UMD Theses and Dissertations
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Item GEOSTATISTICAL ESTIMATION OF BLUE CRAB CALLINECTES SAPIDUS ABUNDANCE IN CHESAPEAKE BAY AT LOCAL SCALES(2022) Jones, Sarah Ann; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increases in the sizes of container ships due to the expansion of the Panama Canal has increased the need for dredging activities in the Chesapeake Bay. Placement of dredged material in the Bay is restricted to winter months owing to concerns for threatened and endangered species. Placement of dredged material in the lower Chesapeake Bay in Wolf Trap Alternate Open Water Placement Site (WTAPS) overlaps with overwintering locations for mature female blue crab. To estimate the potential magnitude of winter mortality in WTAPS and WTAPS Northern Extension (WTAPSNE) resulting from placement of dredged material, a range of geostatistical tools (e.g., inverse distance weighting and kriging) were used to map the distribution and estimate the abundance of blue crab in Chesapeake Bay, WTAPS, and WTAPSNE (i.e., small-scale estimation) from 1990–2020 using data from the winter dredge survey. These analyses indicated that a low proportion of the age-1+ female blue crab population occurs within WTAPS and WTAPSNE (<1.18% and <1.5% respectively). Variability of abundance estimates was high when female age-1+ abundance was less than 150 million in the Chesapeake Bay. Therefore, we suggest the Port limit placement of dredged materials in WTAPS and WTAPSNE when female age-1+ abundance is less than 150 million; we recommend the Port not undertake placement activities when the stock is declared overfished (i.e., when female age-1+ abundance is less than 72.5 million).Item Influence of prey density and dietary supplementation on the growth and development of the blue crab, Callinectes sapidus(2017) Maurer, Leah Marie; Chung, Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The early developmental stages of arthropods often vary and appear to be influenced by dietary conditions. It is hypothesized that food availability and dietary components may affect the number and length of developmental stages of the blue crab, Callinectes sapidus, specifically those that are reared in aquaculture settings. This hypothesis was examined with C. sapidus 1) larvae and 2) juveniles. 1) During the zoeal period, development from stage 1 to megalopae was monitored under a full factorial experiment with treatments: high and low prey density coupled with and without poly-β-hydroxybutyrate (PHB) supplementations. Our data showed that prey density influences variation in the zoeal development of C. sapidus by increasing stage skipping, reducing the number of the stages from 7-8 to 5-8. Additionally, a high prey density coupled with PHB supplementation caused increasing instances of stage skipping. 2) During the juvenile period, the growth was monitored for three molting events (57-165 days) under the following treatments: 0, 5, 10, and 20% chitin supplemented diets and squid control. Our data showed that chitin supplementation did not affect the growth of the juvenile C. sapidus (molt increment or interval).Item Mark-Recapture Assessment of the Recreational Blue Crab (Callinectes sapidus) Harvest in Chesapeake Bay, Maryland(2016) Semmler, Robert Semmler; Reaka, Marjorie L; Hines, Anson H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In Maryland, commercial blue crab (Callinectes sapidus) harvests are monitored through mandatory, annual harvest reporting, but no monitoring exists for recreational fishers. This study used a large-scale mark-recapture program to assess relative exploitation between the recreational and commercial fishing sectors in 15 harvest reporting areas of Maryland, then incorporated movement information and extrapolated reported commercial harvest data to generate statewide estimates of recreational harvest. Results indicate spatial variation in recreational fishing, with a majority of recreational harvests coming from tributaries of the Western Shore and the Wye and Miles Rivers on the Eastern Shore. Statewide, recreational harvest has remained 8% as large as commercial harvest despite management changes in 2008, and remains a larger proportion (12.8%) of male commercial harvest. In addition, this study provides detailed spatial information on recreational harvest and the first information on rates of exchange of male crabs among harvest reporting areas.Item DEVELOPMENT OF A NUCLEIC ACID-BASED SPECIFIC GROWTH MODEL FOR JUVENILE BLUE CRAB, CALLINECTES SAPIDUS(2016) Zaveta, Danielle Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The evaluation and identification of habitats that function as nurseries for marine species has the potential to improve conservation and management. A key assessment of nursery habitat is estimating individual growth. However, the discrete growth of crustaceans presents a challenge for many traditional in situ techniques to accurately estimate growth over a short temporal scale. To evaluate the use of nucleic acid ratios (R:D) for juvenile blue crab (Callinectes sapidus), I developed and validated an R:D-based index of growth in the