1515
DIET AND PREY SELECTION OF PIKEPERCH (SANDER LUCIOPERCA LINNAEUS, 1758) POPULATION IN LAKE EĞİRDİR (TURKEY)
M. A. YAĞCI1, A. ALP1, A. YAĞCI1 and R. UYSAL1
1 Mediterranean Fisheries Research, Production and Training Institute, Eğirdir Area, 32500, Isparta, Turkey 2 University of Kahramanmaraş Sütçü Imam, Agricultural Faculty, Fisheries Department, Kahramanmaraş, Turkey
Abstract - he diet and prey selection of pikeperch (Sander lucioperca L., 1758) were assessed by determining the frequency of occurrence, numeric and weight percentages, and the index of relative importance (IRI%) between January 2010 and December 2010 in Lake Eğirdir, Turkey. Pearre’s index was used to estimate diet selectivity, while the Schoener Overlap Index was utilized to compare diets. he stomach contents of 241 S. lucioperca were analyzed. Pikeperch diet included prey ish, insects and other organisms. he diet was predominantly ish, consisting of Atherina boyeri, Knipowitschia caucasica, Aphanius anatoliae, Seminemacheilus ispartensis and Carassius gibelio. A. boyeri was the most abundant prey ish in the lake; it was a positively selected food item (V= 0.130, X2= 3.359, p> 0.05) and was not statistically signiicant. C. gibelio also inhabits the lake, but was not preferred by pikeperch (V=0.134, X2= 3.582, p> 0.05). In addition, A. anatoliae (V=-0.223, X2=9.977, p<0.01) and Chironomus sp., (V= -0.297, X2= 17.665, p<0.01) were negatively chosen by pikeperch despite their high abundance in the lake. Stomach fullness was highest in January, while feeding density was lowest in November and >50 cm in length pikeperch. Cannibalism was not evident during a decade, due to there being enough food for pikeperch in the lake.
Keywords:Sander lucioperca; diet; pikeperch; prey selection; Lake Eğirdir
INTRODUCTION
he pikeperch, Sander lucioperca, also known as Zander, is a species of ish from freshwater and brackish-water habitats in western Eurasia. Sander lucioperca inhabit Turkish inland waters; the species has a wide distribution that includes Lake Mermere, Lake Beyşehir, Lake Eğirdir and Hirfanlı Dam Lake in Turkey (Balık and Geldiay, 2002; Yılmaz and Ablak, 2003; Balık et al., 2006; Apaydın Yağcı et al., 2006). It can be described as a warm-water species with pre-ferred temperature from 24 up to 29°C, and it is im-portant both in recreational and commercial isher-ies (Lappalainen, 2001; Kangur et. al., 2007). Among the percids, Sander lucioperca is an ecologically
sig-niicant predator in the temperate waters of Eurasia and is of importance to isheries (Popova and Sytina, 1976). Pikeperch has been managed and stocked in Europe in order to regulate forage ish stocks (Pel-tonen et al., 1996). It usually plays a crucial role in eutrophic inland water in the reduction of planktivo-rous and omnivoplanktivo-rous ish abundance (Frankiewicz et al., 1999). Various studies about the feeding ecol-ogy of pikeperch are available in the world (Willem-sen, 1977; Peltonen et al., 1996; Lehtonen et al., 1996; Yılmaz and Ablak, 2003; Specziár, 2005; Balık et al., 2006; Kangur et al., 2007)
consid-1516 M. A. YAĞCI ET AL.
erable proportion of the diet already when the pike-perch is 20-30 mm in length (Lehtonen et al., 1996). Sander lucioperca is non-native in Lake Eğirdir. Ten thousand pikeperch ingerlings were introduced by the then Hydrobiological Institute of the Uni-versity of Istanbul to the lake in 1955 (Campbell, 1992). When the pikeperch were introduced, there were 10 species in Lake Eğirdir. It reproduced rap-idly and became the dominant ish species in the lake. At the beginning of the 1990s, the silver crus-sian carp, Carassius gibelio were introduced into the lake, followed later by tench Tinca tinca in 1996 and sand smelt Atherina boyeri in 2003 (Balık et al., 2004; Balık et al., 2006; Çubuk et al., 2006; Küçük et al., 2009). hese introduced ish species naturally afected the populations. Sander lucioperca directly afected the ish community structure though the efects of predation. he food and feeding habits of pikeperch in Lake Eğirdir were thoroughly inves-tigated by Campbell in 1992; later data are scarce (Becer and İkiz, 1997; Ekmekçi and Erk’akan, 1997; Balık et al., 2006), as is information on the feeding
ecology of Sander lucioperca populations in Turkey. For this reason, this research investigated the diet and prey selectivity of pikeperch in Lake Eğirdir, compared the IRI values obtained from pikeperch of diferent size-classes, and compared these results with other data.
