rss_2.0Oceanological and Hydrobiological Studies FeedSciendo RSS Feed for Oceanological and Hydrobiological Studieshttps://sciendo.com/journal/OANDHShttps://www.sciendo.comOceanological and Hydrobiological Studies Feedhttps://sciendo-parsed.s3.eu-central-1.amazonaws.com/6472618b215d2f6c89dc6424/cover-image.jpghttps://sciendo.com/journal/OANDHS140216Assessment of eutrophication in the Berdan River Basin (Türkiye) using various classification toolshttps://sciendo.com/article/10.26881/oahs-2024.1.03<abstract> <title style='display:none'>Abstract</title> <p>The trophic status of the Berdan River Basin was determined using univariate and multivariate classification tools. The results indicated that the water quality/trophic status of a downstream section of the Berdan River was characterized as “poor/eutrophic” due to anthropogenic inputs from agricultural, industrial and domestic wastewater discharges. Strong and positive correlations between TRIX values and concentrations of eutrophication parameters suggest that nutrient enrichment of water in the Berdan River during its flow will result in further eutrophication in the coastal region of the NE Mediterranean Sea. Therefore, the trophic and pollution status of the Berdan River, as well as other regional rivers flowing into the coastal area of the NE Mediterranean Sea should be monitored to develop action plans and sustainable management of eutrophication in regional rivers and the oligotrophic Mediterranean Sea.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.032024-04-01T00:00:00.000+00:00Integrated multi-trophic aquaculture of the European flat oyster ( Linnaeus, 1758): A case study from Boka Kotorska Bay (Montenegro)https://sciendo.com/article/10.26881/oahs-2024.1.05<abstract> <title style='display:none'>Abstract</title> <p>Although integrated multi-trophic aquaculture (IMTA) is recognized as a strategy to control and minimize the impact of fish farming on the marine environment, there are still many unknowns when it comes to this type of farming. This paper presents the results of research on the growth of European flat oysters in IMTA and monoculture systems. Growth was monitored at three different sites: near fish cages, 100 m from fish cages, and in a monoculture system, during an 18-month experiment. The highest mortality occurred at the site near the fish cages. At the end of the experiment, all monitored individuals reach commercial size, except for four individuals at the site near the fish cages. There were statistically significant differences in oyster growth with respect to site and period. At the site near the fish cages, oyster growth was significantly lower compared to the growth at the two other sites. The most intense growth of oysters occurred during the spring and early summer period. Our results indicate that the production cycle of oysters in integrated aquaculture and monoculture is quite similar and that sites directly adjacent to fish cages should be avoided for oyster farming.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.052024-04-01T00:00:00.000+00:00Do the nutrient compositions and mineral matter contents of meagre () vary depending on the rearing environment?https://sciendo.com/article/10.26881/oahs-2024.1.01<abstract> <title style='display:none'>Abstract</title> <p>This study aimed to compare the nutrient compositions and element contents of meagre (<italic>Argyrosomus regius</italic>) reared in different environments. The biochemical analyses revealed that the ash contents of cage and earth pond-cultured fish were higher than that of wild fish (<italic>p</italic> &lt; 0.05), while there were also significant differences in the protein, fat and moisture contents (<italic>p</italic> &gt; 0.05). The cage-reared fish had the lowest Ca, Mg, P and S levels, while the highest levels were determined in wild fish. The highest Fe, Se and Mn levels were determined in the earth pond-reared fish. Wild fish had the lowest Fe, Zn, Se and Cr levels, while the lowest Cu and Mn levels were determined in the cage-reared fish. The cage-reared fish had the highest Zn, Cr and Ni levels. Wild fish were determined to contain high levels of As, Hg and Pb. The earth pond-reared fish had a high Cd level, while having lower As and Hg levels than those of fish reared in other environments. As a result, farmed meagre are thought to be affected by the metal content in both the feed and the water. The results of the study showed that the content of the meagre flesh varied depending on the rearing conditions.