Scholarly article on topic 'Temporal variation in juvenile fish communities of Kaunas reservoir littoral zone, Lithuania'

Temporal variation in juvenile fish communities of Kaunas reservoir littoral zone, Lithuania Academic research paper on "Biological sciences"

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Academic research paper on topic "Temporal variation in juvenile fish communities of Kaunas reservoir littoral zone, Lithuania"

VERSITA

Central European Journal of Biology

Temporal variation in juvenile fish communities of Kaunas reservoir littoral zone, Lithuania

Research Article

Valdemaras Ziliukas*, Vida Ziliukiene, Rimantas Repecka

Nature Research Centre, LT-08412 Vilnius, Lithuania

Received 21 February 2012; Accepted 07 June 2012

Abstract: The aim of this study was to assess juvenile fish communities in terms of species composition, fish diversity and density in the littoral zone of the Kaunas reservoir before (in 1989-1990, period I) and after (in 1999-2000, period II, and in 2006-2007, period III) launching the Kruonis hydroelectric pumped plant (Kruonis HPP). During the whole research period, 20 fish species were caught. According to the frequency of occurrence, the three-spined stickleback Gasterosteus aculeatus, European perch Perca fluviatilis and roach Rutilus rutilus were regarded as constant species in all investigated periods. Significant differences were established in juvenile fish community density between period I and periods II and III, whereas species richness (S) and species diversity indices (H', J') did not change significantly. The density of the shoreline community in period III was more than two times lower than in period I, probably due to higher fluctuations in water level of the reservoir, resulting from the Kruonis HPP operation.

Keywords: Fish community • Kaunas reservoir • Species diversity • Density © Versita Sp. z o.o.

1. Introduction

The pumped-storage hydroelectric plants play important roles in electrical supply grids by providing electricity during periods of peak demand, storing renewable energy and controlling supply frequency. However, the pumping of water from a lower reservoir to an upper impoundment and the return of that water during power generation can strongly affect the environmental conditions of reservoirs [1].

It is generally known that the littoral area satisfies the ecological requirements of lake and reservoir fish species throughout their life cycle, including spawning, larval, juvenile and adult stages. The littoral zone serves as spawning areas for the dominant cyprinids in European reservoirs - roach Rutilus rutilus and freshwater bream Abramis brama. Cyprinid larvae form shoals in the shallow littoral after hatching and begin to move offshore only after several weeks [2-5].

Littoral habitats may vary substantially in water depth, wave action and turbulence, bottom substratum, density of immersed or submersed macrophytes [6-8]. Juvenile fishes and invertebrates often use habitats

of high structural heterogenity as a refuge against predators and as feeding areas [9-11].

Depending on the spatial and temporal extension, water level fluctuations can influence the dynamic and structure of the phytoplankton [12-14], zooplankton [15] and zoobenthos communities [16-19]. In the littoral zone, water level fluctuations play a major role with regard to the occurrence and distribution of water vegetation and fishes [20-31].

Due to the power station activity, the fluctuation of the water level leads to the absence of the littoral area [32,33]. The flatter the banks and the faster the drop of water level, the greater the loss of juvenile fishes [34,35]. Water level fluctuations in the Kaunas reservoir after the Kruonis hydroelectric plant started operating are described by Gailiusis et al. [36] and Zaromskis [37]. Moreover, the Kaunas HP (Kaunas hydroelectric plant) and Kruonis HPP transformed the hydrological regime and also reduced fish communities in the lower reaches of the Nemunas River [35,38].

Until now only a few studies have been published about juvenile fish communities of the littoral zone of the Kaunas reservoir [39,40]. The aim of this study is to

E-mail: ziliukas@ekoi.lt

Springer

assess juvenile fish communities in terms of taxonomic composition, species richness, fish diversity and density in the littoral zone of the Kaunas reservoir before and after launching the Kruonis hydroelectric pumped plant.

