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1

Effects of fishing and environmental parameters on the commercial bony fish assemblage in the southern Caspian Sea

Fazli Hasan, Kaymaram Farhad, Daryanabard Gholam Reza

Oceanological and Hydrobiological Studies

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2022

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Vol. 51, No. 1

90--99

EN

Since the 1990s, anthropogenic activities have been the major direct or indirect threats to the structural and functional organization of the unique ecosystem of the Caspian Sea (CS). This study attempts to investigate the relationships between fish community structure and environmental parameters and to analyze the Abundance Biomass Comparison (ABC) in the CS. The input data, including catch data by species and environmental parameters, were collected from 1996 to 2017. Of the 13 bony fish species identified, only two species Rutilus kutum and Chelon aurata accounted for 47.14% and 62.65%, and 40.80% and 29.34% of CPUE and NPUE, respectively. DisTLM revealed that five environmental variables showed a significant linear relationship with the NPUE resemblance matrix. Based on the AIC criteria, the combination of year, precipitation, SST_Apr, SSL, SST, GTA, Iranian rivers, and Volga discharges explain 80.3% of the total variability. Based on the ABC curves and W statistics, it was concluded that the fish assemblage was environmentally stressed from 1996 to 2003. The Shannon diversity index (H′) showed a decreasing trend, suggesting that fish species have been exposed to increasing stress over the past 22 years. Considering the current environmental conditions (downward trend in SSL river discharge and increase in SST) and anthropogenic activities, it appears that the downward trend will continue in the future.

2

Numerical study of coastal wave profiles at the sandy beaches of Nowshahr (Southern Caspian Sea)

Mahmoudof Seyed Masoud, Takami Mohammadali Lotfi

Oceanologia

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2022

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No. 64 (3)

457-472

EN

This study aimed to investigate the capability of the one-dimensional (1D) mode of the Simulating WAves till SHore (SWASH), as a non-hydrostatic wave-flow model with six vertical layers, to reproduce the cross-shore wave evolution. For this purpose, the given model was initially calibrated for wave energy and the outputs were then verified with the field data measured at the Southern Caspian Sea. The calibration coefficients obtained for wave breaking are significantly less than the ones which have been mostly reported in previous studies for the two-dimensional (2D) mode of the SWASH. Although the reproduced wave height parameters are generally in good accordance with the field observations, the period parameters and the number of waves are overestimated and underestimated by the model, respectively. Moreover, the inaccuracies at the shallow stations are worse than at the transitional depths. The overestimation in both the reproduced energy of infragravity waves (IG) and their wavelength along with the underestimation in the wind-wave energy content are also among the factors responsible for the model deficiencies. The findings have revealed that the overestimation of the reproduced IG waves is the main reason for the underestimation of the breaking dissipation rate for irregular wave trains in the 1D mode. Therefore, more intensive breaking dissipation via selecting lower coefficient values is necessary to exhaust a certain energy content from longer waves in the 1D mode. This approach ultimately induces an over-dissipation of short wind-waves.

3

Coastal upwelling by wind-driven forcing in the Caspian Sea: A numerical analysis

Fallah Fatemeh, Mansoury Dariush

Oceanologia

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2022

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No. 64 (2)

363--375

EN

In this study, wind-driven coastal upwelling in the Caspian Sea was investigated using a developed three-dimensional hydrodynamic numerical model based on the Princeton Ocean Model (POM). The model was forced with wind fields and atmospheric fluxes from the ECMWF database and it considers freshwater inflows from the Volga, Kura and Ural Rivers. This model was implemented for 10 years (2008–2018). Findings indicated that the upwelling in the Caspian Sea was due to effects of wind and bottom topography, often occurring from May to September. In June and July, in the eastern part of the middle and sometimes southern basins, up to 3°C water temperature difference occurs between coastal and offshore areas. The vertical temperature gradient in the middle basin was larger than that in the southern basin. Upwelling in August in the eastern coasts of the middle basin within 25 km of coast from the depth of 15 m to the surface was shown, which was due to the effects of wind and bottom topography. In the middle basin, the highest vertical velocities caused by upwelling in June, July and August were 12, 13.82, and 10.36 m/day, respectively.

4

Ohrana okruzajusej sredy pri osvoenii neftegazovyh mestorozdenij v rossijskom sektore severnogo Kaspia

Bezrodnyj Y. G., Kuranov A. A.

Prace Naukowe Instytutu Nafty i Gazu

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2012

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nr 182 wyd. konferencyjne

223--229

EN

The Russian sector of the Caspian Sea is one of the most perspective regions of Russia for exploration of hydrocarbon resources deposits. Beginning from 1995, LUKOIL independently and by efforts of its affiliate LUKOIL-Nizhnevolzhskneft Ltd. executes large-scale geological and geophysical investigations of water area of the Russian sector of the Northern and Central Caspian. In 2009 LUKOIL-Nizhnevolzhskneft Ltd. started development and exploitation of the first marine field named after Yu. Korchagin, which is located within the claim "Severny". Brief information is proposed to your attention about ensuring environment protection during hydrocarbon resource deposit exploitation on the North Caspian.

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Influence of the wind field on the radiance of a marine shallow: evidence from the Caspian Sea

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2012

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No. 54 (4)

655-673

EN

The influence of the near-water wind field on the radiance of a marine shallow was studied on the basis of daily SeaWiFS ocean colour scanner data and QuickScat scatterometer wind data collected from 1999 to 2004 in the southern Caspian Sea, where the deep basin borders a vast shallow west of the shore of meridional extent. It was found that radiance distributions, clustered by wind rhumbs, exhibited different long-term mean patterns for winds of opposing directions: within the shallow's boundaries, the radiances were about twice as high for winds having an offshore component with reference to the onshore wind conditions. The zonal profile of radiance across the shallow resembled a closed loop whose upper and lower branches corresponded to the offshore and onshore winds respectively. The loop was the most pronounced at sites with 10-15 m of water for any wavelength of light, including the red region. On the basis of specific features of the study area, we attributed this pattern to sunlight backscattered from bottom sediments resuspended by bottom compensation currents induced by the offshore winds.