ABUNDANCE OF NARROW-CLAWED CRAYFISHES (Astacus leptodactylus Eschscholtz, 1823) AND ITS TRENDS IN LAKE SEVAN, ARMENIA

The narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823) is an indigenous species in Arme-nia. In 1980s it was occasionally introduced in Lake Sevan where its population started to grow. There is a large scale fishery of the crayfish in the Lake, as its demand remains high. Industrial stock of crayfishes at the Lake monitored annually, shows statistically sig-nificant decline in the 2004-2011 period. This decline can be described by logarithmic model y = -577.5ln(x) + 2158, F = 50.27, P<0.001. The catch rate of crayfish net-boxes also shows logarithmic decline F = 9.27, P<0.05 in the 2004-2011 period. Since the net boxes are designed to catch the larger size crayfishes only, the decline indicates a decrease of average size among crayfish population. The female fertility does not show statistically significant correlation with the in-dustrial stock of crayfish. It does, however, show neg-ative correlation with the catch rate of the net boxes: rPearson = -0.686, P<0.05; ρSpearman = -0.647, P<0.05. The correlation can be explained as the big animals are actively removed through harvesting, while small-er animals are not captured; meanwhile the remaining smaller animals produce fewer eggs. Decline of cray-fish stock cannot be explained by diseases and inva-sive species, but can be explained by overharvesting. Continuation of harvesting aimed at supplying the ex-isting demand might result to population decline of more than 70% during next 17 years.