2. Experimental Procedures

2.1 Study site

The Kaunas reservoir (54o51'10''N and 24o10'02''E) was created during the construction of the Kaunas Hydroelectric Plant (Kaunas HP) on the Nemunas River in 1959. Due to the damming of the river, a 20 m high water head formed. The Kaunas reservoir formed above the dam had the following parameters: length - 83 km, average width - 0.67 km (max 3.3 km), average depth

- 7.3 m (max 21 m), area at the maximum water level

- 63.5 km2, total storage capacity - 462 million m3. The average annual flow through outlets of the power plant was 293 m3/s [41]. Presently, the reservoir not only stores water for the Kaunas HP but also serves as a lower reservoir for the Kruonis Hydroelectric Pumped Plant (Kruonis HPP). The first 200 MW unit of the Kruonis HPP was launched in 1992, whereas the fourth was put into operation in 1998.The upper reservoir of the HPP (3.03 km2 in area and 40.7 million m3 in volume) was formed 105 m up from the Kaunas reservoir. One hydro-engineering unit operating in the pump regime at 220 MW power provided 180 m3/s discharge, and a unit operating in the generator regime at 200 MW made 226 m3/s discharge [42]. Construction of a fifth unit is scheduled to begin in 2014.

According to data from the Environmental Protection Agency of Lithuania, during the whole research period (1989-1990, 1999-2000, 2006-2007), the surface water temperature of the reservoir ranged from 10.3 to 21.5oC, pH values ranged from 7.9 to 8.4, oxygen concentration varied from 5.7 to 11.7 mg/l, total nitrogen (N) ranged from 0.84 to 1.89 mg/l, total phosphorus (P) from 0.05 to 0.18 mg/l, and BOD7 (Biochemical oxygen demand, 7 days) from 1.8 to 7.1 mgO2/l. The reservoir was a eutrophic-hypertrophic water body with water transparency in its middle part changing from

1.2 to 2.5 m, and chlorophyll a concentrations from 20.3 to 70.4 |jg/l [45]. The bottom of the littoral zone was sand or a sand-silt mixture. The littoral zone of the reservoir was characterised by a monotonous or patchy vegetation cover pattern. Potamogeton perfoliatus and P. pectinatus were the dominant submerged vegetation species [44]. The sampling sites selected contained various aquatic plant coverings. In each site, macrophyte cover was estimated by visual observation of percent cover. Aquatic vegetation covered 50-75% in one site,

25-50% in one site, 5-25% in two sites, <5% in one site, and it was absent (0%) in two sites.

2.2 Sampling

The data were collected in May, July and September of 1989-1990 (period I), 1999-2000 (period II) and 2006-2007 (period III) at seven study sites of the Kaunas reservoir, (Figure 1) according to Special fishing permits, granted from Environmental Protection Agency of Lithuania for research purpose. The total number of samples collected in the analysed reservoir area, in all periods of study, was 126. Catches in the coastal zone were conducted with a beach seine 15 m in length and 1.5 m in height with a bag (3 mm bar mesh size). One end of the beach seine was held on shore. The other was fully stretched perpendicularly from the beach and swept with the current. The closing of the seine was done on the coast. Each haul covered an area of approximately 250-300 m2. The depth at the sites of catch did not exceed 1.5 m. The plain cover of the bottom made it possible to use seine nets. The main advantages of using seine nets are low selectivity and easy manipulation during the catch [45-48]. The main part of the control catches consisted of 0+ and 1 + juvenile fish, the other part was made of small sized adult fish species (three-spined stickleback Gasterosteus aculeatus, nine-spined stickleback Pungitius pungitius, bleak Alburnus alburnus, gudgeon Gobio gobio, sunbleak Leucaspius delineatus, spiny loach Cobitis taenia, bitterling Rhodeus amarus). The latter often dwell together with juvenile fish in the same habitats.

