Evaluation of bird impacts on historical oil spill cases using the SIMAP oil spill model

The impact of an oil spill on bird and other wildlife species can be estimated using the Spill Impact Model Application Package (SIMAP). SIMAP estimates exposure and impact on bird species and their habitat based on physical fate and biological effects models under a broad range of environmental conditions. This paper presented the evaluations of 14 spill case studies which compared model predictions of biological impacts with field observations after a spill. Most of the observational data on the biological impacts of spills was for oiled birds and other wildlife. The impact of an oil spill on fish and invertebrates was examined in one case study. Error analysis was not performed on the field-base estimates of impact. Biological abundances and impacts are highly variable in time and space and very difficult to measure and quantify. Model-predicted and field-based estimates of oiled wildlife were compared. Uncertainty in the model-predicted number of oil wildlife was most related to mapping of biological distributions, behaviour of individuals, and local population density at the time of spill. The greatest uncertainty was the pre-spill abundance. The number of animals oils was found to be directly proportional to the pre-spill abundance assumed in the model inputs. Relative impact can be inferred from the percentage of population oiled. The total number oiled by a spill can be extrapolated using trajectories of oiled birds and counts of oiled animals collected in the field. 54 refs., 16 tabs., 12 figs