Theses and Dissertations from UMD
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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
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Item POPULATION DYNAMICS OF EASTERN OYSTERS (CRASSOSTREA VIRGINICA) IN THE CHOPTANK RIVER COMPLEX, MARYLAND, DURING 1989 - 2015(2017) Damiano, Matthew; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eastern oyster (Crassostrea virginica) fishery in the Choptank River Complex (CRC) supports a large fraction of Maryland’s harvest. The CRC is also host to some of the largest oyster restoration projects in the world. Yet the relative effects of harvest and restoration on the population dynamics of oysters in the CRC have not been assessed. We developed stage-based population models for each region of the CRC in AD Model Builder using dredge survey and harvest data provided by Maryland Department of Natural Resources from 1989 to 2015. Natural mortality was low during 2004-2015 potentially due to increased resistance to the disease, Dermo. Recruitment was greatest in the late 1990s, 2010, and 2012, which caused an increase in abundance. These models will serve as the foundation of a simulation model that will be used to help fishery stakeholders evaluate management and restoration options in the CRC.Item EFFECTS OF ASSESSMENT FREQUENCY AND DATA-MANAGEMENT LAG ON FISHERY MANAGMEMENT PERFORMANCE: STRATEGIES FOR IMPROVEMENT(2015) Sylvia, Andrea Lynn; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Some challenges of using stock assessments in management decisions are data availability and the allocation of resources to conduct stock assessments in a frequent and timely manner. We conducted a simulation evaluation that included the population dynamics, stock assessment, and management. Our objectives were to 1) determine effects of assessment interval and data-management lag and 2) test methods to reduce data lag by using partial data in the last year of the assessment. We found that increasing assessment interval and data-management lag caused a decrease in average catch and biomass across scenarios, with data-management lag having a larger effect compared to assessment interval. To reduce the effects of data-management lag, lag reduction methods that included some information about the age-composition of the catch and survey performed about as well as not having lag. Stock assessment interval, data-management lag and lag reduction methods should be considered when designing fishery management plans.Item MANAGEMENT AND CONSERVATION OF BROOK TROUT IN WESTERN MARYLAND(2015) Kazyak, David C.; Hilderbrand, Robert H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Widespread declines have been observed in the abundance, distribution, and size structure of Brook Trout for nearly 200 years. Although broadly distributed, Brook Trout are very sensitive to environmental disturbances, and populations continue to disappear. Environmental change further threatens the persistence of wild Brook Trout, and even currently secure populations may be at risk. Life history variation and population substructures further confound management, and their potential influences on population dynamics warrant further investigation. The objectives of my dissertation were to characterize Brook Trout populations in western Maryland and use this information to forecast alternative futures. We used a large-scale mark-recapture survey (>3,000 marked fish), molecular tools, and simulation modeling to gain a comprehensive understanding of the structure and function of Brook Trout populations in western Maryland. We found that rapid visual assessment was a valid technique (92% accuracy after training) for determining sex in Brook Trout. We found significant variability in individual growth rates (0-144 mm*y-1), with marked influences of year, sex, size, and stream. We also detected the presence of cryptic metapopulations occurring on a small spatial scale and in the absence of physical barriers to movement. Population substructures such as sex or lineage are easily overlooked, yet they may have measurable and potentially important differences in vital rates. Simulation modeling under current and alternative conditions suggested that environmental stochasticity exerts a strong influence on the population dynamics of wild Brook Trout in western Maryland. Population dynamics were driven by pulse-driven recruitment that was weakly related to spawner abundance. Changes in adult survival, representative of a range of management scenarios, had a considerable impact on population resilience. Conversely, changes in the growth rates of Brook Trout resulted in small changes to population resilience. Enhanced adult survival resulted in a greater abundance of large fish. Collectively, these results suggest regulatory approaches may offer some utility in promoting population resilience while enhancing the quality of the fishery, but are likely insufficient to fully offset the impacts of predicted environmental changes.