Two replicate beach seine hauls taken at every site were combined into one joint sample. Juvenile fish were

Figure 1. Map of sampling site locations in the Kaunas reservoir. Black dots - sampling sites.

preserved in 4% formaldehyde solution and identified later at the laboratory according to Koblickaya [49] under binocular. The total length (TL) of the juveniles was measured to the nearest millimetre.

2.3 Calculations

In each catch, the number of species and the relative abundance of each species were determined. The unit of effort for the beach seine was defined as an area swept by hauling of the seine net [50,51] and converted to the number of fish per 100 m2. Dominance was expressed as the percentage of the species in the total number of fish captured during each period.

The frequency of occurrence for each species in separate periods was expressed by a frequency indicator (V), which is a quotient of the number of samples in which a given species occurred in relation to the number of all samples (n=42 per period) collected. This indicator expresses the general frequency of occurrence of a given species on a four-stage scale: constant (>70%), common (40-70%), rare (15-40%), and accidental (<15%) [52]. For each sample (n=126)

we also calculated traditional measures of biodiversity: species richness (S), Shannon-Weaver index (H') (log base = 2) and equitability (J'=H'/log(S)) [53,54]. A non-parametric Wilcoxon signed-rank test was used to compare species richness, diversity and density in coastal juvenile fish communities between studied periods. Calculations were done with Statistica for Windows, Version 6.0 (STATISTICA 2001).

3. Results

A total of 34,393 juvenile fish of 20 species were caught in all periods: 19 species (19,272 ind.) in period I, 19 species (10,148 ind.) in period II, and 15 species (5,973 ind.) in period III. 14 species were sampled in all three periods (three-spined stickleback, European perch Perca fluviatilis, roach, bleak, asp Aspius aspius, freshwater bream, ruffe Gymnocephalus cernua, pike-perch Sander lucioperca, white bream Blicca bjoerkna, spiny loach, pike Esoxlucius, dace Leuciscus leuciscus, prussian carp Carassius gibelio, and ide Leuciscus

Common name Scientific name I (n=42) V (%) II (n=42) III (n=42) I (n=42) R (%) II (n = 42) III (n=42) TL range (mm)

Three-spined stickleback Gasterosteus aculeatus (L.) 95.2 96.4 77.8 48.0 47.3 57.3 25-56

