This is a RAPID proposal to assess the immediate impact of the Deepwater Horizon oil spill on near-by resident populations of endangered whale species (sperm whales and beaked whales) and prediction of the long-term effects of the disaster on their population dynamics using statistical and mathematical modeling. The project includes three components: 1) an acoustic experiment in the vicinity of the incident to collect population estimates data and comparison to similar collected data from previous years; 2) the development of statistical models to quantitatively estimate the population of marine mammals before and after the incident in the vicinity of the disaster; 3) the development of a mathematical model to describe the dynamics of the whale population that will be used to evaluate the long term impact of the spill on whale populations.
This project is one of a kind to assess the adverse impact of the BP oil-spill on the marine ecosystem in general, and marine mammal populations of specific species in particular, in and around the oil-impacted area of the Gulf of Mexico. Acoustic data will be collected near the sites where marine mammal phonations were collected by the Littoral Acoustic Demonstration Center in 2001, 2002, 2007 and are as close as 9 miles from the BP oilspill incident site. Therefore, the newly collected data will be unique as we will be able to compare them to the previous data, which will provide base-line estimates of the marine mammal population density. Successful project implementation will provide not only environmental impact assessment of a large-scale oil spill on several species of marine mammals (including endangered sperm whales), but also the foundation for development of a new systematic methodology of population estimation and dynamics based on acoustic cues; this is in contrast with the traditional methodology which is based on visual observations. The collected data, which will be useful for ecologists in the future, and the theoretical research associated with the project will shed light on the debate concerning how the Gulf of Mexico has been affected by the oil-spill. This can help the policy makers in the future. This project will not only assess the impact of the BP oil-spill on marine species in the impacted area, but also can work as a paradigm in the future for similar manmade or natural disasters. The proposed research, with a strong theoretical component, will complement other existing and ongoing research on the BP oil-spill. Furthermore, articipating graduate students will receive valuable interdisciplinary training ranging from data analysis to statistical and mathematical modeling of marine mammal population dynamics.
Prior to the Deep Water Horizon oil spill in 2010, The Louisiana Acoustic Demonstration Center (LADC) possessed acoustic data on marine mammals in three locations of the Gulf of Mexico (GOM) which are 9, 25, and 50 miles away from the oil spill incident. To assess the impact of this spill on a resident sperm whale population, in September 2010 LADC scientists deployed three pairs of environmental acoustic recording system buoys with one pair at each of the three prior locations. The buoys recorded acoustic data on marine mammals continuously for 12 days. Our team was then able to devise methodology to analyze the data before and after the oil spill, estimate the population abundance of sperm whales, and compare the two population abundance estimates before and after the oil spill. Our analysis reveals a decrease in post spill acoustic activity and abundance of sperm whales at the 9-mile site by a factor of 2; whereas acoustic activity and abundance at the 25-mile site has clearly increased post spill. This indicates that some sperm whales may have relocated farther away from the spill site. Follow-up experiments will be important for understanding if such relocation is a long-term one. In order to better understand how man-made disasters may impact marine mammals, we developed a model which describes the changes of the endangered GOM sperm whale population over time. Our modeling tool shows that when using average estimates for the vital (survivorship and maturation) rates of sperm whales, this population is suppose to be growing at a 0.96% annual rate. This shows that the sperm whale population grows slowly and is potentially susceptible to any natural or man-made disaster. When using the worst case estimates for vital rates, the population is supposed to be declining at a rate of 3.6% per year. This means that given this worst cases scenario the population of sperm whales would eventually become extinct. Our analysis further shows that the future growth of the GOM sperm whale population is highly sensitive to small variations in survivorship rates of individual whales, especially that of the matured females. Because of the fragile nature of the population structure, the average scenario growth rate of 0.96% of the GOM sperm whale population can be threatened by any destabilizing factor, be it man-made or natural, pushing the population to lower densities and possibly extinction. It has been indicated by our study that if a disaster, such as oil spills, reduces the survivorship rate of the matured female sperm whales by as little as 2.2% or the survivorship rate of mothers by 4.8%, then the population may begin to decline. Thus, to what extent the external factors may affect the survival rates of sperm whales must be carefully investigated in future studies.
