by Lauren Frisch
New research reveals that human noise pollution could affect the behavior of endangered beluga whales in Cook Inlet, and may add stressors that hinder population recovery.
Sound is critical to many components of a whale’s daily routine. Beluga whales and other marine mammals have evolved to use different sounds to communicate underwater, navigate, forage for prey and detect predators.
Noises generated by humans can tamper with the elaborate aural communication system of whales. “Any time you have masking—which happens when a sound is so loud that it prevents a whale from detecting important acoustic signals—it can create potential for loss of socialization, decreased navigational capabilities or inability to find prey. This can interfere with the important aspects of whales’ lives,” said Rachael Blevins, who earned her PhD in fisheries from the University of Alaska Fairbanks School of Fisheries and Ocean Sciences in December 2015.
Blevins conducted her research as a graduate student in the Marine Ecosystem Sustainability in the Arctic and Subarctic (MESAS) program, which received funding from the National Science Foundation. The project had additional support from the North Pacific Research Board and the UAF Dissertation Completion Fellowship.
The National Marine Fisheries Services estimates there were approximately 1300 beluga whales in Cook Inlet in 1979. The population dropped to about 650 in 1993. By 1998, it dropped to around 350 animals, and has not rebounded since.
This got the attention of Blevins’ advisor and SFOS professor Shannon Atkinson, who is particularly interested in populations that don’t respond well to change. Although research on beluga whales has been extensive, little is known about the Cook Inlet population. Atkinson was motivated to study what might be holding back their recovery.
Blevins and Atkinson gathered baseline data on the sounds used by the belugas and studied how other ambient noise affected them. They monitored underwater sounds in Trading Bay and Eagle Bay in upper Cook Inlet. Whales in Cook Inlet can be exposed to noise from aircrafts, cargo ships, commercial fishing vessels, recreational boats, oil operations and land-based vessels.
Research on how animals use sound is typically conducted through a playback experiment, which involves playing various sounds and seeing how animals respond to them. Because the beluga whales in Cook Inlet are endangered, this approach would have been considered harassment. Instead, Blevins and Atkinson studied the whales using passive monitoring and observational surveys in collaboration with scientists from the Joint Base Elmendorf-Richardson and the Alaska Department of Fish and Game.
In 2010, Blevins placed underwater recorders called hydrophones in the inlet for about six months to collect continuous measurements of human- and animal-generated sounds. Blevins also surveyed people who work on Cook Inlet waters or live nearby, which allowed community members to provide their own observations of how whales have responded to noise. Most of the state’s population lives on or near Cook Inlet, which is home to Alaska’s largest city, Anchorage. Surveying community members provided an important perspective to this research.
Blevins was able to identify the hydrophone-recorded whale sounds based on their tonality, or musical quality. She explained that whales can create a range of sounds that are more musical than the recorded human-generated noises.
“Belugas are nicknamed sea canaries,” Blevins said. “They can make so many different sounds. Although analyzing the recordings could be tedious, at some points I felt like I was listening to recordings of a tropical rainforest, like there were birds or frogs in the background.”
Blevins used an algorithm developed by scientists at the Hawaii Institute of Marine Biology to identify files that were most likely to have beluga calls within the large quantity of data that she collected. She then listened to the top 10 percent of the recordings that were most likely to contain beluga sounds. Comparing the recordings at Eagle Bay and Trading Bay allowed Blevins to consider what various sounds could suggest about whale behavior in this region.
Whale sounds cluster into three main categories: whistles, pulsed calls and click trains. People are most familiar with the high-pitched whistles. Pulsed calls are the noisiest of whale calls, and click trains are a series of clicking noises that are close together.
Information linking particular sounds to behaviors and regions is important baseline data for this population of beluga whales. Pulsed calls are typically a sign of social behavior. Blevins found that whales made more pulsed calls in the summer, which suggests that the whales are more social during the summer months. They tend to aggregate in larger groups, and mothers and calves spend most of their time together in the summer.
Blevins found the whales were more likely to make click trains in Eagle Bay than in Trading Bay. Previous studies on other species of whales have found that whales tend to make lots of click trains when they are foraging. Eagle Bay is a biologically productive region of Cook Inlet with five known salmon runs, and is a likely site for beluga whale foraging.
Blevins used the survey of community residents to learn how they have observed sound level changes in Cook Inlet, and to catalog instances of beluga disturbance. Most people who took her survey believe that noise pollution could be problematic for whales.
Blevins found that belugas in Cook Inlet and other areas react similarly to human noises. “We don’t necessarily have any behaviors unique to Cook Inlet. The whales avoided noise caused by airplanes, human voices and cars in some situations.” However, there were a few cases when curious young whales actually approached noises, such as human laughter and the clanking of an anchor chain.
While noise could be one factor that inhibits whale recovery, this study does not suggest that it is the only factor. “It is important to recognize that sound does have the potential to affect beluga whales, but it is likely not the only thing affecting them,” Blevins said. “The most significant thing for this population is likely the cumulative effect of a number of stressors, including underwater noise pollution, reduction in prey availability and other things that may not be as significant by themselves.”
Blevins hopes future researchers will be able to study the belugas with a combination of visual and acoustic recordings. This combination of research would further the understanding of how particular sounds are used in different types of whale behavior.