European perch Perca fluviatilis L. 92.8 78.6 100 20.6 10.8 9.3 31-78

Roach Rutilus rutilus (L.) 88.1 96.4 88.9 17.0 19.7 24.6 28-73

Bleak Alburnus alburnus (L.) 48.0 75.0 66.7 1.6 9.6 4.2 27-90

Asp Aspius aspius (L.) 40.5 25.0 33.3 0.5 1.6 1.0 35-110

Freshwater bream Abramis brama (L.) 28.6 39.3 33.3 1.4 2.0 0.4 32-102

Ruffe Gymnocephalus cernua (L.) 28.6 32.1 11.1 0.5 1.7 <0.1 43-74

Pike-perch Sander lucioperca (L.) 21.4 14.3 22.2 10.0 1.3 0.4 32-113

White bream Blicca bjoerkna (L.) 16.7 35.7 22.2 0.2 3.3 0.7 35-79

Gudgeon Gobio gobio (L.) 14.3 3.6 0.1 <0.1 31-142

Spiny loach Cobitis taenia L. 9.5 17.8 11.1 <0.1 0.1 <0.1 63-111

Nine-spined stickleback Pungitius pungitius (L.) 9.5 3.6 <0.1 <0.1 36-45

Northern pike Esox lucius L. 7.1 17.8 11.1 0.1 0.2 0.3 46-158

Dace Leuciscus leuciscus (L.) 4.7 17.8 22.2 <0.1 0.7 0.7 33-131

Rudd Scardinius erythrophthalmus (L.) 4.7 25.0 <0.1 0.6 45-65

Sunbleak Leucaspius delineatus (Heck.) 4.7 3.6 <0.1 <0.1 38-54

Prussian carp Carassius gibelio (Bloch) 4.7 7.1 33.3 <0.1 <0.1 0.6 32-72

Ide Leuciscus idus (L.) 2.4 7.1 33.3 <0.1 0.1 0.3 60-130

Chub Leuciscus cephalus (L.) 2.4 7.1 <0.1 1.0 53-96

European bitterling Rhodeus amarus (Bloch) 22.2 0.2 30-45

Table 1. List of juvenile fish species of the Kaunas reservoir derived from the beach seine sampling in periods I (1989-1990), II (1999-2000) and III (2006-2007) by frequency of occurrence (V), relative abundance (R) and total length (TL) range. n - number of samples.

idus) (Table 1). In period III we did not record juveniles of four species: gudgeon, nine spined stickleback, rudd Scardinius erythrophthalmus and sunbleak. European bitterling was caught only in period III. Species richness of communities varied from 3 to 10. The average number of species was relatively stable in all periods.

No significant differences in species richness were found between the three periods (Wilcoxon test, P>0.05; Figure 2).

Concerning the frequency of occurrence (Table 1), the three-spined stickleback, European perch and roach were constant species in all investigated periods. In addition, the bleak was a constant species in period II. Common species were recorded in period I (bleak and asp) and period III (bleak). Four species belonging to the group of rare fish were recorded in period I, eight in periods II and III. The number of accidental species varied from three (period III) to ten (period I).

Species diversity depended on the number of species (species richness) and distribution of individuals between species (species equitability). Diversity indices were similar in the three periods studied. No decrease of diversity was observed in periods I and II. On the contrary, the highest mean species diversity and equitability was observed in period II (H-1.62 and J-0.65), and the lowest in period I (H-1.24 and J-0.54, respectively). These indices did not differ among the periods investigated (Wilcoxon test, P>0.05; Figure 2).

The data of the relative abundance showed that the most abundant species in period I were the three-spined stickleback (48.0%) and European perch (20.6%) followed by roach (17.0%) and pike-perch Sander lucioperca (10.0%). All other species constituted less than 5%. The dominant species in period II were the three-spined stickleback (47.3%) and roach (19.7%), followed by European perch (10.8%) and bleak (9.6%). The three-spined stickleback was the most dominant in period III (57.3%), followed by roach (24.6%) and European perch (9.3%). These three species together

Figure 2. (a) Species richness (S), (b) diversity (H') and (c) equitability indices (J') of juvenile fish community of the Kaunas reservoir (n=42 in period I, n=42 in period II, n=42 in period III). The point represents the mean; column represents the SD; vertical bar represents the range.

Figure 3. Density (ind./100 m2) of the juvenile fish community in the Kaunas reservoir (n=42 in period I, n=42 in period II, n=42 in period III). The point represents the mean; column represents the SD; vertical bar represents the range. The values of a period marked with superscript are significantly different (Wilcoxon test, P<0.05).

constituted, respectively, 85.6% (period I), 77.8% (period II) and 91.2% (period III) on average (Table 1).

The density changes in the juvenile fish community of the Kaunas reservoir, with values decreasing from period I to period III, are given in Figure 3. The mean total density was the highest in period I (397 ind./100 m2), followed by period II (209 ind./100 m2) and III (144 ind./100 m2). Differences in the density of the juvenile fish community between period I and periods II and III were significant (Wilcoxon test, P<0.05).

Fish were arranged according to ranks in descending order of density based on quantitative and qualitative data of the community. The distribution of species abundance (density) dropped rapidly from the peak (a few abundant species) to the elongated tail (rare species). The total average density of dominant species (three-spined stickleback, European perch, roach) decreased significantly from 324 (period I) to 132 ind./100 m2 (period III) (Figure 4).

4. Discussion

Shallow inshore areas of reservoirs can be important habitats for juvenile fish of most species. Such habitats may provide protection from predators, abundant food and suitable conditions for development [32,55,56].

