Habitats of sturgeons in the Lower Danube River and the North Western Black Sea: status of knowledge and perspectives for restoration

FAO Regional Conference on River habitat restoration for inland fisheries in the DRB and adjacent Black Sea areas. 13-15 November 2018, Bucharest, Romania

Radu Suciu – DSTF and IAD RomaniaMarian Paraschiv, Marian Iani, Stefan Honţ – Danube Delta National Institute Tulcea (DDNI)Tudor Ionescu – Lower Danube University Galați

Content:

1. Sturgeons of the Danube River

2. Peculiarities and importance of riverine and marine habitats for the survival of sturgeons

3. Wintering habitats in the Black Sea and in the Lower Danube River (LDR)

4. Spawning habitats

5. Nursery habitats

6. Feeding habitats for juveniles, subadults and adults in the Black Sea

7. Impact of ongoing hydrotechnical works, for the improvement of conditions for navigation in the LDR, on sturgeon habitats

8. Restoration of longitudinal connectivity at Iron Gate dams to provide access to historical habitats

Photo credits: Marian Paraschiv /DDNI

Beluga Sturgeon

Russian Sturgeon

Stellate Sturgeon

1. Sturgeons of the Danube River: historically 6 species; now only 5 species

Juveniles captured in the Black Sea coastal waters / Ciotica (Sept, 1995)

Photo R. Suciu / DDNI

Beluga Sturgeon (Huso huso)

Russian Sturgeon (A. gueldenstaedti)

Sterlet (Acipenser ruthenus)

Photo: R. Suciu /DDNI

Young of the year captured in the LDR at rKm 123 on June 16, 2005

Russian sturgeon (A. gueldenstaedtii)

Stellate sturgeon (Acipenser stellatus )

Adult

Young of the year (YOY)

Sterlet (Acipenser ruthenus)

The only sturgeon species left in the Middle and Upper Danube River (and some tributaries)

Photo: Vasile Otel / DDNI

Beluga sturgeon (Huso huso)

Photos by Marian Paraschiv / DDNI Tulcea

Beluga sturgeon (Huso huso)

Beluga sturgeon femaleTW≈ 210 KgTL = 2.95 mLocation: Isaccea Hatchery of Kaviar House Ltd IsacceaDate: April 2006

Photo: Radu Suciu / DDNI

Ship sturgeon (Acipenser nudiventris)possibly extinct in the LDR but survives in the MDR, Drava and Mura Rivers (?)

Serbia: Danube River Km 1390 - Apatin, Oct. 31, 2003

Sturgeon Live GenBank of the Russian FederationKrasnodar (2001)

Photo: Mikhail Cebanov

Photo: Predrag Simonovic

Donauinsel Vienna, BOKU Life Sterlet Project, 10 Sept. 2017

Photo: Marieta Suciu

• All sturgeons are long-living freshwater fish adapted to live in deep water, on the bottom of rivers, i.e. they almost never swim at the surface of water;

• many species adapted to feed as juveniles and adults in the sea;

• all their life stages in the river and in the sea are bound to habitats located in deep water;

• most sturgeons are lithophilic / hard substrate spawners, i.e. they lay their eggs on hard substrate and after hatching their free embryos hide in crevices;

• some are litho-pelagophylic, i. e. they lay their eggs on hard substrate but their free embryos are pelagic;

• all sturgeons are migratory fish, i.e. at sexual maturation they migrate in rivers to spawn on the same grounds were they were borne (phenomenon called homing);

• blocking the access of adult sturgeons to their home ranges for spawning is causing severe declines of populations / declines of catches and even extinction;

• the process of adaptation to other / new spawning sites is presumed to be possible but it may be hampered by the innate behavior / survival strategy of their early life stages.

