شناسه هاي افزوده :
مهدينژاد، كريم ، همكارطرح , عبدالملكي، شهرام ، همكارطرح , چوبيان، فروزان ، همكارطرح , ارشد، عما ، همكارطرح , صادقيراد، مرجان ، همكارطرح , جوشيده، هاشم ، همكارطرح , نقشي، سعيده ، همكارطرح , نصرا...زاده، حسن ، همكارطرح
چكيده انگليسي :
Persian sturgeon from Kura and Ural Rivers of the Caspian Sea are homogeneous with regard to their main meristic and plastic features. Existence of winter race Persian sturgeon was assumed based on different functional status and maturity stages of spawners entering the Volga River. Persian sturgeon feeds at the shelf zones primarily in the eastern parts of the South Caspian Sea. Individual specimens are found in the North and western parts of the Middle and South Caspian Sea (along Lenkoran shores). Unlike Russian sturgeon, the body is more elongated and bulky, bluish, head length up to 17.6% of body length (TL), snout and postorbital distance are rather longer. Corresponding differentiation rates (t) are 4.51, 4.17, and 4.25, respectively. Head depth is 8.61% of TL. Maximum body depth in females is 17.44% and in males about 16.27% of TL. Ventral scutes/plates 6-12, D 31-50 (39.0 in average), A 16-30 (24.8 in average) . Originally the species is endemic to Ponto-Caspian. Its distribution is in Caspian and Black Seas and rivers entering these water bodies. Species is bottom dweller and occurs primarily at mud and/or sand bottoms. Persian sturgeon undertakes feeding, spawning and post-spawning migrations. Fish enters the rivers for spawning, mainly Kura river and to a lesser extent in to Volga, Ural, rivers of Dagestan (Samur, Terek) and Azerbaijan (Lenkoranka, Astara), and Sefid-Rud River. Persian sturgeon is euryhaline and eurythermic species. The majority occurs in typical marine Caspian waters where temperature ranges from 4.10 - 28.00C, in summer - 12.0-23.50C, in winter - 12.0-14.00C, in spring - 10.0-12.00C. Spawners enter the Volga river at 4-50C, the Ural river - at 5-60C. It is eurybathic species, resides at continental terrace above 100-m depth and makes regular seasonal movements. In winter it occurs at the depth of 20-40 m, in summer - 10-20 m and as an Oxyphilic species, occurs at oxygen concentrations of 71.7- 105.5% of saturation. Persian sturgeon is a heterotrophic species, detects food item with tactile and gustatory receptors and then makes sucking movements with protractile oral apparatus. In Kura river migratory fingerlings (16-73 mm TL) feed on Mysidae, Chironomidae and Gammaridae (total index of stomach fullness - 195-1,000 0/000). In the south-eastern part of the Caspian Sea juveniles aged 2-3 years feed on crab and fish. In the course of growth importance of dietary fish increases up to 70-80%. Persian sturgeon sized up to 81-120 cm feeds primarily on fish (53.4%). Persian sturgeon feeds more actively at diurnal and nocturnal hours. Seasonal changes in diet are characteristic of this species: in spring, the main food items are Gammaridae and fish; in summer - Gammaridae and Cumacea. Indices of stomach fullness in juveniles were higher in spring (57.5 0/000, 32.0% of sampled fish with empty stomachs), than in summer (10.0 0/000 and 50.0%, respectively). Reproduction is sexual and takes place in Sefid Rud and Volga rivers (flow velocity of 1.2-1.6 m*sec-1 and water temperature of 20-250C) in the middle and lower spawning areas. In Kura river spawning grounds are located at the dam area of Varvarinsky reservoir; in Araks - 10 km below the Bagramtapinskaya dam. Before regulation of Kura River and Araks stream, the main spawning grounds were located in the mid- flow Kura River, at Mingechaur - 660 km from the river mouth, in the river Araks - 330 km away at Karadonly. Spawning in Ural River occurs in areas located 1000 km from the the mouth in coincidence with the Russian sturgeon. In the Volga river fecundity of Persian sturgeon varied from 310*103 to 390*103 eggs, as estimated for the period 1991-2000. Reduction in fecundity values (down to 310*103 in 2000) is related to decrease in females in spawning age. In Kura and Ural River populations the averages fecundity was 320*103 eggs (Artyukhin, 1979). Limiting factors in