ABSTRACT. A vertical slot fish ladder was constructed at the small hydro power plant in Świecie-Przechowo on the Wda River, a left tributary of the Vistula River. From 2008 to 2013, fish migration was recorded with a submerged video camera, the images were saved on memory devices, and the video was released on the Internet. This study analyzes the recorded material. Sixteen species of migrating fish were identified in the recordings, among which were diadromous vimba breams, eels, migratory sea trouts, salmons, and river lampreys. A great cormorant was also recorded using the ladder. The analyses permitted estimating the abundance and frequency of the migrations of various fish species through the ladder by month and also to observe fish behavior as they moved through the ladder. The behavior of fish immediately following stocking release was also observed. In May 2011, river lampreys were recorded that probably spawned in the ladder. The most numerous, frequently identified species was brown trout. At least some of the fish population identified as brown trouts were probably migratory sea trouts that had been released as stocking material but had not descended the river to the sea thus creating a “local” population. Large salmonid fishes (migratory sea trouts and/or salmons) migrated in fall, when 58 specimens were noted. Increasing numbers of vimba breams were noted annually. Fish migrating through the fish ladder were recorded mainly from April to July, and no fish were recorded from December to February. The analyses indicated that visual monitoring is an effective method with which to monitor fish. Combining this with other observation techniques permits obtaining even more precise, accurate information not only with regard to the numbers of migrating fish, but also regarding fish species identification, sex, and condition.
Keywords: fish ladder monitoring, fish migration, ichthyofauna of the Wda River
Przyjęto po recenzji 17.02.2014 r.