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Abstract:

This study focuses on assessing the status of fish stocks and the ecosystem of lakes Edward, George, and the Kazinga Channel. Unreliable knowledge of inland fisheries limits their inclusion in development policies and leads to ill-informed management. The assessment of inland fisheries should be increased at the local scale to improve policies and management measures. This requirement was the motivation of this study. The waterbodies assessed are important for fisheries with annual catches of 42,000 t, supporting about 24,000 fishers in Uganda and the Democratic Republic of the Congo (DRC). The proximity of the water bodies to protected areas where other livelihood activities are restricted, makes the fisheries vital. Typical of most inland fisheries, the waterbodies lacked adequate information on the status of exploited stocks. Therefore, the main objective of this study was to improve knowledge of the status of fish stocks and their ecosystems. First, we examined the state of knowledge in the waterbodies to aggregate data and information and establish knowledge gaps. This was accomplished by reviewing literature on primary productivity and water quality, invertebrates, fish fauna, fish life history and ecology, and fisheries. The review provided data on all the above aspects but with substantial temporal gaps due to irregular monitoring. Adequate data exists on the water quality status, extant aquatic taxa (including fishes) and fish catches but with uncertainties in the latter in the part of Lake Edward in the DRC. Data and information gaps existed on the abundance of biotic communities, fish life-history, trophic ecology, and fisheries management reference points (FMRP), the benchmarks used to determine the status of fish stocks. Common FMRP include maximum sustainable yield (MSY), corresponding fishing mortality rate (Fmsy), and minimum biomass that can support MSY (Bmsy). The FMRP are a vital requirement for effective fisheries management, and their absence indicates a substantial gap. The review was followed by stock assessments to evaluate the status of fish stocks using fish life-history parameters and FMRP. We used secondary data and new data from surveys conducted in 2021 and 2022 to estimate life-history and growth parameters of 16 fish stocks in the Ugandan part of Lake Edward and Lake George. The parameters are indicators of the status of fish stocks, particularly in data-poor fisheries but were unavailable or outdated for the stocks studied. The parameters included maximum length (Lmax), mean length in catches (Lmean), coefficients of length-weight relationships, length at 50% maturity (Lm50), fecundity, von Bertalanffy parameters, total mortality (Z), and natural mortality (M). These were estimated using empirical formulae, statistical methods, and analysis of length frequencies. The estimates obtained were consistent with estimates in literature for the same or related species, indicating their reliability for decision making and further assessments. Estimates of Lm50 for four of the stocks assessed belonging to two species (Nile tilapia Oreochromis niloticus and marbled lungfish Protopterus aethiopicus) were lower than baseline estimates in the studied waterbodies, a sign of unsustainable fishing. Also, the mean lengths in catches for all the stocks were less than the optimum lengths (Lopt) that maximize catches with minimal impact on biomass and size structure. In Uganda, enforcement was strengthened since 2018 to eliminate illegal fishing. No significant effect in life-history parameters could be attributed to the changes in management. We estimated the FMRP in two phases with the first estimating FMRP for five exploited fish species (11 stocks) in the Ugandan part of Lake Edward, Lake George, and the Kazinga Channel. The reference points were based on four stock assessment approaches for data-poor fisheries. Many FMRP were estimated including the ratio of current biomass (B) to Bmsy (B/Bmsy) and the ratio of fishing mortality rate (F) to Fmsy, two key FMRP used as measures of the status of stocks and fishing pressure respectively. The status of the stocks was poor and defined as either collapsed, recruitment impaired or overfished. The poor status of the stocks was consistent with high fishing pressure depicted by high values of F/Fmsy. However, higher catches could be obtained under sustainable management. In the second phase, the FMRP were updated by incorporating additional data that became available on the stocks. For comparative purposes, additional stocks from nearby lakes (Victoria and Kyoga) were also assessed. Apart from two stocks in Lake Victoria, the status of all the other stocks was poor and classified as either collapsed, recruitment impaired, or overfished. The last part of this study focused on developing two aquatic ecosystem models, one for each of lakes Edward and George, using Ecopath with Ecosim (EwE). The models developed are considered reliable because of their consistency with ecological principles. Based on the models, inferences can be made on trophic interactions, the ecological characteristics of ecosystems, and the importance of fishing. The models suggested the need for ecosystem-based FMRP to manage the impacts of fishing with an ecosystem perspective, and the need to manage external threats such as pollution since the ecosystems are still maturing and therefore, have limited capacity to recover from disturbances. The stock assessments and ecosystem models performed in this study addressed some of the data and information gaps that were established by the state of knowledge review, but others remain. Major gaps include the uncertainty of catches in the Congolese part of Lake Edward and the abundance of biotic communities. Regular research and monitoring, led by state agencies responsible for fisheries research and management, is recommended to fill the data and information gaps. In the DRC part of Lake Edward, the research and monitoring may be limited by persistent insecurity. The monitoring should be simultaneous with stock assessments to update the FMRP and evaluate management measures. When more data becomes available from future research and monitoring, the reliability of the models, which is currently based on consistency with ecological principles and empirical observations, could be improved by fitting the models to timeseries data. This will support better understanding of the aquatic ecosystems and establish better models to facilitate ecosystem-based fisheries management. Our study established the status of fish stocks in lakes Edward, George and the Kazinga Channel using the FMRP. These showed that the status of the stocks is poor due to high fishing pressure and therefore, the focus of management should be to transform the status of the stocks from poor to healthy status by rebuilding the biomass to Bmsy. Major applicable policy measures include strengthening enforcement to eliminate illegal fishing, livelihood diversification out of fisheries to reduce fishing pressure, closed seasons, and closed areas. The success of enforcement is limited by governance issues and conflicts that must be addressed. Livelihood diversification is limited by poverty and the proximity of the waterbodies to protected areas. It could be enhanced by deliberate development programmes to equip people in fishing communities with life skills to create alternative employment opportunities. The FMRP provide targets or limits to evaluate the success of any management measures that will be undertaken. The estimation of FMRP in this study relied on approaches developed primarily for marine systems. Successful application of these approaches in these waterbodies demonstrated their usefulness for inland fisheries. For this reason, these approaches should be scaled-up to assess more inland fisheries to raise their profile in national, regional, and global development policies.