All estuarine crabs have two larval stages, the zoea and the megalopa. Zoeae are entirely planktonic, whereas megalopae begin as plankton before beginning to search for settlement substrates as late stage megalopae. At both stages, crab larvae are subject to environmental conditions of the estuary. With changing environmental conditions due to anthropogenic activities and climate change, an understanding of how these planktonic larvae respond to environmental conditions is necessary for understanding subsequent larval supply to benthic populations and implication for fisheries management and habitat restoration. For this dissertation, I: 1) analyzed long-term timeseries in the lower Chesapeake Bay for spatial and temporal change in zoeal abundance and to identify the environmental drivers of these changes; 2) examined effects of climate and environmental conditions on long-term change of dominant crab zoeae in the lower Chesapeake Bay; 3) investigated how warming temperatures in the Bay affect phenology of dominant crab zoeae; and 4) conducted a field experiment in the lower Bay to characterize settlement pattern of megalopae and determine environmental predictors of settlement. Zoeal assemblages of the lower Chesapeake Bay were characterized by distinct assemblages in the tributaries versus the mainstem Bay. Zoeae of the estuarine mud crab (Rithropanopeus harrisii) and fiddler crabs (Uca minax and Uca spp.) dominated in the tributaries, whereas a more diverse assemblage of crab zoeae, including larvae of the mud crab Hexapanopeus angustifrons, pea crab Pinnixa sayana, blue crab Callinectes sapidus, squatter pea crab Tumidotheres maculatus, and fiddler crabs Uca spp. were dominant taxa in the mainstem. Salinity was the single most important factor explaining patterns in the composition of zoeal assemblages in space and time. Variability in total zoeal abundance and richness in both regions was also significantly related to salinity. Abundance of four dominant species, Callinectes sapidus, Hexapanopeus angustifrons, Dyspanopeus sayi, and Pinnixa chaetopterana, in the mainstem significantly decreased from 1985-2002, while no significant trend was observed for dominant species in the tributaries. Variability in abundance of dominant zoeae was significantly related to the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO), which likely influenced zoeal abundance via streamflow into the Bay. From 1968 to 2002, I found no significant effect of warming on phenology of the zoeae of dominant species, except Rhithropanopeus harrisii, which had an earlier start of season (date of 10% of highest peak of abundance) as water temperature increased. in a field experiment, settlement of C. sapidus megalopae was episodic, beginning in mid-July and extending into November. in contrast, the settlement periods of R. harrisii and D. sayi were shorter than C. sapidus, begining in early-July and ending in early October. Local conditions, especially salinity and water temperature, were as important as factors associated with transport processes (e.g., tidal range, wind direction, lunar phases) in determining settlement of crab megalopae. This dissertation illustrated that zoeal assemblages and successful settlement of megalopal stage of crabs in the lower Chesapeake Bay were sensitive to changes in environment conditions. These changes in zoeal abundance and settlement success have important implications for adult populations of estuarine crabs.

Food web models are one tool used by resource managers to evaluate changes in trophic interactions in response to changes in biotic and abiotic drivers in an ecosystem. Food web modeling provides a range of potential outcomes for managers to consider, to use in fisheries management. However, it is well known that food web models require large amounts of disparate data, which can amplify uncertainties in model output. Previous studies have leveraged stable isotope data to compare the trophodynamics between modeled trophic levels and in situ data. Here, we provide a new framework to aid users in evaluating the level of agreement between trophic levels generated from food web models and from stable isotope data using a Bayesian statistical approach. Using a previously developed food web model from coastal Louisiana as a case study, this paper presents an updated framework to use stable isotope analysis as a validation method for food web models. The validation process included Spearman-rank correlation analyses in addition to developing and using the first open-source food web model validation visualization tool, EcoTuneR, this webtool provides a more accessible way visualize the Bayesian derived trophic level probability curves with the food web model trophic levels. Reported correlation between the stable isotope trophic levels and the food web model trophic levels were comparable to previous studies (functional group Spearman-rank correlation, R=0.56, n=47, p > 0.001 | niche-aggregated R=0.77, n=17, p > 0.001 | age-aggregated R=0.53, n=34, p > 0.001). Results of the Bayesian model showed that 47% of the food web model species functional groups fell within the 95% credibility intervals of the Bayesian derived stable isotope trophic levels. Acknowledging that all modeling studies have limitations, this case study provides a framework and a new tool for researchers to better consider uncertainties in data and the inherent variability in coastal ecosystems.

