Freshwater Fish Migration of Ob-Taz Mouth Region
The Analyses information of publications by the character of fish migrations in the Ob-Taz mouth region which includes delta of Ob river, Ob and Taz mouthes. The most significant influence on the character of migrations of fish this area have salted waters of the Kara Sea, especially in winter, and deficit of dissolved oxygen in water. In January - March the all South part Tazovskaya mouth and significant region of the southern zone of Ob mouth are in condition of oxigen deficit (zamor). Spring water refreshment (increasing the concentration of oxygen) in Ob mouth usually starts at the end of may - early June and continues 7-15 days. Destruction zamor zone in Taz mouth begin in 10-14 days later than in Ob mouth. Characteristic of reservoirs of this area is also relatively short periods of open water (period without ice cover) and its low temperature in summer. Realization of life cycle of inhabit here fish significantly is complicating by high rate change of these enumerate factors. In reservoirs of the Ob-Taz mouth region inhabit 35 species freshwater fishes, life cycle the majority which are realizing in fresh waters. Coregonus autumnalis and Coregonus sardinella spend the winter mainly in no zamor zone, but for in search of food (both species) and reproduction (onli C. sardinella) migrate in the rivers. Coregonus muksun, Coregonus nasus, Coregonus peled, Coregonus lavaretus pidschian and Stenodus leucichthys do not enter the salty water, but carry out the winter in the most southern of no zamor zone. In the fresh waters of estuaries carry out the winter and other species of the fishes. In the summer in the northern part of Ob mouth the most frequent meet C. autumnalis, C. sardinella, Triglopsis quadricornis and Liopsetta glacialis. In middle zone of Ob mouth from whitefish remains mainly C. sardinella. After spawning into this zone ofaquatorius migrate for search of food Osmerus mordax and Gymnocephalus cernuus. For G. cernuus, as the main object of power, should be Lota lota. In addition in the middle part of the Ob mouth and in northern region of Tazovskaya mouth feed in summer in a small number of Acipenser baerii and Acipenser ruthenus. In late July and early August starts spawn anadrom migration sexual maturity share herd Whitefish to places reproduction. Wintering migration of fishes in the Ob-Taz mouth region notes, as a rule, in late October - early November. Distribution of wintering fishes in no zamor zone of Ob and Taz mouthes is irregular and is connected, first of all, with degree of tolerance of fishes to water salinity. Throughout the winter period, fishes are constantly moving in search of food. Most of the fishes species upon the occurrence of oxygen deficiency migrate to areas with more favourable gas regime. With the advent of spring and the beginning of increasing the oxygen concentration in the water most fish populations approach to the border of zamor front. In the case of abnormal climate, as this has been observed in spring, 2007, the fishes are in zona of the zamor and mostly they die.