UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item MODELING POTENTIAL HABITAT OF CHESAPEAKE BAY LIVING RESOURCES(2012) Schlenger, Adam James; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quantitative understanding is needed to identify the impacts of climate change and eutrophication on the habitat of living resources so that effective management can be applied. A systematic literature review was conducted to obtain the physiological tolerances to temperature, salinity, and dissolved oxygen for a suite of Chesapeake Bay species. Information obtained was used to define required and optimal habitat conditions for use in a habitat volume model. Quality matrices were developed in order to quantify the level of confidence for each parameter. Simulations from a coupled oxygen and hydrodynamic model of the Chesapeake Bay were used to estimate habitat volumes of juvenile sturgeon (Acipenser oxyrinchus) and to assess sensitivity of habitat to environmental factors. Temperature and salinity define spring and fall habitat and a combination of salinity, temperature and dissolved oxygen influence habitat in summer. Both fixed criteria and bioenergetics habitat volume models yielded similar results.Item Bioenergetic responses of Chesapeake Bay white perch to nursery conditions of temperature, salinity, and dissolved oxygen(2009) Hanks, Deanna McQuarrie; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Changes in the physical and chemical structure of estuaries affect the habitat availability for anadromous species. White perch, an estuarine species, are among the most abundant and important fishes in the Chesapeake Bay. Here, I evaluate nursery quality for juvenile white perch by measuring metabolic and growth responses over a range of environmental conditions such as salinity, temperature, and dissolved oxygen. Rearing white perch in 10-d trials varying in temperature, salinity and dissolved oxygen conditions, I estimated growth rates, feeding rates, gross growth efficiency, and routine metabolism. Juveniles experienced higher feeding and growth rates in warmer, more oxygenated waters. In hypoxic environments (<40% saturation), metabolic rates increased as much as 4-fold while growth decreased 3-fold and feeding decreased 2-fold. My results indicate that while white perch are well suited to the saline and thermal conditions present in the Bay, nursery habitat value can be substantially curtailed by hypoxia.Item Cause, consequence, and prevalence of spatial structure of white perch (Morone americana) populations in the Chesapeake Bay(2008-12-11) Kerr, Lisa A.; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Partial migration defines the simultaneous occurrence of migratory and resident groups within populations. Using otolith chemistry (strontium:calcium measures), I documented partial migration for an estuarine-dependent white perch (Morone americana) population in the Patuxent River estuary (Chesapeake Bay, MD). Previous research indicated that as juveniles, a portion of the population remained resident in freshwater natal habitats and another portion dispersed down-estuary into brackish water habitats. I established these behaviors are alternative life history tactics that persist over the lifetime of individuals. Through back-calculation of hatch-dates, juvenile contingents were associated with their respective larval cohorts, indicating that spatial structuring was influenced by time of spawning, and temperature and prey conditions experienced during early life history. Dispersive individuals originated primarily from earlier spawned larval cohorts, characterized by slower growth and higher mortality rates compared to later spawned cohorts, which contributed disproportionately to the resident contingent. Laboratory experiments revealed that partial migration was associated with varying energetic tactics, with dispersive contingent fish exhibiting higher consumption and faster growth rates subsequent to migration. The prevalence of contingent behavior within other white perch populations in Chesapeake Bay was explored using otolith stable isotope (δ18O) values, which had a positive relationship with salinity and together with otolith δ13C serve as a proxy for regional habitats distributed along an estuarine salinity gradient. Resident contingent fish dominated Upper Bay and Potomac River populations, whereas the dispersive contingent dominated within the Choptank, Nanticoke, James, and York Rivers. The consequences of spatial structuring to productivity (spawning stock biomass), stability (variance in spawning stock biomass), and resilience (years to rebuild the population) of white perch populations were examined using an age-structured simulation model. Increased representation of migratory fish resulted in increased population productivity and resilience, whereas presence of the resident contingent within the population contributed to stability. Increased population stability and productivity also occurred when the abundance of the two contingents varied inversely to one another over time (i.e., asynchronous dynamics). The different roles contingents play in mediating population dynamics and long-term persistence highlights the importance of managing for conservation of spatial structure within fish populations.