Chronological effects of the Deepwater Horizon Gulf of Mexico oil spill on regional seabird casualties

In April 2010, the Deepwater Horizon (DH) oil platform in the Gulf of Mexico vented oil uncontrollably for 90+ days. This ʹpersistentʹ spill resulted in oil washing up daily on the shoreline of numerous Gulf of Mexico states, and created an oil spill lasting 30 times longer and 5 times larger than the ʹrapidʹ 1989 Exxon Valdez (EV) spill. There is ongoing controversy regarding the effect of oil spills on seabird population, with few opportunities to analyze its daily effect. This paper describes the daily effect of the DH spill regarding the number of seabirds recovered alive and dead, and compared its overall population effect to the EV spill. Analyzing daily seabird collection data between days 38-138 after the DH spill, the dead bird collection average (48.2+35.5/day) was significantly (p<0.05) more than the live bird collection average (20.8+27.0/day). Data also shows a significant reduction in daily intake of live seabirds after day 110, while the daily dead bird intake saw a significant increase. Between days 110 to 138, live seabird collections only rose by 206 compared to the dead bird collection of 1834. The EV spill yielded 600+ live birds and 35,000 dead ones while the DH spill had 2053 live birds but only 7726 dead ones despite the DH spill being 5 times smaller in spill size. This data reveals that after 110 days of a ʹpersistentʹ spill, collecting live birds significantly decreases while the number of dead birds increases. Also, there were a significantly lower number of dead birds collected during the ʹpersistentʹ DH spill than the ʹrapidʹ EV spill. This study reveals the first concrete evidence suggesting ʹpersistentʹ oil spills may have a greater environmental impact than ʹrapidʹ spills, and immediate reaction is required to lessen the number of seabird casualties.