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Environmental conditions in River Rioni (Georgia) were studied in two seasons, during purported spawning migrations of the common sturgeon. Water temperature and flow velocity were measured in the vicinity of Poti (downstream section of the river) and in the potential spawning areas. At comparable times, water temperature in the spawning grounds was by a few degrees lower than that downstream, the flow velocity being higher and ranging within 1.5 - 2.1 m s-1. As shown by the observations, the area suitable for the sturgeon spawning had shrunk, possibly as a result of river damming. In the areas suitable for the common sturgeon spawning, the river bed was covered by coarse gravel and flattened stones, those measuring up to 30 mm in diameter being most abundant.
Background. Considerable amounts of fish bones and scales were discovered in 1953-1963, in an archaeological excavation pit situated in a former Vegetable Market in Szczecin, on the left bank of River Odra. Materials and Methods. Bone remains comprising 725 labelled collections from various dated sediment layers were identified. Individual bones were compared to those of corresponding extant fish species from water bodies near Szczecin and were identified to bone type and assigned to species. The scales were identified as well. Results. A total of 10 085 (76.2%) bone remains, out of 13 229, could be identified. They belonged to 20 fish species. Most abundant were remains of carp bream (Abramis brama), zander (Sander lucioperca), roach (Rutilus rutilus), tench (Tinca tinca), wels catfish (Silurus glanis), European perch (Perca fluviatilis), northern pike (Esox lucius), and sturgeon (Acipenser sturio). Conclusion. The majority of fish species targeted by early-mediaeval fishermen are also very important in the present-day fisheries in the area. It can be presumed that intensive sturgeon fishery in early Middle Ages markedly contributed to the species′ extinction from the area.
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