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.012024-04-01T00:00:00.000+00:00First record of (Henneguy, 1892) in the narrow-clawed crayfish (Eschscholtz, 1823) from Belarushttps://sciendo.com/article/10.26881/oahs-2024.1.04<abstract> <title style='display:none'>Abstract</title> <p>Porcelain disease, caused by the parasite <italic>Astathelohania contejeani</italic>, is a fatal disease for freshwater crayfish. Previously published data provide information on the occurrence of <italic>A. contejeani</italic> in various crayfish species. However, its prevalence in host populations remains largely undetermined. This issue is relevant to the narrow-clawed crayfish <italic>Pontastacus leptodactylus</italic>, a species of high commercial value in Eastern Europe. A single published report addressed a potential microsporidia infection in <italic>P. leptodactylus</italic>, but without specific data on geographical location and prevalence. We present the first detailed information on the prevalence of <italic>A. contejeani</italic> in the <italic>P. leptodactylus</italic> population from Lake Losvido, including an assessment of the infection rate through both visual and molecular assessment. <italic>Astathelohania contejeani</italic> was observed in 1.56% of 128 crayfish examined visually. Of the 37 asymptomatic crayfish samples analyzed, 29.7% were found to be carriers. This finding suggests that parasitism of <italic>A. contejeani</italic> occurs frequently in the <italic>P. leptodactylus</italic> population in Lake Losvido prior to the manifestation of observable disease symptoms.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.042024-04-01T00:00:00.000+00:00Reproductive biology of the European anchovy (Linnaeus, 1758) in the Turkish Aegean Seahttps://sciendo.com/article/10.26881/oahs-2024.1.02<abstract> <title style='display:none'>Abstract</title> <p>The present study investigated the reproductive biology of European anchovies obtained seasonally from fishermen in İzmir Bay (Aegean Sea). The total length range of the investigated individuals was 9.0 – 15.7 cm. Of the 750 samples in which sex was determined, 34% were males, and 66% were females, resulting in a female-to-male ratio of 1.91:1. The first maturation length was determined to be 10.47 cm for females and 9.95 cm for males. Based on the total values of the gonadosomatic index, it was concluded that the reproductive period of the species falls in the summer season. The batch fecundity of the species ranged from 2.123 to 6.951 oocytes, and the fecundity–length relationship was expressed as F = 1134.4TL – 10034 (R<sup>2</sup> = 0.84). Histological examination of the female ovaries revealed the presence of oocytes at different stages of development, indicating multiple spawning during the reproductive season.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.022024-04-01T00:00:00.000+00:00Comprehensive assessment of water and sediment quality in Lake Nasser, Egypt, using various potential risk indiceshttps://sciendo.com/article/10.26881/oahs-2024.1.06<abstract> <title style='display:none'>Abstract</title> <p>Lake Nasser is a freshwater lake that supplies over 95% of Egypt’s freshwater budget. Therefore, the quality of water in the lake is critical for its conservation. In addition to assessing the metal pollution load, the quality of water and sediment in the lake was assessed by collecting water and sediment samples for metal content analysis. Lake Nasser is a warm monomictic water body with a single circulation cycle in the cold months. Dissolved oxygen content in bottom water samples often dropped significantly to levels below international guidelines, reflecting reduced rates of photosynthetic activity. Although 50% of the lake’s water samples contained Pb concentrations slightly above the World Health Organization’s (WHO) limit for drinking water, the metal pollution index did not exceed the critical level and was classified as low metal water pollution. Based on the geoaccumulation index (I-geo), the enrichment factor (EF) and the pollution load index, the sediments of Lake Nasser are practically uncontaminated with metals. Ni has the highest EF and I-geo values, while Ni and Cd contributed the most to the ecological risk and toxic risk index. The obtained results revealed that Cd and Ni in the sediments may pose a threat to organisms living in Lake Nasser.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.062024-04-01T00:00:00.000+00:00Risk management in the Greek mussel farming through ISO 31000https://sciendo.com/article/10.26881/oahs-2024.1.09<abstract> <title style='display:none'>Abstract</title> <p>The main risks to the sustainability of Mediterranean mussel farming in Greece were assessed using a generic framework derived from the AS/NZS ISO 31000:2009 Risk Management Model. Risk management scenarios were reviewed after they were successfully tested in the field by semi-qualitative/quantitative data generation protocols. A critical synthesis of the results identifies key indicative aspects needed by stakeholders to formulate a valid operational risk management plan for the sector.