Estimating Fish Communities Structure and Diversity from Predeltaic Danube Area

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1 Estimating Fish Communities Structure and Diversity from Predeltaic Danube Area Petronela Georgiana (Călin) Sandu *, Lucian Oprea "Dunarea de Jos" University of Galati, Romania Department of Aquaculture, Environmental Science and Cadastre Abstract The paper is presenting some aspects regarding the structure of fish communities from 22 Km of predeltaic sector of Danube River, between the mouth of Siret River (km 155) and Prut River (Mm 72.5). The aim of the study is to assess the ecological status of the area, using some analytical and synthetic ecological indices, but also diversity and equitability indices. From April to December 2012, in four fishing areas (km , Mm 77-78, Mm 76-77, Mm ), 7121 fish of 31 species, from 7 famillies and 6 orders, were collected. The best represented family is Cyprinidae with 17 species. The numerical abundance ranged between 1fish/species (zingel, Danube streber and Black Sea trout-rare species) and 2035 fish/specie (pontic shad - abundant specie). The pontic shad (43.98%), common bream (12.09%) and Prussian carp (10.66%) are eudominant species, having the biggest potential in fish productivity. Keywords: abundance, Danube, diversity, ecological significance fish communities 1. Introduction Many human uses of Danube River (i.e. transportation, wastes, pollution) are potentially in conflict with the aquatic living resources. In addition, human activities not only have an impact on fish communities, but in the same way also rebound in human communities associated with the exploitation of these resources [1, 2].The structure and the diversity of fish communities is an important feature in the system dynamics because changes in diversity reflect changes in the ecosystem processes, such as productivity, energy pathways and material flow, disturbance regimes, abiotic stress and biological interactions [3]. A good management of the interactive components of the fishery should always lead to a durable exploitation, in terms of biodiversity conservation and protection. In the last years, however, unfortunately, the over-exploitation of * Corresponding author: Georgiana (Călin) Sandu, georgiana_nutu@yahoo.com the fish communities at the same time as the continuous degradation of the habitats led to the decline and even to the extinction of some fish species [4]. Therefore, in order to take some efficient conservation measures, a good knowledge of the species ecobiology and of their interaction with their living environment is necessary [5]. In this work there are presented some aspects regarding the structure and the ecological assessment of the fish communities from predeltaic Danube. The aim of the researches is to highlight the structural changes from the level of the ichthyofauna, by using some analytical and synthetic ecological indices. 2. Materials and methods Fishing area The study area is represented by a region in the predeltaic Danube, located between the Siret River Mouth (km 155) and the Prut River Mouth (Mm 72.5). This region has approximately 22 km, representing the length of the Danube sector in Galati County. Monthly, systematic measurements 227

2 have been made in 4 fishing areas: Galati area (km ), Condrea area (Mm 77-78), Muresanu area (Mm 76-77) and Plopi area (Mm ) (Figure 1). Fishing effort, fishing gears and methods The structure of a fishing unit (FU) is the following: the fishing boat, the gear and 2 fishermen. On the average, in an area more FU operate, making 2-3 operations/fishing day [6]. The fishing has been made through active methods, on areas, with filtering gear: gill net and trammel net type. The constructive characteristics of these varied, depending on the targeted species to be caught: gill nets (Lp m; p ; a mm), trammel nets (Lp m; p ; a mm). The used method for obtaining the capture data is the simple randomized samples. The caught specimens have been identified and divided on species; biometric and gravimetric measurements have been made. The identification of the fish species was made by analyzing the specialized literature [7-10]. Figure 1. Map of fishing area (satellite image) Fishermen teams, from Dunărea de Jos University of Galati, Department of Aquaculture, Environmental Science and Cadastre and from the Institute of Research and Development for Aquatic Ecology, Fishery and Aquaculture Galaţi, have been making scientific fishing, according to the conditions of the authorization issued by National Agency for Fishing and Aquaculture. The calculation of the ecological indices and statistical approaches The structural changes at the level of ichtiocenoses are characterized by using some analytical ecological indices (abundance, dominance, constancy) and synthetic ones (the index of ecological significance), but also diversity and equitability indices [3]. The statistical methods of the data have been made with the computer (MSOffice Excell) and with the software BioDiversity Pro. Formulas The Bray-Curtis (B) dissimilarity index, takes values between 0-1 [12, 13]. B Xij Xik Xij Xij where: Xij, Xik the number of individuals from a species in each sample; Shannon-Wiener ( ) index:, S i1 piln pi pi the abundance ratio of breed i; ln common logarithm. Simpson (D) index is among the first diversity indices (Simpson 1949) [14]. S D 1 pi i1 2 The Simpson (1-D) diversity index is used for the correct estimation of a finite population: 1 D 1 ni ( ni 1) N( N 1) 228

