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ORIGINAL ARTICLE/ORİJİNAL ÇALIŞMA
FULL PAPER TAM MAKALE
ABUNDANCE OF NARROW-CLAWED CRAYFISHES
(Astacus leptodactylus Eschscholtz, 1823) AND ITS TRENDS
IN LAKE SEVAN, ARMENIA
Karen AGHABABYAN1, Gurgen KHANAMIRIAN1, Evelina GHUKASYAN2, Norik BADALYAN2
1American University of Armenia, 40 Baghramian Ave, 0019 Yerevan, Armenia
2Scientific Center of Zoology and Hydrobiology of NAS RA. 7 P.Sevak Str, 0014 Yerevan, Armenia
116 Journal of Aquaculture Engineering and Fisheries Research 1(3): 116-124
(2015) © 2015 ScientificWebJournals (SWJ)
Journal of
Aquaculture Engineering and Fisheries Research
1(3): 116-124 (2015) E-ISSN 2149-0236 doi: 10.3153/JAEFR15012
Received: 31.01.2014
Accepted: 23.03.2015
Published online: 02.04.2015
Corresponding author:
Karen AGHABABYAN, American University of Armenia,
40 Baghramian Ave, 0019 Yerevan, Armenia
E-mail: karen@aua.am
Abstract: The narrow-clawed crayfish (Astacus
leptodactylus Eschscholtz, 1823) is an indigenous
species in Armenia. In 1980s it was occasionally
introduced in Lake Sevan where its population started
to grow. There is a large scale fishery of the crayfish in
the Lake, as its demand remains high. Industrial stock
of crayfishes at the Lake monitored annually, shows
statistically significant decline in the 2004-2011 period.
This decline can be described by logarithmic model y =
-577.5ln(x) + 2158, F = 50.27, P<0.001. The catch rate
of crayfish net-boxes also shows logarithmic decline F
= 9.27, P<0.05 in the 2004-2011 period. Since the net
boxes are designed to catch the larger size crayfishes
only, the decline indicates a decrease of average size
among crayfish population. The female fertility does not
show statistically significant correlation with the
industrial stock of crayfish. It does, however, show
negative correlation with the catch rate of the net boxes:
rPearson = -0.686, P<0.05; ρSpearman = -0.647, P<0.05. The
correlation can be explained as the big animals are
actively removed through harvesting, while smaller
animals are not captured; meanwhile the remaining
smaller animals produce fewer eggs. Decline of crayfish
stock cannot be explained by diseases and invasive
species, but can be explained by overharvesting.
Continuation of harvesting aimed at supplying the
existing demand might result to population decline of
more than 70% during next 17 years.
Keywords: Narrow-clawed crayfish, Astacus
leptodactylus, Abundance, Lake Sevan,
Armenia
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3): 116-
124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
Introduction
The narrow-clawed crayfish (Astacus
leptodactylus Eschscholtz, 1823) is an indigenous
species in Armenia that initially inhabited
freshwater habitats of Ararat Plain. Unlike
neighboring Turkey that hosts two freshwater
crayfishes (Güner
and Harlıoğlu 2009, Harlıoğlu and Güner 2007),
Armenia hosts only one species. In 1980s it was
occasionally introduced into Lake Sevan, and
fairly soon its population and distribution
throughout the Lake started to grow. The
narrowclawed crayfish is actively consumed in the
internal market of Armenia (e.g. over 300 tons
have been sold through various channels in internal
market in 2011) and starting in the late 1990’s they
began to be exported from Armenia. The export
volumes increased during the twelve year period,
2000-2011 from 20 tons per year to 1120 tons per
year (Statistical yearbook of Armenia 2008, 2012).
During this period the main exported crayfishes
stock came from Lake Sevan while a much smaller
portion was supplied by the aquatic habitats of
Ararat Plain and other water reservoirs in the
country. Meanwhile the data collected by N.
Badalyan (2012), in the period of 2004-2011
suggest decrease of the industrial stock of narrow-
clawed crayfishes in Lake Sevan. In comparison to
2004, when the industrial stock was estimated at
1800 tons, they have decreased by 52% in 2011 to
about 860 tons. At current, there is reason to
assume that in the mid-term the situation with
Sevan trout might be repeated, which means that
the population of narrowclawed crayfish may
decline to a level making self-reproduction nearly
impossible.
At the same time, dozens of studies conducted on
various crayfish species show that they are
critically essential component in lake ecosystems.
