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

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: r_Pearson = -0.686, P<0.05; ρ_Spearman = -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.

Keywords

• Narrow-clawed crayfish,Astacus leptodactylus,Abundance,Lake Sevan,Armenia

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