3 ni the number of individuals from breed i; Ni the total number of individuals from the analyzed sample. The equitability refers to the example of individuals distribution between species [15]. The Shannon equitability index has been calculated (relative diversity R ) but also the Simpson E 1-D equitability index. R S Smxa log S E1 D 1 D (1 D) max 3. Results and discussion Between April-December 2012, there were caught 7121 fish, with a total biomass of kg, of 31 species, from 7 families, respectively 6 orders. The autochthon and allochthonous ichthyofauna in the predeltaic Danube is divided in two groups, depending on salinity tolerance: euryhaline and stenohaline species (Table 1). The best represented family is Cyprinidae, of the Cypriniformes order, with 17 species (Figure 2). Table 1. The qualitative structure of ichthyofauna and their salinity tolerance No. Latin name of species Common name Eurihaline Stenohaline 1 Aspius aspius (Linnaeus, 1758) Asp x 2 Blicca bjöerkna (Linnaeus, 1758) White bream x 3 Carassius gibelio (Bloch, 1782) Prussian carp x 4 Abramis sapa (Pallas, 1814) White-eye bream x 5 Ctenopharyngodon idella (Valenciennes,1844) Grass carp x 6 Cyprinus carpio (Linnaeus,1758) Carp x 7 Vimba vimba (Linnaeus,1758) Vimba x 8 Barbus barbus (Linnaeus,1758) Common barbel x 9 ypophthalmichthys nobilis (Richardson,1845) Bighead carp x 10 Abramis brama (Linnaeus,1758) Common bream x 11 Pelecus cultratus (Linnaeus,1758) Ziege x 12 ypophthalmichthys molitrix (Valenciennes,1844) Silver carp x 13 Chondrostoma nassus (Linnaeus,1758) Common nase x 14 Leuciscus idus (Linnaeus,1758) Ide x 15 Scardinius erythrophthalmus (Linnaeus,1758) Rudd x 16 Rutilus rutilus (Linnaeus,1758) Roach x 17 Alburnus alburnus (Linnaeus,1758) Bleak x 18 Acipenser ruthenus (Linnaeus,1758) Sterlet x 19 uso huso (Linnaeus,1758) Beluga sturgeon x 20 Acipenser stellatus (Pallas,1771) Stellate sturgeon x 21 Acipenser gueldenstaedti (Brandt, 1833) Danube sturgeon x 22 Alosa immaculata (Bennett, 1835) Pontic shad x 23 Alosa tanaica (Grimm, 1901) Azov shad x 24 Zinger streber (Linnaeus, 1758) Danube streber x 25 Zingel zingel (Linnaeus, 1758) Zingel x 26 Sander lucioperca (Linnaeus, 1758) Pike-perch x 27 Gymnocephalus schraetzer (Linnaeus, 1758) Schraetzer x 28 Perca fluviatilis (Linnaeus, 1758) Perch x 29 Silurus glanis (Linnaeus, 1758) Wels catfish x 30 Esox lucius (Linnaeus,1758) Northern pike x 31 Salmo labrax (Pallas, 1814) Black Sea trout x 229

4 Figure 2. The numerical structure of fish species Figure 3. The abundance of fish In table 2 there are presented the main analytic and synthetic ecological indices. The numerical abundance of the species and the biomass is given in Figures 3 and 4. It ranged between 1 fish/species (zingel, Danube streber and Black Sea trout species) and 2035 fish/specie (pontic shad abundant specie). The total values of the biomass ranged between kg/specie. Concerning the dominance (D), the species are grouped on 5 classes, depending on the percentage. The pontic shad, common bream and Prussian carp are eudominant species (over 10% from the fish production), which influence decisively the fishing productivity. The common carp, common barbel, ziege, white-eye bream, asp, vimba, wels catfish and pike-perch are subdominant species (2.1-5%). The Azov shad and sterlet are recedent species (1.2-2%), and the other eighteen identified species are underrecedent, with percentage under 1.1%. Dependent on the value of the constant (C), which represents the continuity in the biotope, the Figure 4. The abundance of fish biomass breeds are divided in the following categories: constant, present in % of the months (asp, prussian carp, common carp, vimba, common barbel, bighead carp, common bream, silver carp, pike-perch, wels catfish, white-eye bream, ide, sterlet, white bream, stellate sturgeon). The accessory species ( %) are ziege, beluga, Northern pike, common nase, rudd and pontic shad. There are ten accidental species (1-25%), less common during the year: grass carp, Azov shad, roach, Danube sturgeon, perch, schraetzer, bleak, zingel, Danube streber and Black Sea trout. The values of the ecological significance index (W) shows us that pontic shad (W5) is a eudominant species, common bream (W4), and Prussian carp (W4) are dominant species; these two classes are characteristic species (over 5.1%). There are seventeen accessory species (0.1-5%): common carp, common barbel, white-eye bream, asp, vimba, wels catfish, pike-perch, ziege, sterlet (W3-subdominant species) and bighead carp, silver carp, Azov shad, white bream, ide, stellate sturgeon, rudd, beluga (W2-recedent species). 230

