REVIEW OF AQUACULTURAL PRODUCTION SYSTEM MODELS

The success and profitability of aquaculture production is highly dependent on the proper management employed during the culture period. This management is synonymous with water management since water of suitable quality and quantity is a pre-requisite for any successful aquacultural production. The knowledge of the environment (water) enhances better management. However, the complexity of an aquaculture system which result from multiple interactions makes it difficult to predict how the aquatic community will respond to changes with simple methods of analysis, especially if the methods address a single stressor at a time. These necessitated the development of numerous aquatic ecosystem models such as the Fish Simulation Culture Model (FIS-C), Tilapia Farming Support Tool (TFST), Farm Aquaculture Resource Management (FARM), Pond-Water Availability Period (PWAP) model, AquaFarm and Raceway design and simulation system (RDSS)),which have been used for years as tools to interpret, predict and better understand water quality changes. This paper reviewed existing simulation models of aquacultural production systems with the aim of adopting a suitable one for predicting the environment, performance of African cultured indigenous fish species under different management scenarioes. The reviewed models were found to have addressed specific problem that pertain to some foreign species, production systems and locality. There was none that could be used to model the effects of different management scenario and their effects on African Catfish (Clarials gariepinus) cultured in intensive static aquacultural system. Hence, the problem of predicting the environmental condition, so as to determine point of diminishing returns and optimize yield in an economical way still remains elusive for most fish farms in Nigeria. There is therefore a serious need to develop models that can predict the effects of environment on the performance of indigenous fish species. This will aid stake holders in predicting different management scenario so as to achieve a better crop (fish) yield. http://dx.doi.org/10.4314/njt.v35i2.2

GIS-based site selection and dynamic modelling of Magallana oyster in the Sado Estuary, Portugal

A case study was developed to assess the viability of Portuguese oyster (Magallana angulata) and Pacific oyster (Magallana gigas) aquaculture in the Sado Estuary, Portugal. It applies an integrative methodology for site selection of shellfish aquaculture, complemented with a farm-scale carrying capacity model to evaluate production, environmental effects and socio-economic outputs. The site selection methodology uses a Multi Criteria-Evaluation (MCE) through Geographic Information Systems (GIS) software. When combined, both tools generate a holistic overview of aquaculture opportunities to support strategic planning decisions. The used MCE in this study, considers suitability factors based on water quality and food sources, as well as subsequent factors describing socio-economic and product quality suitability. Combining these to the regulatory and spatial constraints in the study area, a final site selection map was generated, screening out suitable areas for aquaculture. The dynamic model, FARM – Farm Aquaculture Resource Management, was later applied to the identified suitable areas for aquaculture practice, where the production and environmental effects of two different locations were estimated and compared at a farm-scale level. This methodology illustrates how GIS-based models may be used in conjunction with farm-scale carrying capacity models to assist decision-makers in developing a sustainable approach to aquaculture

Mussel farming production capacity and food web interactions in a mesotrophic environment

Low trophic aquaculture (LTA), such as bivalve farming, offers promising avenues to supply sustainable seafood and aquafeed. While bivalve farming usually occurs in highly productive coastal areas which already support numerous human activities and suffer from environmental pressures, numerical tools offer a promising avenue to explore and assess biomass production potential and associated ecosystemic impacts for further development of the industry and prospection of new exploitation sites. In this study, we coupled an ecophysiological model, the dynamic energy budget theory (DEB), with an ecosystem model (NORWECOM.E2E) to simulate blue mussel Mytilus spp. farming production and effects based on the food web in the mesotrophic Hardangerfjord in western Norway. We tested several levels of fjord-scale farming intensity and assessed 2 production purposes: aquafeed and human consumption. Results suggested the Hardangerfjord could host large-scale mussel farming for both purposes. However, large exploitation schemes displayed detrimental effects on individual mussel growth (39% less wet mass after 2 yr) and especially on secondary production (decrease of 33% after 1 yr) due to acute trophic competition. Simulations showed short production cycles for aquafeed were more efficient to exploit primary production, since young and small mussels have lower maintenance and reproduction costs. Dissolved nutrient inputs from salmonid farms had marginal effects on primary production (<2%). However, salmonid and mussel farming activities could compete for the sites with the highest production potential.publishedVersio

