ABSTRACT Lake Amatitlán is the fourth largest lake in Guatemala. It is located within the Pacific drainage basin, 25 km southwest of Guatemala City, and represents the principal water reservoir for the city area and surroundings. Its main tributary is the Villalobos River, which receives water from rivers that are distributed through the 14 municipalities that constitute the lake's 382 km 2 watershed. Due to its location, the lake is highly influenced by urban development and population growth, as well as inadequate watershed management. Urban growth has caused the degradation of the surrounding forests and ecosystems. The Villalobos River has become a conduit for domestic and industrial wastewater that flows into the lake, increasing nutrient loads from anthropogenic activities in the watershed and altering the lake's natural physicochemical and ecological characteristics. Therefore, it has experienced cultural eutrophication and is a hypereutrophic waterbody. To recover, the lake requires strong institutional commitment from the Government, local authorities, and stakeholders of the basin in addition to large investments.
ABSTRACT An environmental assessment of Lake Patzcuaro was conducted through simultaneous and systematic fieldwork on bathymetry, water quality, fisheries and P'urhepecha community interactions, along with a review of scientific literature from 1938 to 2022. This study aimed to develop a proposal to address major regional issues by describing the environmental conditions of the drainage basin, lake and natural resources. Deforestation between 2001 and 2021 resulted in the loss of up to 62.5% of primary forest, equivalent to 58,000 ha, including fir, pine, alnus and oak. The water balance shows a progressive deficit driven by high evapotranspiration and groundwater extraction, totaling up to 32.89 Mm 3 /year. A comparison of morphometric parameters based on bathymetric maps from 1989 and 2019 confirmed a decrease in lake surface area to 100.59 km 2 , a reduction in maximum length to 18.0 km, a decrease in maximum width to 8.4 km, and shoreline length at 90.9 km. These changes, along with declines in water quality, pollution and overfishing, have led to the collapse of local fisheries. In 1988, fish production was 2523 tons. However, it gradually declined, reaching a maximum catch of 54.18 tons in 2005. Human population growth, incompatible land use, pollution, habitat loss and overexploitation are accelerating the environmental degradation of Lake Patzcuaro. Currently, low fish production is primarily for self‐consumption. A strategic plan based on the ILBM‐ILEC methodology is essential to secure sustainable benefits from regional natural resources, with social participation playing a key role.
ABSTRACT Zirahuen is among the youngest and clearest lakes in Mexico. It is situated at an elevation of 2075 m within the Mexican Neovolcanic Axis, which extends from east to west along the 19th parallel. Its primary economic activities include forestry, agriculture, tourism and fishing for indigenous species such as whitefish ( Chirostoma estor copandaro ). The drainage basin of Lake Zirahuen, like many Latin American hydrological basins, is under severe degradation due to deforestation, unsustainable farming and land‐use changes. These issues lead to soil erosion, siltation, reduced water storage capacity, and pollution from agrochemicals. Consequently, there is an increase in economic and social decline associated with poverty and marginalization. This study aims to evaluate the environmental and governance conditions of Lake Zirahuen, using extensive documentary research and fieldwork to verify structural variables and processes. A management and restoration plan is proposed to emphasize the preservation of this important Mexican aquatic ecosystem.
ABSTRACT Cuitzeo is the second‐largest lake in Mexico (452 km 2 ). With an age of 6.0–8.0 million years, it is considered one of the oldest lakes on Earth. Field, laboratory and documentary research were developed to integrate an environmental diagnosis. The lake is very shallow, with a mean depth of 1.6 m. According to electric conductivity values, it is divided into three lacustrine zones: the eastern zone, with very low electric conductivity values (429.0 μS/cm); the western side, with up to 8950.0 μS/cm; and the central part, with intermediate values. Water quality analyses indicate that Cuitzeo is a hypereutrophic aquatic ecosystem, highly turbid and with increasingly saprobic conditions. Despite the basin area (3675 km 2 ) receiving an average annual rainfall and surface runoff of almost 4000 Mm 3 , intensive water overexploitation and high evaporation rates resulting from deforestation and land‐use change cause Lake Cuitzeo to receive less than 10% of the water input from the basin. Consequently, during arid seasons, up to 70% of the lake surface desiccates, and dust storms are present on the western side. The fishery is near collapse due to intensive fishing and frequent desiccation episodes. From 5546 tons/year of fish catch registered in 1993, fish productivity has fallen to less than 250 tons/year in 2006. Forty‐five years ago, up to 18 fish species were registered, of which 15 were native. Nowadays, only six species are present, of which three are native species.
