Marking Persian sturgeon (Acipenser persicus) using new method and tracking them under 10 m depth in the sea

The second phase of the project entitled Marking Persian sturgeon (Acipenser persicus) using new method and tracking them under 10 m depth in the sea was approved in 2004. This project which terminated in April 2009 was carried out during 2004 to 2008 to track coded wire tagged (CWT) sturgeons under 10 m depth. Among the specimens caught, three were juvenile Persian sturgeon tagged in the first phase (2003) were caught in the second phase (2004). The data related to tagging & capture of sturgeon from 2003 to 2008 is included. Totally, 426325 specimens of Persian sturgeon were tagged in 3 weight classes (>3g, 3 to 5g and 6 to 10g). Among the population studied, 101500 of them belonged to specimens of 2003 which were tagged by three hatcheries; Shahid Beheshti, Shahid Rajaee & Shahid Marjani and then released into the rivers (Sefidrud, Tajan & Gorganrud) entering the Caspian Sea. During 2004 to 2008, 324825 specimens were tagged in Shahid Beheshti hatchery and released into the Sefidrud River. Gill net were used to catch the tagged Persian sturgeon specimens under 10m depth. During 2003 to 2008, 3616 Persian sturgeon were captured of which 43 juveniles bore CWT. Among the captured CWT sturgeons, 23 specimens belonged to the 6-10 g weight class, 19 specimens belonged to the 3 to 5g weight class and one sturgeon was >3g. Based on the results, it can be concluded that higher weight at releasing time can lead to higher survival rate and fisheries returns. Some other factors that influence catch rate of CWT sturgeons are as follows: Catch station (highest catch rates in Persian sturgeon juveniles belonged to Chaboksar station), catch season (highest catch rates were recorded in summer which can be attributed to the release of juveniles), catch depth (in winter highest catch occurred at 5 to 10m depth, in other seasons highest catch number was recorded at 3 to 5m depth. Decrease in water temperature is the reason for higher catch numbers at 5 to 10m depth in winter. Also, mesh size can effect on catch rate (highest catch rate belongs to nets with 22mm mesh size). Statistical analysis of results showed significant difference (p<0.05) among the various groups studied. Existence of illegal catch nets in the river can also cause mortality of the released juveniles.