Southeastern Caspian Sea Research Articles

Hydrologic connectivity assessment among natural hydrosystem components using emerging entropy and evolutionary computing methods

Abstract Understanding the interactions among the natural components of hydrological systems is essential for managing water resources, addressing environmental concerns, and mitigating the impacts of natural events such as floods and droughts. In this study, long-term (1993–2019) hydrologic connectivity among precipitation, humidity, evaporation, surface runoff, minimum/maximum temperature, and their interactions with groundwater level (GWL) in the southeastern Caspian Sea region was assessed using mutual information theory and the state-of-the-art jittered genetic programming approach. While the former was used to find dominant components, their effective time delay, and the power of potential nonlinear interactions, the latter was utilized to extract an explicit relation between the GWL and the most influential components. The data were gathered from several piezometers, meteorological stations, and a stream gauge available in the study area. The results showed an overall positive trend in the GWL with an increasing rate since 2007 that reflects the influence of artificial recharge infrastructures built in the study area. Statistical connectivity analyses demonstrated that historical precipitation and streamflow series have the least impact on the temporal variation of the average GWL.

The Effect of Using a Geopedological Approach in Determining Land Quality Indicators, Land Degradation, and Development (Case Study: Caspian Sea Coast)

This study addresses the escalating global concern surrounding land degradation (LD) and its far-reaching implications on water and nutrient availability, as well as on human health and well-being. Focused on the southeastern Caspian Sea region, this research employs a novel remote sensing geo-pedological methodology to comprehensively assess soil and land quality dynamics, particularly influenced by salts, and investigates the intricate relationship between LD and soil development. The study area, marked by a susceptibility to seawater level fluctuations and diverse landforms (lagoons, barriers, and coastal plains) offers a unique opportunity for geopedologic analysis. Utilizing particle size distribution data, six distinct landforms are identified, providing insights into the region’s complex sedimentary history. A soil quality assessment is conducted remotely through the calculation of two indexes—the Integrated Quality Index (IQI) and the Nemoro Quality Index (NQI)—employing both Total Data Set (TDS) and Minimum Data Set (MDS) methodologies. The investigation highlights the role of soluble salts in shaping soil quality, thereby influencing LD and development dynamics. The differentiation of landforms significantly enhances classification accuracy, providing a more nuanced understanding of the multifaceted factors governing LD. The study’s implications extend beyond the southeastern Caspian Sea region, and demonstrate that the potential for incorporating a geopedologic approach when assessing soil and land quality dynamics in arid regions globally. Our analytic approach can inform policymakers and land managers when making decisions to combat LD and foster sustainable land development. This research also contributes towards advancing knowledge in geopedology by providing a robust foundation for future studies aimed at enhancing land management practices in the face of ongoing environmental challenges.

The management of common carp fisheries using spawning potential ratio in the southeast of the Caspian Sea

AbstractSpawning potential ratio (SPR) is an important index used by fisheries biologists and managers to determine how a fishery should be harvested to prevent recruitment overfishing. In the southeastern Caspian Sea, Iran, 3430 common carp Cyprinus carpio were caught by beach seine in 2‐week intervals of two fishing seasons in 2019 and 2020. Fork length (FL) was measured to the nearest 1 cm. The age and maturity stage of 434 specimens, including 236 females and 198 males, were estimated by scale and gonad microscopic examinations. Estimated L∞ was 71.9 and K (growth constant) was 0.09. Instantaneous total mortality (Z) was 1.08, natural mortality (M) was 0.18, and fishing mortality (F) was 0.9. Estimated SPR at current fishing mortality (0.18) was lower than the reference point (0.4). Our findings indicated that fishing mortality should be reduced to F = 0.38 for C. carpio to meet the SPR reference point of 0.4. Further, higher minimum length limits should be set to reduce fishing mortality, and catch quotas for fishing cooperative corporations should be considered to meet the 40% SPR threshold.

