Sex ratio, length and weight frequency of freshwater crayfish (Astacus leptodactylus) inhabiting in Aras reservoir, Iran Aras rezervuar (İran)’ında yaşayan tatlısu ıstakozu (Astacus leptodactylus)’nun eşey oranı, uzunluk ve ağırlık dağılımı

Abstract

Turkce Ozet: Tatlisu istakozu (kerevit) ticari olarak avciligi yapilan onemli sucul organizmalardan biridir. Bu canlilarin besin degerleri de oldukca onemlidir. Kerevitler bentik organizmalar olup, yasamlarinin buyuk bolumunu su ortamlarinin tabanlarinda gecirirler. Bu calismada, Aras rezervuarinda yasayan Astacus leptodactylus’un 2011 ilkbahari ile 2012 kis mevsimleri arasinda esey orani ve bazi biyometrik ozellikleri arastirildi. Kerevitlerin ortalama toplam uzunlugu ve agirligi sirasiyla 106,26±12,9 mm and 38,79±15,5 g olarak bulundu. Bulgular, yakalanan kerevitlerden sadece %13,67’sinin standart ticari uzunlugun (120 mm) ve %19,9’unun standart ticari agirligin (50 g) uzerinde oldugunu gosterdi. Bulgular ayrica, erkek bireylerin disi bireylere oraninin azda olsa daha yuksek oldugunu gosterdi (erkek: disi, 51.86: 48.14). Sonuc olarak, bu calismada elde edilen bulgular, Aras rezervuarinda daha onceden yapilan calismalarla karsilastirildiginda, A. leptodactylus’un yakalanan miktarinda ve yakalanan bireylerin buyuklugunde azalmanin oldugunu, ortamda yasayan kerevitin durumunun birkac yil oncesine gore daha iyi olmadigini, ortaya cikarmaktadir. Bu nedenle, Aras rezervuarinda yasayan A. leptodactylus’un korunmasi ve stok yogunlugunun artirilmasi icin calismalarin yapilmasinin gerektigi dusunulmektedir. Anahtar kelimeler: uzunluk, agirlik, esey orani, Astacus leptodactylus, Aras rezervuari Abstract: Freshwater crayfish are one of the important commercially hunted aquatic organisms. Their nutritional values are also considerably important. Crayfish are benthic organisms which spends most of their life on the bed of aquatic habitats. In the present study, sex ratio and some biometric characteristics of crayfish (Astacus leptodactylus) inhabiting in Aras reservoir was investigated seasonally between spring 2011 and winter 2012. The mean total length and weight for the crayfish were 106.26±12.9 mm and 38.79±15.5 g, respectively. The results revealed that only a 13.67% of the captured crayfish exceeded than the standard commercial size (120 mm) and only 19.9% of the samples had higher weight than the standard commercial weight (50 grams). The results also revealed that male crayfish slightly dominated in captured samples (male: female, 51.86: 48.14). Under the light of this study, it can be concluded that decreased catch value and crayfish size in comparison to previous studies carried out last decade, A. leptodactylus has a critical condition in Aras reservoir. Therefore, it is thought that further researches on the conservation and improving stocking density of this species in Aras reservoir are urgently required. Key word: length, weight frequency, sex ratio, crayfish, Astacus leptodactylus, Aras reservoir