This present study investigates the length‐weight (LWRs) and length‐length (LLRs) relationships of three gobiid fish species, viz., Odontamblyopus rubicundus , Eleotris fusca, and Stigmatogobius sadanundio , from the mangrove reserve area of the Matla River in West Bengal, India. A total of 365 samples were collected monthly from July 2023 to March 2024 using various fishing gears with varying mesh sizes. Out of all the species evaluated, only O. rubicundus did not fall within the predicted range of 2.5–3.5. The 95% confidence interval (CI) and Pauly's t ‐test of b values were tested. Two species, E. fusca and S. sadanundio , showed positive allometric growth, whereas O. rubicundus exhibited a negative allometric growth pattern. The correlation between LWR and LLR was highly significant among all species ( p < 0.05). The study of Fulton's condition factor ( K c ) exhibited values below 1 in O. rubicundus , suggesting variation within the region. The values of the relative condition factor ( K n ) were within the range from 1.09 to 2.08, reflecting a favourable growth condition. These findings contribute to a deeper understanding of gobiid species, which is essential for their conservation and monitoring in the Indian Sundarbans.
Major dams in Zimbabwe are losing more than half of their design capacity in the first 11 to 12 years of operation. Despite these obvious impacts of sedimentation in the country's reservoirs, sedimentation studies have only been conducted once for 90% of the reservoirs. Thus, a sedimentation estimation study was conducted in November 2014 in Lake Chivero to quantity storage loss due to sedimentation, determine the spatial distribution of sediment deposition in the reservoir, update its elevation-capacity curves and estimate its useful life. The study used a dual beam echo sounder for determining depth measurements. Depth measurements were converted to digital elevation models in a Geographic Information System environment. A comparison of the 1953 and 2014 digital elevation models indicated that the lake was losing depth uniformly. The highest deposition depths were observed towards the dam wall and the deep central parts of the lake along the old river channel. Minimal sediment deposition was generally observed at the shallower parts of the lake, on the north-east and south-western locations. A total of 49126170.34 m 3 (18%) of the lake's storage capacity has been lost to sedimentation, which translates to an average annual capacity loss of 792,357 m 3 year −1 (0.295% per year) since construction in 1953. The lake's specific sediment yield and remaining useful life were calculated at 352.31 m 3 year −1 km −2 and 106.63 years; respectively. This loss of storage in the lake will impact the operational and economic benefits for which it was built. It will also affect the habitats of its varied flora and fauna. In the absence of original topographic maps produced at the inundation, the dual frequency echo sounder can be used to generate data to estimate sediment loads into the reservoir as well as update elevation-capacity curves.
The species representing minor fisheries are gaining more economic importance as fishing pressure is increasing on major riverine fishes. Population characteristics or demographic studies of minor fishery resources can provide insight into the impact of environmental issues, conservation status, and help in the management and development of fisheries. We studied the population dynamics of two commercially significant fishes, freshwater garfish, Xenentodon cancila and Cangaturi halfbeak, Hyporhampus limbatus , from Ujani water reservoir (Pune, India) using cast net and gill net on a monthly basis for 1 year. Length-weight relationship (LWR) and population dynamics of both fishes were analysed using FAO-ICLARM Stock Assessment Tool (FISAT). LWR analysis revealed a positive allometric growth pattern in both X. cancila ( b = 3.12) and H. limbatus ( b = 3.15). The estimated potential longevity ( t max ) of X. cancila and H. limbatus was 3.48 and 5.76 years, respectively. The observed length at first capture for X. cancila and H. limbatus was 18.53 and 6.66 cm, respectively. Juveniles of H. limbatus face higher exploitation as compared to X. cancila . Higher natural mortality was observed in X. cancila while fishing mortality was higher in H. limbatus . Recruitment analysis revealed two spawning bouts in 1 year for both species. Xenentodon cancila fish stock is under-exploited and H. limbatus fish stock is over-exploited in Ujani reservoir. Further reproductive biology studies are necessary for the effective development and management of fisheries involving X. cancila and H. limbatus .
