Changes occurring over time in commercially exploited fish assemblages in lowland dam reservoirs

Changes in the ichthyofauna assemblages of three shallow dam reservoirs located in central and eastern Poland are presented based on long-term records of commercial fish catches. As the reservoirs age the evolution in the sizes of the shares of exploited fish species is depicted by temporal trend lines described with regression functions. The species targeted by commercial fishing are assigned to one of four ecological groups - predatory, eutrophying cyprinid, rheophilic, and others, depending on the role they play in the reservoir. Catches of cyprinid fishes from the eutrophying group increased in each of the reservoirs studied as the years passed. This was most notable in the Siemianówka Reservoir since in the period immediately following inundation the slope factor b trend line was 7.25 at r² = 0.9. The population of predatory fish was also noted to increase continually in this reservoir, and this was linked to intense stocking with pike, Esox lucius L. The shares of predatory fish in the other reservoirs decreased from inundation onwards, only to stabilize in recent years at minimal levels with slight increasing trends. As time passed from the inundation of the reservoirs the general dependency between the average shares of fish groups in catches was highly significant for all of fish groups identified.