Population parameters of the non-indigenous invasive shrimp Palaemon macrodactylus Rathbun, 1902 (Caridea: Palaemonidae) from the southeastern Caspian Sea, with implications for range expansions, threats and conservation

Knowledge on invasive species is critical for the conservation. This study is the first documentation on population parameters of oriental shrimp (Palaemon macrodactylus) in the southern Caspian Sea, where the occurrence of invasive species is of great importance. The samples were collected using a small beach seine (35 m long and 2.5 m height) monthly from April 2019 to March 2020, and a total of 1643 specimens of P. macrodactylus were sampled. The growth form of the males was negative and that of females positive allometric nature. From the size-frequency distributions, the shrimp's lifespan was estimated to be about 2 years for both sexes. High recruitment can take place over nearly all months of late summer and autumn. The VBGF parameters were L∞ = 65.00 mm, K = 0.82 y−1, and t0 = −0.80 for males, and TL∞ = 71.00 mm, K = 0.51 y−1 and t0 = −0.59 for females. The estimated Z was 3.65 and 3.10 year−1 for males and females, respectively. The total sex ratio was significantly biased toward females in the population. Length group analysis showed a clear pattern of female dominance in lengths larger than 29 mm. Based on the occurrence of ovigerous females, the reproductive period lasts for seven months (April–October). Fecundity, as the number of both eyed and non-eyed eggs per clutch of females, varied from 71 to 2308 eggs shrimp−1 with a mean of 1074 ± 553.8 (±SD) eggs shrimp−1. The estimated relative number of eggs in a clutch of ovigerous females varies between 1208.8 and 1714, with a mean value of 889.1 eggs. female−1. The egg diameter averaged 0.675 ± 0.063 mm (±SD), ranging from 0.512 to 0.812 mm. The relationships of the total and relative number of eggs in a clutch of ovigerous females with their size were statistically significant, while the egg diameter in ovigerous females was independent of shrimp size (length and weight). P. macrodactylus underwent a life-history strategy including high abundance, short life span, high mortality rate, long reproductive season, and female dominance that showed characteristics of r-strategist species, promoting the invasion of this shrimp in the Caspian Sea as a new area of introduction. We are convinced that P. macrodactylus established in the Caspian Sea it is in the last stage of invasion (impact on the ecosystem).

First confirmed records of white-coat pups of the Endangered Caspian seal Pusa caspica on the coast of Iran

AbstractThe endemic Caspian seal Pusa caspica breeds on land-fast ice or stable drift ice in the northern Caspian Sea. Breeding has rarely been reported in the ice-free south-eastern Caspian Sea. Five carcases of white-coat Caspian seal pups were recovered from the southern Caspian Sea, Iran, during 2019–2022. From survey interviews, two white-coat Caspian seal pups were also observed in Amirabad and between Ghorogh and Rudsar. These records represent very late pupping dates compared to normal pupping periods. Coastal Iran should be surveyed annually for Caspian seal pups to determine frequency of breeding and areas of importance identified in the Iran Caspian Seal Action Plan.

On the seasonal variability of the vertical physical structure of the water column in the continental shelf, South-Eastern Caspian Sea

The seasonal and spatial variability of the vertical water structure as well as the mixed layer depth (MLD) are examined using CTD data measured during 2011-2012 in the south-eastern Caspian Sea in four different areas of the Mazandaran continental shelf. Based on the conservative temperature and potential density profiles, the mixed layer structure is divided into three different patterns, namely classical, stepwise and inclined. Mixed layer with the classical, stepwise and inclined patterns are respectively the most frequent patterns during fall, summer and spring. The classical and inclined patterns are directly influenced by the sharp decreasing and increasing trend of air temperature while the stepwise pattern is formed in transient season (i.e., summer) impacted by the combination of different atmospheric forces. The MLD is estimated using threshold and gradient methods based on the conservative temperature and potential density profiles with different threshold and gradient values. Based on different criteria, the most appropriate method for estimating the MLD in the study region is the threshold method with a threshold value of 1 °C for the temperature profiles and a threshold value of 0.5 kg.m−3 for density profiles. Results show that during fall (spring) the mixed layer is the deepest (shallowest). The salinity inside the mixed layer is high during fall and summer while the mixed layer in spring is fresher. Vertical structures of the water column in considered regions are also different even in the same season. For instance, in Noshahr, the thermocline is formed in a closer distance from the coast compared to that in Ramsar and Babolsar.