Being mainly polytrophic organisms, crayfishes
are key consumers and transformers of energy
between various components of ecosystems, as
they utilize representatives of all trophic levels
(Dorn and Wojdak 2004, Momot et al. 1978,
Momot 1995, Nyström et al., 1996). Crayfishes
can be an essential element in lakes with low
productivity of phytoplankton, since in these lakes
the detritus and the submerged vegetation
(consumed by crayfishes) are the main source of
energy. When functioning as a main predator of
benthos animals, crayfishes are supporting
stability of a wide range of plant-animal
communities (Momot et al. 1978, Momot 1995).
Crayfishes are also important regulators of
biogens, especially phosphorus transferring it from
macrophytes to phytoplankton (Kholodkevich et
al. 2005), and thus having influence on the level of
eutrophication. This is true also for the
narrowclawed crayfish, which had rapidly
occupied the ecological niche vacated by the Sevan
khramulya (Varicorhinus capoeta sevangi Filippi,
1865) – another detritivore, abundance of which
has declined due to overfishing (Gabrielyan 1987).
The population of narrow-clawed crayfishes at
Lake Sevan was studied by number of authors. The
studies have been dedicated on study of spatial
distribution, age and sex structure of the
population, reproduction, and ecological
peculiarities of the species (Badalyan 2011, 2012a,
2012b, Gabrielyan and Ghukasyan 2007,
Ghukasyan et al. 2006, 2007, 2008, 2010, 2011,
Hovhannisyan 1998, Hovhannisyan and
Ghukasyan 1996, Reports of SCZH of NAS RA,
2010, 2011).
Taking above mentioned into account there is a
necessity to identify the population trends of the
narrow-clawed crayfish in the Lake. This will
allow for modeling of the unfavorable scenario of
population decline, which will enable taking of
timely measures to mitigate critical changes of the
population. Thus the current article is focused on
analyzing the collected data, which is aimed at
determination of existing trends and their relations
to various influencing factors and modeling future
trends in Lake Sevan’s population of narrow-
clawed crayfish.
Materials and Methods
Lake Sevan is a largest freshwater Lake Sevan of
Armenia that has a surface area of about 1,250 km²,
is situated on 1,896 meters above sea level, which
makes it one of the largest freshwater high-
mountain lakes of Eurasia; also it is the single
biggest source of water in Armenia (see country
map in Figure 1).
117
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3):
116-124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
118
Figure 1. Position of Lake Sevan in Armenia As a
material for the current article we have used
statistical data published in official annual Reports
of Scientific Center for Zoology and
Hydrobiology (SCZH). The data for these reports
have been collected in frames of annual
monitoring implemented by SCZH at 33 sites
covering the entire shore of the Lake with average
distance between the sites 5.73±2.06 km. The
crayfishes have been sampled using capturing
method (Budnikov Tretyakov1952). The method
is based on sampling of crayfishes by standard
traps with cell size 21x21 mm. The method
provides data on relative abundance of crayfishes.
In total there are more than 17,000 crayfishes
sampled and the initial data on industrial stock of
crayfishes (Kireev 1933), catch rate of the
netboxes and crayfish female fertility was
collected and reported (Reports of Institute of
Hydroecology and Ichthyology of SCZH 2010,
2011). The data of industrial stock is measured as
estimate of tons of crayfishes per annum; the data
on catch rate of the net-boxes is measured as
average number of captured individuals per net-
box; the data on female fertility is measured as
average number of eggs per female. In addition
interviews of five fishery companies operating at
Lake Sevan have been conducted. The main aim
of the interviews was to identify cases of crayfish
mortality due to major diseases listed for the
species (Harlıoğlu 2004, Longshaw 2011); for
implementation of interviews no formal
questionnaires have been developed.
The processing of the collected data was
implemented in two stages: (1) the normality of
distribution of collected data has been tested and
(2) subsequently the appropriate methods of
correlation or regression analysis have been
selected. Taking small sample sizes into account
we have been using Shapiro-Wilk test for testing
the normality. When the response data was
normally distributed we have been selecting linear
regression, otherwise the non-linear models have
been
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3): 116-
124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
119
applied. To characterize the non-linear models we
have been using F-statistics and its probability to
determine the significance of the model (Pagano &
Gauvreau 1993, Wayne 2009). During data
processing we have been using Microsoft Excel
2007 and SPSS 11.0 for Windows. Results and
Discussion
Analysis of the annual data on estimated industrial
stock shows that the variable of industrial stock did
not show normal distribution and the logarithmic
regression method was selected as the one that has
higher probability of F-statistics. Application of
logarithmic regression model for the estimated
industrial stock shows that crayfish population
shows statistically significant tendency of
consistent decrease, F = 50.27, P<0.001 (see
Figure 2). The model is described by equation y =
-577.5ln(x) + 2158, where y is industrial stock, and
x is the year.
