Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

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Subject: search.filters.subject.Blue Crab

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    POTENTIAL FOR SPERM LIMITATION IN BLUE CRABS OF CHESAPEAKE BAY
    (2014) Rains, Sarah; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sperm limitation is a concern for blue crabs Callinectes sapidus in Chesapeake Bay due to their reproductive biology and sex specific fishing pressures from regulations. Our objectives were to 1) characterize differences in sperm quantity per female among six tributaries in Chesapeake Bay and evaluate if it is related to the tributaries mature male:female sex ratio and 2) develop an individual based model to simulate the effect of harvest on the reproductive sustainability of the blue crab fishery. We found that sperm quantity per female varied among tributaries, as did sex ratio, but were not related to each other. Additionally, all simulated fishing scenarios showed no significant differences in sperm per female except for when all mature males were fished at five times current fishing pressure and females were unfished. Our results suggest that sperm limitation is not a concern for blue crabs of Chesapeake Bay under current regulations.
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    THE DISTRIBUTION OF CALLINECTES SAPIDUS MEGALOPAE AT THE MOUTHS OF CHESAPEAKE AND DELAWARE BAYS: IMPLICATIONS FOR LARVAL INGRESS
    (2009) Biermann, Jeffery Lee; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this economically important species. This research seeks to determine the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays, and thereby infer swimming behaviors that may influence ingress to these estuaries. Megalopae and physical conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters in September 2005 and 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations, suggesting a diurnal effect on distribution within the estuary and on the continental shelf. Unlike previous studies, offshore distributions did not indicate surface oriented behavior. Within the mouth of Delaware Bay, limited evidence suggests that megalopae presence in the upper portion of the water column increases in response to nocturnal flood tides. Results suggest photoinhibited swimming near the mouths of Chesapeake and Delaware Bays. In context of previous laboratory studies, these findings indicate that estuarine chemical cues at very low concentrations may induce changes in megalopae behaviors and stimulate molting at least 40 km offshore of estuarine mouths. Results suggest wind-forcing and density-induced subtidal flow are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal-transport.
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    Reproductive Physiology of the Female Blue Crab, Callinectes sapidus: Spawning Induction and Vitellogenesis
    (2009) Bembe, Sarah Elizabeth; Chung, J. Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In aquaculture, spawning is the baseline for production; therefore, the optimization of spawning conditions will directly increase production. The current study aims to optimize spawning conditions for Callinectes sapidus using environmental manipulations of photoperiod and temperature for induction while monitoring the physiological vitellogenin (VtG) levels during ovarian development and maturation. The photothermal manipulations for this study resulted in increased spawning events in 21°C temperatures (compared to 11°C and 15°C) and complete darkness (0L:24D; compared to 8L:16D, 16L:8D, and 24L:0D) while 24L:0D and 11°C suppressed spawning. When assessing the VtG levels in the hemolymph prior to, during, and after all spawning events, the VtG showed a decrease prior to spawning, and significant VtG activity was seen in 21°C for all photoperiods. Overall, spawning and vitellogenesis are temperature dependent events with 67% of the females spawning in 21°C. Photoperiod also has an effect on spawning, but not on vitellogenesis.