Evaluating the Fate and Effects of the Deepwater Horizon Oil Spill on Water Column Biota

The Deepwater Horizon oil spill in the northeastern Gulf of Mexico was not only the largest oil spill in US history, but unprecedented amounts of dispersants were applied both at the subsurface release-point and in surface waters to entrain the oil into the water column. The enhanced entrainment and reduction in dispersed oil droplet sizes caused by dispersant use would be expected to increase water column biota impacts. Thus, evaluation of impacts to water column biota is of particular interest for this spill and in consideration of the risks associated with future deepwater blowouts. Oil fates and effects modeling is being used to investigate water column impacts. The on-going water column exposure analysis considers acute impacts to all life stages of fish and invertebrate distributions, and population modeling to determine long-term effects. Existing fisheries-independent time series data is relied upon for such modeling efforts.  In addition to historical data, several offshore deepwater ephemeral and post-spill field surveys were conducted including mesopelagic mid-water trawls, and 1 m² and 10 m² MOCNESS tows. These data are intended to support modeling efforts and supplement important Gulf-wide fisheries-independent survey data.