THE SEA OF AZOV 527 



of the less saline parts and a decrease of the inflow of organic biogenic 

 subtances would lead to a drop in the level of biological productivity and 

 would have an unfavourable effect on the fisheries of the Sea of Azov. As 

 a result of the building of hydrological installations the feeding areas for 

 fish might be reduced and their passage into rivers for breeding might be 

 hindered. 



F. Mordukhai-Boltovskoy (1953) approaches this problem from a different 

 angle. He starts from the assumption that as things are at present (before the 

 construction of the Volga-Don canal) the Don waters bring into the Sea of 

 Azov an excess amount of plant food, which causes a superfluous develop- 

 ment of plankton and an over-accumulation of organic substances in the 

 central parts of the Sea ; this led to a constant oxygen deficiency and to the 

 suffocation of fish and bottom-fauna over large areas of the sea-bed. In this 

 worker's opinion the loss of 10 km 3 of river water and the freedom of reser- 

 voirs from suspended matter will have a favourable effect on the oxygen 

 conditions of the Sea and on the yield of fish, since it will free the Sea from 

 over-accumulation of organic matter. A loss of 20 km 3 of Don waters must 

 lead to a shortage of food supply and to a lowering of productive yield, 

 both as a result of that shortage and as a result of the great reduction of 

 habitat areas (low-salinity water) for semi-migratory fish. 



Later this problem was again considered by E. Yablonskaya (1955), 

 A. Karpevitch (1955) and a number of other investigators, and the results of 

 their work are given in a two-volume symposium Reorganization of Fisheries 

 in the Sea of Azov (1955). Yablonskaya does not share Mordukhai-Boltov- 

 skoy's view on the over-accumulation of organic substances on the bed of the 

 Sea of Azov. According to the data of T. Gorshkova (1955) such over- 

 accumulation has not been observed, and Yablonskaya therefore assumes that 

 the productive capacity of the Sea of Azov would not be improved by the 

 drop in the outflow from the river Don and by the settling down, as precipi- 

 tates in reservoirs, of the plant food substances which reached the Sea before 

 control of outflow from the river was fairly fully utilized. Yablonskaya there- 

 fore thinks that with a 15 per cent drop in the river outflow zooplankton 

 production, both in the Gulf of Taganrog and in the Sea proper, would be 

 somewhat lowered, while at a 50 per cent loss of river outflow Azov plankton 

 production might go down by about 40 per cent. Benthos biomass in the Gulf 

 of Taganrog might increase as a result of the immigration of larger-sized 

 components of fauna from the west, but its importance for feeding will be 

 reduced. In Yablonskaya's opinion (see also Stark) the benthos biomass of 

 the Sea of Azov proper would change little. Fish feeding on this mass of 

 organisms — the plankton eaters (mainly anchovy and Clupeonella) — will 

 be somewhat less in number. At present benthos-eating fish do not con- 

 sume all the benthos available, and when the river outflow is reduced they 

 will on the whole have enough food, although this will apply to a different 

 extent for different species offish. 



E. Yablonskaya (1957) describes the changes in the conditions of the Sea of 

 Azov connected with the control of the flow of the river Don in the following 

 way: 'the first 4 years (1951-55) were characterized by a reduction of the 



