üzere üç mevsimde toplam 14 istasyonda yapılan örneklemelerde, serpme, elektroşoker, çeşitli göz açıklığındaki solungaç ağları kullanılarak 251 adet birey yakalanmıştır. Her bireyin çatal boy, ağırlık ve sindirim kanalı uzunluğu ölçülmüş, pullarından yararlanılarak yaş tayinleri yapılmış, sindirim kanalı içerikleri incelenmiştir. Sindirim kanalından çıkan besin organizmaları muhtemel en düşük taksona kadar tanımlanmıştır. Bireylerin beslenme şiddeti, sindirim kanalı içerikleri iki farklı yöntemle değerlendirilmiştir. C. gibelio bireylerinin omnivor olduğu ve çoğunlukla alglerle beslendiği belirlenmiştir. Sindirim kanalı içeriğinde besin çeşitliliği en yüksek yaz mevsiminde Sarımsaklı istasyonunda (2,55) en düşük çeşitlilik de yaz mevsiminde, Kumkale istasyonunda (0,70) görülmüştür. Sindirim kanalından çıkan besin organizmaları arasında Heterokontophyta ve Amphipoda üyelerinin önem indeksleri yüksektir.

This study reports the first recorded instance of Atherina boyeri (Risso, 1810) in the Bayramiç Reservoir, located on the Karamenderes Stream. Since 2005, ichthyological researches have been carried out in the Bayramiç Reservoir by various researchers, but none of them have noted the existence of A. boyeri in this reservoir. In the field studies conducted between May 2016 and July 2017, a total of 98 A. boyeri specimens was caught. In these samplings, a 70 m long and 2 m wide beach seine net with 10 mm a mesh size was used. Although a small number of A. boyeri was caught during the first observation in October 2016, more individuals were observed in July 2017. The fork length of the A. boyeri observed was between 2.7-8.8 cm and the weight ranged between 0.06-4.31 g. The bimodal length distribution of the specimens indicates that there have been multiple incidents of adult specimens entering the reservoir and that these individuals have given birth to new offspring. The translocation of A. boyeri into the Bayramiç Reservoir might have been due to unauthorized introduction by fishermen or through illegal release by anglers as fish bait. However, the distribution map of A. boyeri in inland waters in Turkey shows significant overlap with the migration routes of big waterfowl. The waterfowl might partially be responsible for the spread of the adult specimens across short distances.

Several Ponto-Caspian gobiids have expanded from their native distribution ranges to Europe and North America. As knowledge on their bio-ecological features in their native range is still limited, the trophic ecology of monkey goby Neogobius fluviatilis and Western tubenose goby Proterorhinus semilunaris was studied in three natural lakes in the Marmara Region of NW Turkey using the stable isotopes of δ 13 C and δ 15 N. In two of the lakes, the trophic niches (as the isotopic niche) of the gobies were highly divergent with co-existing native fishes, with no overlap. Moreover, mixing models suggests considerable inter-specific dietary differences. In all lakes, the trophic niches of gobies were never significantly larger than those of coexisting fishes. These results suggest that when introduced outside of their natural range, the gobies might integrate into new fish communities via exploiting resources that are underexploited by native fishes or will initially share resources with these species before their niches diverge, perhaps through competitive displacement.

An invasive species, Carassius gibelio, alters the native fish community through trophic niche competition

The ontogenetic diet shift of invasive Carassius gibelio (Bloch, 1782) was investigated in Karamenderes River, Turkey. The fieldwork was performed during summer 2012, autumn 2012 and spring 2013. The fishes were caught by electrofishing and using gill nets. Nine fork length groups were used in order to assess the ontogenetic diet shift. The gut contents were assessed by the index of relative importance that was calculated from the frequency of occurrence, numerical abundance, and volumetric analyses. The most abundant length groups of C. gibelio were 18-20 cm, 6-8 cm, and 27-29 cm length groups during summer 2012, autumn 2012 and spring 2013, respectively. The feeding intensity was the lowest in the length groups of 15-17 cm during summer 2012, in 3-5 cm length group in autumn 2012 and in 24-26 cm length group in spring. Seasonal variations were observed in the ontogenetic diet shift of C. gibelio. Large specimens consumed more animal materials during summer and more algae in autumn. There was not any significant niche overlap recorded between small and large specimens except summer. Any niche overlap between small and large specimens might be advantageous for the establishment success of invasive Gibel carp in Karamenderes River.

