Net cages are mainly located on the coastal areas of Peng-hu and Ping-tung counties. Generally, there are two kinds of disasters occurred in the fish farming industries: one is caused by typhoon attack, while the other is caused by human vandalism. This paper is focus on how to prevent the damages induced by poaching or vandalism. Since high-valued fish are raised in the net cages, they are often become the targets of illegal intruders for stealing at night, especially when the net cages are lack of security system. Under such unsecured situation, entrepreneurs would not dare to invest in this industry and may keep a suspicious attitude towards it. Compare to land aquaculture, marine aquaculture is far more complicated in terms of techniques involved in production progress. Surely over-fishing has serious deplete the stock of biomass in the sea in the past decades. Recently, the skyrocketed oil price even deteriorate the fishing industry to such a level that fishing boats can only operate for a season in each year and end up losing money. However, Fisheries Agency has planned to recycle commercial fishing boats, and hopefully by doing so, this aquacultural industry will turn into a new trend in the near future. This research looks into 700 hectares of net cage park, Southern Oceanic Park, and suggests that the fishery authority turn this area into special district, adjust the fishery law, designate San-fu port as the park¡¦s operation center, finally set up a security system, then we may reduce the damage caused by unlawful activities. The geographical make-up of Liu-chiu provides ideal conditions for the present net cage area. The sea waters outside of San-fu port are also blessed with the same geographical advantage. This research looks at ¡§man-made calamities¡¨, namely vandalism and theft, so as to prevent damage and loss and protect resources and equipment. The areas chosen for this study include the surrounding sea waters of Liu-chiu aquaculture zone and the highly representative San-fu fishing port. There are also discussions on the installation of automatic alarm system in the eventual marine park. As an officer in a law enforcement administration for coastal affaires, my past contact with net cage fishermen revealed the damage and loss they have been undergoing and their sense of helplessness. On top of that, relevant documents turned out to be insufficient. Therefore, this research aims to figure out a way to fill this security gap by integrating public power from governmental services with protection and safety solutions on the part of individuals. To put this initiative to work, it is necessary to map out a special marine park where security mechanism could be automatically triggered by local facilities. This will then allow public power and personal endeavor to work simultaneously in the special zone and prevent any illegal activities. With its high applicability and pertinence, the eventual security system will hopefully entice more entrepreneurs, thus maintaining a sound net cage aquaculture.

Aquaculture plays an increasingly important role in food production as the catches of wild fish stocks continue to decline on a global scale through overfishing. However, the rapid development of intensive cage aquaculture in particular, which requires high inputs of energy, food and capital, can result in adverse effects on the environment. While spatial distribution and sediment loading models for particulate wastes from marine fish cages have been under development for more than 10 years, the models still contain numerous assumptions that limit their usefulness. These include the use of very limited data for fish feed and faecal pellets sinking rates that take no account of food manufacturer, type or size or environmental conditions. The present study provides information on a range of pellet types for three of the most important European farmed fish species (i.e. Atlantic salmon Salmo salar L., sea bream Sparus aurata, sea bass Dicentrachus labrax) that may be readily incorporated into models. Such data, combined with validation of predictions through in situ field investigations is designed to help improve the accuracy and usefulness of solid waste dispersal models. The studies comprise four main sections, i.e., quantifying food and faecal pellet characteristics, examining nutrient leaching rates from uneaten food and fish faeces, determining resuspension characteristics of uneaten food, modelling of solid wastes dispersion and thus the development of environmental tools. Existing literature relating to environmental impacts of cage aquaculture is reviewed and the key factors highlighted. Two preliminary studies provided information on the influence of gravity acceleration on settling velocity determination and appropriate techniques for monitoring the rate of nutrient leaching from faecal wastes. Settling velocities of Atlantic salmon diets were significantly greater at 20 psu salinity than at 33 psu and significantly higher for most pellet types at 10°C than, at 20°C. Settling velocities for unsoaked salmon diets were found to increase with pellet size, from a mean of 5.6 cm s-1 for the smallest pellet (2 mm) to 13.9cm s-1 for the 10 mm standard (20 to 24% fat) pellets. Settling velocities of extruded diets for sea bream and sea bass diets ranged from 3.9 to 10.6 cm s-1, broadly similar to those for salmonid diets. Settling velocities of salmon pellets were not significantly affected by immersion time (0 - 15 min). Given the water depths at fish cage sites and the settling times involved, it is concluded that it is unnecessary to take account of changes in food pellet settling velocity as a result of immersion. Freshly