28_2005_Status-of-sturgeons-in-Slovakia_Holcik-et - Panda

Current status of sturgeons in the Slovakian rivers of the Danube River basin and
proposals for their conservation and restoration
Juraj Holčík 1, Adriana Klindová2, Juraj Masár3, Juraj Mészáros4
1. Introduction
Human impact upon the Danube River basin during past 100 years and its tributaries
caused substantial changes in their morphology and biota. The river continuum is disrupted
and the biodiversity in particular sections of the modified stream changed. Among the most
affected animals are migratory fishes. In the Danube Basin there are sturgeons, the fishes of
ancient origin, peculiar biology and economical importance. Overfishing, pollution and then
the building of dams affected especially the migratory species and forms, such as beluga or
great sturgeon (Huso huso (Linnaeus, 1758), Danube or Russian sturgeon (Acipenser
gueldenstaedti Brandt, 1833), and stellate or starred sturgeon (Acipenser stellatus Pallas,
1771) which already 100 years ago migrated upstream and reached even the upper parts of
Danube and their populations provided highly appreciated meat and caviar. At present their
populations dramatically decreased and all are near their extinction. The same is true for
potamodromous or resident species the ship sturgeon (Acipenser nudiventris Lovetsky, 1828)
and sterlet (Acipenser ruthenus Linnaeus, 1785). Also their populations substantially declined
and the ship sturgeon probably became extinct in the Danube Basin. Present paper was
stimulated by the Sturgeon Workshop jointly organized by the International Association for
Danube Research (IAD), the World Wildlife Fund (WWF) and other institutions and held in
Petronell near Vienna (Austria). Its purpose is to present the current status of sturgeons in the
territory of Slovakia and to propose measures for their protection and conservation. Because
details on the distribution, ecology and bionomy of all Danubian sturgeons are well known
(Holčík 1989, Baruš & Oliva 1995, Reinartz 2002), only the most recent information is
2. Species composition
Corresponding author. Drotárska cesta 19, 811 02 Bratislava, E-mail <juraj.holcik@stonline.sk>;
Ministry of Environment, Nature and Landscape Protection Department, Námestie Ľudovíta Štúra 1,
Research Institute of Animal Production / Worskop of Fishery a Aquaculture, P.O.Box 2, 900 89 Častá,
Juraj Mészáros, ZÚGOV, Ltd. Ul.Svornosti 69, 940 77 Nové Zámky, <srtzn@szm.sk>
Slovak water bodies are now inhabited by two species of sturgeons. The sterlet Acipenser ruthenus Linnaeus, 1758 is found in the proper Danube and the lower courses of its
large tributaries, Morava, Váh, Hron and Ipeľ rivers and also in the Slovak segment of the
Tisza River and some of its tributaries. The second species found extremely rarely is
potamodromous form of the Russian sturgeon - Acipenser gueldenstaedti Brandt, 1833 that
inhabits the proper Danube only. Its last catch composed of two specimens has been recorded
in 1987. At present the conservancy status of the sterlet is considered as vulnerable, and that
of the Russian sturgeon as critically endangered. All other sturgen species occurring in this
Slova-Hungarian segment of Danube before, vanished (EX; Holčík 1995, Hensel & Holčík
1997). According
to Hensel & Mužík (2001) sterlet is classified as LR: cd and
potamodoromous Russian sturgeon as CR.
3. Russian sturgeon
Diadromous Russian sturgeon formerly migrated regularly to Bratislava, where
specimens 2-4 m in length and 80-90 kg in weight spawned in May and June and were found
also in the lower part of both the Váh and the Morava River. However, this form became
extinct since 1967, where one young specimen 355 mm in length probably belonging to this
form has been caught at Radvaň nad Dunajom (r.km. 1749). At present only the resident
potamodromous form appears in this segment of the Danube. Last record of two specimens
over 100 cm in length were listed in Bratislava in 1987 (Holčík 1995a, Hensel & Holčík,
There are not any data on the biology of this species in this segment of the Danube
4. Sterlet
4.1. Sterlet characteristics
Morphological characters of sterlet from this segment of Danube was studied by
Prokeš et al.(2002). It was found that sterlet from the Danube did not differ from the accepted
morphometrical description for this species [Du 32-49, Au 16-34 (39), SD 11-18, SL 56-71,
SV 10-20, Sp.br.11-27, Fu 25-45; Sokolov & Vasil’ev 1989].
