The Deepwater Horizon Oil Spill (DWHOS) was primarily a deep-pelagic event. Variable amounts of discharged hydrocarbons reached the ocean surface and/or seafloor, whereas 100% occurred within the water column. Understanding this pelagic habitat is important because about half of all fish species that occur in the Gulf of Mexico (GoM) spend all or part of their lives in the open ocean. Most mesopelagic (200-1000 m depth) species of fishes vertically migrate each night to feed in epipelagic (0-200 m) depths and return to deep water during the day. This behavior affects rapid cycling of natural and anthropogenic material in the water column. Deep-pelagic fishes are prey for gamefishes, seabirds, and marine mammals. Given the steady growth of oil exploration and operations, the likelihood of future spills emphasizes the need to document acute and chronic effects on pelagic fauna. The DEEPEND (Deep-Pelagic Nekton Dynamics) Consortium will conduct a 3-year sampling and analysis program that builds on two intensive NOAA-supported surveys during 2010-11. DEEPEND will focus on short-term and long-term timescales to appraise the dynamic nature of communities using a suite of integrated approaches. These investigations include: 1) a direct assessment of GoM deep-pelagic community structure including the physical and biological drivers of this structure; 2) a time-series analysis/comparison of biophysical data from the years 2010- 2011 and 2015-2017; 3) a time-series examination of differences in genetic diversity among key species; and 4) a biogeochemical analysis of the effect of DWHOS on pelagic biota.