FAIRBANKS — Moose and caribou are the food of choice for wolves in Interior Alaska, but salmon also can be an important item on their menu, at least for wolves in part of Denali National Park and Preserve.

A recent study using old wolf bones revealed that some living in the northwest portion of the park, near salmon-spawning beds, rely on the fish for a third of their diet. On average, salmon make up about a sixth of the diet of wolves in the area.

“That’s quite a bit for an animal that’s supposed to be relying on ungulates,” said Layne Adams, a longtime biologist with the U.S. Geological Survey’s Alaska Science Center.

Adams co-wrote a paper about the study for the journal Ecological Applications. It appeared two months ago.

While biologists knew that wolves in coastal regions of Southeast Alaska commonly feed on spawned-out salmon, this was the first research to focus on inland wolves eating salmon and the relationship to wolf and ungulate populations, Adams said.

“I think what it shows is the salmon subsidize the wolf population and hold it at a higher level than it would be if the salmon weren’t there,” Adams, who has been studying wolves in Denali more than 20 years, said. “If it wasn’t for the salmon, a lot of those wolves would die.”

But they don’t, and they end up eating more moose and caribou as a result. Moose and caribou densities in the northwest portion of the park, near where salmon spawn, were 78 percent lower than those in the rest of the study area, while wolf densities were only about 17 percent lower in the same area, the biologist said. That translates to a predation rate about three times higher in the areas where salmon are present. The results of the study are “painfully obvious and intuitive,” Adams said.

“The fact you have all this salmon on the landscape and it’s predictable when and where it shows up, why wouldn’t they use a lot of it?” Adams said. “Given the choice, they’d rather be killing and eating moose than eating salmon, but if they’re really hungry they can go find a salmon carcass.”

The study focused on Toklat Springs, an area just north of the park’s northwest boundary where a considerable number of chum and coho salmon spawn each fall after swimming up the Yukon, Tanana and Kantishna rivers. On average, 80,000 chum and coho spawn in the springs, according to the Alaska Department of Fish and Game’s counts.

Salmon show up on the spawning grounds in August, and wolves likely have access to salmon carcasses until they are washed away in the spring. Most of Toklat Springs does not freeze.

“Potentially there could be salmon pretty easily available from August to April or May,” Adams said.

Researchers used bone samples of wolves that died in or near the park between 1986-2002, as well as blood samples from moose, sheep and caribou studies in the same area. Spawned-out chums were also collected from the Toklat Springs area.

The researchers then examined the ratios of nitrogen isotopes in wolf bones and compared them to the prey samples to obtain evidence of the diets of individual wolves.

While the presence of salmon-related isotopes varied widely among 73 wolf samples, a clear pattern emerged, Adams said. Wolves whose home ranges were in areas where there were salmon but few moose and caribou had very different chemical signatures than wolves whose ranges had few salmon or a high density of ungulates.

Salmon contributed up to 34 percent of some wolves’ diet, and the average was about 16 percent, he said.

“They’re eating as much salmon as wolves do in Southeast,” Adams said.

The idea to study salmon consumption by wolves in Denali Park was the result of a comment a decade ago by Fairbanks pilot Dennis Miller, who flies salmon- and wolf-tracking surveys for the National Park Service, Adams said.

Miller was tracking wolves for Adams one fall in the late 1990s when the pilot called and told the biologist he didn’t need radios to find one pack of wolves. It was always in the same place — Toklat Springs.

“It was no suprise that wolves ate salmon, but it made me think if they’re hanging around there all the time they may be eating more salmon than we thought,” Adams said. “When we started running the numbers, we very quickly realized in those spruce flats there’s as much as salmon biomass on the landscape as there are ungulates.”

The study shows how salmon abundance can affect wolf-ungulate relationships, Adams said.

“Current understanding and management of wolf-ungulate systems is based on the assumption that effects of other food sources are minimal,” Adams said.

That may not be true where moose and caribou numbers are low and significant numbers of salmon are within the range of wolves.

“It’s not going to be an important thing everywhere, but there are pretty large expanses of the state where ungulate numbers are pretty low,” Adams said. “In those areas, salmon could be an important thing.”

Many of the wolf bones Adams analyzed were collected by Denali Park wolf biologist Tom Meier, who worked in the park from 1986 to 1993 before moving to Wyoming. The bones of the dead wolves had been stored for several years before Adams decided to analyze them.

“We stored all those wolf bones; it paid off,” said Meier, who returned to Denali in 2004.

The fact that wolves eat salmon was not news to Meier. Wolves frequently hang around salmon-spawning areas during the winter, a fact he and other biologists have noted for years while radio-tracking the wolves.

“We were always seeing wolves hanging out on the Bearpaw (River), Toklat (River), Moose Creek, White Creek ... all the places salmon spawn,” he said. “We knew they (ate salmon). It was interesting that (Adams) was able to quantify it.”

With so few moose and caribou in that part of the park, Meier said, wolves don’t have much choice about eating salmon.

“It seems like a last resort for some of these wolves,” he said. “When we find them around these salmon streams, they can be in pretty bad shape. A lot of the wolves we catch out of Toklat Springs aren’t looking too good.

“It’s awful hungry country out there,” Meier said.

Contact staff writer Tim Mowry at 459-7587.