Master of Science (MS)
Oceanography and Coastal Sciences
Blue runner (Caranx crysos), common around offshore petroleum platforms in the Gulf of Mexico, were found to forage extensively on meso- and macro-zooplankton during the summer months. Larval decapods and stomatopods, hyperiid amphipods, pteropods, and larval and juvenile fishes were common components of their diet. Feeding periodicity results suggest that blue runner around platforms were capable of feeding throughout the night at the same intensity as the day. Size selectivity indicated that larger prey, such as fish were consumed during the night and smaller decapod crustaceans were consumed during the day. Blue runner collected from open waters away from platforms also consumed decapods and larval fish as well as other abundant zooplankton such as chaetognaths. Although certain zooplankton taxa exhibited increased densities near the platform during some cruises, plankton net sampling did not demonstrate consistently elevated densities of zooplankton in proximity to petroleum platforms. Zooplankton density was generally greater during the night samples, however a platform enhancement effect was not observed. Results from ADCP surveys suggested that zooplankton and ichthyoplankton contributed to the measured volume backscattering strength. Diel and between-cruise changes in zooplankton density were correlated with changes in acoustic scattering levels during acoustic surveys conducted around the platforms. These surveys demonstrated the utility of an ADCP to examine small-scale patterns in sound scattering layers in surface waters around platforms, however preliminary analysis did not establish that elevated (or reduced) levels of scattering existed near platforms. Examination of more surveys along with including data on current velocity will provide further insight into the localized effects of these structures. The net and acoustic data collected in this study suggested that more intensive sampling closer to platforms is needed to understand how these structures support large aggregations of fishes such as blue runner.
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Keenan, Sean Francis, "The importance of zooplankton in the diets of blue runner (Caranx crysos) near offshore petroleum platforms in the northern Gulf of Mexico" (2002). LSU Master's Theses. 670.
Mark C. Benfield