O.I. Kirichenko, S.M. Anuarbekov

The Kazakh scientific-research Institute of fisheries, Altai branch, Kazakhstan

The State of the Populations and the Fishery of the Crawfish in the Reservoirs of the Irtysh Basin

The Irtysh River is the trans-coterminous stream that begins in China where it is called Black Irtysh further it runs along the territory of Kazakhstan and it flows into the Ob River that is situated in Russian Federation. The length of Irtysh running in Kazakhstan is over than 1700 km. In the upper current of Irtysh is blocked by 3 dams of 3 hydroelectric power plants, as a result of which there were built 3 artificial reservoirs. The essential fishery farm reservoirs of the Irtysh basin are Zaysan Lake, Bukhtarma Reservoir, Ust-Kamenogorsk Reservoir, Shulba Reservoir and actually the part of the Irtysh River from the Shulba hydroelectric power unit up to the border of Republic of Kazakhstan (the length is about 750 km).

Crawfish of the reservoirs of the Upper Irtysh basin originally is an invader and as a representative of the aquatic fauna and for the first time it was mentioned only in the mid 90s. There (in basin) dwells one of the species of crawfish that is a long-nipped crawfish (Pontastacus leptodactylus Eschholtz, 1832). High productive qualities of the interventionist (high fertility, tachyauxesis, and an early puberty) and favorable conditions of the habitation (an optimal temperature rate, a sufficient provision with feedstuff) promptly helped to attain a significant abundance and create a high commercial concentration. At present time crawfish are one of the largest and the most valuable invertebrates that dwell at the reservoirs of our region. The crawfish of the Irtysh basin are the members of the common biocenosis: in one hand, they protrude as consumers of the pabular recourses of the reservoir; in another hand, they become a feed for some fish, birds and mammals.

Extension and density of the concentration of the crayfish over the water area are unequal and depend upon many factors (presence of well-heated, plant-filled shallows; potential lees and suitable ground for building of shelters). The spreading of the invader in Zaysan is practically omnipresent but the densest swarm of it is fixed in the northwest restricted area and on the Kurchum shore from the cape of Korzhun up to Zholnuskau settlement, at these terrains the effectiveness of the takings compounds about 20-30 specimen per net. The areal of the crayfish at Bukhtarma Reservoir initially covered only limnetic riverine part of it, but at present time the crawfish extended also the upland valley part of the reservoir (Altayka). At present the efficacy of the takings of crawfish varies from 1.1 specimens per net – in mountain part of the reservoir to 48.6 specimens per net – in acustrine riverine part of the Bukhtarma Reservoir. To the recent time, in Shulba Reservoir the crayfish was extended omnipresent making low concentrations in coves where the maximal taking of them in research nets attained 18-25 specimens per net, in 50-meter seine – about 100 specimens per one yield with seine.

Overall dimension-weight parameters of crustaceous in the reservoirs of the Irtysh basin at the spike of the growth of the abundance and the biomass compounded 21 cm with mass not more than 280 gram [1]. At present in conditions of the stabilization of the number of populations and the intensification of the catch of crayfish practically in all reservoirs of the basin occurs the descent of the maximal exterritorial rates. In 2007 maximal parameters of crayfish dwelling in Zaysan Lakewere as following: length 12.1 cm; weight – 85.8 g; in subsequent time, under the influence of the selective catch of fish, was observed the drop of the appropriate parameters to 10.9 centimeters in length and 61.1 gram in weight (table 1).

In the catches from the Bukhtarma Reservoir the average metrical parameters of the crawfish are seemed to be one of the highest, but at the same time there is no distinct tendency towards their decrease. In this reservoir the reserve of crayfish is significant enough, but the intensity of catches still does not reached its optimal rates. The oscillation of the average weight of the crustaceous in yield depends on the quantity of the recruit-stock in comparison in different periods of time.

In 2009-2010 in the yields from Shulba Reservoir in research hauls of fish were crawfish with the following dimension: length – 8-15 centimeters and weight – not less than 195 grams. The intensity of the fisheries of crayfish in this reservoir was not optimal and had the prospects of the ectasia, it is pointed out by the average size weight parameters of crawfish. The average weight of the crustaceous in yields of different years had the tendency to its increase and in spring of 2010 the weight of crawfish attained 87.4 grams. It is the highest rates of crawfish among all the reservoirs of the basin.

