By UW News Staff

Arial Brewer/UW

Beluga whales are highly social and vocal marine mammals. They use acoustics to navigate, find prey, 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.

New research from the University of Washington, the National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center and the Alaska Department of Fish and Game 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 study, published Nov. 30 in the Journal of the Acoustical Society of America, finds 41 distinct types of calls, of which 18 are unique to this population. It also finds that commercial ship noise completely masks these whales’ most commonly used calls.

“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 lead author Arial Brewer, a doctoral student in the School of Aquatic and Fishery Sciences at the UW who did the work in collaboration with NOAA Fisheries’ Alaska Fisheries Science Center.

“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,” she added. “With that information, we can begin to understand if their communication is impacted by human-caused noise.”

Twenty-one populations of belugas are recognized worldwide, including five distinct populations in Alaska. The geographically and genetically isolated Cook Inlet beluga population is the smallest, recently estimated at just 331 individuals. Cook Inlet beluga whales live exclusively in their namesake waters alongside Anchorage, the state’s largest city and busiest port.

The Cook Inlet beluga whale population was listed as endangered under the Endangered Species Act in 2008. A 2016 recovery plan ranked three threats as the highest level of concern, one being human-caused noise. Commercial shipping is the most prominent noise source within Cook Inlet, particularly in the upper inlet where most of the federally-designated 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.

While all whales are affected by noise, 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.”

Cook Inlet’s extreme turbidity, dramatic tides, rapid currents and seasonal ice cover make it an extremely challenging place to study belugas. One way scientists can monitor these highly vocal whales is through sound.

The Cook Inlet Beluga Acoustics Program has been deploying bottom-mounted passive acoustic recorders to monitor belugas and human-caused noise since 2008. The study focused on recordings of beluga whale calls from 2018 to 2019.

“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 co-author Manuel Castellote, a research scientist at the UW-based Cooperative Institute for Climate, Ocean and Ecosystem Studies who manages the acoustics monitoring program. “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.”