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.092024-04-01T00:00:00.000+00:00Toxicity assessment of advanced biological wastewater treatment plant effluent by integrated biomarker response in zebra mussels ()https://sciendo.com/article/10.26881/oahs-2024.1.08<abstract> <title style='display:none'>Abstract</title> <p>In this study, zebra mussels (<italic>Dreissena polymorpha</italic>) were exposed to advanced biological wastewater treatment plant effluent (ABWTPE) for 96 h. At the end of the 96th hour, antioxidant parameters such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GP<sub>X</sub>), glutathione S-transferase (GST), malondialdehyde (MDA) and glutathione (GSH) were examined. The objective of the study was to identify biomarkers that are useful for assessing the potential toxic effects of ABWTPE in freshwater environments. We observed an increase in GP<sub>X</sub>, SOD activity and MDA levels, and a decrease in CAT, GST activity and GSH levels. The results obtained in our study showed that the measured biochemical parameters (GSH, MDA, SOD, CAT, GP<sub>X</sub> and GST) are useful biomarkers in determining the possible toxicity of ABWTPE in aquatic environments.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.082024-04-01T00:00:00.000+00:00Population dynamics and feeding ecology of the western tubenose goby () in the Stugna River, Dnieper River basin, Ukrainehttps://sciendo.com/article/10.26881/oahs-2024.1.07<abstract> <title style='display:none'>Abstract</title> <p>The study investigated the inter-annual and seasonal population dynamics, as well as the feeding habits of the western tubenose goby <italic>Proterorhinus semilunaris</italic> in an invaded river close to its natural range (Dnieper River basin). Material was collected monthly in 2015–2016 and 2018 at one sampling site located in the Stugna River, at a distance of 1100 m from the point where it enters the Kaniv reservoir. Catch-per-unit-efforts (CPUE) of this species at the sampling site varied considerably, both between different months within a given year and between the analyzed years, from 1.1 to 127.1 fish 100 m<sup>-2</sup>. Peak abundances were observed in July in both 2015 and 2018, and then dropped sharply in the following months. The western tubenose goby is characterized by a protracted spawning season, lasting from April to July. A total of 50 prey taxa were recorded in the diet of the western tubenose goby at the sampling site, among which chironomids were the most abundant and most frequently encountered, followed by cladocerans. This gobiid at the sampling site preyed mainly among submerged vegetation, where phytophilous chironomids were the most important prey.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.072024-04-01T00:00:00.000+00:00Morphological variability of otolith organs in three congeneric specieshttps://sciendo.com/article/10.26881/oahs-2024.1.10<abstract> <title style='display:none'>Abstract</title> <p>Morphological features of sagittal otoliths in <italic>Pagellus acarne</italic>, <italic>P. bogaraveo</italic>, and <italic>P. erythrinus</italic> samples collected from the Aegean Sea were used to assess the variability both between <italic>Pagellus</italic> species and between otolith pairs employing scanning electron microscopy (SEM) and contour shape analysis. Twenty-one otolith morphological characters were compared in detail using SEM analysis. Twelve of these characters differ between <italic>Pagellus</italic> species and are suitable for distinguishing between the three congeneric <italic>Pagellus</italic> species. Wavelet functions of otolith contour shape were compared for six <italic>Pagellus</italic> groups. The wavelet functions obtained from the contour shape analysis showed high variability in the antero-dorsal, postero-dorsal, and antero-ventral regions of otoliths among the six groups analyzed. The results of principal component analysis (PCA) of the wavelet data provided a clear distinction between the groups under study. Cluster analysis supported the PCA results and basically divided them into two main branches. One of these branches contained only <italic>P. erythrinus</italic>, while <italic>P. acarne</italic> and <italic>P. bogaraveo</italic> were present in the other branch. This is the first study to provide detailed morphological characters and wavelet analysis of left- and right-side otoliths in these three congeneric <italic>Pagellus</italic> species from the Aegean Sea.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2024.1.102024-04-01T00:00:00.000+00:00A biomonitoring study of : metal bioaccumulation and current status in Iskenderun Bay, eastern Mediterraneanhttps://sciendo.com/article/10.26881/oahs-2023.4.09<abstract> <title style='display:none'>Abstract</title> <p>Concentrations of aluminum, chromium, cobalt, nickel, cadmium, lead, manganese, iron and zinc were determined in sea urchin species, <italic>Diadema setosum</italic> from Iskenderun Bay in December 2022. The level of metals was determined by Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Concentrations of the heavy metals in the examined sea urchins ranged as follows: Al 0.07-7.17 μg g<sup>-1</sup>; Cr 0.07–0.8 μg g<sup>-1</sup>; Co 0.01–0.2 μg g<sup>-1</sup>; Ni 0.2–2.9 μg g<sup>-1</sup>; Cd 0.0–0.02 μg g<sup>-1</sup>; Pb 0.4-3.5 μg g<sup>-1</sup>; Mn 0.03–0.4 μg g<sup>-1</sup>; Fe 1.2-57.2 μg g<sup>-1</sup>; Zn 0.28–2.7 μg g<sup>-1</sup>, respectively. The highest accumulation of Fe and Pb metals was determined in the tissues of the sea urchin. The present study suggests that D<italic>. setosum</italic> could be a potential biological indicator of metal pollution in the Iskenderun Bay. Furthermore, soft tissues generally had lower levels overall. For this reason, the data show that <italic>D. setosum</italic> is a very good heavy metal collector and therefore may be used successfully to monitor heavy metal levels in Iskenderun Bay.