Techno-typological characteristic of Dam-Dam-Cheshme-1 lithic assemblages

The article presents the results of the technical-typological analysis of the lithic assemblages of one of the main sites of the Eastern Caspian – Dam-Dam-Cheshme-1. The site was studied by A. P. Okladnikov (1950s) and G. E. Markov (1970s), and the archaeological materials of the excavations were shared between the Institute of Archaeology and Ethnography of the Siberian Branch of the Russian Academy of Sciences and the Moscow State University. The study is aimed at analyzing the collections obtained during the excavations of A.P. Okladnikov, which are stored at the Institute of Archaeology and Ethnography, Siberian Branch of the Russian Academy of Sciences. The lithic assemblage here is characterized by a small-plate industry, whose production of blade/lets was carried out within the framework of volumetric way. The tool set includes various scrapers, burins, geometric microliths (lunatess and triangles), and notched pieces. The closest analogies are observed with the materials of the grotto of Dam-Dam-Cheshme-2, Kailu, Oiukly and Komishan, located in the south-eastern Caspian Sea.

Coastal system evolution along the southeastern Caspian Sea coast using satellite image analysis: response to the sea level fall during 1994–2015

The southeastern segment of the Caspian Sea (CS) along the Iranian coast, which has a very gentle inner shelf slope, underwent rapid beach evolution in response to water level changes. Based on satellite altimetry data, the CS basin has experienced an accelerated water level fall drop in recent years, leading to an increase in the rate of shoreline changes. The shoreline dynamics and morphodynamics of the Amirabad coastal zone, Gorgan Bay, Miankaleh Spit, and Gomishan Lagoon are evaluated here to determine morphological changes of the study area. Landsat-TM/ETM+/OLI moderate spatial resolution products were acquired at unequal intervals between 1994 and 2015 to monitor the coastal changes using Geographic Information System (GIS) tools. The Digital Shoreline Analysis System (DSAS), a GIS software extension, has been used for estimation of the shoreline rate of change through several approaches, including End Point Rate (EPR), Linear Regression Rate (LRR), and Weighted Linear Regression (WLR). The results show that both Gorgan Bay and Gomishan Lagoon have significantly decreased in size during recent years, mainly due to the fall of the CS water level. Results also show that water level drop of the CS, along with net eastward littoral transport, resulted in the growing of the Miankaleh Spit. Further analysis based on the wave climate in the southeast CS and net estimated longshore sediment transport indicates that the littoral drift contributed to ~ 6% of the total annual elongation of the Miankaleh Spit during the study period.

Length-weight relationship, condition factor and relative condition factor of Alosa braschnikowi and A. caspia in the southeast of the Caspian Sea (Goharbaran)

The main objectives of the present study were to determine the species composition of Caspian shad, genus Alosa and to estimate the LWR, CF, and Kn of A. braschnikowi and A. caspia during different months in the southeastern coast of the Caspian Sea. Two fishing methods, small mesh size beach seine and gillnet were used from December 2013 through July 2014. A. braschnikowi and A. caspia, were distinguished in the southeastern part of the Caspian Sea (Goharbaran), consisting of 57.1% and 42.9% of the Alosa catch, respectively. The slopes (b values) of the length-weight regression were 3.241 and 2.844 which were significantly different from 3 (P<0.05), indicating positive and negative allometric growth, respectively. The average CF of A. braschnikowi and A. caspia were calculated as 0.72 ± 0.12 and 0.83 ± 0.13, respectively. The average CF for both species were significantly different among months (P<0.001). There was a significantly negative correlation between size classes and CF of A. caspia. The Kn was greater than 1 for A. braschnikowi and lower than 1 for A. caspia indicating good well-being of A. braschnikowi as opposed to A. caspia in the southeastern Caspian Sea.

Life history traits of the Caspian stellate tadpole-goby Benthophilus leobergius Berg, 1949 (Teleostei: Gobiidae) from the southeastern Caspian Sea, Iran

The Caspian stellate tadpole-goby, Benthophilus leobergius is endemic to for the Caspian Sea. In Iranian waters of the Caspian Sea, however, little is known about its life history. To address this, life history characteristics were examined in 256 specimens collected from the southeastern Caspian Sea, northern part of the Miankaleh Wildlife Refuge. The maximum observed age was 2+ years for both sexes. The sex ratio of males to females was 1:1.70. Estimated length-weight relationship was TL=0.0088TW 3.289 for males, TL= 0.0099TW 3.191 for females, and TL=0.0086TW 3.270 for the combined sexes. Egg diameter ranged from 0.8 to 1.8 mm with the mean of 1.259±0.50 mm. Mean absolute and relative fecundities were 2117±1243 eggs/female, and 130±77 eggs·g -1 body weight, respectively. Absolute fecundity and egg diameter were found to increase significantly with increasing fish size, whereas relative fecundity decreased significantly with total body weight.