2. Peculiarities and importance of riverine and marine habitats for the survival of sturgeons

Case study: Damming the Danube River at Iron Gates

• 1974 – Iron Gates I / R Km 943

• 1984 – Iron Gates II / R Km 863

The impact of damming the Danube at Iron GatesH. huso (1920 - 2005)

0

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[to

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Catches of beluga sturgeon recorded in Romania during 1920 - 2005

Iron Gates I

No data

Iron Gates II

3. Wintering habitats in the Black Sea and in the Lower Danube River

∆H = 12.5m

Borcea Branch Km 49 /“Devils Bend”

3D bathymetric survey

Beluga male 95710 (70 Kg / 209 cm)59 days

Karkinyt Bay

Wintering site of adult Beluga sturgeons in the

NW Black Sea,Karkinyt Bay

As tracked by satellite transmitters MK 10 - PAT

from Suciu et al. 2015

Wintering habitat at Km 7.7 on Danube branch Bala

3D bathymetricsurvey

ΔH = 4 m

from Suciu et al. 2012

4. Spawning habitats

3D bathymetric map of the spawning habitat for sturgeons atLDR Km 100.5 / Noviodunum (Isaccea)

Longitudinal section through the waiting

site downstream of the spawning habitat

at Noviodunum

Grounds with hard substrate are found were the river meets rocky banks, which often deviate the current and cause counter currents / eddy

Spawning habitat for beluga and sterlet at RKm 100.5 / Noviodunumconfirmed by capturing larvae in 2008, 2013, and 2015

750 m

1000 m

Narrowing effect of rocky banks

22 July 2000

Location of potential spawning grounds - were the river meets rocky banks

Noviodunum, D Km 100.5

Red Rock, D Km 311

Photos: Radu Suciu / DDNI

Spawning habitat for beluga and sterlet at RKm 311, “The Red Rock”, confirmed by capturing fertilized eggs and larvae in 2004, 2007, and 2009

Medium water level (27 May 2000)

Low water level (22 July 2000)

21 Febr. 2017

Waiting place before spawning

LDR Km 311

3 D bathymetric map and profile by Global Mapper v.13.00

Photo: Marian Paraschiv / DDNI

Confirming spawning habitats by capturing larvae :

Setting drift nets atwater dept of 12m

At D K 100.3 (16 Apr. 2015)

Sterlet (29. April 2009) D Km 310.8

12 - 14 day old feeding larvae captured at:

Beluga sturgeon (13 May 2013)D Km 100.3

Typical setup of floats at the anchor and the D-shaped drift net

Feeding / nursery site for YOY sturgeons at Danube Km 309

5. Nursery habitats

Stomach content of YOY sterlets captured on nursery habitat at D Km 123

Location can be demonstrated by capturing YOY sturgeons and extracting their stomach content

Nursery habitats are ideal locations to monitor annual recruitment from the wild

Capturing YOY:

Timing: June – July (5d / week)

Fishing gear: bottom drifting trammel net

YOY beluga of June 2013

6. Feeding habitats for juveniles, sub-adults and adults in the Black Sea

Zatoane

Sahalin

Holostenco et al. 2013

86.5 % of all YOY and juvenile sturgeons

captured during year 2012 in 10 marine areas of

theDanube Delta Biosphere Reserve were

captured in areas 8-SAHALIN and 7- ZATOANE

most important feeding habitats

for young sturgeons on the Black Sea

continental shelf in Romania

Feeding habitats for juveniles, sub-adults and adults in the Black Sea

Ionescu et al. 2017

Locations of feeding habitats in the NW

Black Sea continental shelf were YOY

and juvenile sturgeons (N = 1627) were

captured during 2014 - 2016

Beluga male ID 95710 (TW =70 Kg ; TL =209 cm)

Dep

th [

m]

Date

Hunting for pray fish

Diving for pray

from Suciu et al. 2015

- 25m

June July

Feeding habitats for adult Danube beluga sturgeon in the Black Sea

Swimming depth of beluga male / ID 95719, during May – July 2009

7. Impact on sturgeon habitats of hydrotechnical works for the improvement of conditions for navigation in the LDR

• Blocking of main migration route: submerged sill constructed on the Bala arm km (2015)

• Siltation of wintering holes: St. George arm km 67; Bala arm Km 7.7

• Deepening or straightening the fairway by dredging is perceived by migrant sturgeons as unsafe / threatening: Saint George arm / 2003

• Moving the channel for navigation purposes can affect flow conditions on nearby spawning grounds

To avoid or reduce to the minimum the impact on sturgeon habitats the ongoing navigation project FAST DANUBE (D Km 375 - 862):- has conducted 3D bathymetric survey of all 12 critical points;- technical solutions for each critical point have been studied by 3D modelling;- is willing / keen to adopt solutions less impacting for sturgeon habitats.

