Session B8: Swimming Behaviour of Beluga and Stellate Sturgeons During Their Migration in the Lower Danube River

Abstract: The Lower Danube River (LDR) still supports three naturally self-sustaining species of anadromous sturgeons. Beluga sturgeons (Huso huso) and stellate sturgeons (A. stellatus) are still common while Russian sturgeons (Acipenser gueldenstaedti) became very rare. Studying their swimming behaviour is essential for understanding (i) the impact of construction works aiming to improve conditions for navigation; (ii) sturgeon behaviour in relation to Iron Gate hydropower and navigation systems; (iii) behaviour of young sturgeons during downstream migration towards the Black Sea. A significant number of wild adult sturgeons (N= 103; 39 beluga, 1 Russian and 63 stellate) was implanted with acoustic transmitters, with depth and temperature sensors, and their movements were tracked using arrays of submerged automatic receivers installed in the LDR (R Km 60 – 863) during 2009 – 2014. For some of these fish additional swimming depth data were obtained by manual tracking. Wild born young of the year (YOY) beluga sturgeons (N=27) were captured in the LDR (R Km 123), implanted with acoustic transmitters and released during routine monitoring (June 2010). YOY beluga sturgeons of hatchery origin (N=33) were implanted with acoustic transmitters and stocked in the LDR at R Km 300 and R Km 102 (August 2010). Their movements were tracked and recorded by arrays of submerged acoustic receivers installed on the main Danube (R Km 101) and the three branches of the delta. This paper analyses for the first time on the LDR consistent data (over 70,000 recordings) on swimming speed (upstream and downstream) and swimming depth behaviour of adult sturgeons (beluga and stellate), during spring and autumn migration season, and YOY beluga sturgeons of wild and hatchery origin

Long Distance Migration of Beluga (Huso huso) and Stellate Sturgeon (Acipenser stellatus) in Lower Danube River in Relation with Iron Gate II Dam

Construction of the dams in Lower Danube River (LDR- rkm 0 Sulina – rkm 1075 Baziasi) without fish passages, as well as illegal fishery and river bottom modification due to navigation had negative impact on sturgeon’s populations. Beluga Sturgeon, Stellate Sturgeon and Russian Sturgeon still migrate to spawn in LDR but there is lack of information relating to sturgeons long distance migration in this area. Tagging with Vemco V16 TP acoustic tags, equipped with temperature and depth sensors involved 36 adult Beluga and 44 Stellate Sturgeons provide new data about sturgeon migration. Their migrations are monitored by VR2W receivers, deployed on between rkm 71 and rkm 864. Analysis of data showed that 17% of Beluga and 30% of Stellate Sturgeon never recorded and 30% and 11% of Beluga and Stellate Sturgeon recorded in period more than 30 days after tagging. Only 5% of Beluga and 7% of Stellate Sturgeon have been recorded after a period of more than 1 year. During 2013-2016 4 adult Beluga and 1 adult Stellate Sturgeon were recorded in the IGII Dam area. Results of this investigation showed that sturgeons still approached the IG2 dam and construction of fish passage on this dam is needed

Session E6: Monitoring Strategy of Sturgeon Behaviour to Ensure Functionality of Future Fish Passes: The Iron Gate II Case in the Danube River

Abstract: Preliminary study on sturgeon behaviour funded by the Dutch Partners for Water Programme and the ICPDR Secretariat (2014) has proven that beluga and stellate sturgeons still arrive at Iron Gate 2 dams (Danube R Km 862.8). High water current and impossibility to access Serbian reach of the Danube in the tailrace of Iron Gate 2 HEP (330 m wide) has prevented us from conducting triangulation with the mobile receiver to detect position of the sites where the beluga sturgeon male tended to congregate. The preparatory project funded by the European Investment Bank Luxemburg (2014 - 2015) has adopted a monitoring strategy to achieve the required resolution to positioning the fish pass entrance(s). The strategy is based on four components: (i) detailed 3D bathymetry of the bottom of the river in the area of the tailrace in Romanian and Serbian territorial waters, (ii) water flow velocity profiles recorded at intervals of 100 m, (iii) combined acoustic and radio telemetry tests to achieve the required resolution needed to determine preferred positions in the river of adult sturgeons arriving downstream the dam, and (iv) integration of behavioural data with genetic analysis to distinguish phylogeny of tagged sturgeons in relation to migration seasons and known population segments. Telemetry tests at Iron Gate 2 dams will be conducted by teams from Romania and Serbia under the guidance of a Norwegian expert. Results of this preparatory project fill be incorporated in the planning of a three year large scale study of the behaviour of sturgeons and other migratory fish at Iron Gate dams and reservoirs