The next step in our analysis was to understand
some trends in catch rate of the net-boxes. The
distribution of the variable is out of normal as well
and the logarithmic method has also been selected.
The analysis allows determining of a declining
tendency of catch rate of the net-boxes, F = 9.27,
P<0.05 (see Figure 3).
The latest might be indicating population decline
or decrease of average size of crayfishes; because
the size of the net-box cell made especially to let
the smaller crayfishes to escape the net-box.
Decrease of crayfishes’ size can mean changes in
age structure of population and decrease of number
of old big crayfishes.
It is worth to mention that the catch rate of the net-
boxes has a correlation with industrial stock at
significance level of P < 0.01: rPearson =0.809,
P<0.01; ρSpearman = 0.814, P<0.01, which is an
additional confirmation of the observed
tendencies.
Another pattern is observed during analysis of the
average fertility of females (see Figure 4), which
was growing during 2004-2007 but then starts
declining. Such dynamics can have a possible
explanation that the fertility has late response to
overharvesting; thus while the observed increase
might be a segment of a long-term tendency of
previous years, the decrease that follows might be
an indication of influence of overharvesting. To
understand the true characteristics of the tendency
a longer term investigations are required.
When comparing the catch rate of the net-boxes
versus female fertility the negative correlation
trend is determined at significance level of P <
0.05: rPearson = -0.686, P<0.05; ρSpearman = -0.647,
P<0.05. The fact of the relatively low significance
level of the correlation is probably a result of
relatively small sample size (n = 8). Such tendency
can be explained by overharvesting. Due to
consistent harvesting of large amount of crayfishes
with size of 12 cm and more, the average size of
crayfishes is decreasing. It has the following
consequences: (1) smaller animals are not captured
because they are able to escape the netboxes, but
the big animals are removed; (2) the proportion of
smaller animals in population is increasing and
those smaller females produce fewer eggs.
Continuation of the surveys will allow obtaining
better statistical results.
The cases when decline of narrow-clawed
crayfish’s population occur are well known in
Turkey, Hungary, Russia, and Serbia (Aydin et al.
2012, Dartay and Atessahin 2013, Fedotov et al.
1998, Harlioğlu and Harlioğlu 2004, 2009, Puky et
al. 2005, Souty-Grosset et al. 2006). The
investigations suggest several reasons of rapid and
dramatic decline of narrow-clawed crayfishes. In
Turkey the main driving force of the population
decline is still unclear and while some authors refer
to combination of overharvesting, crayfish plague,
and pollution with main stress to over-
harvesting (Harlioğlu and Harlioğlu 2004, 2009),
the others consider the crayfish plague as the main
factor among others, that causes strong decline
(Kokko et al. 2012, Svoboda et al. 2012). In
Hungary the species has been eliminated in Lake
Balaton and later in the lower stretch of the
inflowing River Zala due to introduction of the
European eel (Anguilla anguilla), and in the
Hungarian part of River Danube due to spread of
introduced crayfish species Orconectes limosus
(Puky et al. 2005). In Russia water pollution was
mentioned as the main cause for declines of local
population of the lower part of River Don (Fedotov
et al. 1998, Souty-Grosset et al. 2006). In Serbia
the species declined in some regions due to
introduction of Orconectes limosus (Holdich et al.
2009). It is also confirmed by other investigations
that the invasive species such as Pacifastacus
leniusculus and the Orconectes limosus can be
major threats to this species (Lózan 2000).
According to our data the epidemics of crayfish
plague, as well as other diseases, well known in
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3):
116-124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
120
other parts of narrow-clawed crayfish’s
distribution range have not been recorded. In
accordance to the information of State
Environmental Effect Monitoring Center the
pollution level of the Lake by chemicals was not
significantly changed. It let us to conclude that the
overharvesting might be one of the main reasons of
declining of narrowclawed crayfishes in Armenia.