DDNI Tulcea is providing assistance on assessment of potential habitat for sturgeon, including spawning, wintering and nursery habitats; currently CH2m / Halcrow is considering to prolong the duration of the survey to a whole year to allow completing the survey in all 12 critical point reaches of the river.

Survey of November 2000:

• deep hole with abrupt

front stair (Δ H≈7m)

• very low water velocity

(0.13 m/s) at 15.8m

• in the LDR these holes are produced by the Coriolis Effect / Force

• Survey repeated in January 2003 found the hole totally silted

The impact of cutting in year 1985 meanders of the St. George Danube branch on the wintering hole at Km 67 / Uzlina

Two adult stellate sturgeons tagged by us in Septemberwith acoustic transmitters were captured there by angler /fishermen in late fall of 1999 (Kynard 2002)

Case study:

Start

Bala arm, April 22, 2015

-18.3-19 -19 -19.2 -18.9

-18

-16.2

-10

-14

-21

-23.3

-25.5

-23

-25.5 -25.3-26.1

-27.7-27

-25.4

-22.5-23

-20

-15.8

-10.5

-16.7

-21.2

-23.9 -23.7

-22.1-21.2

-20

-18.6

-17.6-17

-16.6-16.2 -15.9

-30

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-10

-5

0

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Longitudinal depth profile [m] at the submerged sill, on Bala arm Km 9

8 mReduction of water depth by

Case study: submerged sill on Bala arm Km 9

Water depth [m]

Locationwater

velocity [m/sec]

0.1 at the surface 2.2

7.5 2.16

23 near bottom 1.72

Water velocity survey

on Bala arm: April 22, 2015

Water depth [m]

Locationwater

velocity [m/sec]

0.1 at the surface 1.22

4.5 1.22

10 1.14

13.5 near bottom 0.65

Second half of April – migration period of stellate sturgeons

Admissible maximum water velocity for medium size

sturgeons (like the stellate sturgeon): 1.5 m/sec for 2 minutes

(Peake et al. 1997)

8. Restoration of longitudinal connectivity at Iron Gate dams to provide access to historical habitats

• Completion in year 1974 of the Iron Gate I dam at R Km 943 (without any fish passage) has reduced by half essential spawning and rearing habitats for anadromous sturgeons in the Danube River;

• This dam was followed by a second, Iron Gate II, completed in year 1984 at D Km 863;

• In May 2011 FAO has organized a technical support expert mission (5) to the Iron Gates dams, in RO and SERB, which concluded that construction of fish passages at IG is possible;

• In year 2014, on behalf of the EC, the EIB of Luxemburg commissioned DDNI Tulcea to conduct a preparatory study for a large scale fish behavior study at the Iron Gate dams;

• In September 2018 EC -DG Regio has announced a grant to ICPDR Vienna, DDNI Tulcea and the Sinisa Stancovic Institute of Belgrade to conduct the large scale fish behavior and hydraulic study needed for the feasibility study on fish passages at the Iron Gate dams.

3D bathymetric map d/s Iron Gate II HP dam at D Km 863 / March 2015

General bathymetric map of the LDR reach d/s Iron Gate II HPP, with main characteristic water depth values (survey of DDNI, March 2, 2015)

From Suciu et al. 2015

Romania

Serbia

Serbian fishermen capturing > 100 nase (Chondrostoma nasus) in one 50 m long gillnet (24 Sept. 2015)

Case study: concentration of migratory fishes at Djerdap II dam

Photo: courtesy of Mirjana Lenhardt / IMSI Belgrade

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