Thesis (M.S.) -- Central Connecticut State University, 2006. / Thesis advisor: Timothy Rickard. "... in partial fulfillment of the requirements for the degree of Master of Science in Geography." Includes bibliographical references (leaves 78-86). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 157-168).

Thesis (M.S.)--University of California, Santa Cruz, 2003. / Includes bibliographical references (leaves 71-77)

Thesis (M.S.) in Marine Bio-Resources--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 34-39).

The introduced species Oreochromis mossambicus was studied to determine biological and ecological factors which may underly the rapid initial distribution of the species from its introduction in the 1950's to the relatively low catch rates experienced in recent years. Actual yield, determined from catch statistics for all species, was significantly lower than theoretical yield, based on formulae developed from other similar river systems. The importance of O. mossambicus to the fishery was indicated by the proportional contribution of this species to the catch (approximately 50%). Fluctuations in catch may be related to changes in water levels with a significant decrease in O. mossambicus catch as the water levels rose and this species moved onto the floodplain areas. Analysis of stomach contents revealed a predominance of diatom species, algae and flocculent detritus. There were some differences in diatom species consumed between sites and season although the general food quality was thought to be good based on monthly condition factors. Reproductive traits were similar to those found in other areas. Females incubated the fertilised eggs orally and behavioural differences were noted from changes in sex ratios and mean size caught each month. Condition of females was significantly lower during the dry season post spawning which could relate to the behavioural trait of mouthbrooding when females do not feed. Mean fecundity was low (475 per 100g body weight) and there was evidence of bimodal peaks in spawning activity which corresponded to rising and falling water levels. Growth throughout the year was not significantly affected by the potential changes in food availability created by the degree of floodplain inundation and an increase in allochthonous food sources. Scale rings were found to be fonned bi-annually and may correspond to increased feeding prior to spawning. CPUE varied between sites but was low overall and von Bertalanffy growth parameters indicated that males reached a larger maximum size than females over the same time period (L∞ = 35 and 26.56 respectively). Total mortality was relatively high (Z = 0.56/yr) but figures may relate to local conditions only since many habitats and environmental conditions would be represented in a river of the size of the Sepik. The potential impact of proposed introductions of fish to the river are discussed with regard to management issues.

Lake Victoria contributes more than 60% of the total fish yield in each of the respective riparian countries, Kenya, Uganda and Tanzania. Nile perch Lates niloticus contributed more than 60% to the total yield from the lake. Although accused of causing ecological instability of the ecosystem due to its predatory effects, the fishing industry became socially and economically dependable on the Nile perch. In the mid 1990s signs of overfishing were observed and concerns for the sustainability of the fishery were raised. To properly manage a fishery, knowledge of the factors that regulate the dynamics of the stock(s), their abundance and distribution is essential. Unfortunately data on the status of the Nile perch stocks are inadequate. This study was conducted on the Tanzanian part of Lake Victoria from 1997 to 2001 to address this problem. Reference is also made to the Kenyan and Ugandan national waters for comparison. Bottom trawl and catch assessment surveys were conducted to assess the status of the stocks. Abundance estimates and distribution patterns were determined. Current exploitation levels and practises were analysed and linked to growth and mortality, feeding and reproductive characteristics of the stock to determine status. Key environmental parameters were investigated and linked to the variations in the biological aspects and distribution patterns observed. There was an indication of reduced anoxic problems in the offshore deep waters and signs of improvement in the eutrophic state of the lake. Mean oxygen concentrations in the waters sampled varied from 8.02±0.73 mg L⁻¹ in the surface waters to 3.2±4.36 mg L⁻¹ in the bottom waters of 68 m deep, while Secchi disk readings at stations of 5-10 m depth ranged from 0.84±0.3 m in November to 1.9±1.02 m in August/September and in offshore waters of 50-6Om depth the readings were 3.08±0.62 m in February to 5.52±1.7 m in August/September. Distribution patterns of fish were highly aggregated but variable and were greatly influenced by seasonal patterns of oxygen and temperature, while reproduction and recruitment were related to rainfall patterns. Using the swept area method, biomass was estimated at 306,000 t for the Tanzanian waters and around 620,000 t for the whole lake, with a mean density of 9.87 t km⁻² and 10.56 t km⁻² respectively. Very high fishing mortality (1.55 yr⁻¹) and exploitation rates (0.84) were estimated using an L∞ of 218 em TL and a growth constant (K) of 0.16 estimated during the study. Excessively high fishing effort was observed in the 2000 frame survey while catch compositions reveal high dependence on juveniles for the Nile perch fishery. The size at first maturity was at 54.3 cm TL (1.6-yr.) and 76.7 em TL (2.5 yr.) for males and females respectively. About 83% of the catch survey data were below size at first maturity for males and 99% for females. Bottom trawl data (88% juveniles) suggested high recruitment in the stock. However the models indicated unsustainable exploitation of the fishery. A reduction of exploitation rate by 50% and increase of size at capture for optimum yield is recommended. The dominance of juveniles in the catch with the current yields (estimated at 138 323.85±6 229.14 t) higher than the sustainable yield (calculated at 108941.9 t yr⁻¹, using Cadima's formula) demands immediate management initiatives. Co-management is singled out as the most effective option for a functional system to implement control, monitoring and surveillance strategies within management process. With dynamic systems within the stocks, the environment as well as socioeconomic influences, and with continuous monitoring, adaptive and precautionary management strategies are recommended. Without reliable catch trend data it is difficult to confidently make predictions. The need to have a well-structured catch assessment survey system for reliable catch statistics is recommended. Priority areas to further research are also identified.