The fact of increase of crayfish harvesting is
conditioned by the good demand for the product in
the world (e.g. only in Europe the crayfish demand
can reach 10,000 tons per annum), which is proven
by the increasing export of crayfishes from
Armenia (see Figure 5) to the countries of
European Union, North America, Post Soviet
countries, etc.
(Statistical yearbook of Armenia 2012).
Figure 2. Dynamics of
industrial stock of
narrow-clawed
crayfishes in Lake
Sevan during the
period 2004-2011
Figure 3. Dynamics of
catch-rate of net-boxes
in Lake Sevan during
the period 2004-2011
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3):
116-124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
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Figure 4. Dynamics of fertility of narrow-clawed crayfish’s females in Lake Sevan during the period
2004-2011
Figure 5. Dynamics of export volume of narrow-clawed crayfishes from Armenia during the period
2004-2011
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3):
116-124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
122
The existing approach in capturing of the
crayfishes might cause significant decline of its
population in a mid-term perspective. Assuming
that nothing becomes changed in the crayfish
capturing policy during next decades, the equation
of the first logarithmic model (see figure 2) can be
applied for the forecasting the industrial stock. The
application of the equation shows that there is a
relatively high probability that in 2021 the
industrial volume of crayfishes in the Lake Sevan
will become below 500 tons, and that means
decrease of the crayfish’s population at the Lake
on more than 70% during 17 years. If the
conditions causing the observed decline of crayfish
population remain the same, the following major
consequences have to be expected from the
forecasted population decline. First group of
consequences is related economic aspects of
crayfish harvesting. At current the narrow-clawed
crayfishes are the only seafood product that is
exported to countries of European Union and
North America (Statistical yearbook of Armenia
2008, 2012), which have high food safety and
quality standards. At current there are more than
twenty enterprises harvesting crayfishes, the
export makes more than 15 millions USD per
annum (Statistical yearbook of Armenia 2012).
Significant decline of resource will cause collapse
of some enterprises and decrease of export volume.
The second group of consequences which is not
that obvious is related to the feeding behavior of
crayfishes. In Lake Sevan the narrow-clawed
crayfishes are mainly detritivores, and they
consume the benthic deposits thus preventing
increase of organic pollution which might intensify
the eutrophication of the Lake. The Lake Sevan is
surrounded by four towns and 36 villages; it is one
of the major resorts of Armenia that hosts tourists
in the hotels based at the shore of the Lake. In
addition it is surrounded by fields of potato,
cabbage, and grains, which are consistently
fertilized. The sewage and the fertilizers are the big
sources of nitrogen and phosphorus. Consistent
supply of the Lake with fairly constant amount of
phosphates and nitrates in terms of decrease of
detritivore might have negative effect on the Lakes
conditions and the water quality. Further
investigations aimed at comparing the
concentration of nutrients with other biotic
parameters and modeling of the nutrient transfer
processes will allow understanding the character
and the scale of ecological consequences as well as
preliminary determination of the time frame for the
mitigation.
Conclusion
Observed decline of the population of
narrowclawed crayfish at Lake Sevan has
statistical significance. Most probable cause of the
decline is the overharvesting. In the scenario when
no changes in harvesting policy are made, most
probable consequences of overharvesting are
decline of its population by more than 70% in the
next 17 years, and decline of industrial stock to a
volume below 500 tons. It will have negative
economic and ecological consequences. Economic
consequences are related to decrease of export
volume of crayfishes from Armenia. Ecological
consequences are related to imbalance in the
transfer of nutrients. Further investigations on
modeling of the ecological processes can provide
better understanding of the ecological
consequences and their mitigation.
References
Aydin, H., Harlıoğlu, M.M., Deniz, T. (2012):
Harvest, export and economic status of
freshwater crayfish (Astacus leptodactylus
Esch.1823) in Turkey. African Journal of
Agricultural Research, 7(16): 2463-2468.
Badalyan, N. (2012a): The growing features of
Pontacus Leptodactilus Eshch. of lake Sevan.
Biological Journal of Armenia, 1(64): 108-
110.
Badalyan, N. (2012b): Characteristics of
narrowclawed crayfish (Pontastacus
leptodactylus Eschscholtz, 1823) of the Lake
Sevan under raising of the Lake’s level.
Dissertation seeking for the Academic Degree
of Candidate of Biological Sciences with
specialization 03.00.08 –“Zoology”, 101 pp.