MATERIALS AND METHODS
Investigations were conducted at Lake Eğirdir, which is situated in Southern Anatolia. Its maximum depth is 13 m. With its 47 250 ha surface area, lake Eğirdir is an oligotrophic lake, situated 918 m above sea level (Yarar and Magnin 1997). Pikeperch were collected from January 2010 to December 2010. A total of 241 individuals were caught monthly at four selected sampling sites (Fig. 1). Fishing nets with mesh sizes of 10, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80 and 100 mm were used. All samples were carried out in the morning. he fork length (FL) of pikeperch was measured to the nearest millimeter and weighed (W) to the nearest gram. he stomachs of the specimens were immediately preserved in a plastic barrel con-taining 4% bufered formalin (Buijse and Houthui-jzen, 1992; Balık et al., 2006), and their contents were analyzed in the laboratory. Prey items were counted and identiied to the lowest taxonomic level using the identiication keys of references (Geldiay and Balık 2002; Demirsoy 1997, 1998). he contributions, by weight and number of a given prey category to each stomach content, and inally to the food of all pike-perch in the sample, were calculated (Hyslop, 1980). he fullness index (FI) was determined to investigate the variations in feeding intensity, using the equa-tion:
10000
*
)
/
(
FF
Wsc
W
I
=
(Windell, 1971),where, WSC is the weight of the stomach contents and WF is the total weight of the ish. Fish specimens were divided into ive length groups (10-20 cm, 20-30 cm, 20-30-40 cm, 40-50 cm, >50 cm) to analyze their size-dependent dietary variations. he percentage of the IRI (Pinkas et al., 1971), and three dimensional graphical representation (Cortes, 1997) were used to express prey importance:
IRIi= (Ni %+Wi%)* Oi%
where Wi and Ni are the total net weight and number of prey, and Oi is the number of stomachs containing prey i. To estimate prey preference of pikeperch, the prey selection index V proposed by Pearre (Pearre, 1982) was calculated. he index was determined as follows:
)
*
*
*
(
)
*
(
)
*
(
e
d
b
a
b
a
b
a
V
a=
d e−
e dwhere Va is Pearre’s index for pikeperch selection of species a, ad is relative abundance of species a in the diet, be is the relative abundance of all other species in the environment, ae is the relative abundance of species a in the environment, and bd is the relative abundance of all other species in the diet:
a= ad+ae, b=bd+be, d=ad+bd, e=ae+be .
he selection index (Va) is statistically tested using the chi-squared test: (X2=n*V2), where n=a
d+ae+bd+be.
Diet similarity among length classes, months and seasons were estimated using the Schoener Overlap Index (C) (Schoener, 1970):
Cxy = 1 - 0.5 ∑ |pxi-pyi|
where pxi and pyi are the proportions by number of prey type i in the diets of groups (length or season) x and y, respectively. If the C value is bigger than 0.80, the diet of the 2 groups is similar.
