Transcript River fragmentation disrupts the natural biophysical and

Capacity Building Workshop on
Biodiversity Indicators
SEBI 14 Fragmentation of river systems
Institute for Nature Conservation of Serbia
Serbian Environmental Protection Agency
Jasmina Mijović Magdić
Slaviša Popović
How to interpret the indicator:
River fragmentation disrupts the natural biophysical and ecological processes
essential for maintaining life in freshwaters.
Dams disconnect rivers from the surrounding floodplains,
block migratory fish passage, and retain sediments and nutrients
that nourish downstream ecosystems.
Reservoirs turn running water habitats into lake-like systems,
resulting in the disappearance of fish species adapted to riverine habitats
and the proliferation of other, often exotic species adapted to still waters.
In highly fragmented rivers the diversity of life is likely to have been reduced
and the adaptive capacity of native species impacted.
Therefore an increase in river fragmentation indicates a higher
likelihood of biodiversity loss as well as a disruption in ecosystem service delivery.
Freshwater ecosystems including rivers, lakes and wetlands are extremely
rich in species, but unfortunately, are also amongst the most altered
and threatened ecosystems in the world.
The natural flow regime and the longitudinal and lateral connectivity of rivers,
both essential characteristics that sustain the biophysical and ecological processes
necessary for life in freshwaters,
are disrupted when rivers are fragmented by dams and their reservoirs.
The purpose of the river fragmentation and flow regulation indicator is to provide a
measure of the degree to which rivers’ connectivity and flow regime have been altered by
dams and reservoirs. The impacts of dams and reservoirs vary depending on the number
and size of the dams, where they are located on the river system, as well as the storage
capacity of the associated reservoirs. Fragmentation rankings (i.e., highly affected,
moderately affected and unaffected) are assigned to each large river system using the
number, location, and storage capacity of dams to estimate the proportion of free flowing
kilometars of river length, as well as the annual runoff that is stored behind dams
throughout the system.
The Iron Gates Dams and Disruption of Spawning Migration
Iron Gates dam
Located just below the Iron Gates gorge (Đerdap) between Romania and Serbia, Iron Gates
is the largest hydropower dam and reservoir system along the entire Danube. The system
consists of two main dams, Iron Gates I and II, built in 1972 and 1985 respectively. The dams
are constructed at river km 942 and river km 863 upstream of the Danube delta, in effect
confining migratory sturgeons to 863 km of the river and cutting off important spawning
sites in the Middle Danube. Iron Gates is jointly operated by Romania and Serbia.
Dams block access to most of sturgeon fish spawning areas and therefore it is believed that it is the
one of the main causes for the decline of their population abundance. Construction of hydro energetic
system on the territory of Djerdap gorge led to formation of two reservoirs with total area of
approximately 25,000 ha. ‘’Djerdap I’’ was finished in 1970 and ‘’Djerdap II’’ in 1984, on 943 and 863 km
of river, respectively. Complex of technical and ecological factors caused changes in fish distribution as
well as in commercial fishing. The construction of Djerdap II has shortened migratory ways of Black
Sea migratory species and significantly reduced their catch.
There was only 17,8 km of flow accessible as spawning ground to sturgeon fish species left in Serbia
after the construction of ‘’Djerdap II’’. The exact locations of spawning grounds on our territory still
haven’t been determined. In Bulgarian part of Danube 13 spawning locations have been determined,
located between 840 and 750 km of river while between 600 and 150 km of river 5 spawning locations
have been registered.
Changes in fish fauna caused by the
river fragmentation by transversal
hydrotechnical structures: Danube and Drina river
Danube Sturgeons Species
Beluga Sturgeon
Russian Sturgeon
Stellate Sturegeon
Ship Sturegeon
Sterlet
European Sturgeon
ENDANGERING FACTORS
Over-exploitation
Construction of dams and regulation of river flow
Habitat Loss
Water pollution
Influence of political, social and economic changes on territory
of lower Danube on sturgeon catch
Source of valuable
Beluga caviar
Beluga Sturgeon
(Huso huso)
 The Beluga Sturgeon is the biggest freshwater fish in the world. The largest Beluga ever caught weighed 1,571 kg
and was 7.2 m long. The Beluga is extremely long lived and does not reach maturity until at least 15 years of age.
Beluga Sturgeons are listed as Critically Endangered.
 The Beluga migrates further upstream to spawn than any other sturgeon. However, this migration has been
interrupted – as for all other sturgeons – by the Iron Gates dams.
 Though mainly eating fish, the larger individuals can feed even on aquatic birds. The Belugas are the only true
predators among Danube sturgeons.
 The Beluga is extremely long lived. Individuals can reach more than 100 years in age and can still be caught in
areas where their spawning sites have been cut off.
 60% decline of Beluga catch in 3 years according to data from Romania.
ANNUAL CATCH OF BELUGA IN SERBIA
Statistical Office of the Republic of Serbia
Beluga’s catch statistics were conducted relatively well during the 1960-1996, after which,
due to political and economical situation in the country, it become incomplete and
unreliable From 2003, due to ratification of CITES Convention, beluga’s catch statistic are
conducted again. According to data from 2004, overall catch was 13 individuals, with total
weight 1584 kg, including 3 males (83-93 kg) and 10 females (61-210 kg). All individuals were
caught in period from 08.10 – 16.11.2004, except one female, which was caught in April for
requirements of artificial spawning (200 kg). During 2004, 5 crews of fishermen
participated in beluga catch, every crew with two members. Catch was conducted on
Danube River, downstream from “Djerdap II” dam, on 3 km long area. Research conducted
during 2001 showed that in catch were also present 47 (female) and 35 (male) years old
individuals.
Russian Sturgeon
(Acipenser gueldenstaedti)
Source of valuable
Osietra caviar
Russian Sturgeon was formerly the most widely distributed sturgeon species in the Danube river. It regularly
migrated upstream as far as Bratislava. Today Russian Sturgeons are listed as Critically Endangered.

