Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Expanding the Fisheries Management Tackle Box: A Multiple-Model Approach to Support Better Decisions(2023) Hayes, Christopher Glenn; Wainger, Lisa; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Marine fisheries provide critical ecosystem services but face an array of stressors like climate change and overfishing. Managing fisheries is challenging due to limited information and the need to make complex tradeoffs among ecological and social objectives. Decision processes that include integrated social-ecological models and equitable stakeholder engagement are increasingly recognized as approaches to improve the likelihood of achieving management goals compared to those that rely solely on stock assessment models with limited stakeholder input. Additionally, advanced technologies offer new opportunities to understand marine ecosystem dynamics, including human behavior. This research adds two examples of underutilized tools: multi-criteria decision analysis (MCDA) and agent-based models (ABMs). In the first case, I compared management recommendations for the Chesapeake Bay oyster fishery arising from A) stakeholder engagement using group negotiations and B) preferences elicited from individuals using an MCDA approach. The recommendations were consistent across methods, suggesting that group effects did not bias group negotiation outcomes. The second case investigated New England groundfish reporting behavior based on stock dynamics, quota markets, and fishery observer coverage. First, having an observer onboard was found to significantly reduce the probability and magnitude of reporting error (ie., an observer effect) using a linear mixed effects model of data from vessel trip reports and remote vessel monitoring systems. Next, an ABM was used to explore emergent responses to policy changes - varying levels of observer coverage and the strength of the observer effects - on fish catch, reporting error, and profit outcomes, given fisher interactions and responses to fish population dynamics. Scenarios with strong observer effects resulted in increasing marginal improvements in reporting accuracy at high levels of observer coverage. MCDA and ABM can contribute to a multiple-model approach by allowing fisheries managers to integrate diverse stakeholder perspectives and use additional data sources that could lead to better fishery outcomes.Item Evaluating Substrate Rehabilitation Techniques for Bottom Culture of the Eastern Oyster (Crassostrea virginica) in Chesapeake Bay(2020) Long, Jessie Todd; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The degradation of Chesapeake Bay bottom conditions and oyster beds over the past century from habitat destruction, overharvesting, disease, and sedimentation have resulted in many areas that are detrimental for healthy oyster populations. In leased oyster aquaculture areas, unsuitable bottom characteristics result in suboptimal survival. Although the addition of oyster shell as substrate has been a common practice for building new oyster beds, the current high cost and lack of available shell can make this approach impractical. The goal of this study was to measure the effects of new and traditional bottom rehabilitation techniques (harrowing and shell addition) on oyster survival and growth on three distinct bottom types. The data revealed that treatments, whether singularly or in combination, were insignificant in respect to oyster size and survival across all bottom types. However, the observed bottom type had a significant effect on the percentage of oyster survival.Item Patterns of oyster natural mortality in Chesapeake Bay, Maryland during 1991-2017 and its relationships with environmental factors and disease(2019) Doering, Kathryn Leah; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A common method of estimating natural mortality in bivalves includes several assumptions that are likely violated for oysters Crassostrea virginica in Chesapeake Bay, Maryland. In addition, while oyster disease dynamics are well studied spatially and temporally in the mid-Atlantic region, changes in disease-related relationships have not been investigated in Maryland. We developed a Bayesian estimator for natural mortality and applied it to oysters in Maryland. We then used the model output along with environmental factors and disease data to explore changes in the disease system over time. We found the largest differences in natural mortality estimates between the box count method and Bayesian model 1-3 years after a high mortality event. Some relationships changed over time in the disease system, most notably those associated with MSX, suggesting resistance to MSX has potentially developed. This work improves our estimates of natural mortality and understanding of oyster disease dynamics in Maryland.Item Growth and Physiology of Eastern and Suminoe Oysters and the Implications of Increased Habitat Complexity for Associated Oyster Reef Fauna(2011) Kelly, Christopher James; Newell, Roger I.E.