Lakes and Reservoirs: Research and Management最新文献

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 (L₅₀) 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 L₅₀ 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.

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 (r²) 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.

Identification of Schizothorax curvifrons (Sattar gad) stocks in Kashmir water bodies is crucial for the conservation of species that are losing ground daily. Because of substantial overfishing and pollution in the fish's natural environment, the wild population of these fishes is drastically dropping, which is a troubling situation that justifies a high priority for conservation. Fish populations can acquire morphometric variations as a result of prolonged isolation and interbreeding. The goal of this study was to use the truss network approach to delineate the stock structure of S. curvifrons based on morphological attributes. A total of 167 fish specimens were gathered from the three sampling stations of Kashmir waters, viz. Telbal Nallah, Dal Lake and Anchar Lake. A total of 37 truss distance measurements were established by joining 15 morphometric landmark points on the fish body. For the fish species currently targeted, MANCOVA demonstrated significant (p < 0.001) morphological heterogeneity among sampling locations. Univariate ANOVA test showed statistically significant differences in 21 out of the total 37 studied morphometric variables among the three sampling sites for S. curvifrons. Based on principal component analysis, the first component (PC1) explained the maximum amount of variation in samples, which is 26.9%. The second component (PC2) contributes 16.5%, and the third (PC3) 10.3% of the total variance. Wilk's lambda test found substantial (p < 0.001) differences in the morphometric measures of the fish across all sampling sites. The discriminant function analysis identified two morphological indices that explained 58.8% and 42.2% of the differences between the groups. Discriminant function analysis further revealed 84.6% correctly classified individuals into their respective populations. The findings from this investigation can be used to develop stock-specific management and conservation strategies for the long-term protection of S. curvifrons in Kashmir water bodies.

A badid, Badis assamensis Ahl, 1937, was recorded for the first time from the intermediate zone of a semi-torrential stream called Basistha in Assam, which is a small tributary of the river Brahmaputra. The fish species Badis assamensis is currently listed in the data deficient (DD) category of IUCN. The species has previously been reported in swampy wetlands in the upper reaches of the Brahmaputra valley in Assam; with no detail description on its biology however. The current work redescribes morphology and presents detail reproductive biology of this species based on fresh collection of 377 individuals from the Basistha. length-weight relationships (LWR) analysed in this species indicated an isometric growth; and condition factor (K) indicated a suitable habitat for this species. Badis assamensis exhibits a non-seasonal breeding behaviour twice a year, as analysed from the Gonado-somatic and ovarian indices. During certain period of the year, local people use unscientific ways of fish collection thereby resulting in a steep decline in fish population. The study is believed to lay an insight into this species' geographical range from a swampy wetland habitat in upper reaches of the Brahmaputra basin; to a semi-torrential hill stream habitat in the lower Brahmaputra sub-basin; thereby providing baseline information on this DD species. Analysis of morphometric and reproductive parameters of this species not reported earlier is the major highlight of the present study.

The Kaptai reservoir is one of the important fisheries hubs in Bangladesh for its significant role in the national economy and socio-economic sector. However, easy accessibility to the reservoir along with other human-driven disturbances are pushing the stocks at risk. The sustainable fishery management depends on estimating a stock's total allowable catch (TAC), therefore, a recently developed Monte Carlo method (CMSY) was used for five data-limited stocks (catfish, Sperata aor; snakehead, Channa marulius; carp, Labeo rohita; cichlids, Oreochromis mossambicus and featherback, Notopterus notopterus) to estimate their fishery reference points using their catch, resilience and exploitation record at the first and last catch of the year. A Bayesian state-space implementation of the Schaefer surplus production model (BSM) was also used to compare and justify the output of the CMSY. CMSY estimated the maximum sustainable yield (MSY) to be 378, 110, 74.5, 432 and 99 mt for S. aor, C. marulius, L. rohita, O. mossambicus and N. notopterus, respectively. The result suggests that C. marulius, L. rohita and O. mossambicus fisheries were rebuilding naturally and at underfishing and underfished state according to the values of F/F_MSY and B/B_MSY as per BSM (value < 1). Value of B_MSY greater than present biomass estimated by BSM for L. rohita and O. mossambicus predicts that the stock's overexploitation state seeking serious attention. Although the S. aor fishery seemed to be sustainable and had the potential to produce more, F/F_MSY and B/B_MSY values close to 1 recommend strict management actions for further sustainability. However, F/F_MSY 1.31 for N. notopterus reveals that the stock depleted remarkably making this fishery unsustainable. The study reveals that Kaptai reservoir fisheries require intensive care to maintain sustainable resources. Strict implication of allowable catch limit, mesh size regulation, maintaining water quality, and protection of breeding and nursery ground is highly recommended.

