Stock assessment of juvenile sturgeons in the Iranian water of the Caspian Sea by bottom trawl survey

The sturgeon stock assessment was performed to aim at estimation of absolute and relative abundance and determination of species composition at lower ۱۰ m depths using the Si-Sara۲ RV vessel in the Iranian coasts of the Caspian Sea in Guilan, Mazandaran and Golestan provinces during ۶-۳۰ September ۲۰۱۱-۲۰۱۲. In this study, ۴۰ stations were selected on the basis of stratified random sampling design and then the stock estimation was performed using the swept area method. The study was carried out using bottom trawling with ۹ m head rope. The time and speed of trawling in each station were ۳۰ minutes and ۲.۵ knots respectively. The Catch per Unit of Effort (CPUE) in ۲۰۱۱–۲۰۱۲ were ۷.۰۳ and ۶.۹۶ individuals per trawling, respectively. The catch per unit of area in these years were found to be ۱۶۶۲ and ۱۶۴۴ fish in nm۲, respectively. Total abundance of sturgeon juveniles was ۱۳,۳۲۷,۱۶۴ individuals in ۲۰۱۱. So, the species composition included A. persicus (۸۷.۸%) and A. stellatus (۱۲.۲%). Total abundance of sturgeon juveniles was found to be ۱۴,۳۶۴,۸۸۲ individuals in ۲۰۱۲ and the species composition comprised A. persicus (۶۱.۴%) and A. stellatus (۳۸.۶%). In ۲۰۱۱ the biomass of sturgeons in Iranian coastal water of the Caspian Sea was ۲۹۵ tons and the composition of biomass included A. persicus (۸۱.۵%) and A. stellatus (۱۸.۵%), respectively. In the cruises conducted in ۲۰۱۱, this amount was estimated to be ۲۱۷ tons comprising A. persicus (۵۴.۲%) and A. stellatus (۴۵.۸%), respectively. The results of this study in ۲۰۱۱–۲۰۱۲ showed remarkable abundance of juvenile sturgeons in Iranian coastal waters of the Caspian Sea in late summer and early autumn. So, by conserving these valuable stocks, the number of spawners will be increased in the future.

کلیدواژه ها:

Caspian Sea ، Sturgeon ، Stock assessment ، Bottom trawling ، CPUE