At present sterlet inhabits only the Danube River, lower parts of its larger tributaries
(|Morava, Váh, Nitra, Žitava, Hron, Ipeľ), and also in the Slovak segment of the Tisza River
and its tributaries Latorica and Bodrog (Holčík 1995b, Koščo & Košuth 2004). Recently the
sterlet occurs again in the Váh River where introduction of reared juveniles is realised since
1998 as mentioned below (Table 1). The recreational anglers at Trenčín reported the catch of
20 specimens (Tl 450-670 mm, average Bw 1,500 g) in 2002, 44 specimens (Tl 450-670 mm,
average Bw 1,600 g), in 2003, and 64 specimens (Tl 450-760 mm, average Bw 1640 g) in
4.3. Some data on the ecology and bionomy of sterlet
Sterlet is found almost exclusively in the main river bed and very seldom also in the
anabranches. Before 1992 when the Gabčíkovo River Barrage System (GRBS) was put in
operation, the highest catches came between river km 1749 and 1789 and sometimes as many
as 80 - 300 specimens were caught in one haul. It seems that construction of the GRBS
disunited the original hydrological and physiographical conditions of this segment of river, as
places showing former sterlet groupings are not known. There seems to be a spatial
segregation of both sexes according to Nagy (1987) as females fed mostly on Oligochaeta
(found over bottom with more fine sediments and slower current) while males preferred
Trichoptera and Ephemeroptera (found over gravel bottom and more lotic environment).
Females were older and larger than males reaching 10 years at 620 mm of the total length and
1123 grams, while the oldest males reached 7 years at length of 479 mm and weight of 477
grams. Females grow faster than males from their second year of life (Kovrižnych 1988).
Sterlet in this segment of Danube attains sexual maturity later than in the downstream parts of
the river. Kovrižnych (l.c.) suggested the sexual maturation of females and males at age of
(3) 4-5 and 5-7 years respectively and supposed that females in this segment of Danube spawn
only once or twice during their life.
Current experience with obtaining of brood sterlet reveal that to obtain the sexually
mature females is very difficult. In the period 1989, 1990 and 1991 during the spawning
migration it was possible to get 14, 18 and 62 sexually mature females, respectively, but in the
period from 1999-2002 only 1, 1, 0 and 2 females were obtained, respectively (Mészáros &
Masár, 1992, Turanský & Masár 2002). It is supposed that this is due to operation of the
GRBS causing irregular water level fluctuation and change of places with suitable spawning
ground (Mészáros et al. 2005).
Migrations of sterlet in this segment of Danube needs to be studied. Tagging research
performed in the period 1992-1995 did not display the migrations of sterlet because only two
specimens of 204 tagged were recaptured. One was taken at the same place as tagged one
month before and the second was caught 10 km upstream of its tagging place after 397days
(Holčík, unpubl.).
According to Nagy (1987) the diet of sterlet in this segment of Danube is composed of 46
items, the most important were larvae and pupae of Chironomidae, larvae of Ephemeroptera,
Mollusca, Trichoptera and Oligochaeta, but also the fish remains were found in some
The complete early development of sterlet was not known until the publication by Krupka
et al. (2000) was published. Details are in that paper, but generally the sterlet early
development does not differ from those of other sturgeons studied.
4.4. Population density
There are no data on the population density of sterlet in this stretch of the Danube
River. Judging from the catch statistics its share is low. The percentage of sterlet in the total
catch of all species in the period 1961 – 1979 reached 0.02 % in the commercial catch, and
0.28% in the anglers catch. Although the catch statistics after 1990 is dubious, it seems that
the current population density of sterlet is really higher than 40 years ago. In the catch of 6245
specimens of fish taken in the period 1992 – 1996 by 300 m long haul seine used formerly by
the commercial fishermen the means percentage share of sterlet was 3.3%.
4.5. Fishery for sterlet
Fishing in Slovakia is managed by the Slovak Union of Anglers (SUA) and is
supervised by the Ministry of Environment. Before 1993 the fishing has been carried out by
both commercial fishermen and licensed anglers. By the beginning of eighties three groups of
commercial fishermen with 4-7 professional fishermen per group operated there.
Subsequently this number decreased to 1-2 groups with 8-10 fishermen and since 1993 the
commercial fishery has been forbidden. It was banned by the Council of the SUA, but the
reasons are unknown. The number of licensed anglers performing the recreational fishery in
the Danube has varied between 5000 – 7000 by the beginning of eighties. The present number
of licensed anglers is unknown but it is estimated to be almost the same as before. However,
since 1990 the poaching dramatically increased and therefore the present fishery statistics
does not express the actual fish harvest. The legal size of sterlet is 45 cm of the total length.
This is too low and allows to fish also sexually immature females.
