Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item EFFECTS OF ASSESSMENT FREQUENCY AND DATA-MANAGEMENT LAG ON FISHERY MANAGMEMENT PERFORMANCE: STRATEGIES FOR IMPROVEMENT(2015) Sylvia, Andrea Lynn; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Some challenges of using stock assessments in management decisions are data availability and the allocation of resources to conduct stock assessments in a frequent and timely manner. We conducted a simulation evaluation that included the population dynamics, stock assessment, and management. Our objectives were to 1) determine effects of assessment interval and data-management lag and 2) test methods to reduce data lag by using partial data in the last year of the assessment. We found that increasing assessment interval and data-management lag caused a decrease in average catch and biomass across scenarios, with data-management lag having a larger effect compared to assessment interval. To reduce the effects of data-management lag, lag reduction methods that included some information about the age-composition of the catch and survey performed about as well as not having lag. Stock assessment interval, data-management lag and lag reduction methods should be considered when designing fishery management plans.Item Influences of the biotic and structural components of Crassostrea virginica on the oyster reef community.(2015) Kesler, Karen Elizabeth; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The hard, complex reef structure created by the eastern oyster, Crassostrea virginica, provides refuge and habitat that protects many organisms, allowing them to settle, survive, and spawn. In addition, oysters create copious amounts of biodeposits, which potentially serve as a basal nutrient resource for the reef ecosystem. I investigated the influence of oyster reef structure and oyster biodeposits on the reef community through a series of field experiments and mesocosm studies. Initially, the communities that colonized live oyster reefs were compared to communities that colonized empty oyster shell reefs, to evaluate the potential influence of live oysters that were actively feeding and creating biodeposits. Community assemblages on the two reef types were similar and no differences were seen with species level comparisons of abundance or biomass between the two treatments. The impact of oyster shell structure on energy transfer up the food chain from the basal resource of oyster biodeposits to the predator, Gobiosoma bosc, through the amphipod, Melita nitida was then investigated. Oyster shell structure effectively provided protection to amphipods, with reduction of predation impacts in high complexity habitats when a predator was present. Next, stable isotope signatures (d13C and d15N) of dominant reef species and basal resources, including oyster biodeposits, were measured seasonally to evaluate the major resource contributors to the reef. Overall, most carbon sources appeared to be pelagic in nature and an additional unidentified carbon source from outside of the oyster reef was incorporated into the food web. Finally, a d15N tracer study, utilizing biodeposits labeled with elevated d15N values, indicated that both Melita nitida and Neanthes succinea could incorporate Crassostrea virginica biodeposits and pass these nutrients to higher trophic levels. These studies suggested that oyster structure played a prominent role in defining the oyster reef community by providing habitat and protection for reef organisms. Mesocosm studies and isotopic analysis indicated that while some deposit feeders could consume oyster biodeposits, biodeposits were likely not a large component of their diet. Overall, these results suggest that structure was the dominant factor driving community organization on the reef, with minimal influence from oyster biodeposits.Item Development of methods to test drug sensitivity of fish pathogenic Flavobacterium columnare and drug sensitivity thresholds for F. columnare to the antimicrobial florfenicol.(2015) Gieseker, Charles Michael; Woods III, Lewis C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Antimicrobial drugs play a key role in managing the health of fish in aquaculture. However, public health concerns about antimicrobial resistance--the ability of microorganisms to resist standard antimicrobial treatments--include the potential for antimicrobial use in aquaculture to select for resistant bacteria in and around fish farms. Recent approval of two antimicrobial drugs to treat farmed freshwater fish with infections caused by the aquatic bacteria Flavobacterium columnare and F. psychrophilum created an important need for research to monitor these bacteria for changes in antimicrobial susceptibility and to decide when the antimicrobials should be used. Therefore three studies were conducted. The initial study optimized methods for broth microdilution testing F. columnare and F. psychrophilum and conducted a multi-laboratory standardization trial that set quality control parameters for nine antimicrobials commonly used in aquaculture, thus creating the first standardized testing method. In the second study, we constructed frequency distributions using minimal inhibitory concentrations determined from testing 134 F. columnare with the standardized method. Analysis of the distributions determined the drug concentration--called an epidemiological cutoff value (ECV)--which separated the wild type isolates with no acquired or selected resistance from the non-wild type isolates. The ECV indicated 22 of 134 isolates had decreased their susceptibility to at least 1 antimicrobial. In addition, we developed a laboratory disease model with juvenile channel catfish, Ictalurus punctatus. We compared the virulence of three F. columnare isolates with wild type or three isolates with non-wild type florfenicol susceptibility using the model. We found that five isolates had similar high level virulence and were not affected by differences in florfenicol susceptibility. Finally, we studied if decreased non-wild type florfenicol susceptibility affected the ability of the approved florfenicol treatment to control F. columnare infections. The approved treatment significantly reduced catfish mortality following exposure to an isolate with typical wild type florfenicol susceptibility but mortality was not reduced following exposure to an isolate with non-wild type susceptibility. Taken