Diversity and distribution of larval and juvenile fish in nearshore waters of the Southeastern Caspian Sea and Gorgan Bay

Occurrence and distribution of larval and juvenile fish was investigated in nearshore waters of the southeastern Caspian Sea including the Gorgan Bay. Samples were collected during seven surveys using a fine mesh beach-seine in five sampling sites from July 2014 to June 2015. A total of 15500 individuals mostly juvenile were captured, representing 18 species from 8 families. Most juveniles belonged to Liza saliens, Atherina caspia, Neogobius pallasi and Neogobius melanostomus. The juveniles of Alburnus chalcoides, Vimba persa, Syngnathus caspius and gobies Neogobius caspius and Ponticola syrman occurred in low number (relative abundance 0.1% - 9.3%). Highest number of juveniles were caught in summer season. The occurrence of larval fish in coastal waters of southern Caspian Sea was recorded for the first time (Atherina caspia with minimum length of 12 mm in Caspian and 9.5 mm in Gorgan Bay). In spring, early juveniles of mullet, Liza aurata, increased in the Caspian sites but they moved up to deeper waters by the end of the season. Based on results, the density of juvenile fish (specially Liza saliens) in Gorgan Bay was several times more than Caspian sites so it could be considered an important nursery ground in the region.

Reconstruction of Sea Level Changes using Magnetic Susceptibility Variations in Southeastern Caspian Sea

Reconstruction of Sea Level Changes using Magnetic Susceptibility Variations in Southeastern Caspian Sea

Assessment of Spatiotemporal Phytoplankton Composition in Relation to Environmental Conditions of Gorgan Bay, Iran

Phytoplankton seasonal succession and spatial distribution were studied in Gorgan Bay, Iran, which is a semi-enclosed bay located in the southeastern Caspian Sea. Monthly phytoplankton and physicochemical samples were taken from March 2014 to September 2015. A total of 51 genera from six algal divisions were observed with phylum Bacillariophyta being the most represented (16 genera and on average ~ 59% of biomass). While diatoms were prevalent year-round, strong inter-seasonal variations of other phytoplankton groups were observed in response to environmental parameters. The seasonal succession of other taxa started with Chlorophyta (Chlorella sp.) in spring followed by Cyanophyta (Anabaena sp. and Microsystis sp.) and Euglenophyta (Euglena sp.) in summer, then Chrysophyta (Syndera) and Pyrrophyta (Prorocentrum sp., Exuviella sp., and Peridinium sp.) in the autumn and winter. The sites near the mouth of Gorgan Bay were characterized by slightly higher salinity with an annual mean of ~ 12 PSU compared with ~ 11 PSU for inner regions of the bay. Nitrate was higher in the mouth of the bay as well, with an annual mean of ~ 1.4 ppm compared with ~ 0.80 ppm in the inner region. Orthophosphate was also higher in the mouth of the bay with an annual mean of ~ 0.30 ppm compared with ~ 0.23 ppm in inner part of the bay. Euglena sp. and Microsystis sp. performed better in the mouth of the bay compared with their performance in the inner regions. Nutrients and salinity correlated strongest with phytoplankton in Gorgan Bay. During the period when Cyanophyta biomass was maximum, Microsystis sp. was the dominant taxa of the cyanobacteria present. Inorganic pollution from domestic wastewater in the eastern part of Gorgan Bay appears to be the cause of the Euglena maximum. According to the Palmer pollution index, Gorgan Bay experienced pollution from agricultural discharge and domestic wastewater.

