Poor quality seed is the major constraint limiting both the productivity of potato crops and the expansion of the potato industry in Vietnam. Despite numerous attempts to establish a certified seed system, the most practical solution is to import clean foundation seed of the desired variety and physiological age. With imports from Europe and North America proving to be immature and too expensive, Western Australia (WA) has emerged as a potential source of high quality seed. While seed imports from WA are unique in that the varieties imported have been selected by researchers in Vietnam as being suited to the agro-ecological environment in the Red River Delta (RRD), no assessment of the economic benefits to smallholder potato farmers from the use of WA potato seed has been undertaken. In 2006/08, the yield and profitability of three potato varieties Eben, KT3 and Atlantic in two locations were compared where the crops had been derived from new seed imported from WA (VN0), seed derived from crops cultivated in the RRD after one generation (VN1) and two generations (VN2). There was a significant difference in the yield produced between the three different seed sources but not between the locations. For all varieties, and in both years, the yield decreased with the number of multiplications in Vietnam. Furthermore, the marketable yield declined significantly from the first crop (VN0) to the third crop (VN2). The decline in yield and tuber quality with each successive generation was associated with an increase in PVY and PVX infection. Not unexpectedly, differences in yield and marketable yield between the seed generations had a significant impact on the gross income for each variety. / VN0 seed of all varieties produced the highest gross income (VND 2.4 to 4.1 M/sao) compared to VN1 (VND 1.9 to 3.1 M/sao) which was significantly higher than VN2 (VND 1.4 to 2.4 M/sao). However, while high quality seed is more productive, it is also more expensive. As a result, significant differences were observed between the seed costs. VN0 seed was almost two times more expensive (VND 10,500 – 11,000 per kg) than VN1 and VN2 seed (VND 6,000 – 6,500 per kg). Despite the higher costs, VN0 seed provided the highest net incomes compared to VN1 which was significantly higher than VN2. Farmers who retained seed received a higher net income (VND 0.13 – 0.6 M/sao) than those who did not retain seed. Ways to improve the accessibility of affordable, high quality potato seed to farmers in the RRD are discussed.

Graduation date: 1998

The Eastern stock of Atlantic bluefin tuna (Thunnus thynnus thynnus) has experienced a steep decline, 74.2%, in recent decades, mainly driven by large unreported catches and growth of the capture-based aquaculture of this species in the Mediterranean. This study addresses the potential food-web effects on trophic linkages in the ecosystem through the removal of both small pelagic fish species and wild bluefin tuna (BFT) for capture-based aquaculture operations. An Ecopath model of the Southern Catalan Sea (Western Mediterranean) was modified to include a BFT farm supplied entirely by the area modeled (Coll et al, 2006). Six scenarios were developed to simulate possible changes to the system using Ecosim, including the continued growth of aquaculture operations, as well as changes to the total allowable catch for BFT as set by ICCAT. Species not directly connected with the production of BFT showed large fluctuations in biomass and yield as a result of these simulations. Using these models, increases in biomass of lower trophic level functional groups were observed with reductions in biomass from other top trophic level predators. Jellyfish and benthopelagic fish exhibited an increase in biomass, the largest being 8.76% for jellyfish and 69.76% for benthopelagic fish, while wild BFT biomass decreased 87.26%. Atlantic bonito and swordfish showed similar rates of decline in biomass levels. These outcomes stress that fishing at top trophic levels can have unforeseen outcomes on the structure of the ecosystem, due to the complexity of the food web. Capture-based aquaculture of Atlantic bluefin tuna can be expected to increase along the proposed scenario levels, due to the decision not to place this species on Appendix I of CITES during the CITES meeting of 2010. This study suggests that farming activity has additional impacts on the ecosystems that should be taken into account when evaluating the suitability of this industry and projecting the trends towards the future. Results suggest that, in the case of the Western Mediterranean Sea, increasing BFT farming activities will likely contribute towards further degradation of an already highly exploited marine ecosystem. The development of hatchery technology to close the life cycle and produce juvenile BFT for stocking cages as well as using artificial diets during the grow out stage are required to minimize long-term impacts and support industry expansion.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2004. / Thesis documentation sheet inserted. Appendix reprints five manuscripts and papers co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.

Thesis (Ph. D.)--Texas State University-San Marcos, 2006. / Vita. Appendices: leaves 119-142. Includes bibliographical references (leaves 143-147).

Fuelwood is an important source of domestic energy in rural regions of Brazil. In the Zona da Mata of Minas Gerais, native species from the Atlantic Forest are an important source of fuelwood, supplemented by wood from eucalyptus and coffee plantations. The use of native species is complicated by their increasing scarcity and the recent enforcement of forest policies that prohibit the felling of even dead natives trees without a permit. In this study, the factors contributing to the use of fuelwood in this region, despite the simultaneous use of liquid petroleum gas in most households, are explored by examining fuelwood use patterns in four small rural communities in the Zona da Mata Mineira using household surveys and semi-structured interviews. Two hypotheses were tested using a Jacknife regression. The first hypothesis, based on the energy ladder model, tested the predictive power of socioeconomic status in relation to fuelwood use. Two dependent variables were used to represent the importance of fuelwood to a household: the amount of time a household spent collecting fuelwood (Effort) and the number of purposes a household used fuelwood for (Class of Fuelwood Use). Socioeconomic status did explain a statistically significant percentage of the variance in Effort, but not in Class of Fuelwood Use. The second hypothesis tested for a moderating effect of the availability of fuelwood on the relationship between the socioeconomic status of a household and the dependent variables. The interaction between access to fuelwood and socioeconomic status was shown to explain a significant percentage of the variance in Effort, thereby indicating that the effect of socioeconomic status on time spent collecting fuelwood depends on access to fuelwood. However, there was no statistically significant interaction found between Class of Fuelwood Use and fuelwood availability. The Atlantic Forest Policy was found to have little influence on domestic energy decisions made by surveyed households. Few research subjects had a good understanding of the basic tenets of this policy and the Forest Police do not have adequate resources to enforce the policy at this level.