together, these studies provide methods and research needed to monitor F. columnare for changes in antimicrobial susceptibility and to rationally use florfenicol to control F. columnare infections.Item MANAGEMENT AND CONSERVATION OF BROOK TROUT IN WESTERN MARYLAND(2015) Kazyak, David C.; Hilderbrand, Robert H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Widespread declines have been observed in the abundance, distribution, and size structure of Brook Trout for nearly 200 years. Although broadly distributed, Brook Trout are very sensitive to environmental disturbances, and populations continue to disappear. Environmental change further threatens the persistence of wild Brook Trout, and even currently secure populations may be at risk. Life history variation and population substructures further confound management, and their potential influences on population dynamics warrant further investigation. The objectives of my dissertation were to characterize Brook Trout populations in western Maryland and use this information to forecast alternative futures. We used a large-scale mark-recapture survey (>3,000 marked fish), molecular tools, and simulation modeling to gain a comprehensive understanding of the structure and function of Brook Trout populations in western Maryland. We found that rapid visual assessment was a valid technique (92% accuracy after training) for determining sex in Brook Trout. We found significant variability in individual growth rates (0-144 mm*y-1), with marked influences of year, sex, size, and stream. We also detected the presence of cryptic metapopulations occurring on a small spatial scale and in the absence of physical barriers to movement. Population substructures such as sex or lineage are easily overlooked, yet they may have measurable and potentially important differences in vital rates. Simulation modeling under current and alternative conditions suggested that environmental stochasticity exerts a strong influence on the population dynamics of wild Brook Trout in western Maryland. Population dynamics were driven by pulse-driven recruitment that was weakly related to spawner abundance. Changes in adult survival, representative of a range of management scenarios, had a considerable impact on population resilience. Conversely, changes in the growth rates of Brook Trout resulted in small changes to population resilience. Enhanced adult survival resulted in a greater abundance of large fish. Collectively, these results suggest regulatory approaches may offer some utility in promoting population resilience while enhancing the quality of the fishery, but are likely insufficient to fully offset the impacts of predicted environmental changes.Item DEPTH PREFERENCES OF OVERWINTERTING JUVENILE BLUE CRABS (CALLINECTES SAPIDUS) IN THE MARYLAND WATERS OF THE CHESAPEAKE BAY: A LOCAL SEASONAL STUDY AND PRELIMINARY SHALLOW WATER SURVEY(2015) Kaufman, Anthony Gartner; Miller, Thomas J; Johnson, Eric G; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A series of experimental studies designed to quantify the spatial and temporal patterns of juvenile blue crabs abundance in upper Chesapeake Bay, with an emphasis on the depth distribution during the winter, were conducted. A seasonal sampling of the Rhode and West Rivers was conducted. Concurrently, a pilot-scale shallow water survey (SWS) in four river systems throughout Maryland allowed the abundance of juvenile blue crabs to be estimated and compared to abundance estimates from the Winter Dredge Survey (WDS). The seasonal study results indicated that depth, sediment type and the time of year sampling took place were a significant predictor of juvenile blue crabs distribution and abundance. The SWS indicated that the abundance of juvenile blue crabs is underestimated by the WDS. This work highlights the potential need for additional surveys to index the abundance of juvenile blue crabs as an aid to ongoing management and conservation efforts.Item 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.Item Identifying the elusive dwarf wedgemussel habitat through modeling and field approaches(2014) Campbell, Cara Ann; Prestegaard, Karen L.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Habitat identification is an important step in the conservation of at-risk species, but difficult due to the small, fragmented populations of rare species. In particular, fine-scale habitat features that constrain species occurrence may not be captured by landscape models. Thus, I used both modeling and field-based approaches to identify habitat characteristics for the endangered dwarf wedgemussel, Alasmidonta heterodon. Community analyses and modeling were combined to identify characteristics of suitable habitat for A. heterodon in the Maryland Coastal Plain. Community analyses suggested that landscape, rather than biological, surrogates would be preferable for predictive habitat modeling. Subsequent MaxEnt modeling associated A. heterodon habitat in the Maryland Coastal Plain with the following variables: depth to the water table, pasture/hay land cover, woody wetlands, low intensity development, Tertiary-aged sediments, and minimum elevation. The results from this model directed field work to evaluate thermal, geochemical, and physical characteristics of A. heterodon reaches throughout the species' range. Paired air-water temperature sensors placed in A. heterodon reaches suggested a potential thermal threshold of 29°C. Southern sites had higher maximum water temperatures but exhibited less diurnal variation and lower rates of temperature change than northern sites; characteristics that suggest intermediate to deep groundwater sources. Physical and chemical characteristics were measured along the length of Flat Brook, a stream with A. heterodon in the Delaware River basin. Data indicated that the mussel occurred in reaches that were stable during bankfull and lower discharges and water chemistry data indicated saturation with respect to aragonite during summer base flow. Field studies suggest several potential essential habitats for A. heterodon: (1) habitats with stable streambeds at bankfull and lower discharges; (2) stream waters in equilibrium with aragonite precipitation during baseflow conditions; and (3) habitats with maximum temperatures < 29°C and stable thermal regimes. The different thermal regimes and contributing groundwater sources between northern and southern populations