net-collected salmon faecal pellets appeared to consist of fine solid material approximately the size of the formulated diets. The range of salmon faecal settling velocities was 3.7 to 6.2 cm s-1 (mean = 5.3 cm s-1) at 15°C and 33 psu. There are no significant differences in nutrient leaching of carbon and nitrogen from all six salmon diets after 20 min immersion in sea water. However, a rapid loss of faecal nutrients occurred 2.5 to 10 min after immersion in sea water. Total C and total N were found to leach by as much as 22% and 26%, respectively, after 5 min immersion during one sampling occasion. Experiments conducted in a large-scale flume tank showed the critical resuspension velocities of a range of commercial fish feeds were between 8.63 cm s-1 and 9.53 cm s-1. Above the critical resuspension speed, pellets moved by saltation, i.e. traveling along the sediment by rolling, sliding or hopping on the bed. The velocities of pellet resettlement ranged between 0.79 cm s-1 and 3.98 cm s-1 under the critical resuspension speeds. Field trials, involving the deployment of sedimentation traps, showed a general relationship between sedimentation of material and distance from cages, i.e. more sedimented material was associated with sampling sites closest to the cages. The spatial changes in sedimentation rates in the first trial were between 15.4 and 31.7 g DW m-2 d-1 at 30 m and 10 m stations, respectively. Values in the second trial (38.5-65.5 g DW m-2 d-1) were twice those in the first trial, but followed the same pattern. The model presented in this thesis is a combination of a spreadsheet model (Microsoft Excel 6.0) and Surfer plot program (Golden Software Ltd., ver. 6.04). Excel is used to prepare basic mathematical operations behind the model, including a mass balance submodel and use of a formula for calculating dispersion of uneaten food and faeces on the sea bed developed by Gowen et al. (1989). The operation of the waste dispersion model for marine cages takes into account the various settling characteristics of waste particles. It was verified with a set of in situ sedimentation data obtained from the field trial described above. Results described the waste dispersal around the vicinity of the cage farm. For the future, it is intended that further validation and optimisation of the model will be carried forward by a combination of both increasing user involvement and incorporation of data from comprehensive studies as these become available. Together, these will contribute to reducing and remedying the environmental impacts of future development.

Lake Malawi is a great lake not only because of its size (30,800 km2) but also because of its unique fish diversity. The lake contains the highest number of freshwater fish species in the world. The fish species are hypothesized to have radiated within the lake, which is 1-2 million years old. The collapse of the capture fishery in Lake Malawi between the 1970s and 1990s led to the launch of cage culture of indigenous fish species in 2004 in the south east arm of the lake. While cage culture has been practiced for many years in temperate lakes and seas, the fish farm in Lake Malawi is the first in the African Great Lakes and, therefore, not much information currently exists that is relevant to the impact of cage culture on such a large, species-rich tropical lake. Consequently, a study was done between January and December, 2007, at the fish farm in Lake Malawi to determine potential impacts of cage wastes on the environment. The study found that, just like in temperate systems where 70-87% of C, N and P added through feed get dispersed into the environment, discharges from fish cages in Lake Malawi were between 71-88% of the nutrients added through feed. The discharges were proportional to the amount of feed added so that as production and feed supply increase over time, more cage wastes would be generated and released into the environment. The discharges were exacerbated by poor stocking and feeding regimes. Production periods were longer (mean of 376±42 days) than if recommended stocking and feeding rates were followed. Feed quality may also have affected production performance and waste generation in the cages, but was not studied. The cage wastes were incorporated into the food web and support the wild fishes in the vicinity of the fish farm. Impacts of the cage wastes on the water column and sediments in the vicinity of the cages were minimal during the study period, probably because of rapid and efficient dispersion of the wastes by strong water currents, that averaged 9.3 cm s-1, through the cages and high consumption of the cage wastes by large numbers of wild fishes which aggregated around the cages. The wild fishes also helped to disperse the cage wastes over a larger area through consumption, translocation and defecation. However, as production increases, the amount of cage wastes generated may overwhelm mitigation by dispersion by water currents and consumption by wild fishes, particularly if many cages are deployed close together and interfere with current flows. Based on my observations, a fish farm that produces 15,000 tonnes fish/yr in Lake Malawi would generate 1249, 113 and 21 megamoles/yr of C, N and P, respectively, that are comparable or higher than DOC, TDN and TDP loadings observed in the most disturbed large river systems draining into Lake Malawi. The impacts of these river systems in Lake Malawi have been well documented, particularly around river mouths and in the more densely populated and shallower southern portion of the lake, where algal communities and their sedimentation rates have begun to change. Cage culture discharges may accelerate these changes.