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.092023-12-31T00:00:00.000+00:00Morphological comparison for the dorsal fin of , and (Teleosti: Siluriformes) collected from the Lake Nasser and the River Nile, Egypthttps://sciendo.com/article/10.26881/oahs-2023.4.03<abstract> <title style='display:none'>Abstract</title> <p>The anatomy, growth, and differentiation of the dorsal fin spines of three catfish species collected from the Nile River and Lake Nasser. Egyptian waters are described, and terminology is suggested for their parts. Features of the dorsal fin spine that change with growth are also described. The results showed that in all species studied, the dorsal spine is an elongate, compressed, tapered, slightly arched, osseous structure, bearing a series of retrorse dentations along the anterior and posterior surfaces and has a sharp sagittate tip. The retrorse, anterior dentations are most pronounced in the upper third of the spine and gradually alter in form until they appear as a series of distinct notches on the basal third of the spine. The anterolateral surfaces of the dorsal spine are marked by numerous short, irregular, shallow, anastomosing, longitudinal furrows. In three species (<italic>C. auratus, S. schall, S. serratus</italic>), the posterior process is poorly developed and directed laterally in young individuals and well produced and directed posteriorly in older specimens. In <italic>S. schall</italic> and <italic>S. serratus</italic>, the posterior blocking process of the large specimens has a wavy edge, while in <italic>S. serratus</italic>, it is curved in young individuals and straight in larger specimens.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.032023-12-31T00:00:00.000+00:00Defense responses of the green microalgae to the vanadium pentoxide nanoparticleshttps://sciendo.com/article/10.26881/oahs-2023.4.06<abstract> <title style='display:none'>Abstract</title> <p>Although vanadium-based nanomaterials have found extensive use in industry, their influence on ecosystems and living organisms is not yet well investigated. In this study, hydrothermal methods were utilized for the synthesis of vanadium pentoxide nanoparticles (V<sub>2</sub>O<sub>5</sub> NPs). The gained NPs were characterized using XRD, FT-IR, EDS, DLS, SEM and TEM techniques. Subsequently, the toxic effects of V<sub>2</sub>O<sub>5</sub> NPs on the model green microalgae <italic>Chlorella vulgaris</italic> were evaluated. According to the obtained results, V<sub>2</sub>O<sub>5</sub> NPs caused a significant reduction in cell number and biomass production of algae in a dose and time dependent manner. Moreover, flow cytometric analysis confirmed a reduction in the quantity of living cells. Scanning electron microscopy showed plasmolysis and deformation of the cells after exposure to nanoparticles. The photosynthetic pigments and phenolics content exhibited a decrease in comparison with the control sample. Although, non-enzymatic antioxidant system in <italic>C. vulgaris</italic> displayed an average action, antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) showed a dose dependent increasing trend. These intercellular reactions designated the activation of the antioxidant defense system in response to the induced oxidative stress by V<sub>2</sub>O<sub>5</sub> NPs.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.062023-12-31T00:00:00.000+00:00Species diversity, abundance, and distribution of freshwater prawns along a selected perennial stream in Ngangla Gewog, Zhemgang, Southern Bhutanhttps://sciendo.com/article/10.26881/oahs-2023.4.10<abstract> <title style='display:none'>Abstract</title> <p>The study and diversity of freshwater prawns are of great importance due to growing interest in biodiversity and its relative abundance. The present study was carried out for a selected stream divided into three different habitat types: namely, pond, run, and riffle. The study was focused on the diversity and abundance of prawns. To make it more systematic, a transect was laid upon the stream and it was divided into 30 plots with 100 m intervals. <italic>Metapenaeus rosenbergii</italic>, <italic>Penaeus japonicas</italic>, and <italic>Metapenaeus insolitus</italic> were species recorded in the pond habitat type only. The <italic>Penaeus</italic> genus was the most prominent in the study area while the genus <italic>Metapenaues</italic> was the least abundant. The diversity of freshwater prawns was found to be highest in the pond rather than the run and riffle. Documented information for prawn populations in Bhutan is sparse. Therefore, there is a wide research gap regarding prawn diversity in Bhutan. This study will help to establish a baseline data for the prawn distribution in the proposed study area. The present study will serve as a reference guide for future researchers.