RESULTS
he diet composition of pikeperch
During the study, pikeperch ranged from 21.6 cm to 77.0 cm in fork length (FL) with a mean value of 28.90 cm, and their total weight ranged from 105 to
Table 1. Diet of pikeperch (Sander lucioperca) in Lake Eğirdir, (N): prey number (W): prey weight, (O): frequency of occurrence, and (IRI): relative importance index
N %N O %O W %W IRI % IRI
Fishes
Aphanius anatoliae 16 4.82 9 5.56 12.76 2.89 42.85 0.63
Knipowitschia caucasica 29 8.73 6 3.70 9.11 2.07 40.00 0.59
Pseudophoxinus egridiri 2 0.60 2 1.23 4.09 0.93 1.89 0.03
Pseudorasbora parva 1 0.30 1 0.62 6.17 1.40 1.05 0.02
Seminemacheilus ispartensis 10 3.01 8 4.94 38.22 8.66 57.66 0.85
Atherina boyeri 257 77.41 67 41.36 142.66 32.34 4539.14 67.21
Carassius gibelio 8 2.41 4 2.47 45.48 10.31 31.41 0.47
Fish remains 0 0.00 69 42.59 73.43 16.65 709.02 10.50
Insecta
Calopteryx splendens 6 1.81 5 3.09 0.15 0.03 5.69 0.08
Chironomus sp. 1 0.30 1 0.62 0.02 0.00 0.19 0.00
Odanata larvae 2 0.60 1 0.62 0.04 0.01 0.38 0.01
Other
Components of Myriophyllum spicatum 0 0.00 5 3.09 0.23 0.05 0.16 0.00
Nematoda 0 0.00 2 1.23 0.01 0.00 0.00 0.00
Remains of organisms 0 0.00 87 53.70 108.73 24.65 1323.78 19.60
1518 M. A. YAĞCI ET AL.
4347 gr, with a mean value of 311.14 gr. Mean FL and standard deviations were 29.80±0.58 in sum-mer, 25.77±0.40 in spring, 39.84±0.58 in fall and 29.61±1.05 in winter. It was determined that 33.2 % of them were empty. he percentage of pikeperch containing prey was lowest in summer (52.94%) and above 70.0% in other seasons. he proportion
of pikeperch containing prey was 76.76% in small-sized pikeperch (20-30 cm) and 13.28% in medium-sized pikeperch (30-40 cm). he maximum fullness index was observed in January and July, while the minimum fullness index appeared in August and November (Fig 2). he pikeperch captured in the 4th station had the highest fullness index (Fig 3)
Fig. 2. Fullness index according to months
and feeding was not observed in the 10-20 cm size group (Fig 4). he diet of pikeperch in Lake Eğirdir was comprised of food that included prey ish spe-cies, insects and other organisms (Table 1). Prey ish were found in the stomachs of 97 pikeperch (O = 59.88%, N = 97.29%), represented by A. anato-liae, K. caucasica, Pseudophoxinus egridiri, Pseudor-asbora parva, S. ispartensis, A. boyeri and C. gibelio. he frequency of occurrence of A. boyeri was the highest (41.36%), followed by A. anatoliae (5.56%), S. ispartensis (4.94%) and K. caucasica (3.70%). In-sects were represented mainly by Calopteryx splend-ens and found in the stomachs of 5 pikeperch (O = 3.09%). Organism remains were ingested by 87 pikeperch (O = 53.70%), and components of Myrio-phyllum spicatum and Nematoda were also found in the stomach of pikeperch (O = 4.32%).
he total wet weight of 332 prey items was 441.09 g; prey ish species were the most frequently ingested prey with 75.25% by weight. According to weight, the dominant prey ish was A. boyeri (32.34%), fol-lowed by ish remains (16.65%), C. gibelio (10.31%) and S. ispartensis (8.66%). A. boyeri, K. caucasica and A. anatoliae were signiicantly important prey in the pikeperch diet, in frequency of occurrence and nu-merically, while A. boyeri, ish remains and C. gibelio
were the most common prey by weight. he index of relative importance (IRI) indicated that prey ish (80.30%) had a greater importance than the other prey categories (19.60%) and insects (0.09%). A. boy-eri had the highest index score (IRI = 67.21%), fol-lowed by ish remains (IRI = 10.50%), remains of or-ganisms (IRI = 19.60%), S. ispartensis (IRI = 0.85%), A. anatoliae (IRI= 0.63%), and K. caucasica (IRI = 0.59%).
Seasonal variation of diet composition
1520 M. A. YAĞCI ET AL.
boyeri and K. caucasica were important prey dur-ing sprdur-ing, A. boyeri, S. ispartensis, A. anatoliae and i sh remains during summer, A. boyeri, C. gibelio, S. ispartensis and i sh remains during the fall and A. boyeri and i sh remains the most important prey during winter.
