacturer, the minimum height of reliably registered objects is 40 mm (http://www.riverwatcher.is/). In addition, the counter measures and records the water temperature every three hours.
The counter was put into operation for the first time in September 2019, however, the full analysis of the fish passing through the pass was carried out from 7th October, 2019 to 7th October, 2020. In the initial period in autumn 2019, the operation of the counter and the fish pass was disturbed by a very intense runoff of dying water vegetation and leaves. This problem was solved in December. In addition, due to some failures, the counter did not work in the period from 11th to 26th May, 2020 and from 1st to 14th July, 2020.
During the period under review, the counter recorded 822 fish: 640 of them swam upwards and 182 downwards. They represented 20 species. The most numerous were vimba, chubs and roaches. There were two main periods of fish migration through the fish pass: autumn, with a peak in October, connected with the cooling of the water, in which mainly autumn spawning salmons were recorded (brown trout, salmon, sea trout) as well as vimba and roaches, and spring, with a peak in April-June, when the water heats up, in which mainly vimba and chubs migrated.
In the studies conducted with the use of the Vaki counter in the old fish pass (before the reconstruction) at the Kamienna barrage between 2008-10 (Dębowski and Gancarczyk 2013), only 150 fish swimming upstream were registered in two years time. Much less than in the study discussed here, which lasted only one year. The results obtained indicate a significant improvement in the conditions of fish migration, restoration of connection between the ichthyofauna above and below the tested compartment, increase in the effective population size of potamodromous fish and the range of migratory fish.
The results obtained during this monitoring broadened our knowledge of the ichthyofauna of the middle course of the Drawa. It turned out that in the Drawa a small anadromous population of vimba still migrates – it has not been recorded on this section of the river for several decades, there is a catadromous migration of eels, and small sums flow down the river, so far not recorded here (Czerniawski et al. 2016, Dębowski and Bernaś 2017).
The full content of the report is available in the “Reports on implementation” tab.
Pomimo zakończenia monitoringu przepławki przez Instytut Rybactwa Śródlądowego z Olsztyna, Despite the completion of the monitoring of the fish pass by the Inland Fisheries Institute from Olsztyn, the device installed in the fish pass enables constant, ongoing monitoring of species crossing the facility, as evidenced by its records from the last period. Below there are a few videos of species recorded in December 2020.