Ecological Potential Assessment of Sava Lake Based on Fish Community Composition: Preliminary Results - page 01

Material and Methods

The Sava Lake (N 44° 47' 02.28", EO 20° 23' 25.64"; 73 m a.s.l) is an urban reservoir used for recreation and tourism purposes (Fig. 1). It was created some 40 years ago by embankment of the backwater of the Sava River situated between the right bank of the river and the river island Ada Ciganlija. Sava Lake is located approximately 4 km upstream from the river confluence with the Danube. The reservoir is slightly arched in shape occupying an area of approximately 90 ha. On its southern part a sedimentation unit (18.1 ha) is built up, from which the rest of reservoir is supplied with water. The reservoir length is 4.4 km, and the average width is about 250 m, and the volume is 4 000 000 m3. The average depth is 4.5 m, with a maximum recorded depth of 12 m (Janković et al. 1988).

Data on the fish community in the Sava Lake were obtained from the Annual Fishery Management Plan and the data concern results of the ichthyofauna survey conducted in 2009. The systematic arrangement of the species in the present paper follows that of Kottelat and Fryehof (2007). Species classification into functional ecological guilds and metrics selection was based on the ground of literature (Jennings et al. 1995; Hickman and McDonough 1996; Aarts and Nienhius, 2003; Angemeier and Davideanu, 2004; Noble et al. 2007; Terra and Araújo, 2011) and our own experience. The Shannon-Weaver index (H' = -Σ Pi ln Pi) was calculated taking relative proportion in biomass as an importance value (Odum, 1971).

 

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Figure 1: Satellite image of Sava Lake.

 

Results and Discussion

In Table 1, the list of the recorded species and their relative abundance are presented. The fish community of the Sava Lake comprises 20 species from 19 genera, belonging to 8 families. Out of the total number recorded, 6 species are alien. In terms of biomass, carp (32.9%) was the dominant species, while pikeperch (10.2%) was subdominant. Three species, H. nobilis, H.molitrix, and C. idella, have not developed self-sustaining populations. The calculated value for the Shannon-Weaver index (H') was 2.451.

Table 2, contains selected metrics used for ecological potential assessment of the Sava Lake. The proposed selection comprises of 12 metrics, both qualitative and quantitative, and is based on principles of the reservoir fish assemblage index (RFAI) for American reservoirs developed by Jennings et al. (1995) and Hickman and McDonough (1996). Our objective in this study was to assess ecological potential of a specific water body based on fish assemblage, without any intention to establish a comprehensive system for this type of analysis.

Otherwise, such adaptations according to national, regional and local conditions are commonly applied in studies on aquatic ecosystems condition assessments (Noble et al. 2007; Terra and Araújo, 2011; Sutela et al. 2011). Therefore, the proposed metrics combination was specifically modified to the features of the ichthyofauna of the studied reservoir.

Selected metrics are organized into four general categories: species diversity and composition, abundance, trophic composition, and reproductive composition. Metrics 4, 9, 10, 11, and 12 referred to species classification into functional ecological guilds.

In Table 3, assignment of species into an appropriate ecological guild is presented, where tolerance classification and designations of trophic and reproductive guilds follow those outlined in Aarts and Nienhius, (2003) and Angemeier and Davideanu, (2004).

 

Table 1: Species composition of the fish community in the Sava Lake: B – relative abundance in biomass; asterisk in superscript denotes alien species.
Tab01

 

The piscivore guild comprises species that are obligate piscivores in the sub-adult and adult life stages. Perch was not included in this category because it becomes partially piscivorous at about 12-15 cm in standard length (Kottelat and Fryhof, 2007; Sutela et al. 2011). Five small sized species, feeding mainly on invertebrates/insect larvae, have been classified as invertivores. In respect to reproductive strategy, only species that established self-sustaining populations were considered, and two ecological guilds were selected: lithophilic and phytophilic species. Lithophils are dependent on the availability of clean gravel, rocks, stones, rubble or pebbles of adequate size. In the Sava Lake, this reproductive guild is represented with only one species. Phytophils prefer submerged plants, leaf and roots of live or dead vegetation as spawning substrate. Within this ecological guild 8 species that reproduce in the reservoir have been classified. About general tolerance, only asp was assigned as an intolerant species (Angemeier and Davideanu, 2004).

 

Table 2: The selected metrics for assessment purpose.
Tab02

 

Table 3: Species classification into the selected functional ecological guilds.
Tab03