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 Dynamics of ingress, hatch dates, growth, and feeding of Atlantic menhaden, Brevoortia tyrannus, larvae at the Chesapeake Bay mouth(2011) Lozano, Carlos; Houde, Edward D; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recruitment of Atlantic menhaden to Chesapeake Bay declined in the late 1980s. Although reasons are not understood, a decline in larval supply to the Bay is one hypothesized explanation. The objective of this thesis was to evaluate levels and variability in larval ingress by conducting 18 ichthyoplankton cruises at the Bay mouth during three years at monthly intervals from fall through spring (2005-06, 2006-07, and 2007-08). The concentrations of ingressing larvae were estimated for each year and also for months within each year. Larval spatial and temporal distributions at the Bay mouth were evaluated with respect to tides and day-night differences. Age, growth rates and hatch dates were determined from otolith-aged larvae and compared among years and months. Larvae were most abundant in 2007-08, but grew fastest in 2006-07. Most ingressing larvae hatched in the November to December period. Copepods were the dominant prey in diets of larval menhaden.Item Assessment of Populations with Spatially Explicit Dynamics and the Consequences for Marine Protected Areas(2011) Barkman, Jennifer Shari; Wilberg, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spatial processes can have important consequences in the population dynamics of fishes and marine invertebrates. Therefore fisheries management should consider space in the techniques used to understand population dynamics. The purpose of this thesis was to investigate spatial dynamics of fish populations in Maryland's coastal bays (Chapter 2) and evaluate effects of spatial management (in the form of marine protected areas (MPAs)) on accuracy of abundance estimates (Chapter 3). In Chapter 2, I examined trawl survey data from Maryland's coastal bays to estimate trends in relative abundance of four commonly caught fish species using a generalized linear model that allowed region specific estimates. Species showed different responses in the two regions, but trends over time were not related to local habitat variables. In chapter 3, I examined the effects of an MPA on the accuracy and bias of estimates from spatially aggregate and explicit surplus production models (SPMs) using a simulation experiment. I found that spatially-explicit SPMs produced more accurate estimates of biomass than spatially-aggregate SPMs, and that larger MPAs produced more accurate estimates than smaller MPAs.Item Stated Preference Methods and Models: Analyzing Recreational Angling in New England Groundfisheries(2011) Jarvis, Sonia; McConnell, Kenneth E; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Policy analysis of nonmarket goods requires accurate knowledge about the behavior of economic agents. This dissertation explores several facets of behavior models in recreational angling for three New England groundfish species. Stated preference methods are used frequently for nonmarket applications because data are scarce, but survey design can affect the results of behavior models via changes in respondents' cognitive processes. Methodological biases due to task complexity, measured by survey length, number of alternatives, and the degree of information overlap are observed in discrete choice experiment questionnaires, evidenced by differences in estimated model parameters and error variances. Additionally, ignoring task complexity increases mean marginal willingness-to-pay estimates. Information processing and decision heuristics should be considered in survey design and accounted for in estimated models. Empirical specifications for utility models of recreational angling are also explored because numerous variants are employed in analyzing stated preference data. Inclusion of responses from different survey subpopulations affect estimated utility function parameters and mean marginal willingness-to-pay values. Utility models that are nonlinear in catch are as statistically robust as their linear counterparts but allow for diminishing marginal utility in fish, which is more consistent with recreational angling behavior. Failure to account for sources of heterogeneity such as angler avidity, species familiarity, and demographic information affect behavioral interpretations considerably. Recreational fisheries are commonly managed using bag (creel) and minimum size restrictions. Many surveys include regulations as attributes in choice experiments, but models of angler behavior should not contain regulatory variables explicitly because they rarely factor into angler participation decisions directly. Because catch is random, regulations affect angler decisions indirectly by changing the underlying distributions for keep and release. A framework for understanding the effect of regulations on angler behavior given the stochastic nature of catch is developed. Short-run and long-run fishery implications are evaluated using a bioeconomic simulation.