Most rivers around the Mediterranean region, regardless of size, are interrupted by human induced barriers. Although various studies have been conducted to investigate the impacts of reservoirs on undisrupted freshwater biota, what kind of effects they exert on the distribution of freshwater fish assemblages with respect to the presence of invasive species remains to be answered. To attend to this research need, the Karamenderes River, which is disrupted by the Bayramiç Reservoir, was selected as the research site. Relying on the river continuum concept (RCC), we hypothesized that fish assemblages in a given river would demonstrate a gradual downstream change unless the river is interrupted by any reservoir. The ad hoc unweighted pair group method with arithmetic means (UPGMA) agglomerative hierarchical cluster analyses revealed 11 fish assemblages 100 km down the studied river, which is characterized by four environmental gradients. Besides, co-occurrence network analyses were performed to gain a better understanding of the constructs of the observed fish assemblages. The analyses yielded two distinct clusters along the river and showed that the Bayramiç Reservoir had no decisive part in the spatial clustering of these fish assemblages. The migratory species Anguilla anguilla was found only in and around the river mouth area. The co-occurrence network analyses indicated that the freshwater, estuarine and introduced species were observable in distinct groups. It is notable that the non-native Cyprinus carpio and invasive Carassius gibelio were determined in the native freshwater fish species module. The research evidenced that the reservoir had a triple effect, that is, a migration barrier to migratory fish species, a donor facilitating invasion, and a cause of homogenization of river fish assemblages along the river. The results suggest that the impact of the reservoir should be assessed in view of multiple nested model and fish passageways and controlling invasive species are two contradictory problems as far as the impacts of reservoirs are concerned. Therefore, river management should be performed in a way to allow the native migratory species to migrate freely while preventing the introduced species from moving upstream or downstream to preserve and promote rivers' heterogeneity.

No abstract

Objective:The first aim of this study is to describe the length, weight, condition factor, and GSI of Alburnus istanbulensis (Battalgil, 1941) in two different connected habitats (stream habitat and reservoir lake) in Karamenderes River, Çanakkale. The second aim is to state the growth type of this species in the sampled habitat using the length-weight relationship (LWR) model. Materials and Methods:The sampling areas are Bayramiç Reservoir and two tributaries on Karamenderes River, which feed the reservoir. Sampling was conducted between May 2016 and June 2017, and depending on the habitat types, different gears were used in the samplings. W=aL b equation was used to calculate the length-weight relationship, K=100×W/L 3 equation for the condition factor, and GSI=W G ×100/W equation for the gonadosomatic index. Results:The results showed that the mean fork length of specimens in reservoir and stream habitats were 11.86±1.83 cm and 7.69±3.56 cm, respectively, and body weight of the specimens in the reservoir and stream habitats were 19.28±8.99 g and 8.17±10.82 g, respectively. The condition factor was higher in the reservoir habitat and GSI values were higher in the stream habitats. The growth for all the specimens was positive allometric (b=3.13), whereas in the reservoir habitat the growth was isometric (b=2.99) and in the stream habitat the growth was positive allometric (b=3.12). Conclusions: Determining the biological characteristics of an endemic species makes an important contribution to the conservation of the species. In the Çanakkale region, data on LWR, growth, condition, and GSI values were not available with the valid name of the species. Therefore, this study is important in terms of presenting new data in the Çanakkale region with the valid name of the species. The findings of this study indicate that the A. istanbulensis species exhibited habitat-dependent differences in LWR, growth, and condition.