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.102023-12-31T00:00:00.000+00:00Antioxidant radical scavenging capacity and total carotenoid content of narrow-clawed crayfish (, Eschscholtz, 1823) in Atikhisar Reservoir (Çanakkale, Türkiye)https://sciendo.com/article/10.26881/oahs-2023.4.08<abstract> <title style='display:none'>Abstract</title> <p>In this study, antioxidant radical scavenging capacity and total carotenoid content in the meat and shells of <italic>Pontastacus leptodactylus</italic> were investigated. Concerning the antioxidant scavenging effect, the highest IC<sub>50</sub> values were found to be 388.77 mg g<sup>-1</sup> and 155.53 mg g<sup>-1</sup> for females and males in July and March, respectively. The mean IC<sub>50</sub> values of the meat were calculated as 239.83 mg g<sup>-1</sup> and 105.21 mg g<sup>-1</sup> for females and males, respectively. The mean total carotenoid content in the meat was found to be 14.35 and 12.78 μg g<sup>-1</sup> for females and males, respectively. The results indicated that crayfish meat had antioxidant radical scavenging capacity and was rich in carotenoid content.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.082023-12-31T00:00:00.000+00:00Metal pollution status and health risk assessment of beach sediments along the Mersin coast, Turkeyhttps://sciendo.com/article/10.26881/oahs-2023.4.07<abstract> <title style='display:none'>Abstract</title> <p>In the present study, the ecological risk assessment of metal contamination in beach sediments along the Mersin coast was determined using the metal contents of beach sediments in Mersin, Kızkalesi, Susanoğlu and Taşucu region obtained between 2006 and 2009. Furthermore, the potential health risk assessment for ingestion and dermal contact pathways of adults and children was determined. Ecological risk assessment of heavy metals showed that there is no pollution in the beach sediments for the metals Cu, Pb and Zn for the all studied coasts. However, the high ecological risk indices calculated in this study strongly suggested an apparent Cd, Cr and Ni pollution in the studied beach sediments due to natural and anthropogenic contamination. Study findings indicated the HI values were greater than 1 for the metal Cr. The TCR values were higher than 1.00E-04 for the metals Cr and Ni calculated for adults, and for the metal Cu, Cr and Ni calculated for children, respectively. All these findings showed that there is a high carcinogenic risk for adults and children resident in the Mersin province from carcinogenic Cr and Ni whilst the studied coasts have additional health risks to children from carcinogenic Cu.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.072023-12-31T00:00:00.000+00:00Utilizing fluctuation asymmetry to assess the effects of U-238 radioactivity on the marine ecosystem around the Madras nuclear power plant, Indiahttps://sciendo.com/article/10.26881/oahs-2023.4.05<abstract> <title style='display:none'>Abstract</title> <p>The monitoring of marine ecosystems is crucial due to the growing threat posed by nuclear power plants and other nuclear anthropogenic emissions. In our work, we used a straightforward and low-cost biomonitoring technique called fluctuation asymmetry (FA) to examine the variation between the left and right sides (developmental instability) of organisms’ traits that were influenced by genetic and environmental variables in the early stages of ontogenesis. The specimens of fish (<italic>Leiognathus</italic> sp.) and crabs (<italic>Portunus sanguinolentus</italic>) were collected seasonally and used as bioindicators to determine the effects of Uranium-238 (U-238) radioactivity around a nuclear power plant. The obtained results revealed that FA values were not considered typical values (FA = 0) in all seasons. Moreover, FA values of <italic>Leiognathus</italic> sp. exhibited insignificant fluctuation for a particular characteristic through the different seasons, while a significant fluctuation occurred amongst the characteristics themselves throughout the same season. Inversely, FA values of the four characteristics in <italic>Portunus sanguinolentus</italic> displayed seasonal variation amongst them all. Statistically, there was a strong positive correlation (<italic>r</italic> = 0.5, <italic>p</italic> &lt; 0.05) between U-238 radioactivity in the flesh of both organisms and the fluctuation asymmetry of different traits but it is not a sign that any radioactive pollution exists.