Vital communications among the critically endangered population may be masked by ship noise in their core critical habitat, new research finds.
(NOAA) Beluga whales are highly social and vocal marine mammals. They use acoustics to find prey, navigate their environment, avoid predators, and maintain group cohesion. For Alaska’s critically endangered Cook Inlet beluga population, these crucial communications may compete with a cacophony of noise from human activities.
“The core critical habitat for these whales is a very noisy area. Commercial shipping, an international airport, military operations, and gas and oil exploration are all concentrated there,” said Arial Brewer, NOAA Fisheries affiliate at the Alaska Fisheries Science Center and Ph.D. student at the University of Washington.
A new study is the first to document the complex vocal repertoire of the Cook Inlet beluga whale population. It is also the first to quantify how ship noise may be masking specific beluga calls in this region. The research was a collaborative effort between NOAA Fisheries Alaska Fisheries Science Center, the University of Washington, and the Alaska Department of Fish and Game. The findings can inform decisions on management and recovery actions related to the effect of shipping noise on this endangered population.
“A fundamental knowledge gap for the Cook Inlet beluga population is how they communicate important information. The first step is to describe their vocal repertoire,” said Brewer, who led the study. “With that information we can begin to understand if their communication is impacted by human-caused noise.”
A Population in Peril
There are 21 recognized populations of belugas worldwide, including five distinct populations in Alaska. The geographically and genetically isolated Cook Inlet beluga population is the smallest, with an estimated 331 individuals. Cook Inlet beluga whales live exclusively in their namesake waters alongside Anchorage, Alaska’s largest city and busiest port.
The Cook Inlet beluga whale population was listed as endangered under the Endangered Species Act in 2008. That led to the designation of critical habitat in 2011. However, the population has remained low. A 2016 recovery plan ranks three threats as the highest level of concern:
- Catastrophic events (e.g., oil spills, mass strandings)
- Human-caused noise
- Cumulative effects of multiple stressors (e.g., pollutants and noise)
Commercial shipping is the most prominent noise source within Cook Inlet, particularly in the upper inlet where the critical habitat is located.
”All of that human-caused noise means the belugas may not hear critical communications from each other, such as predator alarm calls or a mother calling to her calf,” Brewer said.
Cook Inlet belugas may be particularly vulnerable to noise as a stressor.
“Cook Inlet is extremely turbid year-round from glacial runoff. It looks like chocolate milk,” Brewer said. “Acoustic communication is extremely important for this population since visibility is so poor. And, unlike other higher arctic beluga populations, this population is non-migratory, so they are exposed to this noise year-round.”
Cataloging the Vocal Repertoire
Cook Inlet’s extreme turbidity, dramatic tides, rapid currents, and seasonal ice cover make it an extremely challenging place to study belugas. To meet this challenge, one way scientists can monitor these highly vocal whales is by listening to them remotely.
The Cook Inlet Beluga Acoustics Program has been deploying bottom-mounted passive acoustic recorders to monitor belugas and human-caused noise since 2008. The program is led by Manuel Castellote, NOAA Fisheries Alaska Fisheries Science Center affiliate/University of Washington, in partnership with the Alaska Department of Fish and Game.
“Until now we did not have a quantified measure of masking by ship noise on Cook Inlet beluga communication. We knew this was a potential disturbance mechanism to focus our research efforts, but we were lacking a good understanding of what vocalizations are most important for beluga,” said Castellote, co-author on the study. “This study provides the first two steps into this direction. We now have a solid understanding of key vocalizations for this population, and how each ship transit is affecting beluga vocal exchange in the core area of their critical habitat.”
For the new study, scientists analyzed recordings from multiple seasons at two critical habitat locations: Susitna River and Trading Bay.
They classified beluga vocalizations into three categories—whistles, pulsed calls, and combined calls—and then further into unique call types.