Budnikov, K.N., Tretyakov F.F. (1952): Rechnie
raki i ikh promysel. M, Pishpromizdat, 96 pp.
Dartay, M., Atessahin, T. (2013): A Study on
Catching Freshwater Crayfish, Astacus
leptodactylus Eschscholtz 1823, and Its Some
Population Characteristics. Turkish Journal
of Science & Technology, 8(2): 125-130.
Dorn, N.J., Wojdak, J.M. (2004): The role of
omnivorous crayfish in littoral communities.
Oecologia 140: 150-159.
Fedotov, V.P., Bykadorova, S.V., Kholodkevich,
S.V. (1998): Crayfish situation in the North-
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3): 116-
124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
123
West of Russia. In: Trond Taugbøl (ed.),
Nordic-Baltic Workshop on Freshwater
Crayfish Research and Management. Eastern
Norway Research Foundation and Estonian
Ministry of Environment.
Gabrielyan, B. (1987): Investigation of Spawning
Migrations of Khramulja Varicorhinus
Capoeta Sevangi (Filippi) by the Method of
Marking with Active Dyes. Biological
Journal of Armenia, 40(1): 79-82.
Gabrielyan, B., Ghukasyan, E. (2007): Ecological
consequences of introduction of hydrocoles in
Lake Sevan. Proceedings of the International
Conference “Natural and invasive processes
of forming the biodiversity of aquatic and
terrestrial ecosystems”, Rostovna-Donu, 81-
82.
Ghukasyan, E., Badalyan, N., Hovhannisyan, R.,
Dallakyan, M. (2006): On the changes of
biological parameters of crayfish in the Lake
Sevan. Biological Journal of Armenia,
34(58): 321-324.
Ghukasyan, E., Badalyan, N., Gabrielyan, B.,
Sahakyan, D., Dallakyan, M. (2011):
Reproduction peculiarities of narrow-clawed
crayfish in Lake Sevan. Proceedings of the
International Conference “Biological
Diversity and Conservation Problems of the
Fauna of the Caucasus”, September 26-29,
Yerevan, Asoghik, 105-108.
Ghukasyan, E., Badalyan, N., Sahakyan, D.
(2010): Ecological peculiarities of
narrowclawed crayfish in Lake Sevan and
dynamics of its industrial stock. in Ecology of
Sevan in the period of raising its level. Study
results of Russian-Armenian biological
expedition on hydro-ecological survey of
Lake Sevan (Armenia) (2005-2009),
Makhachkala. Nauka DNC, 224-228.
Ghukasyan, E., Badalyan, N., Sahakyan, D.,
Dallakyan, M. (2008): Influence of fishery on
the population of narrow-clawed crayfish in
Lake Sevan. Proceedings of the International
Conference “Importance of ecology and
nature protection in the perspectives of
sustainable development” November 20-21,
2008. Yerevan, 65.
Ghukasyan, E., Gabrielyan, B., Badalyan, N.
(2007): Dynamics and some biological
parameters of narrow-clawed crayfish
introduced to the Lake Sevan. Proceedings of
Southern Scientific Center of Russian
Academy of Sciences “Biodiversity and
transformation of mountain ecosystems of
Caucasus”. Rostov-na-Donu. SSC RAC
Press. 3, 114-118.
Güner, U., Harlıoğlu, M.M. (2009): Status of
freshwater crayfish distribution in Thrace
region of Turkey. Reviews in Fisheries
Science, 18(1): 1-6.
Harlıoğlu, M.M., Güner, U. (2007): A New Record
of Recently Discovered Crayfish,
Austropotamobius torrentium (Shrank, 1803),
in Turkey. BFPP/Bull. Fr. Pêche Piscic., 387,
01-05.
Harlıoğlu, M.M. (2004): The present situation of
freshwater crayfish, Astacus leptodactylus
(Eschscholtz, 1823) in Turkey. Aquaculture
230: 181-187.
Harlioğlu, M.M., Harlioğlu, A.G. (2004): The
harvest of freshwater crayfish, Astacus
leptodactylus (Eschscholtz, 1823) in Turkey.
Reviews in Fish Biology and Fisheries, 14(4):
415-419.
Harlioğlu, A.G. Harlioğlu, M.M. (2009): The
Status of Freshwater Crayfish (Astacus
leptodactylus Eschscholtz) Fisheries in
Turkey. Reviews in Fisheries Science, 17(2):
187189.
Holdich, D.M., Reynolds, J.D., Souty-Grosset, C.