209,000 individuals were feeding in the north-western part of the Black Sea in the period 1966-1974. The
current stock size is unknown but regarded as very low.

The Russian Sturgeon was formerly the most common sturgeon species in the Danube river. It regularly
migrated upstream as far as Bratislava. Some individuals have even been spotted in Vienna (river km 1,925) and
Regensburg (river km 2,381).

Individuals migrating in spring enter freshwater just before spawning and spawn in lower reaches of the river
(320-650 km upstream). Individuals migrating in autumn spawn the following spring further upstream (900-1200
km).

The annual catch in ex-Yugoslavia dropped from 14,636 kg in 1983 to 1,636 kg in 1985 (a decline of almost 90%)
due to the construction of Iron Gate II dam in 1984, which cut off spawning grounds.

99% is the decline of Russian Sturgeon catch in 4 years according to data from Romania.
A.guedensteadtii
(before and after Djerdap dam was built)
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
1970.
1975.
ANNUAL CATCH OF RUSSIAN STURGEON IN SERBIA
Stellate Sturegeon
(Acipenser stellatus)
Source of Stevruga caviar
Stellate Sturgeon was always rare in the Middle and Upper Danube, but also ascended several tributaries as Prut,
Tisza, Drava, Sava and Morava. Stellate Sturgeons are listed as Critically Endangered.





The species was never abundant in the Danube River basin. In 2009, the last Ship Sturgeon was caught in
Hungary, in the Middle Danube. There have been no documented catches in Romania for at least 30-40 years.
The last scientifically recorded catch of Ship Sturgeon in Romania was in the 1950s. Ship Sturgeons are listed as
extinct in Romania and Bulgaria.
The Ship Sturgeon likes to live at sea, close to shores and estuaries.
In freshwater it favours deep stretches of large rivers.
The Ship Sturgeon spends at least part of its life in salt water, returning to rivers to breed, but some nonmigratory freshwater populations also exist.
ANNUAL CATCH OF STELLATE STURGEON IN
SERBIA
A. STELLATUS
Ship sturgeon (Acipenser nudiventris)
 Ship sturgeon is widely distributed through Aral, Caspian, Azov and Black Sea basins. Although ship sturgeon
forms both anadromous and residual populations, only residual type is in Danube River. Prefered habitat is based
on ship sturgeon diet, so it dwells in shallow water above muddy bottom.
 Maximal recorded age was 36 years. Males become sexually mature at the age 6-9 years and females at 12-14
years. Spawning period for females is every 2 to 3 years. Ship sturgeon is spawning from the end of April to June,
on temperature 10-15ºC. It chooses gravelly, rocky or stone bottom, with fast river flow.
 It is believed that the ship sturgeon population is in process of disappearing in area of Republic of Serbia, because
last records in twentieth century were in period 1948-1954, when there was recorded only 5 individuals. Only one
new record was in October of 2003, in Danube River near Apatin.
European Sturgeon
(Acipenser sturio)
European Sturgeon was always the rarest sturgeon species in the Black Sea basin and its presence was only
documented until the beginning of the 20th century. Today it is listed as Critically Endangered.
 According to one source, the last record of European Sturgeon in the Serbian part of the Danube river was in
1954.

In the Black Sea basin the European Sturgeon was always the rarest sturgeon species and its presence was only
documented until the beginning of the 20th century.

European Sturgeons enter rivers from January to October, with peak migration usually occurring in periods of
high water between April and May.

During their stay at sea, European Sturgeons stick to estuaries and their muddy bottoms.

We know that this species spawned in the Lower Danube because hybrids with other Danube sturgeon species
were described in the 1930s.
Sterlet (Acipenser ruthenus)
Sterlet lives entirely in freshwater and unlike other sturgeons does not migrate from the Black Sea. Nowadays it is
the most widely distributed sturgeon species in the Danube River basin. It is listed as Vulnerable.





After a decline of stocks in the Danube in previous centuries, the species numbers have been increasing since
the 1980s.
The average reproductive age of this species is comparably low, about 8 years. In the Danube it is even lower –
about 7 years.
This species is largely sedentary, undertaking only short spawning migrations. Tagging has revealed a maximum
migration distance in the Danube of just over 300 km.
The only available catch data for the Danube is for 1958-1981, where catches ranged from 117 tonnes in 1963 to 36
tonnes in 1979, with an average catch of 63.5 tonnes per year.
Hungary, Bulgaria and Romania have all reported re-stocking programmes for their stretches of the Danube.
ANNUAL CATCH OF STERLET IN SERBIA
Acipenser ruthenus
FISH STOCK ASSESMENT
BIOMASS
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
kg
0
2006.
2007.
2008.
2009.
2010.
2011.
2012.
ANNUAL CATCH OF FISH IN DUNAV: 941-845 km between
Djerdap I and Djerdap II
Statistical Office of the Republic of Serbia
Visegrad
Perucac
Water barrier dams on river Drina
Zvornik
FISH STOCK ASSESMENT
BIOMASS
70
60
kg/ha
50
40
DRINA I
30
20
DRINA II
ZVORNIK LAKE
DRINA III
10
0
DRINA IV