We investigated juvenile fish at seven sites to determine the inshore community state before and after launching the Kruonis HPP. Totally, we recorded 20 species of juvenile fish in 1989-1990 (period I), 1999-2000 (period II) and 2006-2007 (period III). Though the number of species decreased from 19 (periods I and II) to 15 (period III), no significant differences in species richness were found between the three periods investigated. A similar pattern was observed earlier in Zarnowiec Lake (Poland) after 10 years of HPP functioning, when the number of fish species decreased from 18 to 9. In the latter lake, diurnal fluctuations of water level reached up to 1 m [32].

The frequency of occurrence of different species in juvenile fish communities varied substantially. Only three species (three-spined stickleback, European perch and roach) were constant in all investigated periods. This ecological parameter partially shows the ability of the species to adapt to the living conditions and depends on the total abundance of the fish [52]. Moreover, fish are good indicators of ecomorphological conditions of the habitat [57,58].

Long-term investigations ofjuvenile fish communities at the Kaunas reservoir were also conducted in 1961-1988, i.e. from the time the Kaunas reservoir came into existence till the Kruonis HPP was launched [39].

Figure 4. Range distribution of the density of juvenile fish of different species (ind./100 m2) in the shoreline community of the Kaunas reservoir. Species: Ga - three-spined stickleback, Pf - European perch, Rr - roach, Sl - pike-perch, Aa - bleak, Ab - freshwater bream, Gc - ruffe, Asp - asp, Bb - white bream, Ll - dace, Pc - Prussian carp. Rare species (see Table 1) combined = others.

29 fish species were found throughout the investigation period (19 species per year on average). In our study, we did not record juveniles of the following eight species: peled Coregonus peled, undermouth Chondrostoma

nasus, barbel Barbus barbus, riffle minnow Alburnoides bipunctatus, vimba Vimba vimba, tench Tinca tinca, European carp Cyprinus carpio and burbot Lota lota. These species are very rare in the reservoir, but occasionally they can be observed in their species-specific habitats. In the last two decades an increase in lacustrine fish species, which are characteristic of eutrophic water bodies, has been noticed, while rheophilic fish species lost their commercial significance.

A fish community consists of a great number of species differing from each other in the dynamics of their abundance. Species diversity is considered to be the main index of the species structure in a community that can be evaluated by information indices. It has been established that the more equally distributed species are, according to their relative abundance in a fish community, the higher is the species diversity in it [59].

The effects of hydroelectric pumped storage plants on fish can be direct, i.e. exploitation of hydroengineering units in the pump regime or in the generator regime might injure fish or have a lethal effect, and indirect, i.e. water level fluctuations in the lower basin. At the current velocity of 9-10 m/s, the penetration of juvenile fish into hydroengineering units of the Kruonis HPP was observed. When one unit was in the pump regime, the injuries of juvenile fish did not exceed 3-5% [40].

The annual cycle of water level fluctuations is due to climatic conditions, whereas weekly and diurnal cycles are determined by the Kaunas HP and Kruonis HPP. Weekly changes in water level usually reached 30 cm and diurnal about 10 cm when only the Kaunas HP was in operation. After the Kruonis HPP was opened, diurnal water level fluctuations became more distinct (max 31 cm) [37,42]. Additionally, macrophyte areas in some places of the littoral zone of the Kaunas reservoir decreased ca. 1.8-fold or even disappeared. If macrophytes areas continue decreasing, the natural fish spawning grounds will have to be exchanged for artificial [40]. Taking into account the plans to increase the capacity of the Kruonis HPP in the future, further significant changes are predicted.

