Landscapes of the Tobol-Ishim interfluve were not stable in the Holocene and varied from forests and drowned floodplains at the beginning of the V and III millennia BC to steppificated territories with a lowered water level at the beginning of the Atlantic Period and in the middle of the Subboreal Period, which determined the main types of economic activities, one of them was fishing. Changes in hydrological regime of water bodies influenced the methods of fishing, including the use of different traps. Thus, in the Neolithic, when the water level decreased, the location of settlements in the system river-creek-lake (for example, Mergen 6), a large number of fish bones, bone harpoons, fishing spears, fishing tackles for catching pike and a total absence of plummets were indicative of individual fishing for large fish and, perhaps, of stop net fishery, which was facilitated by a decrease in the width of watercourses and tombolos. Stop net (stake net) fishery led to a settled lifestyle of the population, collective activities and the emergence of long-term settlements with deep foundation pits of dwellings. When the water level in rivers and lakes increased and floods became more frequent, the life support system changed, the population began to develop coasts more widely, its mobility increased, and they started to build framed above-ground dwellings. Following those changes, biconic, cigar-shaped, and corniculate plummets emerged in the Tobol River Basin and on the adjacent western and north-western territories in the III and early II millennium BC. When the water level was high, it was efficient to fish using traps, seines and, probably, nets, although the latter could also be used in drive hunting for shedding geese and ducks. Subrectangular plummets with one or two ties for fastening, and disk-shaped plummets with a tie in the center had been prevailing since the beginning of the II millennium BC; they existed until the first third of the I millennium BC. This period, the transition time from the Bronze Age to the Early Iron Age, is characterized by the absence of clay plummets, while there are large accumulations of fish scales and bones in the settlement layers. We can suppose that the population of that time (local Late Bronze Age population, mixed with northern migrants who made utensils with cross ornamentation) switched from net fishing to stop net fishing.
Dynamics of plankton biocenoses under water level fluctuations in steppe lakes