This study applies a GIS-based approach to evaluate the spatial suitability of net-cage aquaculture and analyse key water quality parameters in four hydroelectric reservoirs located in the Jamari River basin, Western Brazilian Amazon. The assessment includes one large hydropower reservoir (HPP Samuel) and three small hydropower reservoirs (SHDs): SC Monte Negro, Jamari and Canaã. The methodology followed five stages: (1) temporal analysis of Total Water Surface Area (TWSA); (2) identification of vegetation-free areas; (3) evaluation of depth suitability; (4) compilation of historical water level data and limnological parameters (chlorophyll- a , BOD, total phosphorus, dissolved oxygen); and (5) mapping and estimation of Potential Aquaculture Sites (PAS). Due to excessive seasonal variation (> 70% fluctuation in TWSA), the Samuel HPP reservoir was excluded from the final suitability mapping. In contrast, the SHD reservoirs exhibited environmental stability and fulfilled legal requirements for net-cage installation. Together, they offer an estimated production potential of up to 466 t per year using native species such as Colossoma macropomum . Most water quality parameters complied with Brazilian environmental standards (CONAMA Resolution no. 357/2005). This spatial and limnological assessment provides a technical foundation for implementing sustainable aquaculture systems in Amazonian hydroelectric reservoirs. Further studies should incorporate ecological carrying capacity modelling and environmental impact projections to support long-term sustainable aquaculture practices in these freshwater ecosystems.
This study examines the current state and projected future of India's dams, focusing on the challenges posed by ageing infrastructure, sedimentation, increasing water demands and climate change. With over half of India's major dams now surpassing 50 years of age, the risk of structural deterioration and reduced functionality is escalating. Sedimentation, a critical issue, has led to a substantial decrease in reservoir storage capacity, impacting water availability for agriculture, drinking water and hydropower generation. Additionally, climate change is anticipated to intensify these challenges, with more frequent and severe weather events stressing dams that were not originally designed for such variability. To ensure the longevity and resilience of these structures, comprehensive adaptation measures are essential. Key recommendations include modernising dam infrastructure, implementing advanced sediment management strategies, integrating climate-responsive design features and enhancing real-time monitoring systems. Future research should prioritise climate modelling, innovative sediment control and seismic resilience improvements. Proactive policy, combined with sustained funding and community engagement, is vital to safeguarding India's water resources and addressing the complexities of an evolving environmental landscape.
After five years of impoundment, Bui Reservoir fisheries has evolved with silver catfish, Chrysichthys nigrodigitatus among the most important commercial species. Based on standard length analyses of 162 individuals (62 males, 39 females) from post-impoundment seasonal sampling at three (3) stations, the population structure, well-being, growth type, sex ratio, length at first capture and rates of growth, mortality, exploitation, and other derived parameters of C. nigrodigitatus were estimated to provide requisite information for sustainable management. The population is composed of fewer juveniles and more males than females, with females relatively larger than males (modal size 7.0–7.9 for males and 9.0–9.9 for females). Females were physiologically better than males (79.49% of females had condition factor above 2.0 compared to 53.23% males) notwithstanding seasonal fluctuations. Unimodal length structure was observed for all seasons except for the post-rainy season with 2 modes, all of which, however, indicated a single year class and single spawning. Estimated hypoallometric and hyperallometric growth values among seasons and sexes were not significantly different from the isometric pattern. Estimated von Bertalanffy growth parameters were asymptotic size ( L ∞ ) = 13.07 cm SL, growth constant ( K ) = 1.01 year, −1 and length at time 0 ( t o ) = 0.18. Growth performance index ( ϕ ') was 2.27, indicating slow growth while the lifespan was 2.73 years. Total mortality, natural mortality, and fishing mortality estimates were high (3.56, 2.44 and 1.12 respectively) while exploitation was below optimum ( E = 0.32). Regular assessment of fish population, growth, and other characteristics is recommended to provide requisite information for strategic interventions for sustainable management and development of reservoir fisheries.