5 Table 2. The ecological indices of fish communities from predeltaic Danube River Ecological indices Specie Abundance (A) Ecological Dominance (D) Constancy (C) significance (W) Number Biomass (kg) % Class % Class % Class 1. Asp D C W3 2. White bream D C W2 3. Prussian carp D C W4 4. White-eye bream D C W3 5. Grass carp D C W1 6. Carp D C W3 7. Vimba D C W3 8. Barbel D C W3 9. Bighead carp D C W2 10. Common bream D C W4 11. Ziege D C W3 12. Silver carp D C W2 13. Common nase D C W1 14. Ide D C W2 15. Rudd D C W2 16. Roach D C W1 17. Bleak D C W1 18. Sterlet D C W2 19. Beluga sturgeon D C W2 20. Stellate sturgeon D C W2 21. Danube strugeon D C W1 22. Pontic shad D C W5 23. Azov shad D C W2 24. Danube streber D C W1 25. Zingel D C W1 26. Pike-perch D C W1 27. Schraetzer D C W1 28. Perch D C W3 29. Wels catfish D C W3 30. Northern pike D C W1 31. Black Sea trout D C W1 D1-subrecedent species (<1.1%); D2-recedent species (1.2-2%); D3-subdominant species (2.1-5%); D4-dominant species (5.1-10%); D5-eudominant species (>10%); C1-accidental species (1-25%); C2-accessory species ( %); C3-constant species ( %); C4-euconstant species ( %); W1-subrecedent species (accidental) (<0.1%); W2-recedent species (0.1-1%); W3-subdominant species (accessory) (1.1-5%); W4 - dominant species (5.1-10%); W5-eudominant species (characteristic) (>10%); No crt. In category W1 there are eleven accidental species, with an index lower than 0.1% (norternpike, perch, common nase, roach, Danube sturgeon, grass carp, schraetzer, bleak, zingel, Danube streber and Black Sea trout). Concerning the frequency in the catch (the numerical abundance), from the analysis of the Bray-Curtis similarity dendrogram of the fish species, it can be seen that two species (white bream and rudd) have a maximum coefficient of 100%, because they occurred in the catches only twice (Figure 5). Other clusters of two species (ide and stellate In figure 6 are presented the Shannon-Wiener indices values ( ), the equitability ( R ), the sturgeon) and three species (zingel, Danube streber and Black Sea trout) have a high maximum similarity. From this point of view, there is a great resemblance between the ziege and the white-eye bream (99.40%), which occurred in catches 252 times and respectively 249 times. Other groups of high similarity: between sterlet and Azov shad (96.92%), also between the perch and the wels catfish (96.51%). The pontic shad (43.13%) is isolated from the other breeds, because it registers the highest percent in the catches, during the spring season, when it migrates for reproduction. Simpson diversity index (1-D) and equitability (E 1-D ). The Shannon-Wiener index has the value 231

6 ( ) of 2.12, and the teoretical maximum ( max ) of The specialised literature mentions that for ( ) values between 0 (when there is only one breed in the sample) and 5 (when there are more species) [4, 15]. The equitability ( R ) is 0.62 representing 62% from the real maximum diversity. The Simpson diversity index (1-D), has value between 0-1 [5]. By calculating, a good value has been obtained (0.77), the maximum theoretical value is The equitability (E 1-D ) is 0,80; this represents 80% from the real maximum diversity. Figure 5. The Bray-Curtis dendrogram of similarity, according with catch frequency 4 3,5 3 2,5 2 1,5 1 0,5 0 3,434 62% 2,12 0,968 80% 0,77 ' 1 D Figure 6. The variation of diversity and equitability indices 4. Conclusions The main ecological indices of the fish communities from predeltaic Danube Rivers area, between Siret and Prut River Mouth, were analyzed. In terms of taxonomic point of view, the overall number of fish species caught in 2012 year, was 31, belonging 7 families and 6 orders. From Cypriniformes order, Cyprinidae, the dominant family, was represented by 17 species (Cyprinus carpio, Carassius gibelio, Barbus barbus, Abramis brama, Abramis sapa, Blicca bjoerkna, Leuciscus idus, Vimba vimba, Aspius aspius, Pelecus cultratus, Chondrostoma nasus, Ctenopharingodon idella, ypophthalmichthys molitrix, ypophthalmichthys nobilis, Scardinius erythrophthalmus, Rutilus rutilus, Alburnus alburnus). Other orders and families had the following structure: Clupeiformes order, Clupeidae family, with two species (Alosa immaculata and Alosa tanaica), Acipenseriformes order, Acipenseridae family with 4 species (uso huso, Acipenser 232

