Wildlife Biologist Discovers Possible Factor in Cook Inlet Beluga-whale Population Decrease

Jun 15, 2018

For years the number of beluga whales in Cook Inlet has been on the decline. In 2008 they were put on the endangered species list. Recent research by a University of Alaska Fairbanks grad student has turned up a shift in diet in the Cook Inlet belugas that may help explain part of the decline. 

Mark Nelson is a wildlife biologist with the Alaska Department of Fish and Game. He’s spent much of his career working with marine mammals, and he says biologists in the 1990s noted the decline of Cook Inlet beluga whales. It was a mystery because the population wouldn’t recover despite protections including putting them on the endangered species list.

The population of beluga whales that live in the Cook Inlet has been steadily declining in recent years.
Credit Marine Mammal Commission

“This is the only population of beluga whales that is not doing well,” he said, “All the other populations of belugas are doing quite well.”

Nelson decided to tackle the question for a master’s thesis at UAF. An obvious place to start was diet. In biology, you are what you eat – diet is captured in bones and teeth. Drawing on beluga samples collected in the 1960s at the UA Museum of the North against more recent samples, he tested for carbon and nitrogen isotopes that would suggest dietary shifts. He found them. But he and his colleagues then took an unusual step in sampling for strontium.

“Which is a common isotope used in geology,” he said, “but it’s not all that common in biology. And we were able to apply it to this project to determine there have been some fairly significant changes.”

Nelson says the strontium reveals the Cook Inlet belugas are now taking more prey from fresh water sources, rather than the ocean. He says the discovery is an important piece of the puzzle.

“And we’re trying to gather a few more puzzle pieces as we kind of build this thing to try and understand what happened in the past, and maybe what’s preventing this population from recovering.”

Nelson and his colleagues published their findings this week in the journal Endangered Species Research.