Browsing by Subject "Texas Coast"
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Item Characterizing the Weather Band Variability of the Texas Coastal Current(2014-07-17) Zimmerle, HeatherCurrent velocities from 21 years (1992-2012) of near-continuous observations are used to investigate the Texas Coastal Current on the western Texas-Louisiana continental shelf in the northwestern Gulf of Mexico. Observations were made using the moored current meters deployed as part of the Texas Automated Buoy System (TABS) and historical current meter data. The general coastal circulation is known to be deterministic, with downcoast flow (westward) in the non-summer months (September-May) and a reversal to upcoast (eastward) flow in the summertime (June-August). This study focuses on characterizing features of the Texas Coastal Current that include the onset, frequency, magnitude, and persistence of current reversals along with the upcoast transport that occurs during reversals. The determined interannual variability of the Texas Coastal Current is imperative for understanding the surface transport of water and mitigating associated coastal hazards, including oil, harmful algal blooms, and hypoxia. Results show the onset of the upcoast reversal during the summer with a mostly downcoast flow during the non-summer at upper Texas coastal locations. More persistent currents are observed during the non-summer in the downcoast direction within the weather band frequencies (2-15 days). Currents with longer persistence are found to be relatively slow, generally below 10 cm s^(-1). Fast currents (> 50 cm s^(-1)) tend to be short-lived, typically lasting less than 72 hours. Maximum upcoast transport is observed along the upper coast during the summer, reaching a minimum in the winter and fall. A relationship between the along-shore wind stress and along-shore current velocity is indicated, signaling that the Texas Coastal Current is mostly wind-driven. Spatial variability is present along the southern Texas coast. Current flow is directed downcoast during the summer and slightly downcoast during the non-summer at buoy J, the southernmost location. Currents near the coastal bend tend to be upcoast during the non-summer and slightly downcoast during the summer. Longer persistence is observed at the southern location in the downcoast direction during the summer, with several currents lasting longer than 15 days. Maximum upcoast transport is present during the winter along the southern Texas Coast, reaching a minimum during the summer. Some evidence of a relationship between the along-shore wind stress and along-shore current flow are present, indicating some wind-driven forcing on the current flow. Less seasonal variability is present at offshore locations. Locations on the outer shelf display a general upcoast flow regardless of season. Longer persistence is observed in the upcoast direction on the outer shelf during the summer and non-summer. Maximum upcoast transport is present during the non-summer at all offshore locations. Little correlation is found between seasonal winds and along-shore current flow, meaning mesoscale features, such as Loop Current eddies, provide offshore current forcing.Item Ecological and Molecular Characterization of Avian Influenza Viruses Obtained from Waterfowl on the Texas Coast(2011-10-21) Ferro, Pamela JoyceWe collected 6,823 cloacal swabs over four years (2005?2006: 1,460; 2006? 2007: 2,171; 2007?2008: 2,424; and 2008?2009: 768) from 30 potential avian host species. Most samples (88.3 percent) were from dabbling ducks (genus Anas), while diving ducks (genus Aythya) accounted for 5.0 percent, and geese (genera Anser, Chen, and Branta) 3.0 percent of the samples tested. Waterfowl (Anatidae) comprised 98.7 percent of samples, with 1.8 percent from non-migratory dabbling ducks (genus Anas). All samples were screened for avian influenza virus (AIV) by AIV-matrix real-time RT-PCR (rRT-PCR); all rRT-PCR positive samples (541) were processed for virus isolation as well as 4,473 rRT-PCR negative samples. Differences were observed in apparent prevalence estimates over the four years between virus isolation (0.5, 1.3, 3.9, and 0.7 percent) and rRT-PCR (5.9, 6.5, 11.2, and 5.5 percent). We isolated 138 AIVs, of which two were obtained from rRT-PCR negative samples. Unlike previous reports of seasonal variation in AIV prevalence, we documented differences in prevalence estimates among months using rRT-PCR only during 2008?2009 and by virus isolation only during 2006?2007 and 2007?2008. Several of the AIV subtypes we identified are common in North America (e.g., H3, H4, and H6); H3N8 and H4N6 were the most common subtype combinations isolated. Similar to most surveillance studies, we found no significant difference in AIV infection based on host sex, but did find that juveniles were more likely to be positive for AIV than adults. We also documented that dabbling ducks were more likely to be positive for AIV than diving ducks, although not all dabbling ducks are equally likely to be positive. Molecular sequence analysis revealed no insertions of multiple basic amino acids at the cleavage site, which supported the identification of low pathogenic AIV. Phylogenetic anlyses performed on H5, H6, H7, N1, N2, N3, and N4 subtypes sequenced indicated similarity to other North American isolates with the exception of seven H6 which were more similar in amino acid translation to an isolate from Japan. In sum, this is the first multiyear study of avian influenza viruses on waterfowl wintering grounds of the Central Flyway, a historically understudied area of North America.Item Stable Isotope Dynamics in Cownose Rays (Rhinoptera bonasus) within the Northwestern Gulf of Mexico(2014-07-25) St. Clair, Katherine IThe cownose ray (Rhinoptera bonasus) is a durophagous mesopredator that exerts for top-down control on commercial shellfish stocks along the Atlantic coast. Although the trophic ecology of this elasmobranch has been the subject of extensive investigation, there is limited information available on feeding patterns of cownose rays in the northwestern Gulf of Mexico. Stable isotope analysis has been used to study the foraging ecology of various species, but only recently applied to elasmobranchs. Therefore, this study conducted a controlled feeding trial to determine incorporation rates and diet-tissue discrimination factors for ?^(13)C and ?^(15)N in cownose ray epidermal tissue. Additionally, this study investigates ?^(13)C and ?^(15)N variability in cownose rays captured via entanglement nets, from surveys along the Texas coast from 2009 ? 2012. This is the first study to report ?^(13)C and ?^(15)N incorporation rates in elasmobranch epidermal tissue; estimated ?^(13)C and ?^(15)N incorporation rates were 0.0018 ? 0.0003 days^(-1) and 0.0059 ? 0.0022 days^(-1), respectively. Isotopic incorporation rates were highly variable amongst individuals but did not vary significantly with ray size (disc width or weight). Isotopic equilibrium was not reached between the epidermal tissue and the dietary treatment levels; therefore, estimated diet-tissue discrimination factors (?^(13)C = 4.26? and ?^(15)N = 0.69?) could not be applied for analyses of wild populations. Relative size of Bayesian ellipses, denoting the isotopic niche of cownose rays, varied seasonally in the lower Laguna Madre, with Summer 2012 significantly smaller than all other sampling periods. Female mean ?^(13)C signatures were significantly enriched compared to those of males, indicating that female rays are foraging over longer periods of time within inshore habitats. Isotopic niche size was comparable across the Texas bay systems in 2012, with only the lower Laguna Madre (Spring) significantly smaller. However, mean ?^(13)C and ?^(15)N in cownose rays varied spatially across bay systems along the Texas coast. This initial exploration into the trophic ecology of cownose rays within the northwestern Gulf of Mexico provides evidence of temporal and spatial variability in isotopic signatures, potentially aiding scientists in the management of this species.