Modelling seasonal nutrient inputs from non-point sources across large catchments of importance to aquaculture

Accumulation of nutrients in aquatic systems can have negative impacts on water quality, which can then affect the performance and impact of an aquaculture system. Non-point sources (NPS) and runoff from different land use practices are a major contributor of nutrients to the aquatic environment. However, NPS loading is difficult to identify, and monitoring schemes are often insufficient, particularly across large areas. Aquaculture production areas often extend across large catchments, basins and deltas and knowledge of where there could potentially be higher nutrient loads in the environment would be advantageous to inform strategic site selection and management decisions. This study developed seasonal models within a Geographic Information system (GIS) that can be applied to large catchments of importance to aquaculture to identify areas at risk of nutrient loading from NPS which should be prioritized by monitoring schemes. The models were applied to case study areas in Bangladesh, China, Thailand and Vietnam. The results of the individual models reveal changes in the spatial distribution of priority areas depending on the nutrient (nitrogen or phosphorus) and season. The modelling approach presented here has the advantage that it can be applied to large areas without the need for complex data sets. The model and outputs can also be used to assess impacts of land use and land use change on aquaculture, determine site suitability, establish zones, inform carrying capacity studies and identify potential production and disease risks

Selective Pressure of Antibiotic Pollution on Bacteria of Importance to Public Health

Background: Many bacteria of clinical importance survive and may grow in different environments. Antibiotic pollution may exert on them a selective pressure leading to an increase in the prevalence of resistance. Objectives: In this study we sought to determine whether environmental concentrations of antibiotics and concentrations representing action limits used in environmental risk assessment may exert a selective pressure on clinically relevant bacteria in the environment. Methods: We used bacterial inhibition as an assessment end point to link antibiotic selective pressures to the prevalence of resistance in bacterial populations. Species sensitivity distributions were derived for three antibiotics by fitting log-logistic models to end points calculated from minimum inhibitory concentration (MIC) distributions based on worldwide data collated by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). To place bacteria represented in these distributions in a broader context, we performed a brief phylogenetic analysis. The potentially affected fraction of bacterial genera at measured environmental concentrations of antibiotics and environmental risk assessment action limits was used as a proxy for antibiotic selective pressure. Measured environmental concentrations and environmental risk assessment action limits were also directly compared to wild-type cut-off values. Results: The potentially affected fraction of bacterial genera estimated based on antibiotic concentrations measured in water environments is ≤ 7%. We estimated that measured environmental concentrations in river sediments, swine feces lagoons, liquid manure, and farmed soil inhibit wild-type populations in up to 60%, 92%, 100%, and 30% of bacterial genera, respectively. At concentrations used as action limits in environmental risk assessment, erythromycin and ciprofloxacin were estimated to inhibit wild-type populations in up to 25% and 76% of bacterial genera. Conclusions: Measured environmental concentrations of antibiotics, as well as concentrations representing environmental risk assessment action limits, are high enough to exert a selective pressure on clinically relevant bacteria that may lead to an increase in the prevalence of resistance

Heavy metal contamination of the sea cucumber Holothuria poli cultured in integrated multi-trophic aquaculture in a multi-use coastal area

The accumulation of heavy metals in the edible tissue of the white spot sea cucumber, Holothuria poli, revealed the transfer of metal contaminants to sea cucumbers when produced below fish cages in a Mediterranean port area. Sea cucumbers were cultured on the seafloor directly below a fish cage at 0 m, then at 10 m and at 25 m away from the cage, as part of an open-water integrated multi-trophic aquaculture (IMTA) system, and then at a reference site over 1 km from the fish farm, over a one-year period. At the end of the study, sea cucumbers and seafloor sediments were sampled from the IMTA sites near the fish cages, except at 0 m due to mass sea cucumber mortalities within the first month of the study, and again at the reference site. The concentrations of cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) were significantly higher in sediments near fish cages than the reference site. Localised enrichment from marine aquaculture could explain the significant concentration of metals in sediments below fish cages that are typically ascribed to their use in aquaculture. Arsenic (As), lead (Pb) and mercury (Hg), which are not associated with commercial fish diets, did not vary between sites. Concentrations of iron (Fe), which is available in commercial diets, were similar near fish cages and at the reference site. The body wall/muscle tissue of the sea cucumber. H. poli revealed high concentrations of the essential metals Fe and Zn near fish cages and in natural sediments at the reference site. H. poli can regulate these essential metals that characterised the edible tissue of the sea cucumbers. Non-essential metals like Hg and Cd had the lowest concentrations of all analysed metals in the sea cucumber tissue. However, the bioaccumulation of toxic metals, Hg and As, reveal the bioavailability of these contaminants in sediments and the propensity of bottom-dwelling sea cucumbers to bioconcentrate these metals, when cultured under a commercial fish cage in IMTA and elsewhere in natural sediments in this industrial environment. Holothuria poli did not exhibit bioaccumulation of Cu, Cr, Fe, Ni, Pb and Zn in its body wall/muscle tissue. The bioaccumulation of Hg and As reveal the need to account for the potential effects of farm-level variability throughout longer production cycles and bay-wide dynamics on sediment contamination and bioaccumulation in sea cucumbers until harvest. Site-specific dynamics in ports, whether natural or anthropogenic, can be expected to influence bioaccumulation of metal contaminants and therefore require long-term and fine resolution monitoring for better representation in open-water IMTA production