Fish movement in Relation to water temperature fluctuations in the Lower Danube river Iron gate II dam area

Water temperature plays an important role in the fish life cycle, and have a direct impact over fish species movement behavior, migration, feeding and reproduction. The impact might be different between the rivers because of hydro morphological factors that are specific for each watercourse (sediments, water conductivity, turbidity, total suspended solids etc.). The study focuses on 3 fish species, Vimba bream (Vimba vimba), Common nase (Chondrostoma nasus), Common barbel (Barbus barbus). Total number of 43 specimens from these three fish species were caught, tagged and released in Danube River upstream and downstream the Iron Gates II dam and tracked using acoustic telemetry equipment. The fish movement was followed for eight months, from September 2019 to April 2020. In this time period, data from 26 Vimba bream, 13 Common nase and 4 Common barbel movement were collected. Acoustic telemetry data was used to evaluate fish movement in relation with the water temperature variation of the Danube River. In all three species studied, was revealed a decrease in the number of detections in the moment when the water temperature drop below 12 °C

Понашање скобаља (Chondrostoma nasus) и буцова (Leuciscus aspius) током узводних миграција након њихове транслокације између две бране на Ђердапу

Истраживање понашања риба током узводних миграција пружа информације које могу послужити као основа за доношење мера и програма заштите.1 У циљу проучавања миграција, 14 јединки скобаља и 8 јединки буцова је ухваћено стајаћим мрежама (димензија 30 m × 2 m, промера окаца 40-50 mm) у Дунаву низводно од бране Ђердап 2. Живе јединке су транспортоване до обале и пре оперативног захвата су анестезиране (96% етанол и уље каранфилића). Хирушким путем су у трбушној дупљи јединки постављени акустични одашиљачи Vemco V9P/V13P, а након опоравка транспортоване су и пуштене један километар узводно од бране Ђердап 2.2 Очитавање сигнала је рађено са 18 VR2W пријемника (10 је распоређено низводно од бране Ђердап 2, док је 8 било узводно), као и са мануелним пријемником (VR100). Било је 202.202 детекција скобаља, на 8 пријемника (5 низводно и 3 узводно од бране Ђердап 2), док је једна јединка детектована мануелним пријемником код бране Ђердап 1. Јединке буцова су детектоване 5.640 пута, на 5 пријемника (4 низводно и 1 узводно од бране Ђердап 2). После одређеног времена 66,7% скобаља је детектована низводно од бране Ђердап 2, док је 33,3% остало у језеру (само једна јединка је детектована код бране Ђердап 1), што указује на преференцу ка низводним миграцијама. Слично је и код буцова, где је 75% јединки након одређеног времена детектована низводно од бране Ђердап 2, док је 25% остало у језеру. Даља истраживања треба да покажу разлоге за уочене разлике у времену које јединке проводе у језеру

Preliminary results on the assessment of Danube River fish species migration behavior in relation to Iron Gate I and II dam using acoustic telemetry equipment

The dam’s construction without fish passes had a major impact, obstructing migratory fish populations from moving between different parts of the river systems and utilizing their key habitats. Fish species and fish populations are depending on long migrations are most seriously affected by river fragmentation. Building well-functioning fish passage systems for migratory fish species at Iron Gate I (rkm 943) and Iron Gate II (rkm 863), is crucial for strengthening and re-establishing Danube’s River migratory fish populations. Between March and May 2021, 112 fish specimens were captured downstream Iron Gate II dam. All the fish was previously tagged with 69 KHz ultrasonic transmitters and released upstream Iron Gate II dam reservoir (53 fish) and downstream Iron Gate II dam (59 fish). Some of the acoustic transmitters are equipped with depth sensors, which provide information of water depths used by fish. Fish movements were recorded by a network of 18 ultrasonic automatic Vemco VR2w receivers (10 downstream the Iron Gate II dam and Gogosu branch, 6 in the IG II lake and 2 receivers at the Iron Gate I dam) with a 15 month battery life, positioned in Danube River. Downloading and interpreting recorded data by these receivers will be an important starting point for "We Pass 2" project that will begin in fall of 2021, when will be realized high resolution recordings of 3D fish movements, for finding the best technical solution for their passing upstream or downstream of dams