Lake Malawi is a great lake not only because of its size (30,800 km2) but also because of its unique fish diversity. The lake contains the highest number of freshwater fish species in the world. The fish species are hypothesized to have radiated within the lake, which is 1-2 million years old. The collapse of the capture fishery in Lake Malawi between the 1970s and 1990s led to the launch of cage culture of indigenous fish species in 2004 in the south east arm of the lake. While cage culture has been practiced for many years in temperate lakes and seas, the fish farm in Lake Malawi is the first in the African Great Lakes and, therefore, not much information currently exists that is relevant to the impact of cage culture on such a large, species-rich tropical lake. Consequently, a study was done between January and December, 2007, at the fish farm in Lake Malawi to determine potential impacts of cage wastes on the environment. The study found that, just like in temperate systems where 70-87% of C, N and P added through feed get dispersed into the environment, discharges from fish cages in Lake Malawi were between 71-88% of the nutrients added through feed. The discharges were proportional to the amount of feed added so that as production and feed supply increase over time, more cage wastes would be generated and released into the environment. The discharges were exacerbated by poor stocking and feeding regimes. Production periods were longer (mean of 376±42 days) than if recommended stocking and feeding rates were followed. Feed quality may also have affected production performance and waste generation in the cages, but was not studied. The cage wastes were incorporated into the food web and support the wild fishes in the vicinity of the fish farm. Impacts of the cage wastes on the water column and sediments in the vicinity of the cages were minimal during the study period, probably because of rapid and efficient dispersion of the wastes by strong water currents, that averaged 9.3 cm s-1, through the cages and high consumption of the cage wastes by large numbers of wild fishes which aggregated around the cages. The wild fishes also helped to disperse the cage wastes over a larger area through consumption, translocation and defecation. However, as production increases, the amount of cage wastes generated may overwhelm mitigation by dispersion by water currents and consumption by wild fishes, particularly if many cages are deployed close together and interfere with current flows. Based on my observations, a fish farm that produces 15,000 tonnes fish/yr in Lake Malawi would generate 1249, 113 and 21 megamoles/yr of C, N and P, respectively, that are comparable or higher than DOC, TDN and TDP loadings observed in the most disturbed large river systems draining into Lake Malawi. The impacts of these river systems in Lake Malawi have been well documented, particularly around river mouths and in the more densely populated and shallower southern portion of the lake, where algal communities and their sedimentation rates have begun to change. Cage culture discharges may accelerate these changes.

In recent years, the fishery production has been drastically decreased in Taiwan, mainly due to overfishing and coast pollutions, therefore fishermen and corporation are encouraged by government to invest in ocean cage aquaculture. However the high price fishes in the net cage are often coveted, so the incidences of fish stealing and net cage breaking were found occasionally, which cause great economical loss. Security guards or visual monitoring system has limited effect especially in the night when these intrusions occur. This study is based on acoustic measure to build a net cage alarm system, which includes the sonobuoy and monitor station on land. The sonobuoy is a passive sonar that collects the sounds near the net cage and transmits the suspected signal to the monitor station. The signals were analyzed by the control program on the personal computer in the monitor station, and the alarms at different stages could be activated by the sound levels and durations of the analyzed signals.