The evolution of aquaculture feed supply systems

First paragraph: As any fish farmer knows, feed is usually the most important variable production cost. A simple objective is therefore to minimize waste from uneaten food, which has the added benefit of reducing the risk of environmental degradation. However, decreasing feed level risks reducing growth rate, leadìng to a rise in other costs per unit of production. The optimum biological feeding rate is thus rarely the same as the optimum economic rate. In practice, these calculations are complicated as feed requirement and efficiency of conversion varies with changing environmental conditions including water temperature, oxygen concentration, water quality, current speed, light intensity and day length. Feed utilisation also varies with diet quality and physiological factors such as age/size, life-stage, stress level and endogenous rhythms. lt is therefore not surprising that these factors contrìbute towards an element of uncertaìnty regarding the amount of feed required, often leading to under or over feeding of stock and resultant under performance of the system

Scenario analysis and land use change modelling reveal opportunities and challenges for sustainable expansion of aquaculture in Nigeria

This study explores the critical factors of pond aquaculture development in Nigeria, and opportunities and challenges for sustainable expansion of the sector. Aquaculture’s role in food security especially in developing countries has been recognized, including its growth potential. However, Nigeria’s aquaculture development remains slow. Using Delphi technique, key factors influencing aquaculture were identified: availability/cost of aquafeed, land use change, government policy and climate change. Then scenario planning was used to develop four alternative but plausible pathways (scenarios) for Nigerian aquaculture development to 2035, depicting baseline, favourable, somewhat favourable, and unfavourable situations. For each scenario, future pond aquaculture production was estimated by modelling future changes in land use and pond yield potential. Government estimates suggest a potential of producing 2.5 million metric tonnes (t) of fish annually, but our results suggest Nigeria is unlikely to reach this estimate by 2035 without interventions. While the qualitative scenarios are useful to enhance discussions on potential interventions for improving aquaculture production and sustainability, the quantitative projections can be used for evaluating these interventions

A GIS-based decision support tool for optimisation of marine cage siting for aquaculture : a case study for the Western Isles, Scotland