Annual catches of sterlet in this stretch of the Danube between 1955 and 2004 varied
between 6 and 1140 kg (Fig.1). As it may be seen, in some years the catch of any sterlet has
not been recorded. In the period 1966 – 1978 the sterlet catch significantly decreased due to
increasing content of toxic waters of industrial effects of waste waters and in the period 19791983 not any sterlet catch has been recorded. The mean catch which was 305.94 kg in the
period 1955-1992 i.e. before the GRBS was put in operation, dropped to 245.83 afterwards.
Catch statistics shows that during past 4 years the catch is increasing. It is a question,
however, if this trend will continue also in further years. It is noteworthy, that according to
our present experience the catch of sterlet is composed mostly of fish weighing 1-2 kg, while
formerly the catch was composed of specimens weighing 0.2 – 0.5 kg. This suggests that the
sterlet population in this segment of Danube became older, in other words the natural
reproduction is insufficient and remain prevails over ? depends on? supplement.
4.6 Conservation
Protection of wild animals including fishes in Slovakia is ensured by the Act 543/2002
on the Nature and Landscape Protection and implemented by the Order of the Ministry of
Environment of the Slovak Republic No.24/2003. According to latter the Russian sturgeon is
protected whole year and its societal value is stated for 30,000 Slovak crowns (Sk; i.e. equal
to about 780.- EURO). Fishery rules are in the Order 238/2002 which implements the Act
139/2002 on fisheries. Russian sturgeon is protected whole year and the fishing for sterlet is
banned in the period between March 15 and May 31, and its legal size is stated to 45 mm in
All Acipenseriformes spp. (except Acipenser brevirostrum and A. sturio) are listed in
Annex B (CITES II) according Council Regulation (EC) No. 338/97 on the protection of
species of wild fauna and flora by regulating trade therein, which means that Slovakia is
controlling export and import or re-export with these species apart from others. What is not
mentioned in regulation (more restricted measures regarding holding specimens), sanctions
and competency of all CITES authorities are included in the Act No. 15/2005 on the
protection of species of wild fauna and flora by regulating trade therein.
4.7. Artificial propagation of sterlet
Artificial rearing of sterlet in Slovakia started in 1989, in the Institute of Fishery
Research and Hydrobiology, Bratislava (Nevický & Mészaros, 1992). Afterward it continues
in the Institute of Fishery and Aquaculture at Častá5. The aim was to produce fingerlings for
stocking of natural water bodies and to establish the brood fish stock. The following main
results are compiled from papers by Mészáros & Masár (1992), Turanský & Masár (2000,
2002), Mészáros et al. (2004, 2005), Masár (2002) and Masár & Turanský (2004). Ripeness
of eggs is ascertained by supersonic sonography and oocytes biopsy. Sexual products from
both males and females are obtained by means of hormonal stimulation (Kobarelin, artificial
LH-RH analogue). Concentration of sperms of males from the natural environment is 10
times higher than in those reared in captivity. Eggs from females are obtained by biopsy. First
spermiation of reared males and males from natural environment begins 43-73 and 20-36
hours, respectively and the eggs ovulation appears 23 hours after the hormonal stimulation.
Kryopreservation was also tested, but the results were not successful until now.
embryos are reared in the Rückel-Vacek apparatuses and those from the onset of exogenous
feeding are reared in the nursering tanks with flowing water. Fingerlings fed by tubeworms
display faster growth and lower mortality than those fed by chironomids. The overall
mortality in the period from hatching till stocking ranges from 40 – 45 %. The amount of
fingerlings, localities where they were stocked and size at stocking is shown in Table 1. The
significantly higher number of fingerlings reared and planted in 1989 is due to the fact that in
that year the number of females taken from the Danube River was higher than in subsequent
5. Conservation and restoration proposals
As already stressed out by Bloesch (2003, p. 355): Interdisciplinary / transboundary /
institutional cooperation is a prerequisite for sustainable development of the Danube River
Basin. Although such cooperation is presently existing (…), there is a large potential to
strengthen it… It is especially important for sturgeons which do not recognize political
frontiers, but which are seriously threatened by the political and other human impacts upon
their environment. At present, when the water quality in the Danube River and its tributaries
seems to improve, the most serious danger for sturgeons is poaching and damming of the
rivers in the Danube Basin. Apart of poaching in Slovakia it is the GRBS put in operation on
At present its official name is Research Institute of Animal Production, Nitra, Worskop of Fishery and
Aquaculture, Častá
October 1992. This system has the most serious impact upon abiotic and biotic conditions of
this segment of Danube. The formerly functional ecosystem of the inland delta became extinct
and it is replaced by the artificial system of mutually more or less isolated habitats (Balon &
Holčík 1999, Holčík 2003). Although the following recommendations based on our
experience are aimed on Slovakia, some of them certainly could be used also in other
Danubian countries.
