Lakes and Reservoirs: Research and Management最新文献

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.

Studies on the length–weight relationship (LWR), condition factor (K) and size at first maturity status are important aspects of fish biology and fisheries management. Although many studies have reported about growth parameters of Oreochromis niloticus under various fishery waters and aquaculture systems, a recent invasion of the species in Lake Nakuru (Kenya) is a new case study. Therefore, this paper provides baseline data on LWR, K and Lm₅₀ of O. niloticus in relation to limnological conditions in the lake. Water quality parameters (pH, temperature, conductivity, dissolved oxygen, salinity and total suspended solids) and indicators of eutrophication status (phosphates, nitrates and chlorophyll-a.) were analysed in November 2020 and November 2021. Fish samples were collected using experimental gillnets with assorted mesh sizes from 2 to 4 in., and their morphometric data was analysed. Results show significant spatial variations (ANOVA; p < 0.05) in all the water quality parameters. These parameters, except the temperature, also significantly differed between the study periods (t-test; p < 0.05). O. niloticus was the most dominant species, comprising 75.3% and 90.8%, in 2020 and 2021, respectively. Mean total length (19.80 cm) and weight (169 g) of the fish in 2021 were greater than 19.20 cm and 153 g in 2020. Nile tilapia exhibited an isometric LWR (b = 3), better well-being (K>1), but it matured at smaller sizes (<25 cm) in both sexes. Further monitoring of water quality changes in Lake Nakuru and their future impact on the population of O. niloticus is recommended.

The Ailia coila, a small indigenous freshwater fish species in Kaptai Lake, plays a crucial role in providing employment, food, and financial security for the local people. With a high market demand, the average production of this species over the last 5 years reached about 112.27 metric tons. However, there has been a notable decline in Ailia coila fish production in Kaptai Lake in recent years. Therefore, to understand the current stock status of this species, this study employed a length-based stock assessment method the “length-based spawning potential ratio (LB-SPR)”. Between August 2022 and March 2023, a total of 1219 individuals were collected through fortnightly sampling from two fish landing centers (BFDC fishery ghat and Kaptai boat ghat) and two local markets (Banarupa Bazar and Reserve Bazar). The maximum length of Ailia coila was recorded at 15.7 cm in total length, with an average length of 11.1 (±4) cm. The length-weight relationship was estimated as W = 0.01084 L^2.599 (R² = 0.75). The value of shape parameter ‘b’ is smaller than three which indicate a negative allometric growth pattern. The estimated asymptotic length (L_∞) and length at first maturity (L_50%) were found to be 16.84 and 10.54 cm, respectively. The LB-SPR revealed that the fishery is currently experiencing overfishing, with the spawning biomass (SPR = 32%) below the target reference point. The mean estimate of fishing mortality relative to natural mortality (F/M) was 3.07, more than three times the threshold F/M = 1, indicating extreme fishing mortality in this fishery. The estimated length at first capture (SL_50%) was significantly higher than the length at first maturity (L_50%), suggesting that the fishing is predominantly targeting mature fishes. To enhance the spawning biomass and ensure the sustainability of the fishery, it is imperative to reduce the current fishing pressure and implement appropriate management measures.

Due to having high market demand and consumer preference, four varieties of Anabas testudineus (indigenous, Thai, Thai-Vietnam, and Vietnamese) have been extensively cultured in Bangladesh over the last few decades. But high similarities in their morphometric traits make population differentiation difficult. The present study used phenotypic markers for their discrimination based on traditional morphometry and truss network measurement. We conducted a study of morphometric variability through the traditional morphometry and truss network systems based on 120 specimens of four varieties of A. testudineus cultured in a coastal region of Bangladesh. Significant (p < 0.05) variation was observed in the analysis of variance (ANOVA) for all the measured traits. In each of the truss network and morphometric measurements, three discriminant functions (DF) were found with 100% variability, which accounted for 89.7% and 65.7% for DF1; 9.7% and 25.7% for DF2 and 0.6% and 8.7% for DF3, respectively. In principal component analysis (PCA), four PCs were observed for traditional morphometry with a total variance of 97.44%, while in the truss network system, the total variance was 98.53% in five PCs. Overall, the investigation found four distinct stocks for indigenous, Thai, Thai × Vietnamese and Vietnamese varieties. The outcomes of this study might be useful for differentiating these four varieties of climbing perch population, genetic study, management and conservation of this fishery at home and abroad.