Scotland’s coastal environment has many areas which are potentially suitable for sustainable aquaculture development. However previous studies have shown that aquaculture may have a detrimental impact on sensitive environments. The main objective of this study is to develop a holistic management tool for sustainable coastal marine aquaculture in the Western Isles of Scotland through development of a multi-faceted holistic model that allows consideration of sensitive environments. As the Scottish Government promotes better collaboration and integration of all involved in coastal zone governance (Baxter et al, 2008) this study illustrates the benefits to be gained from harmonized management of information in a Geographical Information System. GIS models are strong support tools designed to aid decision-making. The main strengths are that GIS can generate easily understandable visual displays of results which are based on robust models capable of incorporating vast amounts of spatial data and which can be predictive and can simulate future coastal environment scenarios. Within this study it is demonstrated that GIS-based models can successfully manage and manipulate a wide range of datasets that are essential components in the determination and management of suitable aquaculture locations. The GIS decision support tools evaluated and integrated in this study were based on four main sub models. These were Cage Site Suitability, Particulate Dispersion, Sensitivity Biodiversity Indicators and Visual Landscape Capacity. Exploration of a combination of these sub-models into an overall decision support system was also completed. All sub models developed were flexible, instrumentally coherent and communicatively balanced for the management and planning of the coastal environment . A sub-model was designed to evaluate and optimize the location of marine cage systems. This required development of data layers and modelled sub-components relevant to the important environmental and engineering factors affecting cage designs which included wave climate, bathymetric and substrate profiles. Three cage types were explored; those designed for sheltered, semi-exposed and exposed areas. These environmental factor layers were combined through weighting and Multi criteria evaluation consideration for each cage type. The resulting three sub-models indicated that while the archipelago has quite restricted development potential for cages designed for sheltered environments (91km2), there is a limited development potential for cages designed for semi exposed environments (1543km2) and an optimal potential for aquaculture development with cages designed for exposed environments (3103km2). The greatest potential environmental impact from aquaculture comes from particulate dispersion. Currently, assessing footprints of effect from fish farms is carried out on an individual site basis mostly at ten metre resolution. The sub-model successfully developed in this work resulted in a partially validated multisite particulate sub model at one metre resolution which implemented maximum current velocity as the friction/force image. The sub-model was run on a range of coastal loch fjord systems and demonstrated the variation in particulate dispersion patterns in each fjord system. In all the fjord systems modelled, even where farm sites are close neighbours, there appears to be minimal interaction in the particulate dispersion. While the particulate sub-model is effective and rapid to deploy for multiple sites, it requires further development in order to incorporate the quantitative aspects of particulate dispersion. Aquaculture biodiversity sensitivity indicators were evaluated and five main sub-components were developed; Species sensitive to Aquaculture, Endangered species, Species important to the Western Isles, important spawning and nursery areas and Protected Areas. The sub-model was constructed by combining these layers through weighting and Multicriteria evaluation. The outcomes indicated that within the study area there are 1168km2 (4% of study area) which are highly sensitive to aquaculture activity, although 20595km2 (65% of study area) has a biodiversity that is much less sensitive to aquaculture. This sub-model, and some of its components, can operate as a “stand alone” tool or can be combined into a larger framework. Little modification and re-parameterisation would be required to enable models to be developed to cover the whole of the Scottish coastline, or other coastal locations. Aquaculture can visually affect landscapes, seascapes and can adversely affect visual capacity of different areas. GIS was successfully applied to investigate this contentious issue. This comprehensive and flexible sub-model successfully develops Seascape and Landscape sensitivity analysis of aquaculture structures and also incorporated a novel approach to visual assessment through use of proportional assessment. Combining the sensitivity layers, 6448km2 of the waters of the archipelago (20% of study area) were categorized as having high capacity to incorporate new aquaculture developments, whilst 3301km2 (10% of study area) have a moderate capacity for new aquaculture structures and 1324km2 (4% of study area) have a low capacity for new developments. An overall conceptual framework was designed to explore two methods for the combination of the major sub-models in order to identify the most appropriate areas for sustainable aquaculture with consideration of possible conflicts including conservation issues. Initial evaluations involved the extraction of information from the component GIS sub-models into a structured database. The extracted data provides a range of information that can be used for statistical analysis and decision support, but which leaves the evaluation of the optimal siting of aquaculture at any location in the Western Isles in the hands of the database interrogator. The second method involved combining the sub-models within GIS whole considering trade offs in relation to conservation. This GIS combination of models indicated that, taking many factors into consideration, the Western Isles has 748km2 (2.5% of study area) appropriate for aquaculture development when implementing the C315 and whilst considering the interactions with conservation areas. There were 498km2 (1.6% of study area) appropriate for development when implementing the intermediate C250 cage types but only 15km2 (0.04% of study area) were appropriate for development based on the LMS cage designs for sheltered environments. Both analytical approaches had strengths and weakness and clearly both need to be used in combination to maximise the benefit of the GIS model outcomes. This study has demonstrated the ability to apply scientific rigour to spatial modelling of aquaculture problems including site suitability, biodiversity, landscape capacity and multi-site particulate dispersion. The various sub-models and their components sub-models can be stand-alone decision-making tools or combined into a holistic model which incorporates a flexible method of trade-off management. The range of GIS-based coastal analytical tools developed form the core of a decision support system that can enable the objective management of the increasing demands on the coastal zone, while having the capacity to bring together stakeholders, multiple agencies and governing bodies that are responsible for management and use of these precious and sometimes threatened resources.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Real-world waste dispersion modelling for benthic integrated multi-trophic aquaculture

