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Study reveals shift in diet of Cook Inlet’s endangered belugas

A beluga whale flashes its tail as it dives while a group of whales gathered around a point of land to feed in Turnagain Arm along the Seward Highway on Sept. 17, 2017. (Bob Hallinen / ADN)

A new study of the bones and teeth of dead Cook Inlet belugas revealed that the animals' diet has shifted to more freshwater prey over at least the past 50 years, a finding that researchers hope will help with the conservation of the small and endangered white whales.

"Figuring out what started to drive belugas toward freshwater environments and away from the marine environments might be key in figuring out why they haven't recovered," said Mark Nelson, the lead author on the study.

Nelson, who works at the Alaska Department of Fish and Game, graduated from the University of Alaska Fairbanks in December with a master's degree in marine biology. The study, published Wednesday in the journal, "Endangered Species Research," was part of his thesis. It's a collaboration between UAF and Fish and Game, he said.

The study presents the first evidence of a long-term change in Cook Inlet belugas' feeding ecology — what they are eating and where they're eating it, according to a news release from UAF.

"It kind of ties together this whole picture: Belugas aren't in the same places. They're spending more time in the upper reaches of the Cook Inlet. And, it's showing up in their diet," Nelson said.

The Cook Inlet beluga population has struggled for decades. The population totals about 340 now, far below the 1,300 belugas that scientists say swam in the silty water between Anchorage and the Gulf of Alaska as recently as the 1970s.

The whales were listed as endangered after their numbers crashed in the 1990s. Despite numerous protective measures imposed, the population never rebounded. It's unknown why, Nelson said.

'"No one has ever, to this date, quite figured out why they haven't bounced back," he said.

Nelson said the new study doesn't reveal the whole answer, but it does provide another piece of the puzzle.

By analyzing the chemical elements in belugas' skulls and teeth, Nelson and the research team found that belugas today tend to not only congregate in the Inlet's upper reaches — shifting farther into the Knik and Turnagain arms, where freshwater flows in — but they're also feeding on more prey that live or have lived in freshwater, instead of a more ocean-like environment found in areas such as the lower part of the inlet.

To reach those conclusions, the team studied the isotope ratios of carbon, nitrogen and strontium found in the whale bones and teeth.

Evidence of the change in diet isn't necessarily linked to the decline in belugas, Nelson said. In fact, the teeth and bone samples the researchers analyzed ranged from the 1950s to 2007. They found a shift toward freshwater-influenced feedings beginning as early as the 1950s. The shift steadily continued through the decades, with whales' diet consisting more and more of freshwater prey.

"Belugas out there are doing something totally different than the belugas that were out there 30 years ago," Nelson said.

Matthew Wooller, a professor at UAF's College of Fisheries and Ocean Sciences and the senior author on the study, said the team is continuing its research, with plans to analyze belugas' teeth to determine how the species' diet in the winter compares to its diet in the summer.

Determining what belugas are eating and where can aid in conservation efforts, Wooller said.

"You can start to think about not only protecting the beluga but protecting the diet items — conserving the diet items — and the habitat that supports the beluga," he said.

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