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Gholi hossienpor, R.
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AbstractStock assessment of Urmia Lake Artemia between 2000-2001 revealed intense decreasing cysts and biomass compared the previous years. Reducing annual rain falling from 32 to 18 cm in west Azarbayjan province lowered fresh water entrance from 4 billion m3 to 1.8 billion m3 to the lake as in 2001 the water volume reached to 6 billion m3 . Decreasing more than 2 billion m3 water volume of the lake per year with increasing the evaporation rate and existence of 5 billion tons salt inside the lake increased water salinity from 17% (1999) to 23.3% (2001) with max- min range of 250-258 ppt without any differences between the seasons. Mean transparency measured with Sechi disk was 138 cm (maximum 215 in Autumn and minimum 51 cm in Spring). Annual mean of water temperature 15 with fluctuation of 6 in winter to 22.13 in Autumn. this study, Artemia (different life stages) and phytoplankton were sampled by planktonic net from 12 suit stations which were selected from 36 sites used in previous Artemia stock assessment project done by Gent University, 1995. Phytoplankton sample identified and counted using identifying key and microscopic study. Results showed that in winter, the number of cysts per cubic meter 756 (minimum) and 2015 (maximum) in Autumn, with annual mean of 1000.m-3. Minimum 0.7 g.m-3 biomass wet weight (without cysts) were obtain in winter while the maximum (9.22 g.m-3) was in spring. The numbers of different nauplii stages per cubic meter with range of 0.03 in winter to 9.22 in spring( mean of 2.46) and juvenile stage per cubic meter were between 0.05 in winter to 1.16 in spring( mean= 0.66). It's showed higher percentage of larval stages in spring toward to higher juvenile and adults stages in summer to mid-autumn. Only Dunaliella and Nitzschia were identified but Dunaliella was dominated ( 95% of total identified phytoplankton with higher abundance, 31000 cells.L-1 in spring season(especially in May and June). Total biomass concluding cysts in studied year was 2700 tons( 30 tons cysts and 2670 tons other biomass which with 10% harvestable biomass,3 tons cysts and 267 tons other biomass could be harvested without any diverse effects on Artemia stock. Cysts and biomass were found more in central to southern part of the lake . The best season for cysts harvesting were Autumn follow by Spring and for biomass harvest were Summer follow by Autumn.
Publisher or UniversityIranian Fisheries Science Research Institute
Series : Nr50198;