Diet variation by fi sh size
As shown in Fig. 3, the most important preys of individuals in the 20-30 cm and >50 cm classes
con-sisted of some i sh species, i sh remains, remains of organisms and Nematoda. In addition to prey i sh, pikeperch in the 20-30 cm length class also fed on A. boyeri, A. anatoliae, K. caucasica, C. gibelio, i sh re-mains and the rere-mains of organisms. In the stomachs of pikeperch of in the >50 cm length class, only i sh remains of organisms and Nematoda were found. A majority of 30-40 cm-sized pikeperch consumed A. boyeri (O = 30.95%), and a few pikeperch ingested Chironomus sp. (O = 2.38%). Prey i sh species occur 100% of the 40-50 cm sized pikeperch diet
Autumn Winter
Fig. 5. h ree-dimensional show of seasonal stomach contents of pikeperch in lake Eğirdir. A.b: Atherina boyeri, A.a: Aphanius anatoliae, K.c: Knipowitschia caucasica, S.i: Seminemacheilus ispartensis, C.g: Carassius gibelio, R.o: Remains of organisms, F.r: Fish remains, C.s: Calopteryx splendens, Myr: Components of Myriophyllum spicatum, Nem: Nematoda
cally. A. boyeri and S. ispartensis were most common in the diet of 30-40 cm sized pikeperch; however A. boyeri occupied the highest relative importance in-dex (IRI= 78.07%). In i sh >50 cm sized pikeperch not consumed prey i sh species. Also, cannibalism was not seen in the diets of all individuals (Fig 6).
Prey selection and feeding strategies
A. boyeri, K. caucasica, A. anatoliae and S.
isparten-sis were the most abundant prey i sh in the lake, ac-counting for 88.26% of i sh; they comprise 93.98% of all prey i sh consumed by pikeperch. P. egridiri, P. parva and C. gibelio comprise 3.31 % of all prey i sh ingested by pikeperch although they accounted for 9.77% of the total i sh in the lake. According to the prey selectivity index, P. parva, S. ispartensis, A. boy-eri and C. splendens were positive but their selection indices were not statistically signii cant (p>0.05). A. anatoliae and Chironomus sp. were a common prey
Fig. 6. h ree-dimensional show of seasonal stomach contents in dif erent size groups of pikeperch in lake Eğirdir. A.b: Atherina boyeri, A.a: Aphanius anatoliae, K.c: Knipowitschia caucasica, S.i: Seminemacheilus ispartensis, C.g: Carassius gibelio, R.o: Remains of organisms, F.r: Fish remains, C.s: Calopteryx splendens, Myr: Components of Myriophyllum spicatum, Nem: Nematoda; Ch: Chironomus sp.
20-30 cm FL 30-40 cm FL
1522 M. A. YAĞCI ET AL.
in the lake but negatively selected by the pikeperch. P. egridiri and C. gibelio were negatively selected; their selection indices were not statistically signii-cant (p>0.05). A. anatoliae accounted for 19.39% of the prey ish in the lake but comprises 4.82% of the diet. It was thus negatively selected and its selec-tion index was signiicant (V=-0.223, X2= 9.997 and
p<0.01). Similary, Chironomus sp., was negatively
selected; its selection index was statistically signii-cant (V=-0.297, X2= 17.665, p<0.01) (Fig 7).
Similarity index
Pikeperch had a similar feeding strategy in March, May, June and November because of a high Schoener overlap index (C>0.8) (Table 2). Diet composition in the group over 30 cm in length was
different from that in the other length groups as the C value was smaller 0.8. C; the pikeperch in all sta-tions had different diet composista-tions because of the low values of C (C<0.8). The feeding strategy in
spring and summer was similar (Table 3).
DISCUSSION
he content of the stomachs contained S. lucioperca (77.41%), K. caucasica (8.73%), A. anatoliae (4.82%), S. ispartensis (3.01%), C. gibelio (2.41%), P. egridiri (0.60%), P. parva (0.30%), C. splendens (1.81%, Odo-nata larvae (0.60%) and Chironomus sp., (0.30%). It was determined that 66.8% of specimens had full and 33.2% had empty stomachs. he percentage of full stomachs varied between 51% and 77% in pike-perch populations (Becer and İkiz, 1997; Balık, 1999;
Fig. 7. Percentage of diferent ish species in environment and diet of pikeperch in Lake Eğirdir. *Signiicant at P < 0.01 in the X2- test
Yılmaz and Ablak, 2003; Balık et al., 2006; Apaydın Yağcı et al., 2006; Kangur et al., 2007). he propor-tion of full stomachs found in this study (66.8%) was consistent with previous studies. he pikeperch diet in Lake Eğirdir primarily consisted of prey ish spe-cies, secondly of insects, followed by other food items such as Nematoda, remains of organisms and com-ponents of Myriophyllum spicatum. he diet com-position given in this research was compared with indings in previous researches. he richest pike-perch diet determined in the references was found for pikeperch in Lake Eğirdir (Becer and İkiz, 1997; Balık et al., 2006). he pikeperch diet in Lake Eğirdir
has a normal prey distribution in comparison with other pikeperch populations.