7 stellatus, Acipenser ruthenus, Acipenser gueldenstaedtii), Perciformes order, Percidae family with 5 species (Sander lucioperca, Zingel zingel, Zingel streber, Gymnocephalus schraetzer, Perca fluviatilis), Siluriformes order, Siluridae family, with one species (Silurus glanis) and Salmoniformes order, Esocidae family with one species (Esox lucius) and Salmonidae family with one species (Salmo labrax). The most abundant species was the pontic shad, followed by common bream and Prussian carp. Analytical ecological indices (absolute abundance, constancy, dominance) and synthetic (ecological significance) were calculated, in order to establish the structure and composition of fish communities in the sampling sites. The values of diversity indices showed that the degree of the structural stability of the ichthyocoenoses is relatively good; an important number of species live and growth normally. It s being observed that the best adapted species to living in this sector of the Danube and which bring an important contribution to the productivity area are cyprinids, like common bream, Prussian carp, common carp and common barbel. The structure of the fish communities is various, well balanced. It can be seen that the impact of the anthropic activities is quite significant. Thus, fish community diversity is a basic ecological aspect, knowledge of which is necessary for the correct exploitation, regulation and management of fishing resources since it can provide a first approach to the health level of the Danube system and allows for the identification of response patterns to possible environmental impacts. Acknowledgements Researches was conducted in the framework of the project POSDRU Quality and continuity of training in the doctoral studies no TOP ACADEMIC, funded by the European Union and Romanian Government. The authors thank to the management staff of the project for their support. References 1. Gutierrez-Estrada J. C. R., Vasconcelos, R. and Costa, M. J., Estimating fish community diversity from environmental features in the Tagus estuary (Portugal), J. Appl. Ichth. 24, 2008, Terrance, J. Q. and Deriso, R.B., Quantitative Fish Dynamics, Oxford Univ. Press, SUA, Grall, J. and Coic, N., Summary of methods for assessing the quality of benthos in coastal, REF. Ifremer DYNECO/VIGIES/06-13/REBENT, Bram, G. W. Aarts, Piet. Nienhuis, Fish zonations and guilds as the basis for assessment of ecological integrity of large rivers, Aquatic Biodiversity, Developments in ydrobiology, 2003, 171, Pătroescu, M., Rozylowicz, L. and Iojă, C., Conservation of biological diversity, Ed. Tehnica, Bucharest, 2002, pp Năvodaru, I., The estimation of the fish and fisheries stocks, Ed. Dobrogea, Constanta, 2008, pp ; 7. Bănărescu, P., Class Osteichthyes, Diversity in Living World, Vol II, Inland Waters, Ed. Bucura Mond, 2002, pp Greenhalgh, M., Freshwhater Fish, ardcover, Octopus Publishing Group, ISBN , Otel, V., Atlas of fish from the Danube Delta Biosphere Reserve, Publishing Delta Center for Information Technology, 2007, pp of fishes; Gomoiu, M. T. and Skolka, M., ECOLOGY Methodologies for environmental studies, Ovidius University Press, Constanta, 2001, pp Ţicalo, I., Comparative Research on the structure and dynamics of Bistrita river ichthyofauna and Jjijia (Upper Basin), PhD Thesis, Alexandru Ioan Cuza University of Iasi, 2010, pp Simpson, E.., Measurement of diversity, Nature, 163, 1949, Gheorghe, D. C., Research on the foundation of sustainable exploitation of fishery resources in the Danube and Danube Meadow, PhD Thesis, Dunărea de Jos University of Galati, 2010, pp Gheorghe, D. C., Cristea V. and Ciolac A., Ecological aspects of the ichthyofauna from Fundu Mare Island and Cravia Arms, Scientific Papers- Animal Series, 2010, 54, Washington,. G., Diversity, biotic and similarity indices: a review with special relevance to aquatic ecosystems, Water Res., 1984, 18,