In this study, length-weight relationships of seven catfish species collected from the middle stretch of the Ganga River in India were determined. The specimens were gathered from the Sadiyapur and Daraganj fish landing centers in this region of the Ganga River between November 2022 and October 2023. Digital callipers and digital balances were utilised to measure the total length (TL) and body weight (BW) of all fish specimens. The growth coefficient b ranged from 1.98 for Sperata aor to 3.31 for Sperata seenghala . Also, Rita rita , Sperata aor , Eutropiichthys vacha , Wallago attu and Bagarius bagarius exhibited negative allometric growth ( b < 3) while Sperata seengala and Clupisoma garua showed positive allometric growth ( b > 3). The coefficient of determination ( R 2 ) values ranged from 0.66 to 0.93 across the seven catfish species. Additionally, the relative condition factor ( K n ) value is greater than 1 for all the catfish species, indicating that all the catfish species are in good health.
Fish biodiversity was assessed as a biological indicator of aquatic environmental quality across six wetlands of Lake Tana, Ethiopia. A total of 1616 fish specimens, representing 18 species, four genera and three families, were collected. Labeobarbus intermedius (23.1%–48.9%) and L. brevicephalus (6.7%–44.4%) were the most abundant, whereas L. beso , L. gorguari and L. truttiformis were least common (0%–6.7%). Spatially, Clarias gariepinus dominated at Megech River Mouth (9.4%), and Oreochromis niloticus was abundant at Wonjeta (54.5%) and Ras Abbay (62.5%). Catch Per Unit Effort (CPUE) ranged from below the detection limit to 110.0 fish/h. The Fish Index of Biotic Integrity (FIBI) and Habitat Quality Index (HQI) varied significantly, with the highest FIBI values at Gumara and Megech River Mouths (39.0) and HQI scores peaking at Zewdie Girar (19.0) and Wonjeta (18.5). Multivariate analyses grouped wetlands into three distinct clusters based on the fish assemblage structure: Cluster 1 (Wonjeta, Ras Abbay and Avaj), Cluster 2 (Zewdie Girar and Gumara River Mouth) and Cluster 3 (Megech River Mouth). Principal Component Analysis explained 80.6% of the total variation, whereas Canonical Correspondence Analysis accounted for 98.5% of the variance in fish–environment relationships, identifying water depth, Secchi depth, ammonia, phosphorus and nitrate as key drivers of environmental degradation. Margalef's richness and Hill's diversity indices varied significantly among wetlands, reflecting spatial differences, but showed no significant seasonal variation. Functional feeding group distribution exhibited seasonal shifts, especially among benthic, tolerant and detritivorous species. These findings underscore the ecological importance of Lake Tana's wetlands and the need for targeted conservation measures to sustain fish diversity and habitat integrity.
