Natalia A. Sidorovskaia – nas@louisiana.edu
Department of Physics, University of Louisiana at Lafayette
Lafayette, LA
Azmy S. Ackleh
Department of Mathematics, University of Louisiana at Lafayette
Lafayette, LA
Christopher O. Tiemann
Applied Research Laboratories, University of Texas at Austin
Austin, TX
Juliette W. Ioup and George E. Ioup
Department of Physics, University of New Orleans
New Orleans, LA
Popular version of paper 4pAB5
Presented Thursday afternoon, December 5, 2013
166th ASA Meeting, San Francisco
Ocean deepwater ecosystem state, damage, and recovery are usually not the first priorities in assessing the aftermath of environmental stresses and disasters, because they do not immediately impact human health and well-being and represent enormous scientific challenges. However, a change in marine mammal distribution and abundance caused by environmental stresses can have a major impact on the functioning of the whole ocean deepwater ecosystem and at the same time can reflect changes from shallow to deep ocean layers and provide insight into ocean ecosystem health because marine mammals are the final consumers of production at many oceanic layers (Bowen, 1997; Moore, 2008; O'Hara et al., 2005).
A precedent for the need for long-term monitoring of marine mammal stock was established by observation of negative changes in the resident population of Alaskan killer whales during the decade after the 'Exxon-Valdez' oil spill (Matkin et al., 2008). The observed response of the deep water ecosystem to the 'Exxon-Valdez' oil spill showed a critical necessity to establish sites of baseline data collection and consistent long-term monitoring of ecological impact in the ocean areas of high industrial activities.
Our research group, the Littoral Acoustic Demonstration Center, LADC, advocates passive acoustics as a key cost-effective player in interdisciplinary monitoring efforts, because it can provide relevant interpretable information on the health of the deep water ecosystem on different levels from marine mammal regional population estimates to prey distribution based on collection of only acoustic data. (Marques et al., 2009; Ackleh et al., 2012).
At this conference we present results of the study of regional sperm and beaked whale population responses to the recent Gulf of Mexico oil spill in 2010. Oil spills have a major environmental impact on marine life, and the Deep Water Horizon incident site in particular is in an area densely populated by the Gulf of Mexico's resident populations of endangered sperm whales and elusive beaked whales. These whales spend more than half of their time in deep dives more than 100 miles away from land, so visual observations of them and mortality counts are limited, costly, and weather dependent. However, all deep-diving marine mammal species produce powerful sounds (echolocation clicks) unique to their species throughout their dives, and in the last decade analysis of these sounds was introduced as a new tool for abundance estimation when visual observations are unavailable. Long-term monitoring of whale abundance based on acoustic recordings has not yet been pursued, so this paper reports the first attempt to use multi-year passive acoustic data to study the impact of the spill in the Gulf on the population of sperm and beaked whales.
Prior to 2010, LADC had conducted six passive acoustic surveys in the Gulf of Mexico, and by chance, in 2007 LADC conducted a two-week visual and acoustic survey of marine mammal activity just 9 miles and 23 miles from the Deepwater Horizon (DWH) platform, giving LADC a unique pre-spill baseline dataset of marine mammal activity at the oil spill site. Earlier surveys had also been conducted at sites 50 miles from the DWH platform. LADC was the first research team that recorded beaked whales in the Northern Gulf of Mexico. It is possibly the only dataset of beaked whale recordings in the Gulf before the spill. The pre-spill acoustic datasets also contain a wealth of information concerning the environmental state of the Gulf of Mexico concurrent with marine mammal recordings, such as anthropogenic noise levels including seismic surveys and passing hurricanes, density of food calls emitted by animals before consuming prey, and composition of stock (gender, size) due to variations in emitted signals (Newcomb et al., 2005; Newcomb et al., 2007). In September 2010, LADC returned to those same survey sites to repeat its underwater acoustic recordings (funded by the National Science Foundation and using a Greenpeace ship), gathering data to support the first and perhaps the only comparisons of pre- and post-spill estimates of the regional marine mammal population. (GREENPEACE MOVIE HERE: http://www.youtube.com/watch?v=pb2uL-WyVaE)
To date LADC has completed a limited assessment of the spill impact on two species of marine mammals densely populating the sites near the DWH platform: sperm and beaked whales. Analysis and comparison of the 2007 and 2010 acoustic data have shown completely different regional abundance trends exhibited by sperm and beaked whales. Sperm whale regional abundance estimates based on acoustic recordings show a decrease in the number of sperm whales nearest to the DWH site (9 mi away). The decrease exceeds statistical uncertainties and can be accepted as an existing trend. (Sidorovskaia et al., 2011; Ackleh et al., 2012). We can conjecture that sperm whales prefer feeding grounds further away from the spill site.