Sibley, P.J. (2009): A review of the ever
increasing threat to European crayfish from
non-indigenous crayfish species. Knowledge
and Management of Aquatic Ecosystems,
394-395: 1-46.
Hovhannisyan, R. (1998): Ecological peculiarities
narrow-clawed crayfish in Lake Sevan.
Dissertation seeking for the Academic Degree
of Candidate of Biological Sciences by
specialization 03.00.08 –“Zoology”, 94 pp.
Hovhannisyan, R., Ghukassian, E. (1996): Some
ecological peculiarities of Lake Sevan higher
Crustacea PontAstacus leptodactylus
Eschholtz. Lake Sevan: problems and
strategies of action. Proceedings of the
international conference. Sevan, Armenia,
13-16 October. 1996, 99-101.
Kholodkevich, S.V., Shumilova, T.E., Fedotov,
V.P., Zhuravlev, D.A. (2005): Effects of the
Astacus astacus L. Population on Biomass
of Macrophytes in a Fresh Water Body.
Russian Journal of Ecology, 36(4): 271-276.
Journal of Aquaculture Engineering and Fisheries Research Aghababyan et al., 1(3):
116-124 (2015)
Journal abbreviation: J Aquacult Eng Fish Res
124
Kireev, I.A. (1933). Hydrographic works at the
Lake Sevan. Materials on the study of the
Lake Sevan and its watershed. Tiflis, 5: 6587.
Kokko, H., Koistinen, L., Harlioğlu, M.M.,
Makkonen, J., Aydın, H., Jussila J. (2012):
Recovering Turkish narrow clawed crayfish
(Astacus leptodactylus) populations carry
Aphanomyces astaci. Knowledge and
Management of Aquatic Ecosystem, 404: 12.
Longshaw, M. (2011): Diseases of crayfish: A
review. Journal of Invertebrate Pathology,
106(1): 54-70.
Lozán, J.L. (2000): On the threat to the European
crayfish: a contribution with the study of the
activity behaviour of four crayfish species
(Decapoda: Astacidae). Limnology, 30:
156161.
Momot, W. (1995): Redefining the role of crayfish
in aquatic ecosystems. Reviews in Fisheries
Science, 3(1): 33-63.
Momot, W., Gowing, H., Jones, P. (1978): The
Dynamics of Crayfish and Their Role in
Ecosystems. American Midland Naturalist,
99(1): 10-35.
Nyström, P., Brönmark, Ch., Graneli, W. (1996):
Patterns in benthic food webs: a role for
omnivorous crayfish? Freshwater Biology,
36(3): 631–646.
Souty-Grosset, C., Holdich, D.M., Noël, P.Y.,
Reynolds, J.D. Haffner, P. (2006): Atlas of
Crayfish in Europe. Muséum national
d’Histoire naturelle, Paris.
Statistical yearbook of Armenia. (2008): National
Statistical Service of the Republic of
Armenia, Yerevan, 2008, 589 p.
Statistical yearbook of Armenia (2012): National
Statistical Service of the Republic of
Armenia, Yerevan, 2012, 567 p.
Svoboda, J., Kozubíková, E., Kozák, P., Kouba,
A., Bahadir Koca, S., Diler, O., Diler I.,
Policar, T., Petrusek, A. (2012): PCR
detection of the crayfish plague pathogen in
narrowclawed crayfish inhabiting Lake
Eğirdir in
Turkey, Diseases of Aquatic Organisms,
98(3): 255-259.
Pagano, M., Gauvreau, K. (1993): Principles of
biostatistics. Duxury Press, Belmont, CA. 524
pp.
Púky, M., Reynolds, J.D., Schád, P. (2005): Native
and alien Decapoda species in Hungary:
distribution, status, conservation importance.
Bulletin Francais de la Pêche et de la
Pisciculture.
Reports of Institute of Hydroecology and
Ichthyology of SCZH of NAS RA. (2010):
Scientific Center of Zoology and
Hydrobiology and Sevan National Park,
Yerevan. 6 pp.
Reports of Institute of Hydroecology and
Ichthyology of SCZH of NAS RA. (2011):
Scientific Center of Zoology and
Hydrobiology and Sevan National Park,
Yerevan. 10 pp.
Wayne, D.W. (2009): Biostatistics: A Foundation
for Analysis in the Health Sciences, 9th
Edition. John Wiley & Sons, Inc. 956 pp.