1. The dimensional structure of the crawfish in the research hauls, %

Reservoir	Years	Length, cm										Average length, cm
		7	8	9	10	11	12	13	14	15	16
Zaysan Lake	2007	-	-	4	13	8	33	25	13	4	-	12,1
	2008	4	16	8	20	16	12	12	12	-	-	10,6
	2009	-	4	24	28	20	8	12	4	-	-	10,5
	2010	4	4	12	20	24	16	16	4	-	-	10,9
Bukhtarma Reservoir	2007	-	-	5	30	15	5	25	15	5	-	11,8
	2008	-	4	24	28	8	16	16	14	-	-	10,5
	2009	-	-	-	4	28	24	24	12	4	4	12,4
	2010	-	4	16	4	28	16	8	24	-	-	11,6
Shulba Reservoir	2008	-	4	8	28	28	8	24	-	-	-	11
	2009	-	-	16	28	28	20	4	4	-	-	10,8
	2010	-	4	4	20	16	32	16	4	4	-	11,5
The Irtysh River, East Kazakhstan	2008	-	5	33	14	19	14	10	-	5	-	10,5
	2009	4	8	8	16	24	24	16	-	-	-	10,8
	2010	-	4	4	28	32	24	8	-	-	-	10,8

The dimension-weight parameters of crawfish of the Irtysh River, in comparison with other reservoirs of the basin, are at the medium level, at the same time there is observed the oscillation of the average metrical indexes that is in length and weight of crawfish due to the difference in time and the average weight of the Irtysh crawfish is one of the lowest. It is connected with the fact that the fishery in the inundated reservoirs of the Irtysh practically is not sufficient, the exclusion is the section of the river up to the backwater of the Shulba Reservoir; the abundance of the population in the last years had been developing with fast-paced tempo providing the sufficient inflow of the young recruit-stock that is affected the drop of the average point of the quotient.

In particular reservoirs crawfish becomes nubilous at the age of 3-4years when the length of their body attains not less than 7-8 cm[2]. According to our research work, crayfish of the Irtysh basin reservoirs grow up rather quick and by the tempo of the growth males take the lead over the females, at that time the minimal dimensions of the hard-roed females are equal to 7.0-7.5 cm, and males become eugamic when their length attains 6-7 cm. Longevity of crawfish in the reservoirs of the basin does not exceed 6-7 years. Reproductive structure of the population of the reservoirs, in whole, is characterized by the dominance of mates that is identical for the majority of reservoirs within the area; however, the degree of prevailing is distinct. In preceding years the maximal excess of mates was observed in the populations of Zaysan Lake and Bukhtarma Reservoir; rather equilibrium correlation of genders is typical for the intensively growing population of crawfish of the Irtysh River.

A long-nipped crawfish is characterized by the rather high productive qualities than the other subspecies, at the same time the diversification (phytome and zoic fodder) and sufficient amount of available pabular resources of the reservoirs of the basin define high indexes of the fecundity of females and favorable conditions of habitation are good factors of the efficiency of the reproduction.

The quantity of the fecundity is well correlated with the dimension (coefficient of correlation – 0.75) the larger female the higher its fertility. According to the data of our research the quantity of the worker exuberance of females of crawfish of the reservoirs of the Irtysh basin varies from 5 to 980 berries, the maximal rate was fixed in Shulba Reservoir (table 2). At females of crawfish of the Shulba Reservoir were observed not only individual indexes of the fecundity and also the growth of its population parameters that according to the data of 2010 exuberance of females dwelling in this reservoir compounded 427 berries. In populations of the crustaceans of Bukhtarma Reservoir is observed the variation of the average parameters of the fecundity according to the years, from minimal in 2009 with the following descent in 2010. An individual fecundity of crawfish of Zaysan Lake and the riverine system of Irtysh is slightly lower; average indexes are stable enough in different years and compound 307-382 berries.

2. Dynamics of the fecundity of the crawfish, by years

Reservoir	Years	Number of berries, exemplar		Number, exemplar
		(min-max)	average
Zaysan Lake	2009	150-531	307	15
	2010	5-737	315	18
Bukhtarma Reservoir	2008	112-627	361	25
	2009	165-783	445	18
	2010	131-646	380	12
Shulba Reservoir	2008	174-592	339	20
	2009	132-510	316	13
	2010	140-981	427	25
The Irtysh River, East Kazakhstan	2010	192-761	382	25

For the recent time crawfish was one of the marketable objects practically in all reservoirs of the basin, it was being known that the basic marketable fishery was led in Zaysan Lake, Bukhtarma and Shulba Reservoirs. The favorable conditions of the habitation for crawfish in the reservoirs of the Upper Irtysh made it possible to create new marketable concentrations; during last years takings of crayfish were substantial. So, according to the materials of 2010 it was known that on the Kurchum shore of Zaysan the part of crawfish in total takings of the hydrocele was from 2.2 to 18.55 per cent, on the Tarbagatay shore – about 36 per cent. In Shulba Reservoir taking of the crayfish attained 20 per cent in the catch with the seine and in Irtysh itself in control nets the efficiency was from 0.9 to 3.45 kg per net (data of spring of 2010).