Pikeperch are opportunistic in their feeding habits (Kangur et al., 2007). If food items of choice were not present, alternate food sources such as zooplankton , insects, leeches and frogs, crustaceans; and molluscs were sought (Willemsen, 1977; Campbell, 1992; Becer and İkiz, 1997; Yılmaz and Ablak, 2003; Balık et al., 2006; Apaydın Yağcı et al., 2006; ). Rana and Hirudo inhabiting Lake Eğirdir was not found in the pike-perch diet, though Balık et al. (2006) reported that frogs and leeches were prey for pikeperch in the Lake
Table 2. Schoener overlap index of pikeperch sampled in diferent months
C (%N) Jan. Feb. Marc. Apr. May Jun. Jul. Aug. Sep. Oct. Nov.
Feb. 0.500
Marc. 0.500 0.448
Apr. 0.500 0.135 0.105
May 0.500 0.440 0.953* 0.092
Jun. 0.500 0.525 0.846* 0.130 0.849*
Jul. 0.500 0.560 0.751 0.101 0.751 0.808*
Aug. 0.500 0.648 0.097 0.075 0.089 0.173 0.209
Sep. 0.500 0.484 0.237 0.135 0.233 0.343 0.383 0.344
Oct. 0.500 0.662 0.343 0.135 0.340 0.468 0.377 0.445 0.458
Nov. 0.500 0.344 0.091 0.014 0.071 0.121 0.190 0.476 0.166 0.111
Dec. 0.500 0.344 0.091 0.014 0.071 0.121 0.190 0.476 0.166 0.111 1.000*
Table 3. Schoener overlap index of pikeperch according to size classes, stations, and seasons
C (% N) Size classes 20-30 30-40 40-50
30-40 0.898*
40-50 0.526 0.480
>50 0.133 0.134 0.283
C (% N) Stations I II III
II 0.590
III 0.442 0.442
IV 0.625 0.422 0.758
C (% N) Seasons Spring Summer Autumn
Summer 0.817*
Autumn 0.279 0.435
Winter 0.427 0.553 0.599
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Table 4. Comparison of food in diferent pikeperch (Sander lucioperca) populations
(Campbell, 1992) (Eğirdir Lake, Turkey)
(Becer and İkiz, 1997) (Eğirdir Lake, Turkey)
(Ekmekçi and Erk’akan, 1997) ( Eğirdir Lake, Turkey
(Balık et al., 2006) (Eğirdir Lake, Turkey)
(Keskinen, 2008) (Beyşehir Lake, Turkey)
(Yılmaz and Ablak, 2003) (Hirfanlı Dam
Lake,Turkey)
(Apaydın Yağcı et al., 2006) (Beyşehir Lake, Turkey)
Mysid Mysis sp. Mysis sp Mysis Mysis sp. Mysis Knipowitschia caucasica
Gammarus Gammarus sp. Gammarus sp. Gammarus Gammarus sp. Gammarus Atherina boyeri
Isopod Astacus leptodactyllus Astacus sp. Gastopoda Lumbricus sp. Isopoda Carassius gibelio
Chironomid Chironomidae Chironomid Chironomus Chrinomidae Diptera larva, pupa Tinca tinca
Chrinomid pupa Asellus sp. Chironomid larvae Rana Odanata Fish remains Sander lucioperca Gastropoda Odanata Odanata Hirundo Hirudo Odanata nimleri Odanata Dreissena polymorpha Ephemeroptera Ephemeroptera Calapteryx splendens Sander lucioperca Organism remains Gammarus sp.
