russian version

Katunin D. N.
(CRTC on Bioresources and Fishery)

On dye-outs of Caspian seals and sprats

In 2001 works on assessment of the status of population of the Caspian seal continued. The surveys in Russian Federation have been done by CaspNIRKH within the framework of scientific-research activities, financed by State Committee of Russian Federation on Fishing. In spite of warm winter and relatively unfavorable conditions for reproduction, there were no major cases of dye-outs. Vaccination of some part of population of seal inhabiting M. Zhemchuzhniy island against distemper was done jointly with Vector NGO. In winter 2000/2001 activities on development of methodology for assessment of the number of population of Caspian seal were implemented from helicopter MI-8. During 2001 such activities shall be continued. Among other surveys are those on assessment of nutrition conditions of the Caspian seal, enrichment with whitebait as well as evaluation of fertility of female seals.

During April-May CaspNIRKH found out high level of mortality of Anchovy kilka in water area of Middle and some part of South Caspian which persisted until June-July. Wide scale studies of physiological status of kilka, content of chlororganic pesticides, heavy metals, hydrocarbons, including multi-ring hydrocarbons were implemented.

The highest level of mortality of Anchovy kilka was recorded in water area adjacent to Kazakhstan shelf of Middle Caspian. In spring 2001 this area was marked by upwelling, which has reduced within last three years. Temperature in this part of water area was lower as compared to the central part of sea by 7-8⁰.

Trophical surveys revealed kilka was malnourished due to the lack of nutrients especially that of planktophagus Eurithemora. Kilka fed on larvae of Crustacea – which is of little value in terms of nutrition. The reason was that the species were eaten away by Mnemiopsis in 2000 and failure to bring its number to the “norm” by spring 2001.

Observations over the status of population of Anchovy kilka showed low level of replenishment in 2001. Currently the amount is being specified through special surveys. Kilka catches significantly reduced. Catches per vessel upon different periods of time reduced by 5-10 times.

The main reason for mortality of Anchovy kilka lies in combination of two stress-factors: depletion of part of population and low immunity as a result of toxicosis. Part of population proved not ready for fattening stage and died as a result of continuing impact of two stress-factors. High mortality was recorded in the zone of low water temperatures. Impact of volcanoes on the bottom of the Caspian should not be undervalued since during the last year its activation was recorded in the South Caspian in open sea adjacent to the coast of Azerbaijan and Turkmenistan.

Such volcano processes could contribute to aggressive gassing. However, the main reason is considered to be wide-scale impacts of Mnemiopsis on forage reserves of kilka and hence sharp decrease of its nutrition. Combined with low sustainability to stress-factors as a result of high accumulation of hydrocarbons in kilkas, including multi-ring hydrocarbons (benzopyrene, naphthalene, metylnaphthalene, etc.), heavy metals (zinc, copper) part of population died considerably, especially during April-May.

In 2001 Russian Federation represented by CaspNIRKH, including its institutions “Floating University”, Institute of Oceanology named after Shirshov PAH, Azov Scientific Research Institute of Fishery continued their activities on assessment of population, biomass, spatial distribution of Mnemiopsis, including vertical distribution and age structure of population. At the same time studies of zooplankton, its quantitative and qualitative structure, distribution of kilka, its nutritional state, conditions of nutrition and age structure were done. Five surveys were done on dimensional and weight parameters during navigation period.

Also a program of experimental works was implemented on the basis of Dagestan division of CaspNIRKH in Turali district.

With the help of specialists of Azov Scientific Research Institute of Fishery different-sized Beroe ovata species were selected and placed in experimental vessels. At present experimental works with Beroe ovata and Mnemiopsis are done and their trophic interaction is being studied.

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