Illegal fishing for sturgeons is responsible for plunder of their still existing
populations. In Slovakia poaching represents special problem after 1990. The
fishery control is insufficient as it is carried out by Fishery Guard composed of
anglers from particular organisations of the SUA and also by the professional
guards of the State Nature Conservation of the Slovak Republic and by the Nature
Guard. However, the authority of the Fishery Guards is very low and influenced
by familiar, amicable and/or labour relations. Also the professional level of its
most members of is low. The number of guards belonging to the State Nature
Conservation is insufficient and their activity is focused especially to the protected
territories. We therefore propose to constitute the independent governmental
organisation – The State Fishery Inspection under the Slovak Environment
Inspection. It is noteworthy to mention, that one of us (J.H) such proposal
submitted to the Ministry of agriculture of the Slovak Socialistic Republic and also
to the Ministry of agriculture of Slovak Republic, in 1977 and 1992, respectively,
but it has never been accepted. Similar Inspections exist in many European
countries, among them in Poland, Hungary and Roumania (Gaudet 1974).
Cooperation of such organizations among Danubian countries should significantly
contribute to the problem of the sturgeon conservation.
Total ban to fish the ship sturgeon Acipenser nudiventris, and the potamodromous
Russian sturgeon Acipenser gueldenstaedti should be declared in all Danubian
Legal size of all diadromous Danubian sturgeons should be the same in all
countries and it should be different in the case of sterlet. It should be chosen in
such a way that all immature females will not get fished. This will protect also the
males, as the sturgeon females grow faster than males. Concerning sterlet in the
Slovak-Hungarian stretch of the Danube we propose the legal size 500 mm in Tl,
and widening of the fishing period ban from March 15 to June 15.
Artificial rearing and stocking of juveniles into the Danube and suitable tributaries
should be supported by all countries. However, the artificial propagation has to
preserve genetic heterogeneity. Brood fishes reared in the neighbouring fish farms
should be mutually exchanged.
All juveniles reared in the fish farms should be adapted to the conditions in natural
water bodies before their stocking. They should be fed natural diet and held in
facilities with lotic environment.
Because stocking with juveniles of hatchery origin cannot conserve the sturgeon
populations, spawning grounds should be protected and the fishing in them should
be banned.
All dams should be provided with effective fish passes of the nature-like designs.
At present the bypass channels simulating natural streams proved to be the best. In
Slovakia such bypass channels is necessary to build in the Kráľová reservoir at
Sereď in the Váh River and in the part of GRBS on the Danube River in the
Hrušov reservoir at Čunovo.
The original side-arms of the Danube floodplain between Bratislava and Sap has to
be restored; to ensure the bilateral fish migration functional fish ways between
them and the main river channel, and between particular parts of arms has to be
Scientific ichthyological research focused on sturgeons is necessary to enhance in
all Danubian countries. Molecular analysis of particular populations, their
migrations and gaps in biology and ecology of particular species should be studied.
To realize particular measures some joint project should be prepared and the
International Association for Danube Research (IAD) should ask European Union for
financial and material support.
The Slovak Union of Anglers Council is acknowledged for supply of statistical data.
Colleagues Ivan Krupka, Emanuel Seeman, Ladislav Pekárik, and Miloš Vater supplied also
some useful information and provided technical assistance, respectively. Martin Holčík
performed linguistic revision of manuscript. We thank them all.
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Table 1. Slovak facilities for artificial propagation of sterlet and their production of
yearlings since 1989 (1Drainage canals; 2Hrušov Reservoir; 3Čenkov – Štúrovo; 4Iža;
Hlohovec; 6Trenčín; 7Old bed at Čunovo; 8Štúrovo; 9Piešťany;
(specimens) (Tl in mm)
Institute of Fishery Research
30 - 50
30 – 50
50 – 60
50 – 60
70 – 90
90 – 110
Váh River5
90 – 110
Váh River6
90 - 110
90 – 110
Váh River6
90 – 110
120 – 150
130 – 160
60 – 100
ZÚGOV, Ltd., Nové Zámky;
60 – 100
Research Institute of Animal
Váh River6
100 – 180
Production, Nitra – Working Place of
Váh River9
100 – 180
Fishery Research and Aquaculture,
Váh River5
100 – 180
Váh River10
100 – 180
Váh River11
100 – 180
and Hydrobiology, Bratislava
– Workshop Častá
Centre of the Slovak Anglers Union
Council, Nové Zámky;