Evolutionary trend of the Gorgan Bay (southeastern Caspian Sea) during and post the last Caspian Sea level rise

The Gorgan Bay (GB) is a semi-confined sedimentary environment at the southeastern corner of the Caspian Sea (CS). High sensitivity to eustatic sea-level variations resulted in changes in the sedimentary facies and patterns of erosion/sedimentation for the GB in the last Caspian Sea-level cycle (1977–1995). Therefore, the evolutionary trend in coastal sedimentary environments was studied to determine the pattern of erosion and sedimentation related to sea-level fluctuation cycles. The sedimentology of the bay basin was studied in 500 km2 of the study area in 2001. In addition, coastal changes over the two past and post periods of sea-level rise were studied using satellite images (Landsat 7 with a resolution of 30 m) and ArcGIS 10.1 software. Waves, wave-induced currents and sediment transport were simulated using the MIKE-21 software package. Mixed sediments, particularly at the western and southern areas of the bay basin, were detected through reworking of coarser barrier island sediments into deeper areas. Well-sorted (0.35–0.5φ) sediments, with 98.31 ± 2.8% sand-size particles, were identified as the common texture along the wave-dominated coasts. Sea progradation, destruction of the beach profile and an increase in sea coverage of approximately 15,600 ha around the GB were other impacts of the CS-level rise. Additional impacts included severe erosion and submergence of a 9000 ha area of the flat coastal plains (slope~ 0.035%). The results demonstrate that water-level rise has strengthened the sediment accumulation in the bay inlet and basin at a mean rate of 0.430 MCM and 12.7 MCM, respectively. Both field measurements and simulation results revealed the notable shoaling of the bay entrance at a mean rate of 0.2 m. Simulations concluded that annual longshore transport toward the bay inlet has occurred at a net rate of 80,000 m3 during the last CS-level rise. Natural events after the eustatic cycle in the southeastern corner of the CS resulted in severe shoaling of the GB inlet and basin and restriction in the water exchange between the bay and open sea. Therefore, comprehensive management practices to restore the GB capacity and its natural habitats are critically needed.

Health risk assessment of selected heavy metals in some edible fishes from Gorgan Bay, Iran

The objective of this study was to determine the distribution of selected metal concentrations (Cd, Pb, Cr and Fe) in the muscles of five fish species (Sander lucioperca, Liza auratus, Alosa caspia, Cyprinus carpio and Liza saliens) from Gorgan Bay the south-eastern Caspian Sea, in order to assess health risk to the human via fish consumption by graphite furnace atomic absorption spectrophotometry. Potential health risk assessments based on estimated daily intake (EDI) values and target hazard quotient (THQ) indicated that the intakes of metals by consuming these fish species do not result in an appreciable hazard risk for the human body. The hazard index (HI) calculated was lower than 1 for all the species. However, the results indicate that the concentrations high value of Pb (in the muscle of L. auratus) and Fe for all fish is alarming and do present an appreciable hazard risk for human health.

Gorgan Bay: a microcosm for study on macrobenthos species-environment relationships in the southeastern Caspian Sea

The relationship between spatial patterns of macrobenthos community characteristics and environmental conditions (salinity, temperature, dissolved oxygen, organic matter content, sand, silt and clay) was investigated throughout the Gorgan Bay in June 2010. Principal components analysis (PCA) based on environmental data separated eastern and western stations. The maximum (4 500 ind./m2) and minimum (411 ind./m2) densities were observed at Stas 1 and 6, respectively. Polychaeta was the major group and Streblospio gynobranchiata was dominant species in the bay. According to Distance Based Linear Models results, macrofaunal total density was correlated with silt percentage and salinity and these two factors explaining 64% of the variability while macrofaunal community structure just correlated with salinity (22% total variation). In general, western part of the bay showed the highest number of species and biodiversity while, the highest density was found at Sta. 1 and in the middle part of the bay. Furthermore, relationship between diversity indices and macrobenthic species with measured factors is also discussed. Our results confirm the effect of salinity as an important factor on distribution of macrobenthic fauna in south Caspian brackish waters.