The blue crab (Callinectes sapidus) is a commercially and ecologically importantspecies found along the Atlantic coast of North and South America. These crustaceans play a critical role in coastal ecosystems, serving as both predators and prey in the food web. The blue crab supports a major fishery in Chesapeake Bay, where the species is a cultural icon. Juvenile blue crabs, the smallest and most vulnerable size classes of individuals, are reliant upon structurally complex habitats. Population dynamics of this species are therefore influenced by spatiotemporally fluctuating environmental variables, such as habitat availability. Understanding blue crab ecology is essential for managing their populations sustainably and maintaining the health of their habitats. The primary aim of this dissertation was to quantitatively evaluate the contributions of several widely distributed habitats to blue crab population dynamics in Chesapeake Bay. Empirical valuation of nursery habitat effects on blue crab population dynamics can (i) estimate the optimal extent of habitat required for the long-term sustainability of blue crab fisheries, (ii) quantify how changes in habitat extent will affect blue crab populations, such as alterations due to climate change, and (iii) inform ecosystem-based fisheries management (EBFM) decisions, as a complement to stock assessments. Here, I present four separate but interrelated studies examining habitat-specific demographic rates at multiple spatial and temporal scales. These studies involved a combination of survey data, mensurative and manipulative field experiments, and complex population dynamics models. Chapter 1 evaluates nursery habitat contributions to blue crab population dynamics by examining relationships between juvenile blue crab distributions and multiple environmental variables in three tributaries—the York, James, and Rappahannock rivers—at broad spatial (regional) and temporal (decadal) scales using fisheries-independent survey data and digitized GIS maps of habitat distributions. Chapter 2 examines fine-scale spatiotemporal (i.e., 10s of km2 over biweekly intervals) variation and ontogenetic shifts in juvenile blue crab densities in salt marsh edge, seagrass, shallow detrital habitat, and unstructured habitat under a suite of physical and biological parameters in the York River. Chapter 3 expands on these findings to examine the mechanistic basis for ontogenetic habitat shifts by evaluating differential abundance and survival of juvenile blue crabs across three size classes in salt marsh edge, seagrass, and unstructured sand habitat, with specific attention to effects of refuge, turbidity, and postlarval supply. Finally, Chapter 4 integrates population-scale indices of abundance from two major fisheries-independent surveys with time-series of habitat data to assess the influence of seagrass species on blue crab population dynamics at the scale of Chesapeake Bay.

Sharks of the Atlantic coast of the United States have suffered increased fishing pressure in last three decades. Commercial and recreational catches jumped in the mid to late 1980's, leading to regulation by the National Marine Fisheries Service in the early 1990's. The Virginia Institute of Marine Sciences' shark long-line survey, begun in 1974, and continuing to the present day, is thus well positioned to look at the effects of this fishing mortality on sharks. Using GAM modelling, six of ten shark species analyzed, including the most common species, Carcharhinus plumbeus, suffered declines of from 98-99% of early abundances in the survey. Only two species showed no significant trends, and only one (C. obscurus) showed signs of recovery. Analysis of size changes showed that both C. plumbeus and C. obscurus have suffered declines in both mean and variance of their size distribution since 1974. Analyses of mass changes showed that five of thirteen species have shown biologically significant declines in mass per shark since 1974. Six of the remaining eight showed no trend in mass per shark. Habitat analyses showed that few species showed effects of climate scale variables such as the North Atlantic Oscillation index, Chesapeake Bay discharge, or the Palmer Drought Index. Many species showed significant changes in patterns in abundance with local environmental variables, such as temperature, salinity, and water depth. These patterns, when combined, revealed several groupings of species, including deep-water species, Bay-abundant species, and near-shore species. Another group consisted of species that occur in this area only as they move north and south en route to more northerly areas for summer months. One group was made up of two species (S. acanthias and M. canis) that occurred almost exclusively in cold water (April and May). Analysis of New Jersey long-line data from 1961-62 with a resample of many of the same sites revealed that abundances off New Jersey show a trend in both mass and abundance similar to that found in the VIMS survey data. Overall, this study demonstrated many trends in shark distribution and ecology not previously shown in any way other than anecdotally.