Cobitis taenia Lumbricus sp. Sander lucioperca Knipowitschia sp. Fibrous algae Chironomus sp. Vimba vimba Turbellaria Aphanius anatoliae Fish and organism remains
Sander lucioperca Xeptohygula pfeirferi Gambusia ainis
Dreissena polmorpha Nemacheilus lendli
Radix sp. Carassius gibelio
Nemacheilus angorae Sander lucioperca
Stizostedion lucioperca
(Willemsen, 1977) (Ijssel Lake, Netherlands)
(Lehtonen et al., 1996) (Baltic Sea Area)
(Peltonen et al., 1996) (Vesijärvi Lake, Finland)
(Specziár, 2005) (Balaton Lake, Hungary)
(Kangur et al., 2007) (Võrtsjärv Lake, Estonia)
(Balık, 1999) (Boreal Lakes, Finland)
Present research (Eğirdir Lake, Turkey)
Gymnocephalus cernuus Gymnocephalus cernuus Osmerus eperlanus Diaphanasoma
mongalianum
Gymnocephalus cernuus Osmerus eperlanus Chironomus sp.
Odanata larvae
Osmerus eperlanus Osmerus eperlanus Alburnus alburnus Leptodora kindtii Osmerus eperlanus Cyprinid Calopteryx splendens
Perca luviatilis Perca luviatilis Perca luviatilis Limnomysis benedeni Perca luviatilis Sander lucioperca Aphanius anatoliae
Cyprinid Rutilus rutilus Rutilus rutilus Dikerogammarus spp. Rutilus rutilus Knipowitschia
cau-casica
Zooplankton Clupea harengus Corophium curvispinum Abramis brama Pseudophoxinus
egridiri
Chironomid Gymnocephalus cernuus Sander lucioperca Pseudorasbora parva
Neomysis spp. Lepomus gibbosus Seminemacheilus
ıspartensis
Sander lucioperca Alburnus alburnus Atherina boyeri
Carassius gibelio Nematoda Myriophyllum
Eğirdir. Our results showed that the importance of ish and insect species in the diet of pikeperch 30-40 cm length. Similarly, ish and insect species may be found in the diets of 30-34 cm-long pikeperch (Balık et al., 2006). Balık (1999) observed for S. lucioperca that individuals >30 cm in length consume a signiicant amount of ish species in Lake Beyşehir. In another study, Apaydın Yağcı et al. (2006) reported that S. lu-cioperca consumed Odonata larvae, ish and organism remains, Knipowitschia caucasica, Atherina boyeri, Carassius gibelio, Chironomus sp., Gammarus sp., Tin-ca tinTin-ca and Sander lucioperca in the same lake.
Pikeperch in the present study fed on a variety of prey items, and the diet varied with season and ish size. Most of the prey was determined to be ish organisms. Lehtonen et al. (1996) reported that ish species (Perca luviatilis, Rutilus rutilus, Osmerus op-erlanus, Gymnocephalus cernuus, Clupea harengus) represented the majority of pikeperch diet. he most frequent prey items were reported to be ish ( Knip-owitschia sp., 24.4%, Aphanius anatoliae anatoliae 21.8%, Gambusia ainis 3.8%, Nemacheilus lendli 1.7%, Carassius gibelio 0.2%, Sander lucioperca 0.2%), Rana (2.2%), Hirundo (0.1%), Calopteryx splendens 18.8%), Chironomus (5.1%), Mysis (12.7%), Gam-marus (8.9%), Gastropoda (Graecoanatolica) (0.1%) in Lake Eğirdir (Balık et al., 2006). In our research, ish (97.29%) and Calopteryx splendens (1.81) were the most frequent prey items. According to Camp-bell (1992), the diet of the pikeperch from the Lake Eğirdir was characterized by Mysida, Chironomid, Chironomid pupa, Gammarus, Isopoda, Gastropoda, Dreissena polymorpha, Vimba vimba, Cobitis tae-nia, Sander lucioperca. Willemsen (1977) reported that the diet of the pikeperch from Lake Ijssel in the Netherlands was based on Neomysis spp., Osmerus eperlanus, Gymnocephalus cernua, Cyprinid, Sander lucioperca and Perca luviatilis. According to Popova and Sytina (1976), the diet of pikeperch from various waters, as observed in the USSR, was based on Mys-ida and Gammarus, revealing the habitat structure and ish size of this species in terms of feeding.
