Analysis of landings and environmental variables time series from the Caspian Sea

In the present study, time series encompassing the years 1950-2011 of commercial fish landings from the Caspian Sea were analyzed using min/max autocorrelation factor analysis and dynamic factor analysis. The aim was to identify trends and explore the relationships between the response variables (annual landings of 10 species/groups such as kilkas, kutum, common carp, pike perch, roach, shads, bream, mullets, seal and sturgeons) and explanatory variables (sea level and Volga river water volume). Landings were highly correlated with environmental variables. Both techniques gavecoherent results, indicating that the two most important trends in the response variables are: (i) a decrease in landings during second half of the time-series and (ii) a fluctuating pattern. The main common trends obtained by min/max autocorrelation factor analysis and dynamic factor analysis were positive for kilkas, sturgeons, seal and shads. The most significant min/max autocorrelation factor analysis axis showed a steady stability in the first half and a sharp decrease in the second half, which was similar to the most important common trend of the dynamic factor analysis. Species such as kilka, sturgeons, seal, shads and perch were significantly positively related. On the contrary, landings of mullets and kutum were negatively related to the first trend. Considering our results on the ecological and environmental data, these variables and impacts of human activities should be taken into account when managing coastal environments for the conservation of these species in the Caspian Sea.