Nam Theun 2 hydropower dam was selected for this study to assess how local communities respond to hydrological changes and examine the impacts of these changes to ecology and livelihoods of people around the Nakai reservoir and downstream in the Xe Bang Fai River. The results confirmed that fish and Other Aquatic Animals (OAAs) are essential sources of food and income generation of both reservoir and downstream Xe Bang Fai River households. People living around the reservoir and river consume fish and OAAs almost every meal. Fish and OAAs account for 62% (54% in reservoir and 70% in river) of animal protein intake. Reservoir households, which have limited land and poor soil for rice cultivation, rely on the reservoir fishery not just for subsistence but also for generating income to buy rice for consumption. By contrast, the households living further downstream along the Xe Bang Fai River are likely to own more land and fertile soil for agriculture, and the artisanal fisheries are mainly for consumption, but they also sell part of their catch when they have excess or during the high fishing season at the start of the wet season. The results from the study indicate that the impacts of trans-basin hydropower dams on the ecological functioning and livelihoods of people are significant. The impacts from climate change in the study areas and elsewhere are minor in comparison with the impacts from mainstream and tributary dams. Nam Theun 2 dam has changed the hydrological regime of the Xe Bang Fai River, destroyed the riverbed and disrupted dry season refuge habitats. Many high value species that initially resided in the reservoir have disappeared and are replaced by small and carnivorous species such as Channa striata , as well as alien species such as Oreochromis niloticus and Cyprinus carpio. However, it is unclear whether the species composition in downstream areas has changed because fishers are still learning to adapt to high and strong flows or many fishers have shifted to fish in small streams and swamps as they are concerned about safety issues. Fishers in the reservoir have adapted to the new environment and lifestyle by diversifying their income sources, by opening small village shops, trading and labouring to supplement their income from reservoir fishing. The downstream fishers have more opportunities and more diverse livelihood activities to cope with the hydrological changes and adverse weather. Although rice farming is the most important activity for the downstream villages, most of their immediate cash comes from livestock, in particular large ruminants that provide their main sources of income. However, they also sell some of their daily catch to help purchase foods and maintain food security. The study highlights the need to provide financial and technical assistance for the affected households; to assist them starting new alternative livelihood activities aiming to supplement the declining fish catches in the reservoir and river. These livelihood activities include ecotourism and services, cultivating organic vegetable, working in clothes and agricultural processing factories, promoting One District One Product, and aquaculture. The promotion of reservoir fisheries as an alternative livelihood may be good in the short term, but for the long term and sustainable use of fishery resources, there is a need to look for other options outside fisheries and balance between the need for food security and protection of fisheries resources for future generations. Although the reservoir fishery can support production it requires more investment, thus it is necessary to protect habitat in small streams and rivers in the headwaters of the reservoir to ensure fish can use these habitats for spawning. In the river, critical habitats, such as deep pools and floodplains vital to the Mekong fisheries need protection. Maintaining connectivity between the mainstream and floodplains is also necessary, allowing fish free access to spawning, nursery, feeding and refuge habitats to complete their lifecycles. These protections can be instigated at different scales, such as local, national and regional levels, with participation from local communities and institutions concerned with the fisheries. At the regional level, it could be achieved through the trans-boundary fisheries management framework being developed by the Mekong River Commission.

