Stock assessment of Sturgeon fishes in the southern part of Caspian Sea (Iranian water).

The marine survey for sturgeon stock assessment was conducted in summer and winter in the years 2004 and 2005 to estimate the relative and absolute abundance and percentage composition of each species in the Gilan, Mazandaran and Golestan Provinces. This survey was carried out in the Iranian waters of the Caspian Sea on board the Sisara and Gilan vessels using trawl nets at 2-100 m depths. A representative from Russia was also present throughout this survey. Trawling was carried out in 85 stations that were selected using a stratified random design. The number of stations in each scope was based on the area of the scope in terms of the total area. Trawling and sampling in shallow water up to 10 m were carried out using 9 m trawl nets whereas 24.7 m trawl nets were used for depths more than 10 m. Trawl surveys were carried out in the daytime. Trawling velocity was kept at 2.5-3 kts and trawls lasted half an hour in order to calculate abundance, and biomass of sturgeons using the swept area method. In the 85 stations trawled in summer 2004 totally 170 sturgeons including 142 Acipenser persicus specimens, 19 A. stellatus, 4 Huso huso, 3 A. nudiventris and 2 A. gueldenstaedtii were trawled. In the 85 stations trawled in winter 2004 totally 118 sturgeons including 75 A. persicus specimens, 41 A. stellatus, 1 A. nudiventris and 1 A. gueldenstaedtii were trawled (no beluga specimens were caught in the winter 2004 survey). In the summer survey of 2005 totally 124 sturgeon specimens including 101 A. persicus specimens, 21 A. stellatus, and 2 A. gueldenstaedtii were trawled in a total of 84 trawlings (no beluga and ship sturgeon specimens were caught in the summer 2005 survey). A total of 76 sturgeon specimens were caught in the 85 stations trawled in the winter 2005 survey which included 46 A. persicus specimens, 26 A. stellatus, 3 Huso huso and 1 A. nudiventris (no A. gueldenstaedtii specimen was caught in the winter 2005 survey). Catch per unit area (CPUA) in the summer 2004 survey was 6670 specimens nm2 at depths less than 10 m and 1487 specimens nm2 at depths greater than 10 m (10-100 m depth). These values in the summer 2005 survey dropped to 4572 specimens nm2 at depths below 10 m and 1115 specimens nm2 at depths above 10 m. CPUA for sturgeons in the winter 2004 survey was 2103 specimens nm2 at depths less than 10 m and 1538 specimens nm2 at depths greater than 10 m which in the winter 2005 survey was estimated as 1803 specimens nm2 at depths below 10 m and 923 specimens km2 at depths greater than 10 m. In all the surveys conducted CPUA for A. persicus was higher than that for the other sturgeon species.Catch per unit effort (CPUE) in the summer 2004 survey was 2 specimens per trawl which was comprised of 1.67 A. persicus, 0.22 A. stellatus, 0.02 A. gueldenstaedtii, 0.04 A. nudiventris and 0.05 Huso huso per trawl. CPUE in the winter 2004 survey was 1.38 specimens per trawl which included 0.88 A. persicus, 0.48 A. stellatus, 0.01 A. gueldenstaedtii and 0.01 A. nudiventris specimen per trawl. CPUE in the summer 2005 survey was 1.47 specimens per trawl which comprised 1.2 A. persicus, 0.25 A. stellatus and 0.02 A. gueldenstaedtii specimens per trawl. In the winter 2005 survey CPUE was recorded as 0.89 specimens per trawl which was comprised of 0.54 A. persicus specimens, 0.3 A. stellatus specimens, 0.04 Huso huso specimens and 0.01 A. nudiventris specimens per trawl. Based on the calculations carried out in the marine survey in summer 2004 the estimated absolute abundance for sturgeons was about 9565.523 thousand specimens of which 7704.664 thousand belonged to A. persicus, 101.340 thousand specimens belonged to A. stellatus, 174.164 thousand specimens belonged to A. nudiventris and 297.136 thousand specimens belonged to H. huso. The total biomass of sturgeon was estimated as 11213.132 tons which included 4315.559 tons A. persicus, 14.188 tons A.gueldenstaedtii, 1035.931 tons A. stellatus, 23.222 tons A. nudiventris and 5824.232 tons H. huso specimens. In the winter 2004 survey total abundance for sturgeons was estimated at about 7275.351 thousand specimens which was comprised of 4692.661 thousand A. persicus, 67.332 thousand A. gueldenstaedtii, 2455.469 thousand A. stellatus, and 59.889 thousand A. nudiventris specimens. The total biomass of sturgeons was estimated at about 4942.183 tons which included 1786.100 tons A. persicus, 6.195 tons A. gueldenstaedtii, 2814.507 tons A. stellatus and 335.381 tons A. nudiventris specimens. The total biomass in summer 2005 was estimated at 7939.894 thousand specimens of which 5993.777 thousand specimens belonged to A. persicus, 122.174 thousand specimens belonged to A. gueldenstaedtii and 1823.943 thousand specimens belonged to A. stellatus. The total biomass calculated was 8359.093 tons which was comprised of 5414.795 tons A. persicus, 17.104 tons A. gueldenstaedtii and 2927.194 tons A. stellatus. Total abundance in sturgeons in the winter survey of 2005 was about 4687.167 thousand specimens of which 2720.005 thousand specimens were A. persicus, 1557.123 thousand specimens were A. stellatus, 350.151 thousand specimens were H. huso and 59.889 thousand specimens were A. nudiventris...