It is increasingly being recognised that local people's knowledge can contribute to the ecological and socioeconomic goals of natural resource management programmes. Yet, few studies have examined local people's knowledge concerning freshwater macrophyte diversity. Consequently, the extent to which local people's knowledge can contribute to mitigating freshwater macrophyte degradation and supporting their management remains largely unknown. To contribute towards filling this knowledge gap, we investigated local people's knowledge, perceptions and management practices of freshwater macrophyte species. Data collection involved conducting face-to-face in-depth interviews and focus group discussions among local people who lived in areas adjacent to Lake Baringo, Nyanza Gulf of Lake Victoria and the Kenyan side of Lake Jipe. The sociodemographic characteristics of the respondents were summarised using descriptive statistics. Then, generalised linear mixed-effect models were used to test whether the respondent's sociodemographic characteristics were associated with their macrophyte species recognition skills, benefits and problems associated with macrophytes and management practices. Our respondents named a total of 35 macrophyte species, with each respondent naming an average of six species. Our results showed that respondents who were not involved in fishing and fish-related activities identified more macrophytes than those who participated in such activities. Additionally, individuals who frequently visited the lake named more macrophyte species compared to those who visited either daily or occasionally. While our respondents acknowledged various benefits and problems associated with macrophytes, there was a higher recognition rate for those that directly impacted humans. Regarding local management practices, it was observed that macrophytes were not conserved, with management efforts focusing solely on problematic species. Overall, macrophyte naming skills, knowledge on provisioning and supporting ecosystem services, direct adverse macrophyte impacts and management methods increased with age. We identified knowledge gaps regarding alien species and the indirect impacts of macrophytes. Addressing these gaps is crucial.

The present work was carried out to study the demographic aspects of Cyprinus carpio, an invasive species and an ecological pest capable of universal existence. Data on length–frequency was obtained from the two varieties of C. carpio from the deepest freshwater lake of India, Manasbal Lake, over a time period of 1 year (March 2019–February 2020) and analysed using the FiSAT-II software. The mean total length was reported to be 18.58 cm for C. carpio var. communis and 19.18 cm for C. carpio var. specularis, with the dominant length groups being 20–21 and 19–20 cm, respectively. The length–weight relationship parameters yielded the equation logTW = (2.56) logTL − 1.30, r = 0.94, for C. carpio var. communis, with a condition factor (K) value of 1.42 ± 0.25, and logTW = (2.53) logTL − 1.26, r = 0.93 for C. carpio var. specularis, with a condition factor (K) value of 1.38 ± 0.20. Different parameters obtained from the von Bertalanffy growth equation included L_∞ = 38.85 cm; K = 0.170/year; ø′ = 2.409 and t₀ = −0.93 for C. carpio var. communis, and L_∞ = 30.45 cm; K = 0.210/year; ø′ = 2.289 and t₀ = −0.80 for C. carpio var. specularis. The mortality parameters, including total, natural and fishing mortality, were also estimated for C. carpio var. communis to be Z = 0.08, M = 0.40 and F = −0.32, and for C. carpio var. specularis, to be Z = 0.22, M = 0.49 and F = −0.27, respectively. The exploitation rate (E) estimated for both varieties revealed its very less exploitation, suggesting more efficient methods to explore Manasbal Lake to its full capacity and to determine proper measures needed to be taken to conserve the native fauna.