Beaked whales exhibit a completely different response. The number of animals at the 9 mi away site is considerably higher in 2010 than in 2007. An increase in beaked whale numbers at the 40 km site is also clearly observed from processed data. One of the plausible explanations is that these whales are forced to return to their feeding grounds due to the limitations of prey distribution for this family of marine mammals. In addition, all fishing operations were suspended in the area and that could have been helpful in replenishing squid stock, the main food source for beaked whales. There is very little information about distribution, abundance, and seasonal migration of beaked whales in the Gulf of Mexico. Additional observational data and research are critical to understand their unexpected response.
The next step will be to continue collected data mining to infer secondary information from pre-spill and post-spill recordings, which would allow the discrimination of oil spill effects on abundance from other environmental factors, causing temporal migration away from an area. This pioneering study suggests a need for establishing consistent acoustic monitoring protocols in the oceanic areas of current or potential industrial activities.
References:
Ackleh, A., Ioup, G.E., Ioup, J.W., Ma, B., Newcomb, J., Pal, N., Sidorovskaia, N., and Tiemann, C. (2012). "Assessing the Deepwater Horizon oil spill impact on marine mammal population through acoustics: endangered sperm whales," J. Acoust. Soc. Am.
Bowen, W.D. (1997). "Role of marine mammals in aquatic ecosystems," Marine Ecology Progress Series 158, 267-274.
Marques, T. A., Thomas, L., Ward, J., DiMarzio, N., and Tyack, P. L. (2009). "Estimating cetacean population density using fixed passive acoustic sensors: An example with Blainville's beaked whales," J. Acoust. Soc. Am. 125, 1982-1994.
Matkin, C.O., Saulitis, E. L., Ellis G. M., Olesiuk, P., and Rice, S. D. (2008). "Ongoing population-level impacts on killer whales Orcinus orca following the 'Exxon Valdez' oil spill in Prince William Sound, Alaska," Mar. Ecol. Prog. Ser. 356, 269-281.
Moore, S.E. (2008). "MARINE MAMMALS AS ECOSYSTEM SENTINELS," Journal of Mammalogy, 89(3), 534-540.
Newcomb, J.J., Ioup, G.E., Rayborn, G., Kuczaj, S., Sidorovskaia, N. (2005). "Ambient Noise and Marine Mammal Acoustics," NRL Review, Acoustics, pp. 101-103.
Newcomb, J.J., Snyder, M.A., Hillstrom, W.R., Goodman, R. (2007). "Measurements of Ambient Noise during Extreme Wind Conditions in the Gulf of Mexico," in Proc. "Oceans 2007", pp. 1-6 (10.1109/OCEANS.2007.4449256).
O'Hara, T. M., and T. J. O'Shea. (2005). "Assessing impacts of environmental contaminants," pp. 63-83 in Marine mammal research: conservation beyond crisis (J. E. Reynolds III, W. F. Perrin, R. R. Reeves, S. Montgomery, and T. J. Ragen, eds.). Johns Hopkins University Press, Baltimore, Maryland.
Sidorovskaia, N.A., Ackleh, A., Ma, B., Pal, N., Tiemann, C., Ioup, G. E., and Ioup, J. W. (2011). "Littoral Acoustic Demonstration Center - LADC: Assessing the long-term impact and recovery of marine mammal populations after the oil spill in the Gulf of Mexico," presentation at Marine Mammal Commission meeting, New Orleans, May 2011(invited)