According to the materials of the biological substantiation forecast of the taking of crayfish from basic marketable reservoirs of the Irtysh basin in 2010 should be 432 tonnes, including from Zaysan – 151 tonnes, Bukhtarma Reservoir –191 tonnes, Shurba Reservoir – 50 tonnes and the Irtysh River – 40 tonnes [3]. Though, in spring – summer period of 2010 the large mor of crawfish took place in Shulba Reservoir and then in down – stream of the Irtysh River, the reason of which was not ascertained. For the exact determination of the causes of malady should be in time held the specialized (mycological) laboratorial analysis. Due to the clinical side characterizing the death of crayfish we could make the assumption that the population of crawfish was mow cleaned by the crawfish plague, the disease-producing factor is a fungus – “Aphanomyces astaci” that has high contagiousness and pathogenic power, that is why the disease had rapid character and quick emission. Epizooty can expend either up- or down-stream; earlier the death of crayfish was fixed in Shulba Reservoir then in the second half of June the affection rapidly developed in down – stream. As a rule, when the epizooty of crawfish plague takes place succumb about 90-95 per cent of the population, such situation happened in these reservoirs (when there are occur such diseases like rusty spotted, marmorate illnesses pass away 30-50 per cent of the population). In April of 2010 were held the prognostic researches there were no evident causes of the disease; crayfish presented either in seine or in nets. But in August in the research nets they absented and in the marketable yields there taken 1-2 specimens per day.

The crawfish are susceptible to different diseases as a result of which dyes a part and sometimes whole population. Exactly mass epidermis of the end of XIX – beginning of XX centuries that mow cleaned the populations of crayfish of Europe and Asia, are evoked the interests to the export of crawfish of the Irtysh basin. Rehabilitation of the populations after the mor has a long-time character and requires the conduction of the active restoration measures and the prospects of the craw fishery depend on the development of the crawfish breeding.

Thus, modern state of the population of crawfish of the reservoirs of the Irtysh basin can be characterized by following features: the rise of the abundance and expansion of the areal of the crawfish in Bukhtarma Reservoir; stabilization of the abundance of crayfish in Zaysan Lake; descent of the dimension – weight parameters of crayfish in takings from the commercial reservoirs under the influence of the selective haul; invariably high efficiency of the hauls in conditions of high spissitude of populations in basic commercial reservoirs of basin (Zaysan Lake, Bukhtarma Reservoir); mass death of populations of crayfish in Shulba Reservoir and the Irtysh River.

The problem of infestation of the alien species belongs to one of the important directions of the fundamental and applied investigations that are why such works should be always held. The world community recognized this problem as global and therefor were adopted amicable settlements where were underlined that control and regulation of the self – settling and naturalization of the alien species are concerned as the principles of conservation of the biological diversification. The invasive species contacting with populations of aboriginals considerably transform the structure of ichtiocenosises that is fraught with the degradation of ecosystems.

All the stated above allow to conclude that the problem of biological invasions of the alien species to the territory of Kazakhstan is the most important aspect of safeguarding of the ecological security of our country. That is why we think that on the borders of our country the veterinary sanitization control for the importing of live hydrocoles should be toughen with the aim to expose their basic transitive ways, work out forecasts and measures of prevention of the invasions and abatement of their aftermath.

Reference

1. Исмуханов Х.К., Кириченко Б.Г. Экспансия речного рака в водоемах Верхнего Иртыша // Вестник сельскохозяйственной науки Казахстана. – 2009 – №2 – Алматы. – С. 52-54.

2. Румянцев В.Д. Речные раки Волго-Каспия (биология и промысел) – «Пищевая пром-сть». Москва, 1974, С 86.

3. Определение рыбопродуктивностирыбохозяйственных водоемов и/или их участков, разработка биологических обоснований общих допустимых уловов и выдача рекомендаций по режиму и регулированию рыболовства на водоемах международного и республиканского значения на 2010 год. Раздел: Зайсан-Иртышский бассейн. Часть 1: Отчет о НИР (закл.) /Алтайский филиал КазНИИ рыбного хозяйства. – Усть-Каменогорск, 2009 – 170 с.