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 Investigating the role of the Mid-Atlantic inner continental shelf as a marine finfish nursery: a comparative approach(2010) Woodland, Ryan Jordan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The paradigm of estuarine-dependence in marine fishes has been challenged by evidence of facultative recruitment by juveniles to both estuarine and inner continental shelf (ICS) nursery habitats. This ecological flexibility suggests that the potential nursery area for marine fishes may be more expansive than previously considered. Two lines of investigation were undertaken to evaluate the overarching hypothesis that ICS habitats serve a nursery function for finfish that also use estuarine nurseries: 1) a direct comparison of seasonal, annual and compositional assemblage structure between an ICS habitat of the Middle Atlantic Bight (Delmarva Peninsula) and an adjacent estuary (lower Chesapeake Bay); and 2) an investigation of trophic structuring within an ICS demersal finfish assemblage with an emphasis on ontogenetic niche. In comparisons between nursery types, there was a strong seasonal similarity in assemblage structure between the estuary and ICS despite significant differences in abundance estimates at the species level. Juvenile trophic niche of two indicator species, bluefish and bay anchovy, was wider and more diverse in the estuary yet physiological condition was similar or higher in the ICS. In focused studies on the ICS food web, diet overlap was common among consumers, yet stable isotope evidence indicated prey resources were partitioned along vertical (trophic position) and horizontal (pelagic-benthic pathway) trophic axes. Benthic and pelagic food webs were tightly coupled in most juvenile phase finfish; yet, this relationship showed signs of decoupling in older age classes, suggesting an increased reliance on benthic trophic pathways with age and size. Several prey species that link pelagic and benthic food webs were shown to be important in the diets of demersal finfish, particularly mysid shrimp. Comparative assemblage and food web studies demonstrated that the ICS functions as summer nursery habitat for a wide variety of temperate marine finfish that also use proximal estuarine nurseries. The contribution of ICS nurseries to annual juvenile production represents a critical, but unknown component of population demographics for many marine species and must be considered to conserve essential fish habitats and account for recruitment variability in fisheries stock assessments.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 Ecology of Juvenile Bluefish, Pomatomus saltatrix, in Maryland Coastal Waters and Chesapeake Bay(2005-12-12) Callihan, Jody; Secor, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shallow coastal ocean environments may function as important nursery habitats for juvenile bluefish, yet little ecological research has been conducted in ocean habitats. This thesis examines seasonal production, growth rates, and diet composition of juveniles in Maryland's coastal ocean environment and the Chesapeake Bay estuary. Summer-spawned juveniles dominated in ocean habitats and exhibited rapid growth rates, 2.0 - 2.4 mm d-1, which were likely fueled by an abundant forage base of young-of-the-year bay anchovy present in ocean environments during late summer/early fall. This summer cohort was rare in the Chesapeake Bay, where spring-spawned juveniles dominated. These results suggest ocean habitats provide principal nurseries for summer-spawned bluefish, and that the Chesapeake Bay and other estuaries are principal nurseries for spring-spawned juveniles. Accordingly, year class strength is likely shaped by contributions of juveniles from both oceanic and estuarine nursery habitats.