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The introduction of a non-native oyster species (Crassostrea ariakensis) into Chesapeake Bay has been proposed as a way to help restore the oyster fishery and enhance the ecological services historically provided by eastern (Crassostrea virginica) oysters. A comparison of growth, mortality, and physiology between diploid C. ariakensis (Oregon strain) and diploid C. virginica was undertaken in quarantined mesocosms simulating mesohaline Chesapeake Bay. Growth of C. ariakensis was greatest during the late winter and early spring periods, with oyster condition substantially reduced during the summer due to low clearance rates and elevated respiration rates. Stunted growth and high mortality characterized the C. virginica treatment, although the reasons for this are unknown. Additional quarantined laboratory studies, conducted in Florida for both oyster species in conditions simulating a subtropical estuary examined the potential of C. ariakensis to expand southwards. While growth of C. ariakensis was comparable to that of C. virginica, mortality of C. ariakensis reached 100% by the end of the study, but remained relatively low for C. virginica. Physiological studies under quarantined temperate euhaline conditions (Wachapreague, Virginia) confirmed that C. ariakensis is physiologically intolerant to warmer water (> 20ºC) because of low clearance rates. Oysters create reefs that provide refuge for prey species, and enhanced foraging opportunities for predatory fish species. Predator-prey interactions between organisms found on oyster reefs, such as grass shrimp (Palaemontes pugio), white perch (Morone americana), and striped bass (Morone saxatilis) were conducted on habitats of varying complexity. Habitats consisted of flat sand, and medium and high complexity structures constructed in mesocosms from PVC pipe. As structural complexity increased so did the attraction of grass shrimp and white perch to structure regardless of the provision of food resources or presence of striped bass. The attraction of grass shrimp to structure decreased when high densities of conspecifics were present. The presence of prey and/or predators enhanced white perch utilization of structure and increased complexity decreased their swimming and shoaling activity. Habitat complexity and the threat of predation interact to alter grass shrimp and white perch behavior under intermediate levels of structural complexity.Item CHEMICAL INDUCTION OF SETTLEMENT IN LARVAE OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN)(2009) Grant, Melissa; Meritt, Donald W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, I treated competent C. virginica larvae with select chemicals to identify those which are capable of inducing settlement behavior at an average salinity of 9.6 (±0.1). The compounds γ-aminobutyric acid and acetylcholine chloride, both at 10-4M, did not significantly increase the percentage of larvae exhibiting settlement behavior. As compared with the control, a significant increase in settlement behavior was induced by treatment with 3-isobutyl-1-methylxanthine, 5-hydroxytryptamine, and L-3, 4-dihydroxyphenylalanine all at 10-4M, as well as ammonia as a solution of 7.9mM NH4Cl (pH=8.0). These findings differ somewhat from the results of similar studies involving other species in the Crassostrea genus and may be of value to hatchery personnel or researchers interested in the chemical induction of settlement behavior in the eastern oyster.Item COMPARISONS OF MACROFAUNA ASSEMBLAGES ON RESTORED AND NON-RESTORED OYSTER REEFS IN MESOHALINE REGIONS OF CHESAPEAKE BAY IN MARYLAND(2008-01-04) Rodney, William Stanley; Paynter, Kennedy T.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently restored oyster sanctuary reefs in Maryland allowed for a unique opportunity to observe the abundance and species composition of macrofauna assemblages on unexploited reefs with high concentrations of mature oysters and undisturbed reef architecture. These observations provided insights on the potential changes to reef dwelling macrofauna communities and various reef ecological functions resulting from reef restoration. I sampled macrofauna at four restored oyster sanctuary reefs and adjacent non-restored plots located outside sanctuary boundaries. I then compared the effects of study site location and habitat quality (restored vs. non-restored) on macrofaunal density using thirteen response variables. Motile macrofauna density was an order of magnitude higher on restored reefs and sessile macrofauna density was two orders of magnitude higher on restored reefs. Two out of four functional feeding groups: suspension feeders and carnivore/omnivores, were more abundant on restored plots. Results indicate that restoration improved reef ecological structure and function.