In real-world situations, marine fish farms accommodate multiple fish species and cohorts within the farm, leading to diverse farm layouts influenced by cage dimensions, configurations, and intricate arrangements. These cage management practices are essential to meet production demands, however, farm-level complexities can impact model predictions of waste deposition and benthic impact near fish cages. This is of particular importance when the cages are used for integrated multi-trophic aquaculture (IMTA) with benthic feeders, where this waste not only affects environmental conditions but also provides a potential food source. The Cage Aquaculture Particulate Output and Transport (CAPOT) model incorporated multiple species, cohorts, and cage arrangements to estimate waste distribution from a commercial fish farm in the Mediterranean between October 2018 and July 2019. This spreadsheet model estimated dispersion for individual fish cages using a grid resolution of 5 m x 5 m. The study categorized discrete production periods for each fish cage every month, aligning with intermittent changes in biomass and food inputs due to different cage management practices throughout production. This approach facilitated the use of detailed input data and enhanced model representativeness by considering variations in cage biomass, food types, settling velocities, and configurations. Model outputs, represented in contour plots, indicated higher deposition directly below fish cages that varied monthly throughout fish production cycles. Deposition footprints reflected changes in cage biomass, food inputs, and farm-level practices reflecting this real-world scenario where aquaculture does not follow a production continuum. Moreover, cohort dynamics and cage movements associated with the cage management practices of the fish farm influenced the quantity and fate of wastes distributed around fish cages, revealing variability in deposition footprints. Clearly, these findings have important implications for the design of benthic IMTA systems, with species such as sea cucumber and polychaetes. Variability in waste deposition creates challenges in identifying where the benthic organisms should be placed to allow optimal uptake of waste to meet their food requirements and increase survivability. Evidently, models have an important role to play and this study emphasizes the need for representative input data to describe actual food inputs, cage biomass changes, and management practices for more representative farm-scale modelling and essentially to improve particulate waste management. To effectively mitigate benthic impacts through IMTA, models must quantify and resolve particulate waste distribution and impact around fish farms to maintain a balanced system with net removal of wastes. Resolving farm-level complexities provides vital information about the variability of food availability and quality for extractive organisms that helps improve recycling of organic wastes in integrated systems, demanding a more representative modelling approach

Real-world waste dispersion modelling for benthic integrated multi-trophic aquaculture

In real-world situations, marine fish farms accommodate multiple fish species and cohorts within the farm, leading to diverse farm layouts influenced by cage dimensions, configurations, and intricate arrangements. These cage management practices are essential to meet production demands, however, farm-level complexities can impact model predictions of waste deposition and benthic impact near fish cages. This is of particular importance when the cages are used for integrated multi-trophic aquaculture (IMTA) with benthic feeders, where this waste not only affects environmental conditions but also provides a potential food source. The Cage Aquaculture Particulate Output and Transport (CAPOT) model incorporated multiple species, cohorts, and cage arrangements to estimate waste distribution from a commercial fish farm in the Mediterranean between October 2018 and July 2019. This spreadsheet model estimated dispersion for individual fish cages using a grid resolution of 5 m x 5 m. The study categorized discrete production periods for each fish cage every month, aligning with intermittent changes in biomass and food inputs due to different cage management practices throughout production. This approach facilitated the use of detailed input data and enhanced model representativeness by considering variations in cage biomass, food types, settling velocities, and configurations. Model outputs, represented in contour plots, indicated higher deposition directly below fish cages that varied monthly throughout fish production cycles. Deposition footprints reflected changes in cage biomass, food inputs, and farm-level practices reflecting this real-world scenario where aquaculture does not follow a production continuum. Moreover, cohort dynamics and cage movements associated with the cage management practices of the fish farm influenced the quantity and fate of wastes distributed around fish cages, revealing variability in deposition footprints. Clearly, these findings have important implications for the design of benthic IMTA systems, with species such as sea cucumber and polychaetes. Variability in waste deposition creates challenges in identifying where the benthic organisms should be placed to allow optimal uptake of waste to meet their food requirements and increase survivability. Evidently, models have an important role to play and this study emphasizes the need for representative input data to describe actual food inputs, cage biomass changes, and management practices for more representative farm-scale modelling and essentially to improve particulate waste management. To effectively mitigate benthic impacts through IMTA, models must quantify and resolve particulate waste distribution and impact around fish farms to maintain a balanced system with net removal of wastes. Resolving farm-level complexities provides vital information about the variability of food availability and quality for extractive organisms that helps improve recycling of organic wastes in integrated systems, demanding a more representative modelling approach