This research focuses not only on the interaction between the floating platform for cage aquaculture and the waves but also on the incident wave¡¬s energy transformation. The floating platform was simulated with a 1:30 physical scale model in the hydrodynamic laboratory. A total four wave gages and one load cell were used in this study: two wave gages installed in the upstream of the platform, one gage in the net cage and one gage in the downstream side of the platform; while one load cell measuring the mooring line tension at the anchor. All of the measurements were recorded in the data acquisition system for further analyzing reflected waves, transmitted waves, the wave height in the net cage, and the correspondent mooring line tensions. Furthermore, the movement of the platform and volume deformation of the fish net are recorded by the video camera, and then analyzed by the image processing method. First, the true color images were transferred into grayscale images, and then passed through mean filter, noise filter and median filter step by step. Finally, a weighted-algorithm was used to calculate the coordinates of the desired point form the resulted image matrix. Thus, the motion of the floating platform and the volume deformation of the fish net can be obtained by analyzing the variation of these points captured through the image processing procedure. For the ability of resistance to wave attack for a floating platform, it often estimated by inspecting the reflection and transmission coefficients of the platform. Besides the function of wave resistance ability, the stability of the floating platform, maximum tension in the mooring lines and the net volume deformation coefficient are also important factors for optimum design of a cage platform. According to the results of this research, we conclude some important facts as below: (1) For short-period waves, the net mesh size and twine diameter have influenced the magnitude of reflected waves and the motion of platform; and it makes little difference in the transmission coefficients, wave height ratios inside of net cage, and the maximum tension force in the mooring cable. (2)With the respect of transmitted wave coefficients: the wave transmission phenomena are not obvious for short-period waves, but these phenomena will gradually increase when the incident wave periods are getting longer. (3)Under the pure wave test condition, the net volume deformation coefficients are about 1% only, which means that the deformation of the fish net does not change at all, and it may be due to the overweight of the bottom frame. (4) Tension-leg type mooring system seems able to provide better stability of the platform than catenary type mooring system.

The research focuses on the application of site selection for cage aquaculture in Taiwan by developing the site evaluation DSS (Decision Support System). The modeling aspect of the system belongs to the domain of multi-criteria decision theories, which AHP (Analytic Hierarchy Process) and Fuzzy Set theory were used. Two case studies based on real world and hypothetical data were conducted to verify the integrity of the system. According to the literature review and the interview with several domain experts, various impact factors were identified first. The corresponding weights of each factor were then decided by analyzing the questionnaires designed based on the concept of AHP. The following work was to evaluate those impact factors based on the experience of domain experts using some appropriate approaches. To represent the domain knowledge, it is appropriate to use rule based inference system. Besides, fuzzy set theory was chosen to describe the antecedent and consequence of the rule base due to the considerations of uncertainty from human experts and ocean field data. Several related mythologies derived from the fuzzy set theory were used, such as the operation of fuzzy composition, determination of suitable membership function, fuzzy relationship matrix, fuzzy inference, defuzzification, and fuzzy pattern classification. All impact factors were categorized into three different types of membership functions that were designed specifically for the site selection of cage aquaculture. The consequence in the rule base, which is the site suitability, was also represented as the unique membership function. To calculate the fuzzy relationship matrix, the current research found that the operation of ¡§algebraic product and bounder sum¡¨ would produce better results than the commonly used ¡§max-min¡¨ operation. Each impact factor would have the associated fuzzy relationship matrix derived from the rule base. The site suitability in term of a fuzzy set can then be inferred by the fuzzy composition of current situation of the factor and the relationship matrix. By multiplying the AHP weight and the fuzzy suitability, the final site suitability index, taking all the impact factors into consideration, can therefore be derived. The real data in Feng-Gang, located in the southern Taiwan, were collected and evaluated using the site selection DSS. The results show Feng-Gang is suitable for the development of cage aquaculture, which is validated by the current prosperous business locally in cage aquaculture. As for the evaluation of multiple sites, 18 hypothetical sites near shore around Taiwan were chosen to calculate the corresponding suitability indexes, which were then be partitioned into several groups using the fuzzy pattern classification. Based on the results, the sites that were classified in the same group have similar cultivation conditions, which also proves the applicability of the site evaluation DSS.

