Some Environmental Factors Effects on Species Composition, Catch and CPUE of Kilkas in the Caspian Sea

This study evaluates changes in species composition, catch, and CPUE of three species of kilkas in the Caspian Sea from 1961 to 2009. The effects of fluctuations in sea level rise and fall on the catch of kilka as well as the impacts of a recent invasion by Mnemiopsis leidyi (Ctenophora) were assessed in terms of species composition and CPUE of kilkas in the Iranian coastal region of the Caspian Sea. We found a negative correlation between long-term sea level changes and total catch (R2 = –0.56; P 0.001, which significantly declined in 1995 when the sea level increased to its highest level. Comparing catch per unit effort (CPUE) values during the pre-invasion (1996– 1999) and post-invasion (2000–2009) periods indicated significant declines in anchovy and bigeye kilka, while common kilka increased significantly after the ctenophore invasion. During 2000– 2009 overfishing, together with various environmental impacts following the introduction of Mnemiopsis, were major factors that contributed to changes in species composition and the collapse of kilka stocks in the Caspian Sea.