Betül BARDAKCI ŞENER, Eyüp Mümtaz TIRAŞIN, Aydın ÜNLÜOĞLU

The Influence of Lake Level Fluctuations on Fisheries in Lake Van

The impact of hydrological regimes on the productivity in lake ecosystems has received considerable attention in recent decades. This study tested the hypothesis that water level fluctuations influence the fisheries productivity of Lake Van. Monthly water level data from 2000 to 2014 were obtained from Hydroweb and fisheries data corresponding to the same time period were acquired from the Turkish Statistical Institute. In order to test whether water level fluctuations demonstrated significant concordance with fish landings, landings data as a dependent variable, and seasonal water level amplitude and mean annual water level as independent variables were used in a linear regression analysis. The regression analysis proved insignificant results. The general trend of a linear decline, with a rate of -575 tonnes per year, observed in the landings did not match the seasonal and inter-annual water level variations which occurred in the lake during the same period. The consistently declining yields might result from a prolonged overexploitation and/or a constant recruitment failure. The estimated values of the seasonal and inter-annual relative fluctuation index (0.402 and 0.097, respectively) were rather low indicating that Lake Van is hydrologically stable with limited aquatic/terrestrial transition zone interactions and a relatively low nutrient load.

Su Seviyesi Değişimlerinin Van Gölü’ndeki Balıkçılığa Etkisi

Hidrolojik rejimlerin göl ekosistemlerindeki verimlilik üzerindeki etkisi son yıllarda büyük ilgi görmektedir. Bu çalışmada, Van Gölü su seviyesindeki değişimlerin balıkçılık üretimini etkilediğini öngören hipotez test edilmiştir. 2000-2014 yılları arasına ait aylık su seviyesi verileri Hydroweb'den, aynı döneme karşılık gelen balıkçılık verileri ise Türkiye İstatistik Kurumu'ndan alınmıştır. Su seviyesindeki değişimlerin, avlanan balık miktarları ile anlamlı bir ilişki gösterip göstermediğini test etmek için doğrusal regresyon analizinde bağımlı değişken olarak avcılık verileri ile bağımsız değişken olarak mevsimsel su seviyesi genliği (amplitüt) ve ortalama yıllık su seviyesi değerleri kullanılmıştır. Regresyon analizi sonucunda anlamlı bir ilişki bulunamamış, avcılık miktarlarında gözlenen yıllık -575 tonluk doğrusal düşüş trendi, aynı dönemde gölde meydana gelen mevsimsel ve yıllık su seviyesi değişimleriyle uyumluluk göstermemiştir. Av ürün miktarlarındaki kalıcı düşüşün sebebi, uzun süreli aşırı avcılık ve/veya stoka katılımda süregelen azalmalar olabilir. Mevsimsel ve yıllık bağıl dalgalanma endeks değerleri sırasıyla 0,402 ve 0,097 olarak hesaplanmıştır. Bu değerlerin oldukça düşük olması Van Gölü'nün hidrolojik olarak kararlı olduğunu, su/kara geçiş bölgesi etkileşimlerinin sınırlı düzeyde kaldığını ve göle nispeten düşük nütrient girişi gerçekleştiğini göstermektedir.

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