Osteology of Hyrcanian crested loach, Paracobitis hircanica (Pisces, Nemacheilidae)

This study was carried out to describe of osteological structure of the newly described crested loach, Paracobitis hircanica Mousavi-Sabet et al., 2015. For this purpose, ten specimens were collected from the Zaringol River, in the southeastern Caspian Sea basin. After clearing and staining, osteologicl characteristics were examined. The obtained results showed that the P. hircanica is osteologicaly characterized by plate-like protrusion in epibranchial-4, no sesamoid ossifications, five hypurals, free and long epural, no connection between retroarcticulare and dental, loss of preethmoideum-I and basibranciale-4, alveolar bony capsule and presence of the manubrium.Our Nature (2015), 13(1): 8-18

Study on Metal Concentrations in Tissues of Mallard and Pochard from Two Major Wintering Sites in Southeastern Caspian Sea, Iran.

We examined concentrations of cadmium, chromium, iron, lead and zinc in the kidney, liver, and pectoral muscle of Mallards (Anas platyrhynchos; n = 30) and Pochards (Aythya ferina; n = 30) from two important wintering sites in the southeastern Caspian Sea in the winter of 2012. Mean lead concentrations (µg g(-1) ww) in livers (2.36 ± 1.00) of Pochard and in kidneys (3.43 ± 0.91) of Mallard exceeded the exposure threshold levels in liver (1.5 µg g(-1) ww) and kidney (3 µg g(-1) ww) of waterfowl. Mean cadmium concentrations in livers (1.63 ± 0.66) of Pochards exceeded the background level of this metal in liver (1 µg g(-1) ww) of waterfowl. Chromium, iron and zinc concentrations were within the normal range as reported in other duck studies. Gender-related and inter-specific variation of metal concentrations in analyzed tissues were observed (t test, p < 0.05). Our results indicated that waterfowl using the Miankalah and Gomishan International Wetlands are being exposed to elevated concentrations of cadmium and lead.

Potential human health risk assessment of heavy metals in the flesh of mallard and pochard in the South Eastern Caspian Sea region of Iran

Every year, migratory waterfowl are hunted and consumed by people in Golestan Province of Iran. Due to the heavy metal contamination of wintering habitats, an estimation of the human health risks associated with the consumption of these ducks is necessary. Therefore, this study was conducted to estimate the health risks of exposure to cadmium (Cd), total chromium (Cr), iron (Fe), lead (Pb), and zinc (Zn) due to the consumption of pectoral muscle of mallard (Anas platyrhynchos) and pochard (Aythya ferina) harvested and hunted in the South-Eastern Caspian Sea region of Iran. The mean values of these metals in the pectoral muscle of mallards and pochards were used to calculate estimated daily intake (EDI), estimated weekly intake (EWI), and target hazard quotients (THQ). The EDI (µg/day/70 kg body weight) for Cd, Cr, Fe, Pb, and Zn in mallard were 0.2, 0.04, 58, 1.1, and 12.8, respectively. The EDI (µg/day/70 kg body weight) for Cd, Cr, Fe, Pb, and Zn in pochard were 0.8, 0.1, 69, 0.8, and 13.4, respectively. The estimated total THQ (higher than 1) indicated that heavy metal levels in pochard flesh were unsafe for consumption. The EDI and EWI of the metals examined were below those recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and oral doses suggested by the United States Environmental Protection Agency (USEPA). There appears to be little risk of exposure to metals associated with the consumption of mallard and pochard in this region.

Study of arsenic distribution in sediments of the southeastern Caspian sea

Geochemical studies of sediments, water bodies like rivers, estuaries and the sea bed, can be an effective step to find the source and distribution model assessment of environmental pollutants in a region. Sediments are the final destination of heavy metals in aqueous environments contamination, including arsenic entering the water resources in different ways, causing hazards such as poisoning, and carcinogenesis in living bodies. Study arsenic levels in the eastern part of the Caspian Sea, 30 stations were selected in the Calculation of aggregated fine-grained organic matter in two seasons of the arsenic concentration in both summer and winter by using Inductively Coupled Plasma - Mass spectrometry (ICP-MS) was determined. Geochemical index, Enrichment factor and pollution index were determined low pollution to non-pollution area and cause of arsenic to the environment, erosion of the Geological formation of the bay, leading GORGAN River carry deposits upstream of surroundings were. Primary cause of arsenic to the environment, geology and upstream sediment erosion and transport by rivers is leading to Gorgan Bay and surrounding areas. Compare these results with other parts of the Caspian Sea show that arsenic levels observed in this study in the Gorgan Bay and surrounding areas has been less than other part of the Caspian Sea.