Actual Status of Eber Lake in Terms of Fish Community Structure

Lake Eber is a small, shallow tectonic lake, located in the central part of Anatolia. Lake is under effect of pollution and exotic fish species. In order to define environmental degradation within the lake and its effects on fish assembly in a historical perspective field study was conducted. Water sampling was conducted seasonally between December, 2012 and September, 2013. Physico-chemical paramaters as dissolved oxygen, pH, total phosphorus and total Kjeldahl nitrogen was assessed. Trophic state index was calculated from phosphorus concentrations and trophic state of the lake was assessed. Fishing was carried out in April, 2013, on randomly selected eight stations with benthic multimesh nets (30 m long, 1.5 m depth, 12 different mesh size from 5x5 mm to 55x55 mm) and fyke net. Fish assembly, catch data (catch per unit effort), length-weight relationships of the species with enough sample size is reported.


Introduction
Lake Eber is a small, shallow tectonic lake, located in the central part of Anatolia, it is surrounded by Emir Mountains from the south and Sultan Mountains from the north (Atalay 1977;Köle et al. 2016).Eber is the biggest lake in the Akarçay River Basin after drying of Akşehir Lake.Basin which the lake resides is a closed basin, made up mainly by Akarçay River which is also the main influent into the lake.Changes in climatic conditions which are effecting the water regime, and anthropological activities are the main threats for the basin and lake itself.
Eutrophication is the process of nutrient accumulation causing water body to become more productive (Moss 1988).This process promotes algal blooms causing high variations in dissolved oxygen content of water and can cause release of bloom related algal toxins.From fisheries perspective, all this can lead to fish deaths and in the long term changes in fish fauna.In addition to this environmental degradation, presence of exotic species can speed up this process.Introduction of fish species can alter ecosytem and effect biodiversity by means of predation, competition, hybridization and habitat alteration (Cowx 1998).Lake Eber is under effect of these anthropogenic pressures.This study aims to define environmental degradation within the lake and its effects on fish assembly in a historical perspective.

Materials and Methods
Water sampling was conducted seasonally between December, 2012 and September, 2013 whereas fish sampling was conducted in April, 2013.Physico-chemical parameters such as dissolved oxygen (DO; mg/l) and pH were recorded in situ with YSI 5739 and YSI 33 SCT meter respectively.Chemical parameters such as total phosphorus (TP; mg/l), total Kjeldahl nitrogen (TKN; mg/l) was analyzed in an accredited laboratory conditions (OSİB SYGM 2013).
In order to determine trophic status of the lake Trophic State Index (TSI) developed by Carlson (1977) is used.Trophic state according to total phosphorus (TSITP) is calculated using the formula below.
= 10(6 − (  ( 48  ) ( 2) ) Fishing was carried out on 8 stations with benthic multimesh nets (30 m long, 1.5 m depth, 12 different mesh size from 5x5 mm to 55x55 mm) and fyke net following TS EN 14757 sampling standart.Due to low water depth, no significant stratification was observed in the lake and benthic positioning of the multimesh gillnets sufficiently sampled the water column.Species identification were done according to Battalgil 1944, Bogutskaya 1997, Geldiay & Balık 2007;Kuru et al. 2014. Total length (TL), Fork length (FL) and Standart length (SL) were measured to nearest millimeter with ruler (TL>15 cm) and digital caliper (TL<15 cm).Weighing was conducted with analog and digital scales.Sampled fish were kept in ice until all measurements were finished.
Catch per unit effort (CPUE) was reported as number of specimens and grams of fish catch per multimesh net.Length weight relationships were calculated using the Ricker (1975) (LWR) model ( =   ); in which W is total weight (g), TL is total length (cm), a and b are the equation parameters calculated by the least squares method using the logarithmic form of the equation.Significance of the regression was reported by the correlation coefficient of the regression (R 2 ), and signifficant differences from isometric growth (H0: b = 3) were assessed (p).LWR and frequence analyses were conducted with FSA package (Ogle 2014) developed for R 3.4.0(R Core Team 2014).

Properties of water body
Physico-chemical properties of the water is summarised in Table 1 with the results of similar analysis reported in Günay et al. (1985) and Kazancı et al. (1999) for comparison.Phosphorus concentration from Akşehir Lake is added from Numann (1958) since at this date lakes connect at certain dates throughout the year.Phosphorus levels for Eber Lake can be lower than this value (0.02 mg/L) since Akşehir Lake is the last residence for water in the basin.
Water pH seems to show variances throughout the year and there seems to be a shift to the basic side when compared to previous readings.High values of total phosphorus and nitrogen compounds seem to indicate eutrophic conditions.Nitrogen compounds seem to increase significantly over the years.Trophic state index scores for total phosphorus (TSITP) was high and indicating hypereutrophic tendency after 1980's.Rather than showing a recovery or stabilization, these values showed a significant increase after these dates.

