Changes in the productivity of recreational and commercial fisheries in the Gulf of Mexico can have profound ecological and economic consequences. Next to issues of food and human safety, one of the most immediate questions following the Deepwater Horizon (DWH) oil spill, and subsequent use of dispersants, was to ask to what extent the spill impacted the growth and productivity of important recreational and commercial fisheries in the Gulf of Mexico. The proposed research focuses on this question through Project Theme iii, which addresses the “Environmental effects of the petroleum/dispersant system on the sea floor, water column, coastal waters, beach sediments, wetlands, marshes, and organisms; and the science of ecosystem recovery.” To address this concern, growth of representative fish species will be compared before and after the DWH oil spill event, with additional comparison to a control area that was not physically impacted (i.e., following a Before-After-Control-Impact, or BACI, design). Age-specific growth of fish prior to the DWH oil spill will be estimated using their otoliths, which are calcareous structures found in the inner ear of finfishes. Otoliths show annual patterns of concentric growth rings similar to a cross-section of a tree trunk, and they record the entire growth history of the fish from birth to capture. Fish species chosen for this study are representative of different habitats (inshore estuarine areas, reefs, sand/mud, offshore waters) and trophic levels (detritivore, demersal carnivore, piscivore, pelagic carnivore), and include spotted seatrout, red drum, striped mullet, sheepshead, southern flounder, red snapper, gag, gray snapper, greater amberjack, and king mackerel. Spatial and temporal changes in growth of these fishes will be estimated through the growth increments in their otoliths and then incorporated into age-based stock production assessments to estimate changes in productivity. The impact of the DWH oil spill at a fisheries ecosystem level will be modeled using the historical growth of these fishes using otolith sclerochronology, where the widths of the growth increments (rings) are matched to known environmental variables (e.g., El Niño years) in a manner similar to dendrochronology used in forestry. Sclerochronology will be used in combination with multivariate models (Autoregressive Integrated Moving Average or ARIMA models) and intervention (impact) analysis to statistically evaluate impacts of catastrophic events, such as the DWH oil spill. Intervention analysis will estimate whether an event, such as the DWH oil spill, has changed the mean level of growth observed prior to the event, as well as estimate the magnitude of any change. This study will develop the framework to provide a better understanding of the relative impacts of environmental catastrophic events, such as the DWH oil spill, on growth and production of important coastal fish stocks in the Gulf of Mexico.