Description of the biology of Caspian vimba,Vimba vimba(Linnaeus,1758),in Gorgan Bay-Miankaleh Wildlife Refuge(southeast Caspian Sea)

We collected Vimba vimba throughout the spawning season(mid April to mid June,2007) in Gorgan Bay(south-western Iran) and investigated its age,growth,and reproductive traits.The maximum age was 5+ years.Both sexes grew allometrically(positive for males:b=3.140 9 and negative for females:b=2.791 4).The von Bertalanffy growth functions were described by the formulae Lt=32.565(1-e-0.184(t+0.530)) for males and Lt=35.950(1-e-0.179(t+0.529)) for females.The overall sex ratio was balanced,but males were predominant in the smaller size classes and females in the larger size classes.Based on the gonadosomatic index(GSI) values,spawning appears to occur between late April and late May in the bay.The highest mean GSI was 6.44 for males in early May and 20.36 for females in late April.Absolute fecundity varies from the minimum of 5 436 eggs for age 3+ fish to the maximum of 36 141 eggs for age 5+ fish.Fecundity was also positively correlated with fish size(length and weight).Egg diameter ranged from 1.05 to 1.70 mm in the mean of 1.42 mm.There was no correlation between female size and ova diameter.

Mud Diapirism on the Gorgan, North Iran

The several mud volcanoes have been exposed at the Gorgan area in the north Iran. The Garniarig-Tapeh is the biggest mud volcano and the investigation of its tectonic geomorphology is the main aim in this paper. Also, we have determinated tectonic and geologic setting of Naft-Lije mud volcanoes and several Salses as the exposed mud diapirs at Gorgan on the northern margin of Iran. These mud volcanoes have been formed during quaternary of as a shield shape hill or pool on the flat plain in coastal region SE Caspian Sea. There are flat area and several mud volcanoes that they have been triggered by buoyant driving mechanisms, have been appeared during dormant periods of mud volcanoes activity. This mechanism has been developed in neotectonic regime by convergent setting between The Cimmerian and Eurasian plates. Finally, the main characteristics of the Gorgan area have presented.

The Effect of the Land Use/Cover Changes on the Floods of the Madarsu Basin of Northeastern Iran

In order to understand the effect of the land use/cover change on the hydrologic regime of the Madarsu Basin in Golestan province of Iran, we selected the two floods of June 1964 and June 2003 with equal amount of rainfall but different rate of runoff. For these floods the closest time images of MODIS were selected. On these images we analyzed the land use/cover types and calculated their area and change rate between two floods. We also calculated the Curve Number (CN) for each land use/cover type according to the US Soil Conservation System (SCS) model. The results showed that: the intensity of the peak floods has increased from 1960 to 2002, and the natural lands of forests, rangelands, and bare lands have been decreased from 1960 to 2002. While the agricultural lands showed increase during the same period. The CN value has also increased during the study period causing the decrease of moisture retention capacity of the soil. As a result, despite the equal rainfall, the discharge rate of 2003 flood was about 10 times larger than that of the 1964 flood, which is the direct effect of the land use/cover change from the stable forests and rangelands to the unstable agricultural lands on the both soil moisture retention capacity and run off rate.

ASSESSMENT OF BED-LOAD PREDICTORS BASED ON SAMPLING IN A GRAVEL BED RIVER

Bedload transport in alluvial channels has been extensively studied and different equations based on field and/or experimental data have been proposed.Prediction of bed-load transport rate using different equations results in wide ranges which are not always reliable.In this study,some of the universal bedload predictors were evaluated with measured load by a Helley-Smith sampler in the Node River,a gravel bed river in the northeast part of Iran.From 19 sets of data,14 series of data were used to evaluate the bed-load transport equations.The results show that the equations presented by Van Rijn,Meyer-Peter and Mueller,and Ackers and White may adequately predict bedload transport in the range of field data.