Award: OCE-1043261

Following the Deepwater Horizon Oil spill, in September 2010 our team conducted a 7 day cruise aboard the RV Pelican to the Louisiana shelf (Figure 1). We completed 12 cross-shelf transects, which included acoustic surveys for plankton and fish, and generated distribution maps of various physical properties, including dissolved oxygen, temperature, salinity, chlorophyll a fluorescence, and colored dissolved organic matter (CDOM). CDOM, which in some cases can be used as a proxy for oil, appeared to be associated with river flow from the Atchafalaya River and Mississippi River. Low dissolved oxygen was observed in patches, primarily in the deeper regions of transects in the middle and eastern portions of the Louisiana shelf. An additional vessel used trawls at discrete points along each transect to collect fish for species identification to verify acoustic surveys. This field work builds on 5 previous years of high-resolution mapping of hydrography, oxygen, plankton and fish in the northern Gulf of Mexico, including our previous survey region in the "hypoxic zone" west of the Mississippi Delta. Our "metrics" of species diversity and abundance, fish diets, fish growth rate potential and ecosystem models will all be extremely useful to assess the possible effects of the oil spill on the living resources of the northern Gulf of Mexico. Our team is comprised of partners from University of Maryland, Oregon State University, East Carolina University, Louisiana State University, NOAA Great Lakes Environmental Research Laboratory, University of Akron, and University of Michigan. Fish acoustic surveys from the 2010 cruise revealed interesting patterns in dissolved oxygen and fish response. We saw a "double layer" of low dissolved oxygen in portions of the water column, with DO sharply dropping below 15m depth, increasing to higher oxygen below 17m depth, and then gradually decreasing to the bottom of the water column. Acoustic surveys showed fish distributed themselves along oxygen gradients (Figure 2). Scattering strength, which serves as a proxy for fish abundance, revealed high densities of fish in both the eastern portion of our survey area in shallow nearshore areas, as well as in the western region a bit further offshore (Figure 3). Preliminary identification of fish species from trawling suggests that high numbers of croaker were caught throughout the survey area. These and other data are currently being incorporated into our ongoing living resource modeling efforts to provide spatially-explicit habitat assessment for fishes in areas of the northern Gulf of Mexico affected by low oxygen and the oil spill. Last Modified: 12/06/2011 Submitted by: Stephen Brandt