Shelf and slope waters in the DWHOS area are known to serve as critical spawning, nursery, and foraging habitat of several important oceanic species including billfishes, tunas, and other pelagic taxa (swordfish, dolphinfishes)—based on ichthyoplankton surveys by DEEPEND investigators. The aim of this component is to investigate potential ecological effects of the DWHOS on pelagic fishes during the early life period. We will contrast catch data of larvae and early juveniles before (2006–2009) during (2010), and after (2015-2017 ~ DEEPEND) the DWHOS to improve our understanding of the causes of temporal variability as it relates to the DWHOS. Generalized additive models (GAMs) will be developed for periods before to characterize habitat associations and create habitat suitability models for assessing potential impacts. In addition, life history and ecosystem parameters that favor the production and survival of pelagic fish larvae collected from 2015 to 2017 will be compared to estimates before (baseline) and after the DWHOS. Ichthyoplankton surveys will be conducted in shelf and slope waters of the NGoM (same location as pre-spill baseline ~ 92-88 W longitude and 27-28 N), and fish larvae and juveniles will be collected from epipelagic waters with two net gears: neuston tows at surface and oblique bongo tows to ~200 m. A suite of environmental parameters will be measured at sea or extracted from remotely sensed/archived datasets to characterize nursery habitats or associations (using GAMs) of selected taxa. After all species are identified (visual or genetic), length and weight of each will be measured, and stomachs will be extracted, weighed, and individual prey items identified to assess potential changes in prey availability. Apart from basic catch numbers, life fitness or life history traits (condition, growth, mortality) and ecosystem health proxies (assemblage biomass and biodiversity) will be determined using baseline and DEEPEND samples.