Fish and aquatic invertebrates represent the Danube Natural Reserve aquatic fauna.
The fish population is an important component of the Delta's biodiversity. Fish play an important role in the tropic chain. Moreover, no other component of the fauna has the same economic importance.
The extremely large biodiversity and large density of the fish population is due to the diversity of the natural conditions and by the dimensions of the Danube Natural Reserve. In accordance with the data communicated by the Hydrobiological Institute, 95 fish families live here pertaining to 31 families, including the fish listed in L.R.E., namely sturgeons (as the atlantic sturgeons) salmons (Black Sea and Danube salmon), perch (Zinger strebel and Zinger zinger). 15 species of fish out of the 32 listed in the U.R.B.(Ukrainian Red Book) live in the Danube Natural Reserve.
Sturgeon is the most interesting fish for the fishery industry but, the Danube shad is more economically important. The annual average shed capture is 400 tons.
Currently, the reproduction conditions are one of the most important factors influencing the fish population. During the 1960-1970 period, the massive construction of dams caused the destruction of around 300.000 ha of land used for spawning. The main factor directly influencing the fish reproduction condition in the lower part of the river is the water level regime (the height and ration of the freshet).
One can notice the sudden reduction of the sturgeon population, which formerly played an important role for the fishery industry, and also for the Black Sea ecosystem. We have to stress that Acipenser Nutriventis and Atlantic sturgeon (Acipenser sturio) have always been rare species in this region. Nonetheless, the Ancipenseruthenus was formally an object of the industrial fishing, but since 1964, it has not been registered any more in fishery reports, although the number of young, migratory Acipenseruthenus is sometimes the largest of all the sturgeon species.
As to the Huso huso, Acipenser guldenstadti colhicus and Acipenser stellatus population, sudden decrease is noticeable. In 1994, the Huso huso was listed in U.R.B.(Ukrainian Red Book) and it's fishing was prohibited. The same year, Ukraine unilaterally prohibited the sturgeon fishing thus, since 1995 only experimental fishing for scientific purposes has been carried out. Currently, the Danube is the only river, flowing into the Black Sea, where migratory sturgeons spawn.
Rare endemic species, such as Zinger streber, Zinger zingel, gymnocephalus schraecter and others have not been accidentally caught by the industrial fishing installations. Thus, no special measures are necessary to protect them or any other small species, except to preserve the existent conditions.
The Danube shed represents almost half of the industrial fishing (48.6%); it is typical migratory fish that spawn beyond the Ukrainian sector of the river. Because of the pelagic type of their spawn, the species has become resistant to the sudden decrease of the area of their traditional territories; contrary to the phytophile species, whose population has suddenly decreased.
The qualitative component of the aquatic invertebrates in Danube Natural Reserve is distinctive because of the so called relict ponto-caspic fauna. These water-living species emerged and were formed 1,5 millions years ago, in the antic semi-salted waters that are presently the Aral Sea, the Caspian Sea, the Azov Sea and the Black Sea. In the Caspian Sea and in certain areas of the Black Sea and of the Azov Sea, the unique habitat of these water-loving species is preserved, a habitat which is remarkable by the richness of the species and which plays an important role as a food provider for fish.
In the Ukrainian sector of the Delta, including the Danube Natural Rezerve, the relict species of the aquatic invertebrates are numerous. They represent the basis of the plankton and of the biotic (Cenozoic). In the composition of the aquatic habitats of the Danube Natural Reserve, 96 relict ponto-caspian species can be found, among which 3 hydroids species, 12 worm species, 1 specie leech, 22 mollusk species, 2 crustaceous species, 9 crustaceous-mollusk species and 1 ticks species.
The impact of the works to deepen the river bed shall be approximately the same for both choices, nonetheless the construction of the canal in accordance with choice 1 shall have a greater
impact on the Bystroe channel.
The main impact factor is the construction of the maritime canal by depositing sand at river mouth, and the most important negative consequences for the aquatic fauna of the Bystroe canal shall be caused by the infiltration of salted water into this channel. These consequences can be significant for the biocenosis of the Bystroe channel, but they shall not affect the aquatic, fauna in the entire delta. To reasonably predict the possible impact of the opening of the mouth of the Bystroe channel, a scientific evaluation on this channel is necessary, and the models conceived for other channels cannot be applied to this particular one.
The impact on the marine ecosystem
The depositing of the excavated soil into the deep sea is an impact factor that can be found in both cases. The consequences shall be more serious in the case of choice 1 , taking into consideration that the volume of the excavated soil is bigger.
In the areas -or the construction works, the impact factors affecting the aquatic fauna are similar for both choices. The volume of the excavated soil and its loss during the execution of works to deepen the bed in the construction stage, as well as in the exploitation stage, are 23% smaller in choice 2. The area of the marine subsoil to be deteriorated shall be basically the same in both choices. The probable losses of spawning areas in choice 1 and 2 shall be 75, respectively 45 ha, but these figures are only estimated.
Comparing of the impact on the shore fauna envisaged by choice 1 to the impact envisaged by choice 2 is not likely to have a relevant outcome, as circumstances are different for each area. The main impact factor in the Jebriansk gulf (a slow water circuit) can lead to the degradation of the water quality, following the construction of the sea access canal and of the widening of the bed during the exploitation stage. In the Bystroe channel area (deposits of sand at the mouth of the branch) the main factor shall be the construction of the protection dams which shall cause the change of the components of the bottom biocenosis and shall impede the migration of fish to the sea.
As stated in the report, the fauna in both choice areas is equally valuable. It is stressed that the biotic bottom groups in the Jebriansk Gulf are unique, but it is also supposed that the negative results shall be only partial, due to the anthropic influences after the construction of the Ust- Dunaisk port.
Generally speaking, it is our opinion that the damages of the aquatic fan including the marine, shall be equally important in both choices.