Yazarlar

• Sökmen, Teoman Özgür(3)
• Altuner, Zekeriya(1)
• Aydın, Erdinç(1)
• Caf, Fatma(1)
• Demir, N.(1)
• Demir, Nurullah(1)
• Fakioglu, O.(1)
• Güneş, Muharrem(1)
• Gürbüz, Hasan(1)
• Kivrak, Ersin(1)
• Korkmaz, A. Şeref(1)
• Korkmaz, A.S.(1)
• Kırıcı, Muammer(1)
• Sülün, Ali(1)
• Türk, Cebrahil(1)
• Zencir Tanir, Özge(1)
• Zencir, O.(1)
• Özdemir, Nurgül Şen(1)
• Şen Özdemir, Nurgül(1)

• ArticleAçık Erişim2026/r/ebyu/10713
  Assessment of Population Parameters for Fisheries Management in a Pressured Ecosystem: A Case Study of Sapanca Lake (Türkiye)

  Şen Özdemir, Nurgül; Aydın, Erdinç; Sökmen, Teoman Özgür

  Sapanca Lake is a tectonic freshwater lake ecosystem whose water balance and ecological integrity are increasingly threatened by urbanization, pollution, climate change, and declining water levels. To assess recent changes in the fish community, length–weight relationships (LWRs), condition factors (CFs), sex ratios (F/M), and standing stock biomass estimates were determined for eight fish species (Blicca bjoerkna, Scardinius erythrophthalmus, Carassius gibelio, Esox lucius, Silurus glanis, Perca fluviatilis, Abramis brama and Cyprinus carpio) sampled between December 2024 and April 2025. According to standing stock biomass assessments, Cyprinus carpio showed the highest biomass (297.67 tons), while Abramis brama had the lowest (22.72 tons). Most species showed positive allometric growth (b > 3), suggesting generally favorable feeding conditions. In contrast, the main predatory species, E. lucius (b = 2.89) and Silurus glanis (b = 0.21), exhibited negative allometric growth, likely due to limitations in food availability and prey abundance. The CF values were generally >1, indicating good physiological status; however, lower CF values in A. brama (1.18) and B. bjoerkna (1.19) suggest species-specific ecological limitations. Sex ratio analysis revealed pronounced female dominance across species, ranging from complete female dominance (F/M = 1/0) in Carassius gibelio to a female-biased ratio of 1/0.04 in Scardinius erythrophthalmus, likely driven by seasonal sampling effects, sex-specific behavior, and species-specific reproductive strategies. Overall, the results indicate increasing trophic imbalance and ecological stress in Sapanca Lake, emphasizing the need for standing stock biomass assessments and ecosystem-focused fisheries management in tectonic lakes under hydrological pressure.

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• ArticleAçık Erişim2026/r/ebyu/10291
  Composition of Commercial Gillnet Catches in a Groundwater-Fed Lake: Mesh-Specific Patterns and High Representation of Non-Indigenous Carassius gibelio

  Sökmen, Teoman Özgür

  Small inland lakes support substantial freshwater biodiversity, but independent fish surveys may be constrained by specialised equipment, trained personnel, seasonal replication, and sustained funding. This study evaluated whether repeated observations of routine commercial gillnet catches could characterise the gillnet-catchable fish subcommunity of Çaltıcak (Taşkısığı) Lake, a shallow, approximately 90-ha groundwater-fed lake in Sakarya Province, Türkiye, and support surveillance of the non-indigenous Carassius gibelio. Fish were obtained over 17 sampling nights from 12 February to 3 June 2026 using five separate single-mesh monofilament gillnets (40, 50, 60, 75, and 80 mm mesh-bar length). Total design-based nominal mounted-area effort was 22,451.7086 m2-night, and catch was expressed as area-standardised numerical and biomass catch per unit effort (NPUE and BPUE). A total of 863 individuals from eight species were examined. Blicca bjoerkna, C. gibelio, and Scardinius erythrophthalmus were the most numerically represented species. C. gibelio constituted 26.42% of the examined catch and had a strongly female-biased catch composition (95.2% female). Smaller-bodied cyprinids occurred mainly in 40–50 mm meshes, whereas Cyprinus carpio and Silurus glanis occurred mainly in 80 and 60 mm meshes, respectively; Esox lucius was an exception, occurring mainly in 40–50 mm meshes. The combined catch corresponded to 0.038438 individuals m−2 night−1 and 0.015831 kg m−2 night−1. Approximate overnight soak duration varied seasonally from 9 to 16 h, but exact set and retrieval clock times were not recorded. Deployment coordinates were also not recorded, and sampling was confined to routine commercial fishing zones during February–June. Accordingly, the findings apply only to the gillnet-catchable fish subcommunity and must not be interpreted as a lake-wide fish-community or stock estimate. Repeated monitoring with georeferenced deployment and exact effort records would strengthen this catch-based baseline.