Wetland ecosystems in the Himalayan region face growing threats from climate change, human activities and environmental degradation. This study introduces an integrated approach to assess and predict the water quality index (WQI) for effective wetland management, focusing on the Alital and Bandatal Lakes in Nepal's Sudurpaschim Province. These lakes were selected due to their distinct ecological and geographical characteristics, as well as differing levels of human impact. A total of 40 water samples (20 from each lake) were collected, and 16 physicochemical parameters, including turbidity (Tur.), total dissolved solids (TDS) and major ions were analysed. Hydrochemical properties were characterised using graphical methods, such as the Gibbs and Piper diagrams and the WQI was computed using the arithmetic average method. The hydrochemical facies analysis indicated that carbonate weathering was the dominant process in both wetlands, with Bandatal showing significant anthropogenic influence. The findings revealed that Alital maintained ‘Excellent’ to ‘Good’ water quality, with an average TDS of 64 mg/L and Tur. of 2.14 NTU, reflecting minimal human impact. In contrast, Bandatal exhibited ‘Poor’ to ‘Unsuitable’ WQI classifications, with TDS averaging 115 mg/L and Tur. reaching 63.6 NTU, highlighting substantial human influences. An artificial neural network (ANN) model was developed to predict the WQI, demonstrating outstanding accuracy with an R 2 of 0.99 for both the training and testing phases. These results underscore the potential of the ANN model for proactive wetland management, aligning with sustainable development goals (SDGs) related to clean water and ecosystem restoration and providing globally applicable insights for wetland conservation.
Ayu Plecoglossus altivelis altivelis is a commercially and recreationally important freshwater fish in Japan. This species is categorised into two ecological forms: amphidromous migrating between rivers and sea and landlocked migrating between rivers and lakes or dam reservoirs. Despite its ecological and economical values, growth analysis has been developed limitedly in the early life history of particularly the amphidromous form, and the growth potential of the landlocked form throughout an annual life history remains almost unknown. This study investigated the allometric growth and condition factors along with their variation among months and life stages of artificial landlocked ayu in Haidzuka Dam reservoir and its connected Tabusa River. A total of 281 individuals were collected monthly from October 2017 to September 2018, and their total length (TL) and body weight (BW) ranged from 1.11 to 14.98 cm and 0.001 to 32.148 g, respectively. Although the allometric coefficient ( b ) of the length–weight relationship varied from 2.71 to 3.44 among months, it indicated overall positive allometric growth ( b = 3.83) calculated from the equation BW = 0.0013TL 3.83 . The growth pattern altered significantly among life stages from positive allometric for larvae, juveniles, and youngs to negative allometric for adults. The calculated asymptotic length and growth coefficient of the logistic growth model were 17.71 cm and 3.91 year −1 , respectively. Significant differences were found in allometric ( K A ) and Fulton's ( K F ) condition factors among months, while there was no difference in relative condition factor and relative weight ( W R ). Life stage-specific analysis also revealed that the adult stage was nutritionally healthier compared to other life stages based on K A and K F . Only K F showed significant correlations with both TL and BW, making it an ideal condition factor to predict the wellbeing of ayu in this reservoir. Moreover, the Wilcoxon signed-rank test for W R showed no significant divergence from 100, suggesting a balanced habitat in this reservoir for ayu. These findings will be crucial for further studies and to develop appropriate strategies for the sustainable management of artificial landlocked ayu in dam reservoirs.
The assessment of nutrient and heavy metal accumulation in lake sediments is essential for understanding their role in the ecohydrological dynamics of lake ecosystems, as sediments can function both as a sink and source of nutrients, metals and various contaminants aquatic ecosystem. The main objective of this study was to evaluate the concentrations of nutrients and heavy metals and their accumulation in the sediments across different sampling locations of Loktak Lake and to compare them against geochemical background values and sediment quality guidelines. The key findings of the study revealed substantial nutrient accumulation in sediments from the Keibul Lamjao National Park site, which can be attributed to the decomposition of organic matter from dense floating vegetative masses called ‘ Phumdis ’. Iron concentrations in sediments were significantly high, ranging from 909.83 to 1004 mg/kg and its enrichment is likely due to diffused surface runoff from the iron-rich soils from the surrounding catchment entering the lake through feeder rivers and other anthropogenic influences. The average metal concentrations were in the order of Fe > Mn > Zn > Cu, and all values were below the average shale concentrations and the Interim freshwater Sediment Quality Guidelines (ISQG) set by the Canadian Council of Ministers of the Environment (CCME). The evaluation of the heavy metal pollution status of the lake sediments based on various pollution indices such as the contamination factor, degree of contamination, modified degree of contamination, geoaccumulation index, pollution load index and potential ecological risk index, suggested an overall low level of metal pollution in the sediments of Loktak Lake. The findings of this study provide a crucial baseline for understanding on the sediment-associated nutrient and metals dynamics in Loktak Lake which can aid in the formulation of long-term lake management strategies for preserving the ecological integrity and health of this precious lake ecosystem of the region.
