Browsing by Subject "southern flounder"
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Item Distribution, condition, and growth of newly settled southern flounder (Paralichthys lethostigma) in the Galveston Bay Estuary, TX(Texas A&M University, 2006-08-16) Glass, Lindsay AnnSeveral flatfish species including southern flounder (Paralichthys lethostigma) recruit to estuaries during early life. Therefore, the evaluation of estuarine sites and habitats that serve as nurseries is critical to conservation and management efforts. I used biochemical condition and growth measurements in conjunction with catch-density data to evaluate settlement sites used by southern flounder in the Galveston Bay Estuary (GBE). In 2005, beam-trawl collections were made in three major sections of the GBE (East Bay, West Bay, Galveston Bay), and three sites were sampled in each bay. Within each sampling site, replicate collections were taken from 1) the marsh edge, 2) an intermediate zone, and 3) the open bay. The average size of southern flounder collected was between 12 and 19 mm standard length, and peak densities occurred in January and February. Catch data indicated that numeric densities of southern flounder were significantly greater in East Bay (2.75 per 100 m2) than in West Bay (0.45 per 100 m2) or in Galveston Bay (0.91 per 100 m2). Habitat-specific variation in density was not found. Otolith-based estimates of age indicated that the majority of southern flounder collected were 35-45 days old and derived from early December to early January hatch-dates. Growth rate differences were negligible across bays and habitats, with the average growth rate being 0.40 mm/day (range 0.21-0.76 mm/day). RNA:DNA ratios indicated that newly settled southern flounder in the GBE were in relatively high condition. Habitat-specific differences in RNA:DNA ratios were not observed; however, ratios were significantly lower in West Bay (average 8.0) than in East Bay (average 9.5) or in Galveston Bay (average 9.8), suggesting the condition of new recruits may vary across the GBE. Findings from this study indicate that southern flounder use a variety of habitats within the GBE during early life, and survival and recruitment success appear favorable regardless of settlement site. As a result, recruitment success of southern flounder may be less a function of the quality of nursery sites/habitats within the GBE than of other factors (e.g., larval supply to the estuary).Item Spatial and Temporal Shifts in Estuarine Nursery Habitats Used by Juvenile Southern Flounder (Paralichthys lethostigma)(2012-10-19) Furey, NathanielSouthern flounder (Parlichthys lethostigma) is a recreationally and commercially important flatfish species found in the Gulf of Mexico, and recent analyses indicate that the northern Gulf of Mexico population is in decline. For proper management, knowledge of habitats used throughout the juvenile stage is needed. The aim of the current study is to examine habitat use of young-of-year (YOY) southern flounder in the Galveston Bay complex using habitat distribution models and acoustic telemetry. A set of habitat distribution models examined how habitat use changes during the first year of life. In addition, southern flounder were tagged with acoustic telemetry transmitters and monitored with a novel receiver array that allows for measurements of fine-scale movements. These movements were compared to habitat maps to examine habitat selection. Habitat distribution models determined that habitat requirements for southern flounder change with ontogeny and season. Newly settled southern flounder were most influenced by physicochemical parameters and the presence of seagrass beds. YOY southern flounder, however, showed increased occurrence at freshwater inlets during summer and fall months, and occurrence decreased at tidal inlets during the fall. Predictions of habitat suitability across the Galveston Bay complex indicate that the factors influencing occurrence of southern flounder change with season, ontogeny, and availability of suitable habitats. With acoustic telemetry, it was apparent that habitat use by southern flounder was nonrandom and influenced by benthic and other physicochemical conditions. Habitat analyses indicated that southern flounder used sand habitats more frequently than seagrass, oyster reef, or salt marsh habitats. Telemetry results also indicated that depth and water temperature were important determinants of habitat suitability for YOY southern flounder, with individuals preferring deeper and cooler regions of the water column in Christmas Bay. Both model and telemetry analyses indicate that habitat use by YOY southern flounder is dynamic across multiple spatial and temporal scales, with distributions and movements influenced strongly by ontogenetic changes in habitat associations, temporal and spatial variability in physicochemical conditions, and tidal cycles.