The purpose of this study was to identify continuing education and training needs of aquaculture Extension agents, specialists, and program administrators on the list serve AQUA-EXT. Ten competency areas were evaluated regarding perceived importance, and need for continuing education or training. In addition, 14 resources on the Aquaculture Network Information Center (AquaNIC) website were evaluated from this population for frequency of use and recommended improvements. Lastly, demographic data were collected to determine possible relationships to continuing education and training needs. The survey population was the AQUA-EXT list serve membership (N = 223), of which 174 responded. AQUA-EXT is a Web based mail group established by the Cooperative State Research, Education, and Extension Service as a means of disseminating information to the Extension community with work and interest in aquaculture. Data were collected with an online survey conducted via the interactive and encrypted Web site www.survey.vt.edu. Upon completion, data were exported into, and analyzed via the Statistical Package for the Social Sciences (SPSS). A majority of Extension agents, specialists, and program administrators did not require significant continuing education or training to accomplish their work effectively. However, general agreement among the three groups was for continuing education in the areas of program evaluation, information technologies, and human development. Regarding the AquaNIC website, 52% of Extension agents, 71% of specialists, and 81% of program administrators reported having used AquaNIC, however, use was infrequent. Recommendations to enhance Web site utility focused on requests to update and incorporate more comprehensive and in-depth information for all resource areas. Demographics indicated that mean ages for Extension agents, specialists, and program administrators were 47.9, 50.5, and 51.5 years respectively. Sixty three percent of agents indicated having master's degrees, and 63% and 72% respectively of specialists and program administrators indicated having doctorates. Means for years in their present position were 13.4, 13.2, and 8.4 years respectively for Extension agents, specialists, and program administrators, and 16.6, 16.1, and 15.5 respectively regarding total years in Cooperative Extension or Sea Grant. No statistical relationships between demographics and continuing education and training needs for Extension specialists, specialists, and program administrators were found. / Ph. D.

During the 1990s, shellfish hatcheries operating on the Eastern Shore of Virginia noticed an increase in mortalities of their clam larvae; it was suspected that this was a result of the deteriorating quality of the estuarine water used by aquaculture hatcheries. Many hatcheries obtain their facility process water directly from nearby streams and estuaries. During the same time period, there was also an increase in the use of plastic mulch on some of the vegetable fields on the Eastern Shore. The increased runoff commonly associated with these plastic-covered fields often contains copper-based bactericides that are used on the crops. The plasticulture fields were often located adjacent to the same estuaries from which the shellfish hatcheries draw their water. High levels of copper were measured in multiple surface water locations near these fields. Runoff associated with the plasticulture fields contained up to 238 ug/L dissolved copper, well in excess of the copper concentration of 16.4 ug/L dissolved copper known to affect the mortality of larval clams. Surface water samples collected from nearby unimpacted water bodies contained less than 4 ug/L dissolved copper. Sorption studies conducted with synthetic estuary water quantified the dissolved copper sorption capacities of eight sorbents, including GACs, zeolites, a greensand, and an ion exchange resin, Amberlite IRC-718. These isotherm studies showed that all sorbents removed soluble copper, and that increased salinity and a greater contact time were shown to increase sorption. Utilizing the Freundlich isotherm, the capacity of the eight sorbents studies ranged from 25 to 221 ug/g with a 24-hour contact time. Column studies with an influent concentration of 300 ug/L dissolved copper showed that using 10 grams of a GAC sorbent, a flow rate of 5 mL/min maintained the target effluent concentration of less than 16.4 ug/L for approximately 100 hours. A similar column using 10 g of resin sorbent at a flow rate of 12.5 mL/min maintained the target effluent concentration for approximately 300 hours. The high removal capacity of the resin makes it a desirable treatment for controlling copper in estuarine water used for aquaculture. Utilizing the sorbent capacities obtained from the Freundlich isotherm and a batch treatment, a typical 500 gallon tank used for clam aquaculture would require approximately four pounds of a GAC sorbent, or two pounds of the resin sorbent to reduce a source water that contains 300 ug/L of dissolved copper to below the larval clam toxicity level. Both sorbents would require a 24-hour contact time. / Master of Science