The impact of watergate operation on hydrology and habitat, and their effects on fish migration, fish diversity, population structure, and recruitment of fisheries resources were studied in the Nam Kam River system, a tributary of the Mekong in Thailand. The factors that influence the migration of fish were identified and the effectiveness of fish passage facilities installed at watergates in the river system were investigated. The flow regime and flood cycle were modified by watergate operation, which is designed to control floods in the wet season and retain water for irrigation in the dry season. Fluctuations in flow and water level were created and varied along the river in the wet season. Timing, frequency and duration of floods in each habitat down the river were altered. Operations for irrigation removed low flows and created longer periods of no flow in the dry season. The river becomes stagnant and water levels in the floodplains above the watergates are higher than pre-construction. Many new nursery and feeding habitats were created after construction, but water abstraction also disconnected the floodplain below the watergate and the mainstem river. Flow modification driven by watergate operation for flood control is likely to delay water level rise at the onset of the flood in the downstream area that trigger upstream migration of fish into the Nam Kam River system, especially pangasids. The watergate operation limits the upstream migration of adult fish at the onset of the flood season and inhibits the upstream migration of late migrating species, the downstream migration of fish, and drifting of eggs, larval and juvenile fish since all sluice gates were closed at the end of the flood season. Longitudinal migrating species are more likely to be impacted than lateral migrating species and this will impact on the overall population structure of fishes. Several longitudinal migratory white fish species, main channel residents and main channel spawners declined in abundance or were absent in the upstream area above Thoranit Naruemit Watergate and it most likely resulted from hydrological alteration driven by watergate operation. Fish larvae and juvenile fish in this river system were dominated by resident grey and black fish, while recruitment of white fish species was limited as watergate operation obstructs the upstream migration of adult fish during the spawning season. Diversity of fish in the river decreased from downstream to upstream area, it shows a negative relationship with number of barriers. The relative abundance of white fish was significantly different between the floodplain above and below Thoranit Naruemit watergate during the study period. Seasonal distribution of fish in the Nam Kam River system is different from the free-flowing Songkhram River. At the end of flood season, diversity of fish in the regulated river was high since larvae and juvenile fish and many white and grey fish species are stranded in the floodplain above the watergate after sluice gates were completely closed. These fish have subsequently adapted to feed and grow in the poor habitat conditions during the dry season. Genetic study of two target species, Hemibagrus nemurus and Osteochilus hasselti, indicates high genetic diversity and big population sizes maintained by gene flow from the downstream populations and nearby populations when the watergates are opened. Populations of the two target species in the most upstream lake, Nong Han, are contributed by migrating fish from Mekong River and resident populations with in the river system. Rate of migrations, small genetic distances and genetic differentiations between subpopulations of the target species support the occurrence of gene flow in this river; many subpopulations have little genetic differentiation between samples although there is the series of barriers in the river system. By chance, population size of the two migratory species migrating through the Thoranit Naruemit and Suraswadi fish passes were relatively big and bigger than populations along the river suggesting that upstream migration of target species is only partially limited by watergate operation. This is probably because the Nam Kam River is a rather short river and gene flow in the river system was supported by the operation schedule that fully open the watergates in flood season and the fish pass operation at the onset and the end of flood season. Thus, the most important things that need to be addressed to maintain fisheries resources in this river system are watergate and fish passage operations. Fish passage facilities in the Nam Kam support migration of more than 135 fish species and mitigate the impact of delayed watergate opening on the recruitment of fish in this river system. However, the operational schedule needs to be adjusted since fish can only use the fish passes when the sluice gates are closed or partially opened dring high river discharge in the wet season. Upstream migration is only completely unobstructed when the watergates are open to maximum capacity. The watergate and fish passes management schemes in the river system are key important factors to mitigate the impact on hydrological changes and habitat changes, to enable free movement of fish through the river system and enhance the fisheries in the Nam Kam River system. Recommendations for watergate and fish pass operation based on the integrated knowledge gained from this study are provided.

The level of stress imposed by population pressure, handling and live transportation on planted catchable-sized rainbow trout in a northern Utah stream was examined. Production of adrenocorticotrophin, as measured by interrenal ascorbic acid and serum cortisol levels, did not occur in transported or planted fish. Dead or moribund fish collected from stream or live boxes comprised 13 percent of the 2,000 fish planted. Aeromonas salmonicida, the causative agent of furunculosis, was isolated from 41 percent of 106 moribund fish sampled. In addition, 39 percent of the samples exhibited bacterial growth other than A. salmonicida. Apparently, handling, transportation, and planting did cause low levels of stress sufficient enough to induce stress-mediated diseases such as furunculosis.

Thesis (Ph.D.)--University of Iowa, 2002. / Includes bibliographical references.