First Winter Foraging Ground For Endangered Cook Inlet Beluga Whales Identified

Scientists have gathered crucial information that may help NOAA Fisheries in their efforts to recover endangered Cook Inlet beluga whales. Using acoustic equipment attached to the bottom along river banks at multiple locations in lower Cook Inlet, scientists identified the first winter feeding habitat for belugas in Tuxedni Bay.

"A key threat that may be affecting Cook Inlet beluga whale recovery is noise caused by human activities in the inlet," said lead author, Manuel Castellote, NOAA affiliate, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington. "This studyprovides important baseline information on Cook Inlet beluga whale habitat use and the noise they are exposed to in an area of the inlet for which we haven't had a lot of data."

According to co-author Verena Gill from NOAA Fisheries Alaska Regional Office, the study provides insights into a critical time: September 1 to May 15. That's when Cook Inlet beluga whales are actively using Tuxedni Bay on the west side of lower Cook Inlet to feed.

"Managing future human activities to minimize habitat degradation and acoustic disturbance in this winter foraging refuge may be a key to support continued recovery of this endangered whale population," she added.

A Closer Look at Cook Inlet Beluga Acoustic Study Findings

During this year-long study, scientists focused on collecting data on the remote, roadless, and relatively pristine west coast of lower Cook Inlet.

The region supports a rich marine ecosystem with large salmon runs, important seabird colonies, and shorebird roosts. It also is visited by baleen and toothed whales and porpoises. Two of the most productive bays along the west coast of lower Cook Inlet are Tuxedni and Chinitna, along with the salmon-producing rivers that flow into them.

Before the early 1990s, both bays were important habitat for belugas. However, sightings have been uncommon in these areas as the population declined and contracted its distribution into upper Cook Inlet. Consequently, research focus has been on the upper inlet-until now!

Passive acoustic equipment. Credit: NOAA Fisheries

From September 2021-2022, scientists used passive acoustic equipment, left in the water year round, to capture seasonal distribution and foraging occurrences of Cook Inlet beluga whales. They put them in two main bays and rivers-Tuxedni and Chinitna on the west coast of the lower Cook Inlet. They collected data on the presence of harbor porpoises, killer whales, and humpback whales in these areas. They also collected data on human-caused noises that could potentially disturb these animals.

"We detected belugas in Tuxedni Bay and river for 127 days during the winter, suggesting this is an important winter feeding ground. This is equivalent to the number of whales seen in their most important summer feeding habitat, the Susitna Delta," said Castellote. "We know a lot less about what belugas do, where they go, and what they eat in the winter compared to summer so this is a milestone for us."

But the findings for Chinitna Bay and surrounding river areas were surprising. Based on sound recordings, the whales were only detected 21 days in September through February. During this time, they were never detected as feeding.

NOAA scientists deploying scientific equipment. Credit: NOAA Fisheries.

"We detected a higher presence of harbor porpoises, killer whales, and humpback whales in Chinitna Bay as compared to Tuxedni Bay during winter months," said Castellote. "The belugas that were detected were in very shallow habitats. They were less vocal, and the sounds they used were much shorter and softer than typical. This suggests that they could be avoiding killer whale predators."

However, due to their findings in Tuxedni Bay, scientists see real opportunity through this study to be proactive in marine spatial planning.

"More often resource managers are faced with the challenge of having to mitigate threats in areas of high human use that overlap with beluga habitats. In this case, maintaining the status quo may be all that is needed to protect this relatively pristine habitat and keep Cook Inlet belugas on the road to recovery," emphasized Gill.

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