Feeding behaviour of the prawn Macrobrachium rosenbergii as an indicator of pesticide contamination in tropical freshwater

The purpose of this research was to develop and standardize a novel feeding bioassay with Macrobrachium rosenbergii for use in the laboratory and allowing it to be easily deployed under field conditions. Standardization of the test aimed to minimize feeding rate variations and to ensure that subsequent statistical analyses have sufficient power to consistently detect changes in feeding rates. These were accomplished through the development of a post-exposure feeding toxicity test under laboratory, microcosm and in situ/field conditions. This procedure was proven to be repeatable and economical. M. rosenbergii as test animals were available in terms of quantity and uniformity in sizes. The standard guidelines and procedures for M. rosenbergii bioassay developed from this study include the size of test animals (9-10 mm), density in exposure containers (10 animals in 500 mL of medium in the laboratory, 10 animals in field chambers with 98.6 mL volume), exposure time (24 hours), feeding period for post-exposure feeding (4 hours) and number of replicates for the feeding test (10 replicates for individual measurements). The tiered approach used in the preliminary risk assessment of pesticide using TOXSWA was capable of screening the risk level of pesticide in the study area, identifying profenofos and dimethoate as test chemicals for the lethal and sub-lethal experiments. This model was beneficial in the preliminary risk assessment of pesticides in the tropics, since it was not necessary to set up laboratory work. This method could also provide preliminary data to support the environmental planner and decision/policy maker. This is an alternative way to develop a cost efficient model to inform and warn the risk of pesticide use. The effects of pH, temperature and hardness on control post-exposure feeding rates of M. rosenbergii were assessed and indicated that M. rosenbergii was very sensitive to acidic and basic conditions. The use of post-exposure feeding inhibition as the endpoint under laboratory conditions revealed that prawns were sensitive to pesticides (chlorpyrifos, dimethoate and profenofos) and a heavy metal (zinc). Post-exposure feeding rate inhibition could be used as a sublethal endpoint as the EC50 values obtained for chlorpyrifos and zinc were lower than their lethal levels. Mortality of prawn was also another endpoint used to define the toxicity of pesticides such as carbendazim, in which mortality occurred during exposure, but post-exposure feeding rate of the surviving animals did not decrease. The microcosm experiments were able to link the laboratory toxicity tests and the effects observed in the field. Microcosm studies provided another dimension to studies looking at pesticide effects on aquatic systems. In this research, carbendazim affected feeding and survival rates in the microcosm set-up but in the laboratory only mortality showed a significant difference (P < 0.05). In situ bioassays were able to show the effects of pesticides on post-exposure feeding rates using the methods developed. Post-exposure feeding rates were significantly lower than control in farms using pesticides while in uncontaminated sites (pesticide-free), the post-exposure feeding rates did not decrease. However, mortality was observed even in the uncontaminated sites which could be attributed to other factors such as low dissolved oxygen and presence of some other unidentified chemical substances. The degree of mortality and the effect on feeding rates depends not only on the type and concentration of the known pesticide but also on water quality parameters. The basic methods developed for in situ bioassay from this research is a simple, easy and fast way to determine the effect of pesticides because the results can be seen in the field. The procedures developed and results obtained from this study can be used as a basis for further toxicity studies on M. rosenbergii and other potential tropical species.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

European lobsters utilise Atlantic salmon wastes in coastal integrated multi-trophic aquaculture systems

In this study, we investigated if juvenile European lobsters Homarus gammarus would eat waste from Atlantic salmon Salmo salar cages in a coastal integrated multi-trophic aquaculture (IMTA) setup and if there were any impacts on growth. Trophic interactions between salmon and lobsters were assessed using δ15N and δ13C stable isotope analysis and fatty acid profiling from fish feed as indicators of nutrient flow. Analysis revealed that lobsters directly utilised particulate waste from salmon production, as levels of indicator fatty acids from salmon feed were significantly higher in lobster tissues near the fish cages compared to the control site. Route of uptake may have been direct consumption of waste feed or faecal material or indirectly through fouling organisms. Stable isotope analysis did not indicate nutrient transfer to lobsters, suggesting that the duration of the study and/or the amount of waste consumed was not sufficient for stable isotope analysis. Lobsters grew significantly over the trial period at both sites, but there was no significant difference in lobster growth between the sites. Our results show a trophic relationship between salmon and lobsters within this IMTA system, with no apparent advantage or disadvantage to growth