Increased domestic and international demand for aquatic foods have greatly enhanced aquaculture practices and production in Bangladesh, which is reflected in the national economy. However, the impacts of a fast growing aquaculture sector through the involvement of stakeholders, poorer sections throughout the value chain and broader rural livelihoods are largely underdeveloped and have frequently been ignored. The present study explores the impacts of dynamic aquaculture sector on stakeholders at production level and supply chain and test the hypothesis that aquaculture is enhancing rural livelihoods and benefiting the poor. Three aquaculture production systems in three areas of Bangladesh were selected for the study. These were prawn production in gher system in Jessore, pond fish culture in Mymensingh and rice-fish farming in Dinajpur. This selection allowed analysis both the impacts of domestic and export marketing of aquaculture products. Participatory research data collection tools; focus group discussions and participatory mapping were commonly used along with questionnaire surveys to ensure participation of stakeholders. Aquaculture, in general, found to have had significant impacts on rural livelihoods. The greatest effect of aquaculture on farming households were observed in income and consumption. Integrated aquaculture systems were the regular source of fish and vegetables and constitute more than half of the fish and vegetables consumed by farming households. While income from aquaculture was the highest among the several household income sources, the main cash crop differed between the systems studied. Prawn, fish and rice was the main cash earning crops for gher farming, fish farming and rice-fish farming respectively. Qualitative investigation suggested that aquaculture not only increased income through greater production volume, but also improved farmers’ assets through income diversification to farm and non-farm sources. The other important outcomes of aquaculture were the enhancement of social safety nets through increased sharing of inputs and labour among farmers. Commonly the aquaculture systems were found to be more intensive with an increasingly commercial attitude over the last ten years, which affected the intra-household labour distribution leading to a greater role for women in production management. While the three activities; fish feed preparation, feeding and growing vegetables performed by vast majority of women could be attributed to their inherent involvement with agriculture, hard physical work like harvesting ponds and pond construction were mostly carried out by the women from poor households as a strategy to reduce hired labour cost. The women’s’ increased involvement in aquaculture not only increased their overall workload, but also empowered them in household decision making to some extend. However, involvement in decision making was related to the level of involvement in production activities. The impacts of aquaculture spread beyond the farming households to the broader rural livelihoods. Wage labourers and fishers (harvesting teams) two of the poorest groups of people directly involved were benefited most over the last ten years. Intensification of aquaculture increased the demand for hired labour leading to a structural shift in the agricultural wage labour market in farming communities. About half of the agricultural labourers were found part-time employed in aquaculture activities in Jessore and Mymensingh. In Dinajpur intensification of rice cultivation had a much higher effect on the demand for labour than aquaculture. Increased employment in rural areas increased real labour wages by about one fifth over the last ten years and subsequently improved livelihood outcomes. Declining fish catch due to both decreased natural fish stocks and more restricted property rights, professional fishers benefited by diversifying their livelihoods into the aquaculture sector. While, many of the fishers permanently changed their profession to prawn marketing in Jessore, the rest were full-time or part-time employed in harvesting ponds and/or retailing fish in markets. Such diversification of income greatly reduced seasonal vulnerability and improved livelihood outcomes. The role of fish marketing, which is a critical institution in rural livelihoods, was found to facilitate the growth of the aquaculture sector. High demand of aquatic products and the diverse options of marketing fisheries enabled farmers to meet their initial requirements. More commercial operations of aquaculture increased farmers’ awareness and linkages to markets. However, typically the worse-off farmers were the slowest to capture new market opportunities, often due to their poor resources and human capital. Fish marketing was found to be run by the private sector and government provided the infrastructure facilities, except prawn processing plants, which were developed by private sector. While the fish market transactions were fairly efficient, markets facilities and infrastructure were commonly poor and need of government investment for improvement. A gradual growth of fish and markets in the rural areas was observed in the study; this was driven by the increased demand for fish through increased population and supply from aquaculture. The marketing intermediaries provided important services despite their small share of consumers’ price and ensured a fair share for farmers. The auctioneers provided a vital role in running the supply chain with investment and credits, which ensured fair competition in the pricing process. Marketing of aquatic products was not only a mechanism of product transaction, but also provided critical livelihoods for rural poor. On average about one hundred people, including retailers were involved in auction markets and eight people in prawn depots. Importantly the number of people in marketing was found to have increase over the years. Access for different groups of poor people to marketing jobs was found to be significant in rural livelihoods. The asset base and daily earning indicates that more than three quarters of the marketing intermediaries were poor; some of them were from poorest and low cast Hindu society. Greater flexibility of entry and exit to the jobs enabled the poorer sections to diversify their livelihoods, which enabled to cope with seasonal variability of opportunities and stable income. The marketing employment provided then increased livelihood welfare and social security. Finally, it can be concluded that the promotion of aquaculture not only increased much needed food availability but also generated critical livelihoods and marketing is not just a mechanism of product flow, but also providing livelihoods welfare to poorest sections of the society. The micro level findings of the study regarding impacts of aquaculture indicate that aquaculture production and marketing have significant impacts on enhancing rural livelihoods in Bangladesh.

Thesis (M.S.)--University of North Carolina at Wilmington, 2004. / Includes bibliographical references (leaves : 53-58).

