Comparing some biological characteristics of two sturgeons species, Persian sturgeon (Acipenser persicus Borodin, 1897) and Russian sturgeon (A. gueldenstaedtii Brandt & Ratzeburg, 1833) in the Caspian Sea

The objective of this study was to compare the biological parameters such as length, weight, age, caviar production indices, caviar/weight, condition factor and sex ratio of Persian sturgeon (Acipenser persicus Borodin, 1897) and Russian sturgeon (A. gueldenstaedtii Brandt & Ratzeburg, 1833) in the Caspian Sea during 1990-2014. All these characteristics (except condition factor) of Persian sturgeon were greater than the Russian sturgeon. In the long period, annually average (&plusmn;SD) fork length ranged from 129.3 (&plusmn;11.87) to 140.9 (&plusmn;15.99) cm for Russian sturgeon and 145.7 (&plusmn;17.61) to 157.4 (&plusmn;19.31) cm for the Persian sturgeon. The annually caviar harvest for the Russian sturgeon ranged from 3.86 (&plusmn;1.05) to 5.02 (&plusmn;1.82) kg with a caviar/weight ratio were ranged from 16.9 (&plusmn;4.12) to 20.1% (&plusmn;5.12), while comparatively for the Persian sturgeon was greater and ranged from 4.84 (&plusmn;1.62) and 7.04 (&plusmn;2.58) kg with a caviar/weight ratio of 16.2 (&plusmn;3.99) to 21.1% (&plusmn;5.20). The age of both species ranged between 6 to 40 years but the modal age of Russian sturgeon was less than Persian sturgeon. The male:female sex ratio of Russian and Persian sturgeons were 0.23:1 and 0.57:1, respectively. The sex ratio of Russian sturgeon was significantly different from sex ratio of Persian sturgeon (p<0.001). The condition factor of Russian and Persian sturgeons were 0.92 (&plusmn;0.16) and 0.74 (&plusmn;0.13), respectively. Moreover, results of the MANOVA revealed significant differences in population structure of two species (p<0.001). Therefore, different conservation and management activities need for these two valuable sturgeons in the Caspian Sea.