Given the limited and geographically narrow research on macroinvertebrate distribution in subtropical wetlands, this study aims to provide a comprehensive assessment of species assemblages and ecological health across multiple sites in Deepor Beel, a well-known wetland and Ramsar Site in north-eastern India. The current study examines the complex impact of anthropogenic pressures on benthic macroinvertebrates. During the post-monsoon and winter seasons of 2023–2024, samples were collected systematically from three important locations, including touristic destinations (Station-1), garbage dump sites and densely inhabited areas (Station-2), and flow-out points (Station-3). The recorded dataset includes 467 members from 14 families spread throughout 8 orders and 3 separated phyla. The phylum Mollusca appeared as the major taxonomic group (53.74%), controlling the gathered samples, with Arthropoda (45.18%) and Annelida following in hierarchy. Within this taxonomic framework, significant information was discovered, identifying Viviparidae, Lymnaeidae, and Planorbidae as the most abundant families, accounting for 16.27%, 15.84%, and 15.84% of total individuals, respectively. Furthermore, an in-depth examination of richness (Margalef richness) and diversity (Shannon-Wiener Index) indices demonstrated a deteriorating tendency from areas less affected by human interventions to those bordered by a trash dump and residential agglomeration. Macroinvertebrate saprobic scores show that Station-3 near the flow-out point to the river Brahmaputra (5.5) is in good environmental condition, whereas Stations-1 and 2 (4.9 and 4.66) are moderately polluted and impacted by anthropogenic activity. Redundancy analysis highlights the association between moderate pollution indicator taxa Gerridae (Hemiptera), Hydrophilidae (Coleoptera), and Hirudidae (Hirudinea) and increasing organic loads (BOD, COD) at Station-1 and 2. The combination of macroinvertebrate family data and water quality parameters underlines the need for a comprehensive approach to assess the health and sustainability of lake ecosystems. The study's findings have implications for developing educated conservation and management policies in the face of growing anthropogenic threats.
The widespread use of plastic materials globally has sparked concerns regarding microplastic (MP) pollution, which is prevalent in water bodies worldwide and poses threats to aquatic life. Despite this, there remain uncertainties regarding the quantity, types and chemical makeup of MP, particularly in tropical urban lakes. This study aimed to examine the presence, distribution, types and chemical composition of MP in both the surface water and sediment of Air Hitam Lake, located in Samarinda City, East Kalimantan, Indonesia. Field sampling was conducted in February 2023 at 10 sites within the lake. The average concentration of MP in water was measured at 0.91 particles per litre, while sediment concentrations reached 375 particles per kilogram of dried sediment. Higher concentrations were observed near the lake inlet. Fibres were the most commonly observed type of MP in both surface water (79%) and sediment (76%) samples, followed by fragments and films. There was no significant correlation between MP concentrations in water and sediment. Fourier Transform Infrared (FTIR) analysis revealed the presence of polyester, polypropylene, nylon fibres, polyethylene, polystyrene polyvinylchloride in the samples, with polyethylene being the predominant compound, accounting for 46% of all surface water and sediment samples. The presence of MP derived from the degradation of larger plastic debris originating from visitors and the local community who dispose of plastic trash improperly highlights the importance of implementing effective plastic waste management strategies in communities surrounding the lake. This is crucial for preserving the ecosystem benefits provided by the lake. This study contributes to addressing knowledge gaps regarding MP pollution in tropical urban lakes and lays the groundwork for further research into inland freshwater environments.
