Tracking Marine Mammal Recovery after the Deepwater Horizon Oil Spill

LADC-GEMMLADC-GEMM studies acoustic signals in spill vicinityDid whale and dolphin populations change after the oil spill? Prior monitoring indicated that large numbers of these deep-diving marine mammals were living near the Deepwater Horizon site. The Gulf of Mexico Research Initiative recently awarded the LADC-GEMM consortium a grant to study endangered sperm whales, beaked whales, and dolphins to answer that and related questions.

Watch a video about Sidorovskaia’s 2010 acoustic survey expedition below:

(Video Credit: Greenpeace USA)

LADC-GEMM Director Natalia Sidorovskaia with the University of Louisiana at Lafayette shared some thoughts about their project that will establish a precedent of continued acoustic monitoring data and provide regional stock population assessments.

“Changes in marine mammal distribution and abundance can impact and reflect the health of the entire deep-water ecosystem. Our research seeks to help us understand what may happen to marine mammals during and after events, such as oil spills or other environmental and man-made stressors, and help guide ocean management decisions about conservation, regulations, and mitigation.”

LADC-GEMM stands for Littoral Acoustic Demonstration Center – Gulf Ecological Monitoring and Modeling. Their study will provide relationships among short- and long-term marine mammal population variations with environmental factors such as natural and human-induced disasters, weather conditions, seasonal migration, industrial operational noise, and food supply.

LADC team deploy an Environmental Acoustic Recording System (EARS) buoy from Greenpeace vessel Arctic Sunrise in September 2010. (Photo credit: Greenpeace)

The consortium pairs acoustical, oceanographic, and visual data collection with mathematical predictive modeling and integrated data analyses to understand patterns in species distribution, pollutants, and human activities. Sidorovskaia explains that their team is uniquely positioned to conduct Gulf marine mammal population studies and assess environmental impacts.

“We’ve conducted annual acoustic surveys of Gulf mammals since 2001. In 2007, we conducted a two-week survey in the oil spill vicinity. When the spill happened, we realized we were the only group that had baseline data about mammal activity there, so we returned in September 2010 funded by the NSF Rapid Grant and donated free ship time by Greenpeace. With the BP/Gulf of Mexico Research Initiative funding, we can continue our experimental observations for the next three years.”

Monitoring marine mammal sounds is important because they do everything acoustically, using “clicks” to communicate with each other and explore their environment.

“They send out a signal and it bounces off a target. They can figure out where the sea bottom is and determine if an object is a squid, a ship, or something else. Then they either can locate and grab it, ignore it, or get away from it.”

A Gulf of Mexico sperm whale begins a deep dive, September 2010. (Photo credit: Greenpeace)

Using integrated passive acoustic monitoring, the team will record the unique sounds that the whales and dolphins make. Sidorovskaia said that the collected acoustic data also will contain a wealth of information about the ocean environment the whales inhabit. Their computer programs will decode this information and pair changes in marine mammal populations with environmental factors.

“We collect about 200,000 readings per second when recording acoustic events. We intend to take this tremendous amount of data and further develop our algorithms that allows us to distinguish the identity and number of young adults, females, and calves. From that, we will model future population development and anticipate increases and decreases in marine mammals that may help resource managers and responders be better prepared for stressors and perhaps reduce their effects.”

When a sperm whale produces a sound, it starts as a main pulse that goes out into the water. Some of the acoustic energy propagates throughout the whale’s body and then returns, reverberating off of an air sac in the back of the whale’s head like an “echo.” The intensity and timing of the echo is a function of the size of the whale’s head. Researchers use this data to determine size, life-stage, and gender – parameters that improve population prediction models.

Dr. Natalia Sidorovskaia is Professor and Chairperson of Physics at the University of Louisiana at Lafayette and is the LADC-GEMM consortium Director. (Photo provided by Natalia Sidorovskaia)

Understanding marine mammals’ interactions with their food is an important component in studies about the larger ecosystem. Monitoring at deep depths provides data on the mammals and their prey.

“The mammals produce a unique signal before they capture food, allowing us to estimate how much food is there both up and down the food chain. We will look at the whole system and the connections between the oil spill, marine mammals, and lower trophic levels. A change in marine mammal distribution and abundance caused by environmental stresses provides insight into ocean ecosystem health since mammals are consumers at many trophic layers.”

The sensitive equilibrium among fish, mammal, and plankton populations is important for a healthy ocean. Sidorovskaia explains that marine mammals are sensitive to noise and if an area is acoustically noisy, such as from oil-spill recovery work or oil and gas drilling and exploration operations, the common expectation is that the animals will leave. However, that may not happen.

“The question is what if there is a lot of food present? If the food is spread out, the whales might leave. But what if their food is only in that particular area? Will they stay or leave for a short while and return when it’s quiet? The spill site was where the Japanese fleet fished for squid, suggesting it is an important foraging area for beaked whales. Our preliminary data points to beaked and sperm whales responding differently after the recovery work stopped and the area quieted. The data we will collect will help us separate factors which influence whaler behavior.”

The research team will compare different data collection technologies to find the most cost efficient and comprehensive integrated passive acoustic monitoring approach for improved future deep-water mammal studies. Technology must be designed with low power consumption for longer recording times at sea and low noise generation so that it does not interfere with recordings.

“Whales spend more of their day actively diving than on the surface and are very vocal in deep water, searching for food and communicating with the rest of the pod. One way to collect sound is by using acoustic receivers towed behind vessels, but they are close to the surface and can miss many deep-sea sounds. Recording in the deep ocean is difficult, expensive, and has other problems. We will compare autonomous surface vehicles for towing, bottom-moored buoys, and deep-diving gliders which we can remotely control and provide recommendations for improved data acquisition methods.”

To bring their research to the broader science community and the public, the team will incorporate their activities and findings into NOAA kiosks at science education centers, give presentations in schools and museums, and hold student competitions to build and operate small gliders and autonomous vehicles that are similar to modern technologies used in underwater acoustic exploration.

“We want children to understand and get interested in this type of science, showing them the amazing intelligence of dolphins and whales and their importance to the health of our oceans. We also want to reach their parents, some of whom might influence or perhaps make business and regulatory decisions. We want to work with other researchers to determine where to take the science of marine mammals. We all need a healthy marine environment – we are all interconnected.”

The LADC-GEMM consortium includes the University of Louisiana at Lafayette, the University of New Orleans, the University of Southern Mississippi, Oregon State University, and several technology companies from the Gulf Coast states. For more LADC-GEMM program and people information, click here.