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

Abstract

Abstract:The narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823) is an indigenous species in Armenia. 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 significant 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 industrial stock of crayfish. It does, however, show negative 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 smaller animals are not captured; meanwhile the remaining smaller animals produce fewer eggs. Decline of crayfish stock cannot be explained by diseases and invasive species, but can be explained by overharvesting. Continuation of harvesting aimed at supplying the existing demand might result to population decline of more than 70% during next 17 years.