Discussion
Elements which can be helpful to determine water quality is showing that lake is hypertrophic.Most of the parameters reach levels that can be classified as the worst class (class IV) according to criteria for water quality (SKKY 2004).Increased pH is typical for eutrophic lakes as can be seen in Lake Mogan (Mangıt and Yerli 2010) and Lake Uluabat (Elmacı et al. 2009), similar shallow lakes with hypertrophy tendency.Oxygen levels in lake seem to be high throughout the year.This over saturation with oxygen is typical in shallow lakes with dense submerged macrophytes as Lake Eber.Phosphorus (TP) and nitrogen compounds (TKN) seem to increase over the years compared to Günay et al. (1985) and Kazancı et al. (1999).
Fish sampling data revealed that A. nasreddini and C. gibelio is widespread in the lake whereas S. lendlii, C. simplicispina, C. carpio, T. tinca and K. caucasica are not caught by every gillnet.C. gibelio seem to dominate fish populations in the lake by means of indiviuals and biomass.According to results this invasive fish species constitutes 35% of the fish specimens and 73% of fish biomass.By means of population size it is followed closely by A. nasreddini (34%) and C. simplicispina (28%) however in terms of biomass it is by far the dominant species.Invasion potential of C. gibelio is demonstrated clearly in Lake Eber. A. nasreddini constitues 34% of the specimens sampled.Eber Lake is the type locality of A. nasreddini and this species is listed under Critically Endangered status by IUCN (2017) due to pollution and desiccation.However high the CPUE may seem in this study it is clearly under threat of C. gibelio.
This recent fauna is a consequence of pollution brought by Akarçay River and fisheries activities.In this study E. lucius and C. carpio can not be sampled by gillnets however the latter is sampled by fyke nets.Both species are present in the lake however according to fisherman catch of these species dropped significantly as it can be interpreted from gillnet catch results.In addition to this decrease in economically important species C. carpio and E. lucius, T. tinca is under serious fishing pressure too.Only four specimens were caught in this study.
Fish fauna is compared to the previous studies in order to interpret long term changes in the lake (Table 3).Changes in fish fauna and environmental degradation through the years summarised in Figure 5.
C. carpio and E. lucius assumed to have a natural distribution in Turkey however both of them are translocated extensively (İnnal and Erk'akan 2006, İnnal 2012, Tarkan et al. 2015).But due to having a report in the beginning of 1900's, these species are listed under native status. A. nasreddini has not been reported by Deveciyan (1915), but due to similar lateral line scale count it can be mistaken as Rutilus rutilus (Linnaeus, 1758).In addition to this possible confliction, Deveciyan (1915) reported 3 more species namely, C. carpio, E. lucius and Squalius recurvirostris Özuluğ & Freyhof, 2011 (given as Leuciscus cephalus).Other species were probably distributed in the lake however main focus at these years were fisheries rather than biological diversity.Therefore we colored these boxes as gray to indicate this probability.Following Deveciyan (1915), no reports had been found until Kosswig (1952).In this study by Kosswig, fauna for Eber Lake with Akşehir Lake combined since at that time connection between these lakes was not distrupted.And to our knowledge this was the first and last detailed report about the lake.There seems to be drastic changes in the fish fauna over the years.C. gibelio seem to enter this lake after 2000's and possibly with the help of environmental degradation it became the dominant species.Species with possible low tolerance to eutrophication such as Gobio intermedius Battalgil, 1944 and S. recurvirostris are replaced by tolerant C. gibelio, K. caucasica and T. tinca.
In order to restore the lake, pollution need to be controlled.However even if influent is controlled there won't be an immediate shift to eutrophic state.Water quality of the lake need to be monitored closely and possibly some other measures can be taken to control eutrophication.Also fisheries activities need to be monitored carefully and measures to remove C. gibelio from the lake need to be considered.
Length-weight relationships (LWRs) of the species with enough sample size is given in Table2.Model fit is successive for A. nasreddini, C. gibelio and C. simplicispina.However, coefficient for determination (R 2 ) value for S. lendlii is 0.71 indicating a failure in model fit possibly due to variative weights at same length rather than sample size.All b values for the species (except S. lendlii) with enough number of specimens for the model are over three indicating a positive allometry.Lengthweight relationship plots, residuals of the regression model and frequency analysis of A. nasreddini, C. gibelio, C. simplicispina and S. lendlii are illustrated between Figures 1-4.

Figure 1 .
Figure 1. A. nasreddini length weight relationship plot, regression model fit plots and length frequency

Figure 4 .
Figure 4. S. lendlii length weight relationship plot, regression model fit plots and length frequency

Figure 5 .
Figure 5. Environmental degradation and fish fauna in Lake Eber

Table 1 .
Some physico-chemical parameters for Lake Eber with TSI values calculated for TP

Table 2 .
Fish abundance and length weight relationship values * Catch per unit effort: Catch per multimesh net (30 m)