suggest that geographic region be a consideration in species' reintroductions. Until essential habitats are identified and management plans instituted, all populations should be similarly protected and the loss of individual populations prevented.Item Marine influence on juvenile fish trophic ecology and community dynamics in Maryland's northern coastal lagoons(2013) O'Brien, Michael Henry Patrick; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Marine influence on Maryland's juvenile lagoon fish community was examined under varied levels of internal and external forcing. In 2009, stable isotope analysis showed increasing marine carbon dependency by bay anchovy with decreasing distance to the marine inlet. Following large seagrass losses, no similar trend was detected in 2012. Weakfish showed no structured dependence on marine carbon in either year. Diet contents lacked corresponding year-to-year changes in pelagic versus benthic prey items. In 2009, serial changes with distance to the inlet occurred in species assemblage, which may have been associated with internal seagrass structure. No gradient occurred in 2012. Analysis of a 24-year survey indicated a shift from marine-pelagic to structure-oriented species, associated with increased seagrass and tide level, and decreased North Atlantic Oscillation index. In Maryland's northern lagoon, the strength of marine influence on juvenile assemblages depended on the interplay between internal bay structure and external marine forcing.Item Taurine: An Indispensable Ingredient in the Development of Sustainable Aquafeeds(2013) Watson, Aaron Mackenzie; Place, Allen R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquaculture as a global industry is at a crossroad; increased production cannot rely on the unsustainable harvest of forage fish for feed production. The use of fishmeal and fish oil as components in feeds for aquaculture, most notably for high value marine carnivores must be reduced or eliminated. The most promising and sustainable sources of replacement feed must be plant derived, such as soybean meal, wheat flour, and corn gluten along with dozens of other plant derived sources. Likewise for fish oil the most promising sources are plant oils such as soybean and canola oil supplemented with necessary omega-3 fatty acids. This work was undertaken to examine the effects of switching marine carnivores from fishmeal-based feeds to fishmeal-free, plant-based diets. The majority of this research has been conducted with cobia, Rachycentron canadum, a promising species for intensive aquaculture due to its rapid growth rates, high disease resistance, and lack of a major commercial fishery as competition. A variety of plant proteins, plant protein blends and alternative lipid sources were examined for digestibility and efficacy as fishmeal replacement sources in regards to their effects on growth rates, feed conversion, and a range of physiological characteristics. This work has explored the hypothesis that marine carnivores have lost the ability to synthesize taurine, a non-protein amino acid, in sufficient quantities and must therefore be supplied through the diet, and should be considered essential for all marine carnivores. By measurement of gene expression of the genes in taurine biosynthesis, this work shows that cobia do not possess the ability to regulate taurine biosynthesis confirming taurine must be supplied through the diet. Overall, this work has developed multiple plant protein-based feeds that perform equivalently or better than commercial and commercial-like diets. Taurine has been shown to be an essential ingredient when seeking to reduce or preferably, eliminate fishmeal and thereby making aquaculture sustainable in providing protein to meet the world's growing population.Item SEA LAMPREY (PETROMYZON MARINUS) POPULATION DYNAMICS, ASSESSMENT, AND CONTROL STRATEGY EVALUATION IN THE ST. MARYS RIVER, MICHIGAN(2013) Robinson, Jason Michael; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The St. Marys River is a major producer of invasive parasitic sea lampreys (Petromyzon marinus) to Lake Huron. My dissertation seeks to inform the management process for sea lamprey through a combination of statistical and simulation modeling. In Chapter 1, I developed a spatial age-structured model and applied it to the sea lamprey population in the St. Marys River. The model included a stock-recruitment function, spatial recruitment patterns, natural mortality, chemical treatment mortality, and larval metamorphosis. Recruitment was variable, and an upstream shift in recruitment location was observed over time. During 1993-2011, transformer escapement decreased by 86%. The model successfully identified areas of high larval abundance and showed that areas of low larval density contribute significantly to the population. In Chapter 2, I evaluated six methods of estimating sea lamprey density and abundance including the currently used sampling-based estimates, generalized linear and additive models, the population model from Chapter 1, and a hybrid approach. Methods were evaluated based on accuracy in matching independent validation data. The hybrid method was identified as the best method to inform sea lamprey control decisions in the St. Marys River due to its consistent performance. In Chapter 3, I used a resampling approach to estimate the effect of sampling intensity on the success of sea lamprey control and examined the economic tradeoff between assessment and control efforts. Sea lamprey control actions based on assessment outperformed those implemented with no assessment under all budget scenarios. The sampling intensity that maximized the number of larvae killed depended on the overall budget, with increased sampling intensities maximizing effectiveness under medium to large budgets. In Chapter 4, I conducted a management strategy evaluation using a stochastic simulation model to evaluate several fixed and survey-based Bayluscide-based treatment strategies for sea lamprey. The model incorporated population dynamics, sampling and assessment, and larval control actions. Treatment options with higher cost resulted in larger long-term reductions in transformer escapement, but increasing treatment effort did not result in a proportional decrease in transformer escapement. Survey-based treatment scenarios were the most desirable from both an economic and population control perspective.