The present study describes the length-weight relationships (LWRs) and length-length relationships (LLRs) for three species: Parambassis baculis (Hamilton 1822), Gagata cenia (Hamilton 1822) and Mystus tengara (Hamilton 1822) from the Jorasar river in Sonitpur district of Assam, India. The study shows positive allometric growth (3.133) for M. tengara , isometric growth (2.916) for G. cenia , and negative allometric growth (2.295) for P. baculis , with regression coefficients ( r 2 ) 0.953, 0.969, and 0.955, respectively. The Parameter a was recorded as 0.007 for M. tengara , 0.013 for G. cenia , and 0.030 for P. baculis . The current study will contribute to the conservation of these ichthyofaunas while enhancing fish stock analysis for appropriate management.
Lake Ahémé is one of the main fishing areas in the Couffo basin. Porogobius schlegelii (Gunther, 1861) is one of the fish most exploited by artisanal fishing after the cichlid species. Sustainable management of the species requires reliable data on the current pressure of traditional fishing in order to find measures to adjust fishing activities to the recruitment capacity of the species. Therefore, from January to December 2020, data on total length, total weight and sex were collected monthly on a total of 3447 specimens of P. schlegelii caught by local fishermen. The size at first maturity ( L 50 ) determined with the statistical package sizeMat was estimated at 6.5 and 6.2 cm for males and females, respectively. The asymptotic length obtained with the TropFishR statistical package was 14.8 cm for both sexes. The growth coefficient and growth performance index were 0.87 year −1 and 2.28, respectively, with a normalised adjustment value of 0.21. Estimates of total, natural and fishing mortality were 3.55, 1.53 and 2.02 year −1 , respectively. The current exploitation rate was 0.57 and as such remained above the exploitation rate at 50% of its unexploited biomass ( E 0,5 = 0.37). Therefore, a reduction in the current exploitation rate is required by at least 35.1% to maintain sufficient biomass. The estimated size at first capture of 5.9 cm is smaller than L 50 for both sexes. These parameters clearly reflect a current trend of overexploitation. Monitoring of fishing efforts and sensitisation of fishermen to catch fish measuring at least 9.3 cm (optimal length) are among the management measures recommended to sustain the P. schlegelii fishing in Benin.
ABSTRACTMorphometric analysis plays a key role in understanding the geological and hydrological behaviour of watersheds and their prioritisation for soil conservation. The Punarbhaba‐Atrai‐Jamuna river system of northwest Bangladesh is agriculturally important, but the watersheds are frequently affected by droughts in summer and river erosion during the monsoon season. The morphological studies on this river systems are very limited, and hence, the aim of this study was to investigate the morphological characteristics of their largest basins and prioritise the studied watersheds based on erosion vulnerability using two approaches. The remote sensing tools were used to delineate and analyse the linear, areal and relief aspects of the morphometric indices of the six largest river basins of Dinajpur district as the conventional methods of determining the morphological characteristics of a basin are expensive and time‐consuming. The studied basins included the following regions—Dinajpur Sadar‐Birganj (DS‐B), Dinajpur Sadar‐Khansama (DS‐K), Chirirbandar‐Khansama (C‐K), Nawabganj‐Chirirbandar (N‐C), Birampur‐Parbatipur (B‐P) and Hakimpur‐Parbatipur (H‐P). The results of the bifurcation ratio, length of overland flow, drainage density, drainage texture and constant channel maintenance indicated that the watersheds were well‐dissected and had less flood and erosion risk. The values of form factor, elongation ratio, circularity ratio and compactness coefficient dictated an elongated shape of all the basins with a mature geological adjustment. The multi‐criteria prioritisation, combining morphometric analysis with land use factors, offers a holistic understanding of watershed vulnerability signifying DS‐B and N‐C the most vulnerable watersheds, which require a sustainable development decision making framework for their management. This research also provides the brief morphological features of the three complex river system to design management practices for conservation and open a dimension for future research on the application of soil erosion models to estimate soil loss.