This research provides a comprehensive picture of the economic status of the U.S. catfish industry through investigating several critical economic aspects such as technological progress, functional production relationships in intensive systems, regulatory costs, and economic contribution of the industry. The use of primary data is a unique aspect of this work reflecting the economic realities of catfish farms. Primary data collected through extensive in-person farm surveys covered over two-thirds of the catfish production areas in the U.S. The results of the study provided evidence of intensification in the U.S. catfish industry through increased adoption of two relatively new alternative production systems viz; intensively aerated ponds (6,315 ha) and split ponds (1,176 ha). The use of complementary technologies such as hybrid catfish on 53% of the catfish producing area and increased fixed-paddlewheel aeration rate of over 7.8 kW/ha also provided proof of technological progress on U.S. catfish farms. This study also identified critical factors contributing to productivity in increasingly adopted alternative production systems through two distinct production function models. Feed fed, as well as stocking biomass were found to be significant variables in both production functions. Results indicated further room for improvement in the use of inputs to increase production, especially in feed management. Along with identifying the nuances in the catfish industry, the study quantified regulatory costs on U.S. catfish farms at $45 million. Although faced with several hardships on the production front, the U.S. catfish industry contributes over $1.9 billion to the regional economy, supports more than 9,100 jobs, and generates over $78 million in tax revenues. The findings of the study serve a multitude of stakeholders including aquaculture farmers, researchers, Extension specialists, and policymakers who work towards improving the economic sustainability of the catfish industry as well as the U.S. aquaculture industry.

Thesis (MBA)--Stellenbosch University, 2005. / Some digitised pages may appear illegible due to the condition of the original hard copy / ENGLISH ABSTRACT: This study investigates the current level of aquaculture production in South Africa and factors which will help with its further expansion. Aquaculture provides jobs, can assist in alleviating poverty, can earn substantial amounts of foreign exchange and can give rise to various multiplier and linkage effects within the economy. As fishery products are processed further, it is significant that benefits have the potential of becoming more pronounced. Although the South African aquaculture industry has played a negligible role in the development of the domestic economy, its contribution has increased in recent years. Despite providing few employment opportunities, the local aquaculture industry is export-orientated and has the potential of becoming an important foreign-exchange earner. In addition to being able to assist the country's balance of payments, a larger domestic industry could, through its various linkages with the rest of the economy, provide the impetus for the establishment of various related industries. It is not only through these effects that the aquaculture industry could help create new employment opportunities, but the industry itself becomes more labour intensive the further it moves down the processing chain. The prospect of these potential benefits has moved the state to establish various aids to assist the development of the local industry. The most important of these are the Strategy for Biotechnology Development in South Africa, the White Paper on the Promotion of Small Business and a joint mariculture forum between industry and the state. There are factors in favour and factors against the aquaculture expansion. The benefits are too important to be discarded. And the disadvantages can be eliminated by various techniques that have already proved themselves elsewhere in the world. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die huidige vlak van akwakultuur in Suid-Afrika en die faktore wat die uitbreiding daarvan sal beinvloed. Akwakultuur skep werksgeleenthede, help met die verligting van armoede, dit kan aansienlike hoeveelheid buitelandse valuta vir Suid-Afrika verdien en gee aanleiding tot verskeie vermenigvuldiger effekte na die res van die ekonomie. Hierdie effekte is geneig om van groter omvang te wees indien visprodukte verder verwerk word. Alhoewel akwakultuur tot op hede 'n weglaatbaar klein bydrae gemaak het tot die ontwikkeling van die Suid Afrikaanse ekonomie, het hierdie invloed in die afgelope jare toegeneem. Die akwakultuur industrie onderhou relatief min werksgeleenthede, maar is uitvoer ge-orienteerd en het die potensiaal om in belangrike verdiener te raak van buitelandse valuta. Behalwe vir die voordelige uitwerking wat die bedryf het op die betalingsbalans, kan 'n groter akwakultuur bedryf, deur verskeie vermenigvuldiger effekte, aanleiding gee tot die oprigting van verbandhoudende bedrywe. Behalwe vir die werksgeleenthede wat hierdeur ontstaan, word die visbedryf algaande meer arbeidsintensief en voorsien dit meer werksgeleenthede soos daar langs die waarde toevoegingslyn afbeweeg word. Die verwagte voordele wat die industrie kan bied, het die staat oortuig om sekere hulpmiddels tot stand te bring om die uitbreiding te bevorder. Die belangrikste hiervan is die totstandkoming van 'n Strategie vir Biotegnologiese uitbreiding, 'n beleidsdokument vir die bevordering van klein besighede en 'n akwakultuur samewerkingsplatvorm tussen die staat en die bedryf. Daar is faktore wat die plaaslike uitbreiding ondersteun en ander wat 'n nadelige invloed mag veroorsaak. Die positiewe faktore is te belangrik om die geleentheid nie te benut nie. Die nadelige faktore kan voorkom word deur tegnieke te gebruik wat hulself reeds suksesvol bewys het.