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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Evaluating the Consequences of Alternative Atlantic Striped Bass Harvest Control Rules on Their Prey, Atlantic Menhaden(2022) Schiano, Samantha E.; Nesslage, Genevieve; Wilberg, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Harvest control rules (HCRs) are automatic fishery management procedures that are agreed upon in advance and that dictate the rate of fishing that can take place. I evaluated a suite of single species and dynamic multispecies HCRs to evaluate their relative performance in achieving management goals for the striped bass (Morone saxatilis) and Atlantic menhaden (Brevoortia tyrannus) stocks using a linked, age-structured predator-prey simulation model. First, simulation model inputs were updated using the most recent stock assessment information, and striped bass length- and weight-at-age estimates were updated using otolith-based ageing data. Linear models evaluating change in striped bass length- and weight-at-age over time and between sexes identified an increase in size of as much as 30% between 1998 and 2019. Additionally, striped bass continued to grow past age-15, indicating that future striped bass stock assessments should consider expanding the number of ages included in the model. The updated predator-prey simulation model was then used to compare performance of a suite of 27 HCRs. The most influential factor determining performance of striped bass HCRs was striped bass fishing mortality (F). Atlantic menhaden had little effect on striped bass spawning stock biomass (SSB) at both high and low percent composition of Atlantic menhaden in striped bass diets. Traditional single species HCRs performed well, specifically those for which striped bass are managed at or below their target F. Although there was no single HCR that performed well for both stocks given their current reference points, both single species and dynamic multispecies HCRs that involved the “40-10 rule” for striped bass (lower threshold at 10% of unfished SSB and upper threshold at 40% unfished SSB) performed best across all striped bass performance metrics.Item Influence of environmental conditions on the age, hatch dates, and growth of juvenile Atlantic menhaden in the Choptank River, MD(2016) Atkinson, Alexandra Nicole; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Since 1993 Atlantic menhaden has experienced sustained low juvenile production (recruitment) in the Chesapeake Bay. Factors controlling growth, abundance, and mortality of larval and juvenile menhaden change throughout ontogeny such that larval growth rates could carry over to juvenile growth and survival. The effects of winter thermal conditions on the hatch dates and growth of larval and juvenile Atlantic menhaden in Atlantic shelf and Chesapeake Bay habitats were examined using otolith (ear-stone) increment analyses and growth models. For 2010-2013, truncated hatch-date distributions provided evidence for a winter recruitment bottleneck in Atlantic menhaden caused by cold temperatures. Hatch-dates of surviving juveniles were skewed towards warmer months for years characterized by colder temperatures. Reduced larval growth rates, influenced by reduced temperature and food availability, carried over to juvenile growth rates. A growing degree-day model performed well in simulating observed juvenile growth rates in the Choptank River tributary of Chesapeake Bay.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 An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.