One of the main limiting factors for fish communities in many reservoirs is the scarcity of spawning areas in the littoral zone, which is usually a result of high fluctuations of water level. These fluctuations during the spawning season also play an important role in the regulation of fish eggs and larval survival [26,60,61]. When water level is high and relatively stable during spring, the reproductive success of many fish species is highly related to the quantity and quality of flooded spawning places along the reservoir shoreline [4,62]. The Lithuanian Ministry of Environment requires that variation in water level of the Kaunas reservoir

during spawning (April, May, June) should not exceed 10 cm per day. This restriction does not apply for the rest of the year [41]. Water level fluctuations caused by hydro-peaking is considered to be one of a few environmental impact factors which influences fish distribution and the success of fish reproduction and have become a central theme of ecohydrology in reservoirs [63,64].

Similar to a study carried out in 1961-1988 [39], the three-spined stickleback, roach and European perch were the dominant species in our study in the Kaunas reservoir, however in different proportions. It was observed that, depending on a studied period, the inshore community was dominated by three fish species. The dominance of only a few highly abundant species was also observed by others investigators [11,32,52,56,65]. Decrease in the dominance of pike-perch was quite obvious (the average of its relative abundance dropped to 0.4% in period III compared to period I). On the other hand, after opening the Kruonis HPP, the relative abundance of some rheophilic species (asp, dace, ide, chub) increased, although altogether these species did not exceed 2.0-3.4% of the total number of individuals captured. At the time when three units of the Kruonis HPP were operating in the generating regime, the current velocity of water was found to increase to 0.3-0.4 m/s in the area near the reverse canal [41].

The density of a juvenile fish community is a significant ecological indicator enabling a better estimation of the ecological state of the water body [66].

A comparative analysis of juvenile fish density in the Kaunas reservoir shows that earlier long-term investigations documented significantly higher fish densities. For instance, the mean density of the juvenile fish community in 1961-1988 was 468 ind./CPUE (catch per unit of effort for 1 haul of beach seine) [39].

Fishes in lakes and reservoirs prefer littoral areas over open waters; therefore, fish abundance and biomass increase from offshore to inshore habitats [67-69]. Routledge [70] predicts that changes in species density indicate the effects of various factors on the entire community. The rank distribution of separate species in a juvenile fish community is assumed to have a form of a sharply descending curve, because the largest portion of abundance of the whole community falls to a few first-ranked species (three-spined stickleback, European perch, roach). These species were top-ranked in the community in all three periods of our investigation. The juveniles of valuable species (pike-perch, freshwater bream, asp) are in the middle of the rank line or in the tail. Such species arrangement according to density is characteristic of the communities in which the change of

abundance of separate species is conditioned by many factors of similar impact [70].

A total of 20 species, of which 14 were in all three studied periods, were recorded during biocenological studies ofjuvenile fish communities in the littoral zone of the Kaunas reservoir before (1989-1990, period I) and after (1999-2000, period II, and 2006-2007, period III) launching the Kruonis HPP. According to the frequency of occurrence, the three-spined stickleback, European perch and roach were categorized as constant species (V>70%). These species were dominant and most abundant in all three studied periods in the reservoir and together constituted, respectively, 85.6% (period I), 77.8% (period II) and 91.2% (period III) on average. The greatest changes in the littoral zone of the Kaunas reservoir, in different studied periods (both before and after launching the Kruonis HPP), took place in the density of the juvenile fish community. The density of the juvenile fish community differed significantly between period I and periods II and III (Wilcoxon test,

References

P<0.05), whereas species richness (S) and diversity indices (H', J') did not change significantly (P>0.05). The density of shoreline community in period III was more than two times lower than in period I, which was probably due to higher fluctuations in water level of the reservoir, resulting from the Kruonis HPP operation. The findings of our study show that the structure and density of juvenile fish, which are useful for the fishery resource protection, should be integrated to the whole package of the Kaunas reservoir water resources management.

Acknowledgements

The authors would like to thank anonymous referees for their constructive and helpful review of an earlier draft. We also would like to thank Biruté Jankauskiené and Virginija Zaliené for the English language improvements in the manuscript.

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