Stock enhancement and density-dependence of Caspian kutum (Rutilus kutum Kamensky, 1901) in Iranian waters of the Caspian Sea

The Caspian kutum (Rutilus kutum Kamensky, 1901) is an important economic species in the southern, uniquely Iranian waters of the Caspian Sea. The present study aimed to assess the desirable levels of the Caspian kutum for stock enhancement with two scenarios using fingerlings released (FR) and recruitments (R) density-dependence and macrobenthic production (P). Based on the results, in the years 1989-2018, the FR increased from 72 million in 1989 to 400 million in 2009 and then declined to 176 million in 2018. In contrast, the R with a lag of 2 years declined from 44.53 million in 1991 to 25.77 million in 1998, increased to 65.07 million in 2005, and then collapsed to 25.01 million in 2018. Based on FR-R relationships of Ricker and segment regression models, the lowest level of FR, which resulted in the highest R (39 million), was about 200 and 150 million fingerlings, respectively. Based on the P/Biomass ratio of macrobenthic species, the annual production was 241.6 thousand mt. It concluded that the desired number of the Caspian kutum fingerling concerning stock enhancement could be lower than 150 million to prevent overcompensation in the Iranian waters of the Caspian Sea

Geographical distribution of commercial bony fishes in Iranian waters of the Caspian Sea

The beach seines catch and effort data from 1996 to 2011 categorized in four periods and used in this research. Geographical coordinates of beach seines determined by portable GPS and distribution maps of important and commercial species prepared by catch per unit effort (CPUE). The concentration of beach seines in the western coast of Golestan province, Kiashahr area and eastern part of Anzali was more than another part. The daily effort in Kiashahr and Anzali area was very high, thus the fishing stress in these areas was more than another part of Iranian coastal waters of the Caspian Sea. The number of species in catch composition increased from east to west and the beach seines of Guilan province had total of commercial species, but the number of commercial species rarely was five species in Golestan province and especially in eastern coast. Relative frequency and distribution of Kuttum in the east Babolsar area and then between Sepidroud and Anzali lagoon were more than another part. The ISI index of Kuttum was high in all of the area except east coast of Golestan province. The main distribution of Mullets determined in the western coast of Golestan province and the Amirabad fishing area and in these areas, the ISI index of Mullets was high. The main distribution area of common carp determined in east coast of Golestan and the ISI index of common carp was very low in other parts. Density and distribution of Kolmeh were high in eastern and western coasts of Iranian waters of the Caspian Sea and the density of this species was very low in Mazandaran province. The density of Zander was very high in surrounding of Sepidroud River and Anzali lagoon. The ISI index of commercial species in Guilan province was more than other provinces except Kuttum, mullets and common carp

Stock assessment of kutum (Rutilus frisii kutum) in the Iranian waters of Caspian Sea

This study was conducted to determine catch and fishing effort trends, length and age composition, growth and mortality parameters and estimate biomass and acceptable biological catch of Kutum in the Iranian coastal waters of Caspian Sea from 2013 to 2015. The catch of Kutum was 6112.8 and 5599.2 tons and CPUE were 181.1 and 183.5 kg/haul in 2013-2014 and 2014-2015, respectively. The mean (± SD) of fork length were observed 39.4±6.1 and 40.7±5.6 cm and for total weight were 805.1±378.0 and 891.5±384.6 gram in 2013-2014 and 2014-2015, respectively. The most predominated of length class was obtained 40-42 cm and frequency of immature individuals were observed 37.8 and 44.4 percent during two sampling period, respectively. The range of age was from 2 to 11 year and fish with 4 to 6 years comprised up to 84 percent. In length – weight relationship a, b and r2 were calculated 0.011, 3.02 and 0.96 respectively. K value, L_∞ and t0 were calculated 0.19 (/year), 61.3 cm and -0.99 respectively. Mortality parameters such as Z, M and F were calculated 0.82, 0.36 and 0.46 respectively and Exploitation rate were calculated 0.56. The biomass of kutum estimated 41000 tons and the acceptable biological catch calculated 8250 to 9750 tons. The biomass of Kutum decreased in recently years in spite of produce and release of huge fingerlings. This recruitment (produce and release fingerlings) must be continued for stability of stocks and fishing stress must be decrease by anyway

The response of phytoplankton assemblages to environmental parameters in the Azad Dam Lake in the west of Iran

Seasonal variations of phytoplankton abundance, species composition, and their interaction with environmental parameters were investigated in the Azad Dam Lake, in the West of Iran during 2015–2016. Sampling was conducted seasonally at five stations in the lake. Multivariate statistical analyses were carried out to define the abiotic variables influencing phytoplankton community composition. A total of 51 taxa of phytoplankton belonging to six phyla were identified. Bacillariophyta (diatoms) were most diverse with 22 taxa, comprised more than 90% of the total density. Despite the low Shannon–Wiener index (H ′) diversity (0.10–1.54), pointing out the dominant density of Bacillariophyta resulted in high water quality. Statistical analysis showed seasonal phytoplankton assemblages differences indicating a biogeographical gradient. Distance-based Linear Model (DisTLM) analysis displayed six environmental variables showing significant relationships with the phytoplankton abundance in the resemblance matrix (p < 0.05). Based on Akaike's information criterion (AIC), the combination of total phosphorus (TP), water temperature (WT), Secchi disc depth (SD), total nitrogen (TN), nitrite (NO2−), and dissolved oxygen (DO) by the DisTLM model elucidated 63.1% of the total variability. Since the dam is newly constructed and has not yet been exploited, and the factors caused by human activities that threaten the lake have not yet spread much, findings of the present study suggest Azad Dam Lake appears to have been not highly affected by anthropogenic activities up to now.This paper investigates the variation of the phytoplankton community and its interaction with environmental parameters in the Azad Dam Lake in Iran. We show that the diversity index was low, pointing out a high level of Bacillariophyta dominance. Moreover, environmental variables show significant relationships with phytoplankton abundance