he temporal study of the diet revealed that in spring, summer and winter it was dominated by
Atherina boyeri, whereas in the fall there was an in-crease in the consumption of ish remains. Balık et al. (2006) reported seasonal changes in the pikeperch diet in Lake Eğirdir. he four species (A. anatoliae, Chironomus sp, Mysis sp, Gammarus sp) showed a lower mean number of prey in spring. he decrease in feeding rate might be attributed to the shortage of food during this season. he consumption of My-sis sp., Gammarus sp., Astacus sp., Chironomid lar-vae, Odonata, Ephemeroptera, Chironomid, Sander lucioperca have also been reported by Ekmekçi and Erk’akan (1997) for pikeperch throughout the year in the lake. In addition, Becer and İkiz (1997) reported that Gammarus sp (58.86%), Mysis sp (23.43%) and Asellus sp (15.24%) represented the largest proportion pikeperch diet in Lake Eğirdir, followed by Lumbri-cus sp., (0.43%), Turbellaria sp., (0.06%), Astacus lep-todactylus (0.55%), Chironomidae (0.06%), Odonata (0.06%), Xeptophygula pfeirferi (0.15%), Dreissena polymorpha (0.34%), Radix sp., (0.03%), Nemacheilus angorae (0.8%) and Sander lucioperca (0.46%).
In Yılmaz and Ablak’s research (2003) in Hirfanlı Dam Lake Gammarus, Diptera (Chironomus larvae and pupae), ish (Sander lucioperca, Tinca tinca, Alburnus orontis), ish remains, Odonata nymphs, organism remains, Mysis, Isopoda and ibrous algae were determined in the stomach contents of the S. lu-cioperca. Peltonen et al. (1996) reported that the diet of pikeperch in Lake Vesijärvi was mainly formed by Alburnus alburnus, Rutilus rutilus, Osmerus operla-nus and Perca luviatilis. Moreover, Keskinen (2008) reported that S. lucioperca in boreal lakes consumed Osmerus eperlanus and Stizostedion lucioperca. Specziár (2005) found that pikeperch 5-10 mm, 20-60 mm and 20-60-100 mm in length mainly fed on Eud-iaptomus gracilis, Diaphanosoma mongolianum and Leptodora kindtii, respectively. Pikeperch in Lake Balaton over 50 mm were fed chiely on Gymno-cephalus cernuus, Lepomis gibbosus and Alburnus alburnus, whereas the diet of littoral zone specimens consists of Limnomysis benedeni, Dikerogammarus spp. and Corophium curvispinum (Specziár, 2005)
1526 M. A. YAĞCI ET AL.
negatively preferred by pikeperch in Lake Eğirdir, but their selection indices were statistically signii-cant (p<0.01). On the other hand, Balık et al. (2006)
noted that Knipowitschia sp., Aphanius anatoliae anatoliae and Calopteryx splendens were density-selected prey of pikeperch in the Lake Eğirdir. Our calculations of Pearre’s selectivity showed that K. caucasica (V=0.122, p>0.05), P. parva (V= 0.028, p>0.05), S. ispartensis (V= 0.115, p>0.05) and A. boyeri (V= 0.130, p>0.05) were neutrally selected. Balık (1999) observed that pikeperch feed when 21-30 cm in length, with feeding declined in ish 11-20 cm in length. Similarly, in our research, the fullness index of pikeperch was also found to be the lowest in those 10-20 cm in length, increasing in those 20-30 cm in length.
The mean cannibalism proportion pikeperch populations were reported as 0.14% in Lake Ijs-sel (10), 96% in Lake Eğirdir (13), 20.9% in Lake Beyşehir (Balık, 1999), 40.5% in Hirfanlı Dam Lake (2), 0.1% in Lake Beyşehir (4), 0.6% in Lake Eğirdir (Balık et al., 2006). The cannibalism proportion in this research was 0% for the pikeperch population. It seems that in recent years the population of prey ishes increased along with the increasing density of sand smelt (Atherina boyeri) in Lake Eğirdir. In con-clusion, this research shows that pikeperch, S. lucio-perca, feed on very dense ish species, and the diet and feeding feature changes by month, season, ish length and habitat. Also, in past decade, cannibal-ism among pikeperch has not occurred, because the populations of the sand smelt (Atherina boyeri) are abundant in the lake.
Acknowledgments - his study was supported by the General
Directorate of Agricultural Research and Policies, Ministry of Food, Agriculture and Livestock, Turkey (TAGEM/HAY-SÜD/2010-09-01-01 Project No).
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