This paper is to investigate the wave-induced dynamic properties of the floating platform for cage aquaculture. Considering the calculation efficiency and its applicability, this problem is simplified by: (1) assuming the flow field is inviscid, incompressible and irrotational; (2) the form drag and inertia drag on the fish net is calculated by the modified Morison equation (or Morison type equation of relative motion), including the material and geometric properties; (3) the moorings is treated as a symmetric linear spring system and the influence of hydrodynamic forces on the mooring lines is neglected; and (4) the net-volume is assumed as un-deformable to avoid the inversely prolonging computing time because the mass of fish net with is too light comparing with the mass of floating platform and cause the marching time step tremendously small to reach the steady-state condition which may lead to larger numerical errors (e.g. truncation errors) in computation. The BIEM with linear element scheme is applied to establish a 2D fully nonlinear numerical wave tank (NWT). The nonlinear free surface condition is treated by combining the Mixed Eulerian and Lagrangian method (MEL), the fourth-order Runge-Kutta method (RK4) and the cubic spline scheme. The second-order Stokes wave theory is adopted to give the velocity on the input boundary. Numerical damping zones are deployed at both ends of the NWT to dissipate or absorb the transmitted and reflected wave energy. The velocity and acceleration fields should be solved simultaneously in order to obtain the wave-induced dynamic property of the floating platform. Thus, both the acceleration potential method and modal decomposition method are adopted to solve the wave forces on the floating body, while the wave forces on the fish net are calculated by the modified Morison equation. According to Newton¡¦s second law, the total forces on the gravity center of the floating platform form the equation of motion. Finally, the RK4 is applied to predict the displacement and velocity of the platform. Firstly, the NWT is validated by comparing the wave elevation, internal velocity and acceleration with those from the second-order Stokes wave theory. Moreover, the numerical damping zone is suitable for long time simulation with a wide range of wave depth. The simulated results on wave-body interactions of fixed or freely floating body also indicate good agreement with those of other published results. Secondly, in the case of the interaction of waves and the floating platform, the simulated results show well agreement with experimental data, except at the vicinity of resonant frequency of roll and heave motions. This discrepancy is due to the fluid viscous effect. To overcome this problem and maintain the calculation efficiency, an uncoupled damping coefficient obtained by a damping ratio (£i=0.1 ) is incorporated into the vibration system. Results reveal that responses of body motion near the resonant frequencies of each mode have significant reduction and close to the experimental data. Moreover, the results are also consistent well with experiments in different wave height, mooring angle, water depth either with or without fish net. Therefore, the suitable value of the damping ratio for the floating platform is £i=0.1. Finally, the present model is applied to investigate the dynamic properties of the floating platform under different draft, width, spacing, spring constant, mooring angle and depth of fish net. Results reveal that the resonant frequency and response of body motion, mooring force, reflection and transmission coefficients and wave energy will be changed. According to the resonant response, the platform with shallower draft, larger width, longer spacing between two pontoons, smaller spring constants, or deeper depth of fish net has more stable body motions and smaller mooring forces. Irregular wave cases are presented to illustrate the relationship with the regular wave cases. Results indicate that the dynamic responses of body motion and the reflection coefficient in irregular waves have similar trend with regular waves. However, in the irregular wave cases, the resonant frequency is moved to the higher frequency. Similarly, resonant response function is smaller but wider, which is due to the energy distribution in the wave spectrum.