Sustainable aquaculture in Saldanha Bay, South Africa

Saldanha Bay, located near the coastal town of Saldanha, in Western Cape Province of South Africa, possesses excellent conditions for mussel and oyster aquaculture. Its linkage with the adjacent upwelling current system provides a very productive environment for phytoplankton growth, and this has led to the development of a vibrant shellfish aquaculture industry. The main objectives of this work are to develop a model which simulates the main ecological processes within the Bay, to determine the Bay’s carrying capacity for mussel and oyster production, and to produce a management tool for decision making. Bivalve aquaculture has great growth potential and may be important for human food security as mankind faces a projected need of an additional 30 X 106 tonnes per year of aquatic products by 2050. Bivalve aquaculture is organically extractive, and can additionally provide significant ecosystem services in top-down control of eutrophication, and creation of structure for stimulating biodiversity. When managed properly, this form of aquaculture has a very low environmental footprint, mainly associated with organic enrichment of the sediment. This impact is even less relevant in upwelling systems such as Saldanha Bay where particles tend to be flushed out in the surface layer, and in all cases it must be borne in mind that by definition shellfish aquaculture results in a net removal of seston from the water column. This model was developed using EcoWin an object oriented approach to ecological modelling. The model for Saldanha Bay was set up using oceanographic and water quality data collected from Saldanha Bay, and culture practice information provided by local shellfish farmers. The first step was the construction and calibration of the ecological model, in order to provide a general description of the biogeochemical behaviour of the Bay, followed by the addition of the shellfish aquaculture component. EcoWin successfully reproduced the key ecological processes, correctly simulating a mean phytoplankton biomass of 7.5 chl a L-1. The aquaculture module simulated an annual harvested biomass of about 3000 t y-1, in good agreement with reported yield. Six production scenarios were explored, for illustrative purposes: - Increase in stocking density of shellfish - Two alternatives for aquaculture development in particular areas of Saldanha Bay - Prediction of the maximum production capacity of the Bay. These results were analysed in terms of their impacts and potential.This study demonstrates the relevance of aquaculture-oriented ecological models in evaluating different stakeholder-defined development scenarios, and their utility in avoiding the social and environmental impacts of testing different scenarios in situ. The present application of EcoWin shows great potential for supporting both water managers and industry in Saldanha Bay

Goods and Services of Marine Bivalves

The aim of this book is to review and analyse the goods and services of bivalve shellfish. How they are defined, what determines the ecological functions that are the basis for the goods and services, what controversies in the use of goods and services exist, and what is needed for sustainable exploitation of bivalves from the perspective of the various stakeholders. The book is focused on the goods and services, and not on impacts of shellfish aquaculture on the benthic environment, or on threats like biotoxins; neither is it a shellfish culture handbook although it can be used in evaluating shellfish culture. The reviews and analysis are based on case studies that exemplify the concept, and show the strengths and weaknesses of the current applications. The multi-authored reviews cover ecological, economic and social aspects of bivalve goods and services. The book provides new insights for scientists, students, shellfish producers, policy advisors, nature conservationists and decision makers. This book is open access under the CC BY license.publishedVersio

Revisiting ecological carrying capacity indices for bivalve culture

Ecological carrying capacity (ECC) indices for bivalve culture rely on key ecosystem turnover rates: 1. clearance time (CT), the time needed for the cultured bivalves to filter the entire bay volume; 2. renewal time (RT), the time required to replace the entire bay volume with external water; and 3. production time (PT), the time needed for phytoplankton biomass renewal via local primary production. These turnover rates are conceptually straightforward but lack measurement standardizations in the context of ECC assessments. This study compares simple turnover rate methods with more complex approaches designed to address key assumptions and improve accuracy. Method comparisons were performed across multiple embayments (systems) in Prince Edward Island, Canada. When crop aggregation and system-scale refiltration effects were considered, CT increased by a factor of 14 to 22 depending on the system and species under cultivation. Seasonal temperature considerations further impacted CT by a factor of 38 to 142. Regarding RT, validated hydrodynamic models and tidal prism models produced remarkably different outcomes; the tidal prism approach underestimated RT by 77–94% across the studied systems. Conversely, PT was unaffected by contrasting phytoplankton parameterization; pre-aquaculture (1969–1970) and contemporary (2011−2012) datasets led to similar PT outcomes. However, other metrics revealed a contemporary shift towards low phytoplankton biomass and smaller phytoplankton cells (picophytoplankton); these observations suggest that PT provides insufficient granularity regarding microalgae biomass replacement. Overall, the study rejects a common assumption that the bay-scale turnover rates serving the conventional CT/RT and CT/PT indices can be easily and accurately parameterized; these indices should be used cautiously in assessing the sustainability of farming activities.publishedVersio

Development of tools for the management of oyster nurseries: static and dynamic modelling

Ecological models have been applied for carrying capacity assessments of oyster aquaculture, and have shown to be very useful in guiding the planning and management towards production optimization. However, the existing models are mostly directed to the grow-out phase (production of adult oyster), lacking models to be applied in nurseries (production of juvenile oyster). This work presents two models to support the management of oyster nurseries that are targeted to farmers: - A static mass balance model for oyster nurseries, which estimates the maximum stock for typical external food concentrations of the nursery. Part of the work developed herein contributed to its development (available online at: http://seaplusplus4.com/oysterspatbud.html). - A dynamic model for oyster nurseries, which simulates the individual growth, food availability and stock evolution over time. The model was conceptualized and implemented as part of this work, and further validated with three data sets from the scientific literature. In this work, it is shown the application of both models to simulate a commercial nursery. The results show that both models can provide useful information, and thus guidance to farmers, even when there is a lack of data or knowledge about some features of the system, required to properly drive the models