Understanding tilapia mortalities and fish health management in Lake Volta: a systematic approach

Unusual fish mortalities in aquaculture threaten global food security and carry significant socio-economic burdens. In 2018, Nile tilapia (Oreochromis niloticus) suffered unusual patterns of mortalities, attributed to disease-causing agents in Lake Volta cage aquaculture. In recent times, disease investigations have shifted from single to consideration of multiple factors to understand the puzzling range of causal risk factors. This study therefore aimed at expanding on tilapia mortality risk factors, while documenting fish health and Lake Volta management practices for sustainable aquaculture. We interviewed relevant aquaculture stakeholders operating on Lake Volta and conducted thematic analysis on their responses to map out mortality risk factors and management practices. The identified risk factors were conceptualized in established models of causation web and Social-Ecological System to explain the practical significance of the findings. The results showed that the risk factors of tilapia mortalities are a combination of pathogens and non-infectious factors mediated by weak law enforcement. The results further suggested mortality reinforcing mechanisms through the horizontal transmission of pathogens, namely, Streptococcus agalactiae and Infectious Spleen and Kidney Necrosis Virus. Moreover, the recognition of weak enforcement as a possible factor reinforcing human activities is a non-infectious route that can be deleterious to fish health. Health management practices comprised phytotherapy, vaccination, heat shock treatment, biological controls, and best husbandry practices. Lake management involves creating a waterfront buffer of 85.34 m, surveillance, and executing the framework guiding aquaculture development on the Lake. The findings are suggestive of complementary quantitative studies that augment the qualitative evidence herein. Such follow up studies can disclose precise mortality risk factors to inform policy directives and effective remedial strategies that can secure fish and lake health

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East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’ vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales

Are we ready to track climate-driven shifts in marine species across international boundaries? - A global survey of scientific bottom trawl data

Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio-temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate-driven ocean changes.En prensa6,86

A communal catalogue reveals Earth's multiscale microbial diversity

Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe

A communal catalogue reveals Earth’s multiscale microbial diversity

Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity

Bioeconomic modelling of shrimp aquaculture strategies for the Mahakam Delta, Indonesia

Bioeconomic modeling was used to evaluate traditional and extensive shrimp production in the Mahakam Delta and impacts of adopting Better Management Practices (BMP) for semi-intensive and integrated mangrove-shrimp culture. Modeling outcomes indicate that traditional production is not financially viable, failing to generate a positive 10-year Internal Rate of Return (IRR). Such practices persist in the Mahakam Delta as capital costs have been depreciated against past financial returns, input costs are negligible, risks are minimal, opportunity costs are low and options to intensify production have been retained by producers. Returns from BMP-guided semi-intensive culture (20% IRR) are marginally higher compared to extensive culture but entail a 10-fold increase in operating costs and greater risks. Integrated mangrove-shrimp production gives a reasonable IRR (53%) but costs remain high, management demanding and risks uncertain. Risk adverse operators with short-term leases may favor traditional and extensive practices. Sustainable intensification, allied to social capital development and rehabilitation of mangrove ecosystem services and environmental flows, is needed to reconcile multiple demands

Improving the usage of fisheries statistics in Vietnam for production planning, fisheries management and nature conservation

The organisation of a fisheries statistical system dictates the potential usage of its information output. Information is used for planning of food production (fish as a commodity), for fisheries management (fish as a renewable natural resource), and for nature conservation (fish as an indicator for ecosystem quality). In this sequence, the required temporal, spatial and categorical resolution of data increases, while aggregation into meaningful ecological spaces requires a subtle way of organising the data flow. The effective usage of the present fisheries information of Vietnam is constrained by (1) its low categorical resolution and (2) the non-transparent aggregation of data into mere administrative spaces. Information requirements can be better articulated with the instalment of mandatory evaluation procedures at all levels in the fisheries administration. Our examples range from the national administration of the 4 million ton marine fisheries in Hanoi, to the local administration of a fishing commune in the Red River Delta.Categorical, temporal and spatial resolution Aggregation Monitoring Information requirements Evaluation

Nanoscale analyses of the surface structure and composition of biochars extracted from field trials or after co-composting using advanced analytical electron microscopy

Biochars have been recognized as an important material to improve soil properties. In a number of studies their beneficial properties have been found to increase with residence time in soil and during the composting process. The beneficial properties have been correlated with surface functional groups resulting from the interactions between char particles, inorganic and organic matter in the soil and soil biota. These interactions result in the formation of organo-mineral phases on the internal and external surfaces of the biochar. A paucity of information exists, particularly from longer-term field trials, on organo-mineral phases present on both the internal and external surfaces of the biochar. To characterize the structure of, and interface between, the carbon and mineral phases, we examined biochars recovered from two field trials and after composting from different countries using high resolution scanning electron microscopy (SEM), atomic resolution transmission electron microscopy (TEM) and scanning TEM (STEM), energy electron loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS) at resolutions of 1-20 nm. The work revealed the formation of porous agglomerates of different minerals/inorganic compounds bound together with organic compounds on the surfaces of the biochar. In some cases, these agglomerates were bound together to form organo-mineral associations. The analyses also showed that the organic compounds containing both N and C functional groups and mixed valence iron oxide nanoparticles are possibly interacting with the organic compounds. The analysis also showed the formation of pores at the interface of the carbon matrix and organo-mineral aggregates

Balanced harvest in the real world. Scientific, policy and operational issues in an ecosystem approach to fisheries

The concept of the Ecosystem Approach has entered the fishery harvesting discussions both from fishery perspectives (Reykjavik Declaration; FAO 2003 Annex to the Code of Conduct and from the principles of the Ecosystem Approach adopted by the CBD in 1995. Both perspectives establish the need to maintain ecosystem structure and functioning, whether for sustainable use of biodiversity (CBD) or simply to keep exploited ecosystems healthy and productive (fisheries). In response, the “Balanced Harvest” (BH) concept was suggested by a group of scientists brought together by the IUCN Fisheries Experts Group during the CBD CoP 10 in 2010. The meeting and the BH concept as consolidated there highlighted some of the collateral ecological effects of current fishing patterns and unbalanced removals of particular components of the food web, stimulating a critical rethinking of current approaches to fisheries management. The meeting on “Balanced Harvest in the real world - Scientific, policy and operational issues in an ecosystem approach to fisheries” (Rome, September 29-October 2, 2014) examined the progress made since 2010 on a number of fronts. It considered questions related to the scientific underpinning of the BH concept, including theory, modelling, and empirical observations. It began to explore the economic, policy and management implications of harvesting in a more balanced way