Lake Victoria is known for its cichlid fish species flock of 500 or more, which have been drastically decreased due to mass extinction. The lake's fisheries transformed from artisanal to industrial, with exotic species displacing the indigenous flock, changes linked to local and global anthropogenic consequences. Cage aquaculture has been established in the lake as a result of dwindling catch fisheries, a growing human population, and increased demand for fish. This dissertation investigates: 1) the distributional ecology of fishes along a limnological gradient in Lake Victoria, Kenya; and 2) the effects of cage aquaculture in the lake on limnology and fish communities, as well as the scientific and social correlates of proper implementation and growth. In April/May and July/August 2017, fish distribution patterns in the lake were surveyed using gillnets at eleven littoral sites and trawls at thirty lake-wide locations. From November 2018 to July 2019, four sites arrayed on an inshore-offshore gradient were sampled using paired cages and control stations. Using established protocols, water quality variables were sampled and analyzed. The status of variables and their associations were investigated using descriptive and exploratory statistics in the R statistical programming language. There was a limnological gradient, with nutrient concentrations, chlorophyll-a, and turbidity decreasing dramatically from the inner gulf to the outer waters. In the gulf's eutrophic waters, indigenous catfishes and cyprinids were abundant, while Nile perch and haplochromines were abundant in the open less eutrophic waters. Along the inner gulf-open lake gradient, Nile perch population structure, size at 50% maturity, and feeding patterns differed. There were no significant variations in environmental metrics between the paired cage farms and the controls, implying that inputs like sewage and agricultural runoff contribute more to eutrophication and the state of the gulf. Near cages, the average monthly total fish biomass was higher than in control areas. In the inner gulf, non-haplochromine fishes were many and diversified, with some species being particularly prevalent near cages. Based on biophysical constraints and overlap between cage aquaculture, fisheries, and biodiversity conservation in the lake, it was projected that cages could yield 250,000 metric tons of Nile tilapia per year. The findings indicate that, when correctly managed, cage aquaculture in Lake Victoria has a positive impact on both biodiversity and economic prosperity in the region.

Understanding cage aquaculture adoption decisions and factors affecting adoption is necessary to ensure that fish production from cage aquaculture in Ghana is both significant and sustainable. The goal of this study was to provide a framework for understanding cage aquaculture adoption decisions and to identify factors affecting adoption, to inform decision makers as they formulate policies aimed at promoting cage aquaculture adoption in Ghana. I surveyed 122 respondents comprising current cage fish farmers, farmers who have abandoned cage aquaculture, and potential adopters of cage aquaculture such as, fish traders, fishermen and land-based fish farmers. Respondents answered questions related to knowledge, interest, constraints in cage aquaculture, and demographics. I used non-metric multidimensional scaling and discriminant function analysis to identify unique groups within the respondents, classify respondents according to their position in the innovation-decision continuum, and identify factors affecting cage aquaculture adoption. Based on their differences in knowledge and interests, I placed respondents into one of three stages of the cage aquaculture innovation-decision process model I developed: (1) Unawareness, (2) Knowledge, Persuasion, and Decision (KPD), and (3) Implementation (Confirmation and Abandonment). Respondents in the KPD and Implementation stages had knowledge, were more interested in cage aquaculture, and were aware of constraints in cage aquaculture, whereas respondents in the Unawareness stage lacked knowledge and interest in cage aquaculture, and did not clearly understand the constraints. Respondents who were males, belonged to the tribes Ewe and Akan, and who had fishing experience tended to be more interested in cage aquaculture. The lack of capital, high input costs, inability to adequately market fish, theft, lack of information sources, conflict over water use, and cage destruction by storms, were identified as the main constraints to cage aquaculture adoption in Ghana. The results of the study suggest that programs aimed at encouraging new entrants into cage aquaculture should focus on demographic characteristics such as gender, and tribe. However, demographic characteristics may affect adoption decisions and it may be important to consider them as such. Some recommendation to address the major constraints in cage aquaculture include: the Fisheries Directorate should (1) develop an efficient extension program that farmers can access regularly, especially, for farmers with no other information sources, (2) provide feed subsidy to enable farmers produce fish at competitive prices, (3) facilitate the formation of fish farmers' cooperative groups that would purchase large quantities of feed, (4) encourage local production of high quality fish feed, and (5) develop credit facilities that can be accessed by individuals interested in cage aquaculture to assist potential farmers who would, otherwise, not be able to adopt cage aquaculture . In addition, fish farmers should (6) be proactive in marketing their fish by identifying potential niche markets prior to production, and (7) join cooperative groups to ease the burden of accessing loans to increase production. / Master of Science