laboratory. R:D based growth estimates of crabs collected in the Patuxent River, MD indicated growth ranged from 0.8-25.9 (mg·g-1·d-1). Overall, there was no effect of size on growth, whereas there was a weak, but significant effect of date. These data provide insight into patterns of habitat-specific growth. These results highlight the complexity of the biological and physical factors which regulate growth of juvenile blue crabs in the field.Item ECOLOGY OF A FATAL BLUE CRAB VIRUS: DETECTION, RANGE, AND PREVALENCE OF CALLINECTES SAPIDUS REO-LIKE VIRUS(2015) Flowers, Emily Maya; Schott, Eric J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Callinectes sapidus reo-like virus (RLV) is a fatal to blue crabs and consistently found within the Chesapeake Bay. Development of a sensitive and reliable RT-qPCR assay permitted a precise assessment of RLV prevalence in crabs captured from locations near and far from soft-shell crab production sites. Viral prevalence was temporally and spatially highly variable, but outbreaks of RLV appeared to be localized to an area of 1 - 2 km2. When significantly different between sites, higher prevalence was observed near soft-shell crab production. RLV prevalence was not correlated with crab characteristics, with the exception of larger mean carapace width for infected crabs. Sequences of RLV PCR products were used to compare genotypes of outbreak and non-outbreak infections. Identical genotypes were found in outbreaks from the middle Chesapeake Bay and Long Island, NY. Together, the prevalence and genetic data are consistent with RLV outbreaks being caused by focal spread of the virus through a local population.Item An evaluation of the synchronization in the dynamics of blue crab (Callinectes sapidus) populations in the western Atlantic(2011) Colton, Amanda Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Blue crab populations along the east coast of the United States are known to fluctuate in size annually. Previously, the degree of coherence in abundance between these populations was unknown. My research used a combination of fishery-dependent and fishery-independent data to quantify the amount of synchrony among blue crab populations and to determine the mechanisms that drive abundance fluctuations. This was done by first fitting catch-survey models to time series of survey abundance and catch to obtain absolute abundance estimates. Subsequently, I used multivariate techniques to quantify the extent and pattern of synchronization. I found that a latitudinal pattern among blue crab populations exists among all the regions except Chesapeake Bay, which appeared to be anomalous. A combination of larval mixing in the coastal ocean and a Moran effect appear to be drivers of the synchrony among blue crab populations although more investigation into these mechanisms is needed.Item THE MITOCHONDRIAL GENOME OF THE BLUE CRAB (CALLINECTES SAPIDUS), AN INFORMATIVE GENETIC MARKER FOR THE EVOLUTIONARY BIOLOGY AND POPULATION GENETICS OF THE SPECIES(2009) Feng, Xiaojun; Place, Allen R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The blue crab (Callinectes sapidus) is a widely distributed decapod which ranges from Nova Scotia to the northern Argentina coasts. It is one of the most abundant estuarine invertebrates, supporting both commercial and recreational fisheries along the Atlantic and Gulf coasts. This thesis presents data clearly establishing the unprecedented hyper-variability in the mitochondrial genome of C. sapidus. This variation extended to multiple regions, including the cox1, nad2, and nad4 protein coding loci as well as ribosomal 12s RNA molecule. The haplotype diversity of the nad2 gene approached 1, with a nucleotide diversity approaching 1%. This hyper-variability in the mtDNA allows using a single mtDNA gene (nad2) to distinguish hatchery-produced crabs from wild crabs after release to the wild. I found no dominant mtDNA haplotypes in wild populations but instead a distribution of a few low-frequency recurrent haplotypes with a large number of singletons. Because of this high diversity and extensive population mixing, the geographic structure in wild populations exhibits panmixia from the Atlantic to Gulf of Mexico. Some of the high genetic diversity found seems to stem from the heteroplasmic nature of the blue crab mtDNA. By cloning high fidelity PCR products, I confirmed single individual crab and megalopa harbored dozens of copies of mitochondrial haplotypes. A copy number analysis indicates discovery of unique haplotypes was probably not saturated with the possibility of inadequate sampling. The heteroplasmy in the blue crab appears to be under maternal inheritance without paternal contribution. While minor haplotypes are represented in wild populations, other minor haplotypes contained stop codons and/or non-synonymous substitutions which may influence the viability of the mitochondria. Given the blue crab inhabits a broad variety of environments and that the mtDNA genome appears to be under selective pressure, the potential for mtDNA functional correlates with this genetic diversity maybe at the basis for the robust physiological capability of the species.