The Introduction of a Marine Species Atherina boyeri into Bayramiç Reservoir, Çanakkale

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

Ontogenetic Diet Shift of Invasive Gibel Carp (Carassius gibelio, Bloch 1782) in Karamenderes River (Turkey)

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

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

Carbon and nitrogen stable isotope analyses were used to determine isotopic niche width of the invasive fish species Carassius gibelio to help assess the niche overlap and potential impact of this species on the native fish fauna in the Karamenderes River, northwest Turkey. C. gibelio had the highest niche area of the coexisting species. The greatest overlap of isotopic niche was between C. gibelio and Mugil cephalus in the river mouth. The freshwater species displayed similar patterns when taking into consideration their relative abundance and isotopic overlap. While C. gibelio is likely to outcompete some species at some localities, the species was found co-occurring with others by maximum tolerable overlap degree and apparently utilised vacant niche space at some stations. Overall our results indicate that C. gibelio has extensive niche overlap with the native fish species making it a strong competitor, and because of its high abundance and high niche width this invasive species represents a serious threat to the native fish fauna, particularly in the river mouth.peerReviewe

[Report from] Joint EIFAAC/ICES/GFCM Workinggroup on eels (WGEEL)

Source at https://www.ices.dk/Science/publications/Pages/Scientific-reports.aspx