Fish Migratory behaviour In proximity to the Iron Gate Dams

River infrastructures, such as hydropower plants Iron Gate I (IG; rkm 943) and II (rkm 863) represent major obstructions to fish migration in the Danube River. Knowledge about fish behaviour and movements in the vicinity of major river structures is required to build effective fish passages to protect migratory fish species, with acoustic telemetry being an useful method for observing such behaviour. From autumn 2019 to the spring 2021, the movement of 185 fish (barbel Barbus barbus, nase Chondrostoma nasus, vimba bream Vimba vimba, asp Leuciscus aspius, Pontic shad Alosa immaculata, and carp Cyprinus carpio) were monitored in the Danube River upstream and downstream of the IG II dam using acoustic telemetry. The movements of tagged fish were recorded by a combination of automatic tracking of fish passing receivers deployed in the river and manual tracking by boat. Of the 101 fish released downstream of IG II, 48% moved upstream from their release site and were detected close to IG II. The remaining 84 tagged fish were released in the reservoir between IG I and II, with 49% of fish moving further upstream in the reservoir and 18% reaching IG I, while 48% of the tagged fish moved in a downstream direction and were recorded below IG II. No fish released downstream of IG II were detected in the reservoir between two dams, which indicates that the ship locks on either side of the river do not represent viable routes for upstream migration around IG II. There was also no clear pattern in which side of the river tagged fish preferred to move along. To conserve migratory fish species, dam management strategies that take into account the behaviour of fish around such structures is necessary. Acoustic telemetry can be used to inform and guide towards construction of the safe fish passage or adapt structures to improve the movement and fish migration

Spatial movement of the Wels catfish (Silurus glanis) in the Danube

Wels catfish (Silurus glanis, Linnaeus, 1758) is one of the most targeted species for recreational and commercial fishing in the Danube River, even though studies of behavior and movement patterns of Wels catfish in the Danube are rare. Wels catfish was caught downstream of Iron Gate II hydropower dam and tagged with an ultrasonic transmitter (Vemco Ltd, V16TP). Nine autonomous receivers (Vemco Ltd, VR 2W) recorded detections of spatial movement downstream of Iron Gate II dam between Serbia and Romania for almost two years, between the years 2015 and 2017. Our telemetry data found that Wels catfish exhibit relatively short movements within a maximum range (≈ 12 km), but as a territorial species most of the time it was recorded by the two receivers, close to the Iron Gate dam and location where it was caught. The longest displacement from the preferable place under Iron Gate II dam was migration to Romanian ship lock and turbines located in the right arm of the Danube River. Location under the river dam is already recognized as a place of aggregation of the fish and thus preference of predatory catfish is strongly connected with food availability. Our data revealed that dam and ship lock blocked further migration of this fish. The last signal received was during the winter 2017, which was a period with extremely low temperature and ice cover on the Danube River. Considering the fact that the ice displaced whole receiver deployment downstream the dam, we might conclude that the tagged catfish disappeared because of ice movement during the winter season. Results can be used for management ensuring habitat requirements and developing of restoration and conservation strategies

Circadian activity of the Wels catfish (Silurus glanis) in the Danube River

In this study, the movements and behaviour of Wels catfish (Silurus glanis, Linnaeus, 1758) were monitored during the different seasons when the water level in the river changed significantly. Wels catfish was caught on the Danube River, rkm 863, and tagged with an ultrasonic transmitter. Deployed Vemco receivers recorded detections of spatial movement between years 2015 and 2017. Our telemetry data found relatively short movements within a maximum range (~12km), but as a territorial species most of the time it was recorded by the two receivers, close to the Iron Gate dam and location where it was caught. Circadian rhythm showed that in the summer period, nocturnal activity is evident while during winter Wels catfish stayed most of the time at the same depth under the water surface. Wels catfish changed depths during the autumn and spring when more activity was recorded. The last signal received was during the winter 2017, which was period with the low temperatures and ice cover on the Danube River. This research shows the value and importance of installing coded acoustic transmitters in fish and monitoring their movement using a series of autonomous receivers deployed in the Danube River. Research by telemetry can be used to better understand fish behaviour and movements and to help improve large river management measures

Nuclear Markers of Danube Sturgeons Hybridization

Acipenseriformes are composed of 25 sturgeon species and two paddlefish species distributed exclusively in the northern hemisphere. The Danube River and the Black Sea were originally inhabited by six sturgeon species but two are extinct and only four are still reproducing currently in the Lower Danube: Huso huso, Acipenser stellatus, A. gueldenstaedtii and A. ruthenus. Sturgeon species hybridize more easily than other fish and the determination of pure species or hybrid status is important for conservation and for breeding in fish farms. This survey demonstrated that morphological determination of this status is not reliable and a molecular tool, based on eight microsatellites genotypes is proposed. This method, based on three successive statistical analyses including Factorial Correspondence Analysis (FCA), Structure assignation and NewHybrids status determination, showed a high efficiency in discriminating pure species specimens from F1, F2 and two kinds of backcross individuals involving three of the four reproducing Lower Danube sturgeon species