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.052023-12-31T00:00:00.000+00:00Annual, seasonal and spatial differences in the growth rate of Baltic cod larvae and early juveniles in relation to zooplankton biomass fluctuations in 2006-2014https://sciendo.com/article/10.26881/oahs-2023.4.02<abstract> <title style='display:none'>Abstract</title> <p>It is an acknowledged theory that a faster growth rate, determined by various environmental drivers, may boost the survival of larval and juvenile fish. In this study we examined the differences in the growth rate of larval and juvenile cod (age 2 – 136 d; SL: 4.1 – 39.2 mm) between the years 2006 and 2014, sub-areas of the Baltic Sea (Bornholm Basin, BB; Słupsk Furrow, SF; Gdansk Basin, GB), and seasons (spring and summer). The average growth rate for all specimens was 0.25 mm/d, with significantly lower values between 2012 and 2014 than between 2006 and 2011. A reduction in zooplankton biomass, especially the large zooplankton fraction, was observed after the 2006–2008 period, which was related to the prevailing temperature conditions in the surface layers. The reduction in zooplankton biomass was accompanied by changes in the structure of zooplankton: less <italic>T. longicornis</italic>, <italic>C. hamatus</italic>, and <italic>Pseudocalanus</italic> spp., and more <italic>Acartia</italic> spp. The results suggest that the inter-annual differences observed in zooplankton biomass and structure are likely responsible for the observed reduction in the growth rate of cod larvae between 2012 and 2014 compared to the years between 2006 and 2011. The growth rate reduction could be one of the reasons for the decline in the recruitment of eastern Baltic cod between the years 2013 and 2015, after the high recruitment years of the period 2011-2012.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.022023-12-31T00:00:00.000+00:00Estimation of zooplankton density with artificial neural networks (a new statistical approach) method, Elazığ-Türkiyehttps://sciendo.com/article/10.26881/oahs-2023.4.11<abstract> <title style='display:none'>Abstract</title> <p>This study was carried out to predict the zooplankton density in the Cip reservoir (Elazığ) with an artificial neural network, using some water quality parameters. The plankton samples were collected monthly from Cip Reservoir in 2021- 2022, using a standard plankton net from three stations. Water temperature, dissolved oxygen, pH, electrical conductivity, secchi disk, alkalinity, total nitrogen and total phosphorus were measured. The actual values of zooplankton density and results obtained from the artificial neural networks were compared. Mean absolute percent error (MAPE) values were calculated with actual values and ANNs values. ANNs values were determined to be close to the real data. MAPE percentage value at the first station was determined as 1.143 for Rotifer, 0.118 for Cladocera, and 0.141 for Copepoda. The MAPE percentage value at the second station was determined as 0.941 for Rotifer, 0.377 for Cladocera, and 0.185 for Copepoda. The MAPE percentage value at the third station was determined as 0.342 for Rotifer, 0.557 for Cladocera, and 0.301 for Copepoda. In the present study, it has been seen that artificial neural networks with a learning feature are successful in predicting zooplankton densities in an aquatic environment. It can be concluded from the study that ANNs are a powerful tool for understanding their relationships with the environment</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.112023-12-31T00:00:00.000+00:00Differences of water chemistry, bird assemblages and nutrient loads introduced by waterbirds into morphologically similar waterbodieshttps://sciendo.com/article/10.26881/oahs-2023.4.04<abstract> <title style='display:none'>Abstract</title> <p>The number and structure of waterbirds is affected by the size of the waterbody, the presence of islands and macrophytes, but also by their trophy status. The aims of the study were to compare nutrients in water, numbers of waterbird assemblages, and the loading of nitrogen and phosphorus introduced by waterbirds in two similar waterbodies with different rates of water discharge. This study was conducted in two eutrophic shallow waterbodies, P1 and P2 in 2016 and 2017. The median concentrations of NO<sub>2</sub><sup>-</sup>, NO<sub>3</sub><sup>-</sup> and NH<sub>4</sub><sup>+</sup> were 4.0 times, 3.2 times, and 1.7 times greater in the P1 than in the P2 location, respectively. Similar proportions of organic matter in sediments were statistically greater in P1. The number of birds was also significantly greater in P1 than in P2. The waterbirds (<italic>Anas platyrhynchos, Aythya fuligula, Fulica atra, Phalacrocorax carbo</italic> and <italic>Chroicocephalus ridibundus</italic>) excreted 5.2 times more total phosphorous and 3.3 times more total nitrogen in P1 than in P2. Significant negative correlations were also found between the concentrations of NO<sub>3</sub><sup>-</sup> and the number of waterbirds in P1.</p> </abstract>ARTICLEtruehttps://sciendo.com/article/10.26881/oahs-2023.4.042023-12-31T00:00:00.000+00:00en-us-1