Reproduction efficiency are mainly hydrological conditions at the river, primarily, water temperature. Spawning in Kura is suspended from mid-summer to September due to high water temperatures. Development patterns in Persian sturgeon follows the same stages characteristic of all sturgeon species, i.e.: embryo, prelarva, larva, fingerling, juvenile and adult (Detlaf et al., 1981). Duration of embryonic period (2-10 days) similar to Russian sturgeon; these species could not be distinguished at embryonic and early larval stages. Larvae start active feeding at 17-17 mm TL, 9 days after hatching. Persian sturgeon shows moderate weight gain during the first year of life which increases considerably in 8-year-old fish. In succeeding years, the build-up of weight goes more slowly. To the contrary, linear growth is particularly rapid during the first two years but decreases abruptly later on. Persian sturgeon population from Ural River ranks below the Kura population with regards to growth rate. In terms of sexual structure of the population a decrease in females abundance is obvious; in 1999-2000, proportion of females in the Volga river was equal to 17.0%, males - 83%. In the Ural and Kura rivers females/males ratio was approximately equal to 1:1. The majority of males in the Ural River are represented by fish aged 10-21 years (84.7%), modal age group is 12-17 years (54%). Males aged over 21 year are scanty. Females are mostly 15-24 years old (76.4%). The main part of the population is represented by specimens aged 7-20 years (42.5%). In the Volga River fish age is ranged from 14 to 36 years where 74.2% are between 20-26 years of age. Mean age of females is 24.4 and males 23.4 years (Putilina, 1983). In 1991-2000, length of migratory spawners in the Volga river delta ranged from 68.0-107.0 cm, weight- from 4.7-13.2 kg and age from 4-12 years. Males aged 7-30 years with average of 12-17 years, entered the Kura River while females were between 13 to 34 years and more frequently 19-24 years entered the river. Persian sturgeon caught at sea ranged from 3 to 33 years and large proportions of fish (60.5%) were between 7-14 years. In 1983, length of Persian sturgeon in the Volga River varied from 109 to 200 cm. The mean body length was 169.9 cm in females, 162.1 cm in males while in 2000 the corresponding figures were 152.2 and 134.1 cm respectively. In 1999-2000, length of Persian sturgeon varied between 105-242 cm in females, 86-226 cm in males and up to 75% of the catch comprised of fish with total length of 160- 170cm. The biggest catch in Azerbaijani waters was observed in 1936 with 1540 tons. In early 1950s fishing yield dropped to 630 tons and by 1960s to 310 tons. In Iranian waters Persian sturgeon catch was 250 tons in early 1950s and reached 920 tons in early 1960s. Catches in the Volga and Ural rivers were not recorded due to insignificant proportion of the species in total catch. In the Volga River the share of Persian sturgeon ranged from 0.4 to 0.03% in 1991-2000. Prior to 1865 the main fishing gears used at the Caspian Sea were beach seines and later on hooked gears and different nets - floating, stationary, etc., were employed. Since 1962, fishing (with beach seines) was transferred to the rivers, except for Iran. Since 2001, Persian sturgeon of the Volga River is used only for reproduction purposes. Heavy fishing activities have caused drastic decline in Persian sturgeon catch. In 1980s they composed 4.0% of total sturgeon catches from the Volga River but in 2000 the share of this species decreased to only 0.03%. At the Ural River it did not exceed 5%. Fishing at sea leads to extraction of immature fish which results in reduction of spawning population, natural reproduction and stocks fall. The main factors, which contribute to decline of Persian sturgeon populations are stream regulation/ damming at the rivers, loss of spawning grounds, increasing trend of pollution in rivers and the Caspian Sea and fishing at sea. In order to restore Persian sturgeon stocks, appropriate measures should be undertaken to increase artificial reproduction of this species at well-equipped and managed hatcheries