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• ArticleAçık Erişim2026/r/ebyu/10110
  Seasonal Dominance over Morphometric Effects in Regulating Antioxidant Defense in Two Freshwater Capoeta Species

  Kırıcı, Muammer; Özdemir, Nurgül Şen; Güneş, Muharrem; Sökmen, Teoman Özgür; Caf, Fatma; Türk, Cebrahil; Demir, Nurullah

  Antioxidant defense systems in fish are highly sensitive to environmental variability and provide valuable indicators of physiological stress in aquatic ecosystems. This study evaluated the combined effects of seasonal variation, morphometric parameters (total length, total weight, and condition factor), sex, and species identity on oxidative stress markers and antioxidant defense responses in Capoeta umbla and Capoeta trutta collected from the Karasu River (Türkiye). Fish were seasonally sampled between April 2023 and March 2024, and malondialdehyde (MDA) levels and the activities of key antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR), were analyzed in edible muscle tissues. Length–weight relationships and Fulton’s condition factor were calculated to describe growth patterns and physiological status. The results indicated that seasonal variation was the primary factor influencing oxidative stress responses and antioxidant defense patterns in both species. Higher oxidative stress levels and increased antioxidant enzyme activities were generally observed during the summer period, reflecting physiological responses to elevated environmental temperatures. Morphometric parameters and species identity showed comparatively weaker associations with antioxidant variability. Overall, the findings highlight the dominant role of seasonal environmental dynamics in regulating oxidative balance in freshwater Capoeta species and support the use of antioxidant biomarkers as effective tools for assessing ecosystem health under changing environmental conditions.

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• ArticleAçık Erişim2016/r/ebyu/16749
  Density and biomass of fish populations in Kirmir stream of Sakarya river, Turkey; [Sakarya nehri’nin Kirmir çayı’ndaki balık populasyonlarının yoğunluğu ve biyoması]

  Zencir Tanir, Özge; Korkmaz, A. Şeref

  In this study, Zippin’s triple-catch removal method was used to estimate density and biomass of fish species in Kirmir Stream of Sakarya River, Central Anatolia Turkey. A total area of 1.5256 ha was sampled and 4167 fishes were caught using electrofishing between February 2007 and November 2007. A total of 9 fish species representing 2 families Cyprinidae and Cobitidae were recorded. Fish species identified are as follows: Chub (Leuciscus cephalus Linnaeus, 1758), barbel (Barbus plebelejus escherichi Heckel, 1843), Capoeta tinca Heckel, 1843, spirlin (Alburnoides bipunctatus Bloch, 1782), Capoeta capoeta sieboldi Steindachner, 1864, tirgis-nase (Chondrostoma regium Heckel, 1843), bleak (Alburnus orontis Sauvage, 1882), spined-loach (Cobitis taenia Linnaeus, 1758) and angora-loach (Noemacheilus angorae Steindachner, 1897). A. orontis was the most dominant species, constituting 1199 fish and 28.77% of the total fishes, followed by C. tinca (1173 fish and 28.15%), B. p. escherichi (584 fish and 14.01%), L. cephalus (454 fish and 10.90%), A. bipunctatus (322 fish and 7.73%), C. regium (245 fish and 5.88 %), N. angorae (107 fish and 2.57%) C. c. sieboldi (65 fish and 1.56%) and C. taenia (18 fish and 0.43%). The density and biomass values were estimated as 11456 fish ha-1 and 346.78 kg ha-1 in February 2007, 8982 fish ha-1 and 279.82 kg ha-1 in May 2007, 6320 fish ha-1 and 251.52 kg ha-1 in August 2007 and 2887 fish ha-1 and 168.87 kg ha-1 in November 2007, respectively. The lowest density and biomass values were observed in November 2007.

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• ArticleAçık Erişim2011/r/ebyu/17216
  Seasonal variation of phytoplankton composition in a medium-size river: The Kirmir and its tributaries Ankara, Turkey

  Zencir, O.; Fakioglu, O.; Demir, N.; Korkmaz, A.S.

  The aim of this study was to determine the seasonal variation of phytoplankton in a connected river system, the Kirmir and its tributaries the Suveri and the Ilhan. The samples were collected from a total of ten selected stations on the main river and tributaries in November 2006, February, May and August 2007. A total of 57 phytoplankton species from Bacillariophyta, Chlorophyta, Chrysophyta, Cryptophyta, Cyanobacteria, Euglenophyta and Pyrrophyta were identified. Bacillariophyta species were dominant in all stations during the research period. Caloneis bacillum, Cocconeis placentula, Cyclotetta meneghiniana, Diatoma vulgare, Gomphonema ventricosum, Nitzschia sigmoidea and Ulnaria ulna appeared at high densities in the samples. The maximum phytoplankton abundance was found in the Kirmir on all sampling dates. Furthermore, some species which are indicators of pollution were found in the Kirmir.

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• ArticleYalnız künye2007/r/ebyu/17795
  Water quality and phytoplankton of major lentic water bodies of the northeastern region of Turkey (Erzurum vicinity)

  Kivrak, Ersin; Gürbüz, Hasan; Altuner, Zekeriya; Sülün, Ali

  This paper reports the results of a long-term research related to water quality, trophic status and phytoplankton species composition of major lentic water bodies in northeastern Turkey. Phytoplankton of studied water bodies consisted of 253 taxa from 79 genera belonging to Bacillariophyta, Chlorophyta, Cyanophyta, Euglenophyta, Dinophyta, and Chrysophyta. Bacillariophyta were generally dominant in the phytoplankton community of studied water bodies. Seasonal development of phytoplankton exhibited two peaks: one in late spring and the other one in autumn. The trophic status and water quality properties of the studied water bodies are discussed in detail in the text.

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