A hierarchical classification system of Iceland's watersheds and rivers is presented. The classification is based on Iceland's substrate, climate, water, biota, and human cultural influences. The geological formations of Iceland are very different in character depending on their age and formation history. Three major types of formations occur: Tertiary, Plio-Pleistocene, and Pleistocene. These formations have different hydrological characters and different landscapes. There are also large differences in the climate within Iceland. Four major river types are found in Iceland: spring-fed rivers in Pleistocene areas, direct runoff rivers in Plio-Pleistocene areas, direct runoff rivers in Tertiary areas and wetland heath rivers in Tertiary areas. Eleven biogeoclimatic regions occur in Iceland, each having a different watershed type. The classification together with life history theory can explain the distributions, abundances, and life history strategies of Icelandic salmonids. Oceanic conditions must also be considered to explain the life history patterns of anadromous populations. When the freshwater and marine habitat is stable, the life history patterns of individuals in a population tend to be uniform, one life history form being most common. In an unstable environment many life history forms occur and the life span of one generation is long. The properties of the habitat can further explain which life history types are present. In the most stable and favorable rivers of Iceland resident life history forms are more common. Such a classification of a river habitat greatly aids the understanding of the habitat and how it enables and constrains the salmonid populations within it. Consequently adaptations in life histories are better understood and conservation, utilization, and management of these valuable natural resources are made more coherent and efficient. / Graduation date: 1991

Commercial harvest of sh stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional di erences in the e ectiveness of sheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scienti c trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important sheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of ground sh populations. A positive abundance-occupancy relationship was estimated for the majority of ground- sh populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to sheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable shing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

The green porcelain crab, Petrolisthes armatus, has recently invaded oyster reefs of the South Atlantic Bight at mean densities of up to several thousand individuals m-². Despite the crab’s tremendous densities and wide-spread occurrence, its population dynamics, the reasons for its success, and its ecological impacts have remained unknown. We used field monitoring in two estuaries of coastal Georgia to assess spatial and temporal patterns of distribution, demographics, reproduction, and effects on native crabs. We used field and mesocosm experiments with constructed oyster reef communities of varying native species richness and adult porcelain crab additions to assess why the invader is successful and how it impacts native species and communities. We found P. armatus distributed throughout the estuaries, primarily in the lower regions and low intertidal. Sex ratios were 1:1 throughout the year. During warmer months mean densities ranged from 1,000-11,000 crabs m-², 20-90% of mature females were gravid, and numerous recruits were present. Despite decreases in density of 64->99% in the winter, populations rebounded in the spring. Maximum mean densities were 37 times the highest densities ever recorded and population fecundity exceeded that of the native range by an order of magnitude, but correlations did not show significant negative effects of P. armatus on native crabs. Field experiments suggested that invasion was successful due to tremendous recruitment overwhelming biotic resistance by native species richness or predation. The crab only needed structure to invade, but the presence of adult conspecifics significantly enhanced recruitment (i.e., intraspecific “invasional meltdown”). We documented several impacts on native biota, including the (1) suppression of oyster growth, benthic algal biomass, native crab recruitment, and native goby densities and the (2) enhancement of bivalve recruitment, macroalgal cover, and survivorship of oyster drills. We did not, though, see an effect on native taxonomic richness. The large direct and indirect effects of P. armatus on growth, survivorship, and recruitment of virtually all of the most common native species on oyster reefs in the short-term (4-12 weeks) and at relatively low experimental densities (750-1500 crabs m-²) imply considerable long-term consequences for a major hard-substrate habitat of the South Atlantic Bight.

Fuelwood is an important source of domestic energy in rural regions of Brazil. In the Zona da Mata of Minas Gerais, native species from the Atlantic Forest are an important source of fuelwood, supplemented by wood from eucalyptus and coffee plantations. The use of native species is complicated by their increasing scarcity and the recent enforcement of forest policies that prohibit the felling of even dead natives trees without a permit. In this study, the factors contributing to the use of fuelwood in this region, despite the simultaneous use of liquid petroleum gas in most households, are explored by examining fuelwood use patterns in four small rural communities in the Zona da Mata Mineira using household surveys and semi-structured interviews. Two hypotheses were tested using a Jacknife regression. The first hypothesis, based on the energy ladder model, tested the predictive power of socioeconomic status in relation to fuelwood use. Two dependent variables were used to represent the importance of fuelwood to a household: the amount of time a household spent collecting fuelwood (Effort) and the number of purposes a household used fuelwood for (Class of Fuelwood Use). Socioeconomic status did explain a statistically significant percentage of the variance in Effort, but not in Class of Fuelwood Use. The second hypothesis tested for a moderating effect of the availability of fuelwood on the relationship between the socioeconomic status of a household and the dependent variables. The interaction between access to fuelwood and socioeconomic status was shown to explain a significant percentage of the variance in Effort, thereby indicating that the effect of socioeconomic status on time spent collecting fuelwood depends on access to fuelwood. However, there was no statistically significant interaction found between Class of Fuelwood Use and fuelwood availability. The Atlantic Forest Policy was found to have little influence on domestic energy decisions made by surveyed households. Few research subjects had a good understanding of the basic tenets of this policy and the Forest Police do not have adequate resources to enforce the policy at this level.