Existing scientific methods can be combined with insights on the socio-ecological landscape of Afrotropical lakes to provide better policy options for stakeholders and to develop more efficient resource management strategies. Using integrated African resource and ecosystem maps and an approach for the developed Governance Index for Prioritisation (GIP) of Lake Victoria resources, our study highlights prospects for adopting the GIP methodology to increase understanding and management of Afrotropical lakes. The use of GIP is recommended for adoption and promotion in areas where such approaches appear defensible for the assessment of lake-wide practices, and in areas with robust indigenous knowledge to provide a broad view of the ecological health of the Afrotropical ecosystem.

As aquaculture intensifies, maintaining conducive conditions for sustainable production becomes a key priority. The expansion in farm number and perfarm production puts pressure on the environment and increases susceptibility of the cultured fish to disease, leading to production loss by the investors. This study was conducted in cage aquaculture systems located in three riparian counties in Lake Victoria, Kenya to investigate the combined role of biosecurity and adherence to best management practices (BMPs) by looking at the knowledge, attitude, and practices (KAP) of the cage aquaculture farmers. Additionally, it examined the link between biosecurity, BMPs, and water quality in the context of promoting fish health and preventing fish kills in the cage aquaculture of Nile tilapia in Lake Victoria, Kenya. Gulf and open water locations were included in the study design. A semi-structured questionnaire was used to gather qualitative information on the KAP of fish farmers to biosecurity and BMPs in the cage aquaculture farms. For water quality analysis, quantitative data was utilised. Results showed that the farmers had a positive attitude towards various biosecurity and BMP concepts and a moderate level of knowledge, but the practices on the farm were not in concurrence with both their attitudes and knowledge. Using a customised aquaculture performance index score, which assessed compliance to some BMPs and biosecurity, only 8% of the farms under investigation had a good score, while 24% had an average score and the majority (68%) had a poor score. Additionally, a good aquaculture performance index score was inversely related to ammonia levels. This finding suggests the need to locate cage fish farms in areas with better water circulation. The study highlights the need for capacity building on the importance of adherence to biosecurity and BMPs in the cage aquaculture of Nile tilapia in the lake for enhanced productivity and sustainability of the lake ecosystem.

Environmental contamination by plastics has been receiving considerable attention from scientists, policymakers and the public. In this study, the process-based model NICE-BGC was extended to couple with LAKE2K in a stratified water quality model to evaluate the global plastic dynamics in both lotic and lentic waters. The new model could simulate riverine plastic transport in inland waters with and without the presence of global major reservoirs and lakes. The result showed the simulated plastic transport with the presence of reservoirs becomes slightly smaller than that without the presence of reservoirs. In particular, the plastic burial simulated by the model became different with and without the lake model when the density of plastic was higher than that of water. This result showed there are limits to the application of the same partial differential equations as in inorganic carbon for the derivatives either with or without the reservoirs as assumed in a previous study by this author, especially when the plastic density is higher than that of water. The model also simulated plastic sedimentation in the global lakes and reservoirs together, and showed that more plastic deposits in the reservoirs than in the lakes with the exception of the Caspian Sea and most of lentic waters are found to deposit more microplastics than macroplastics as pointed out in a previous study. Finally, the weighted average of plastic budget in the global major rivers with the effect of anthropogenic factors such as construction of artificial dams and global lakes in lentic water was quantified. The simulated result also showed that incorporation of the lake model in NICE-BGC led to improved estimates of plastic dynamics in inland waters, and may aid the development of solutions and measures to reduce plastic input to the ocean.