Is a fish diet healthier for wolves than one comprised solely of red meat? That's hard to say, but some wolves in Denali National Park and Preserve have found that salmon is a great supplement when moose or caribou are scarce.

And when you have a source of 80,000 fresh salmon, why overlook it?

According to a paper published in January in Ecological Applications by Layne Adams, a biologist with the U.S. Geological Survey's Alaska Science Center and six colleagues, the chum and coho salmon that move up the Kuskokwim and Kantishna rivers more than off-set the relative lack of big game prey for the wolves in the park's northwestern corner.

Although the potential for salmon to be important to inland wolves had been suggested by other biologists, park officials say this is the first research to focus on the food source and its relationship to wolf and ungulate populations. The study looked at wolves in Denali north of the Alaska Range.

In the northwest portion of the park, it was found that the fall runs of chum and coho salmon formed a food supply comparable to the area’s moose population. On average, around 80,000 chum and coho return up the Kuskokwim and Kantishna rivers, park biologists note.

To determine how important salmon were, or were not, to wolves, Mr. Adams and his colleagues made use of bone samples from wolves that were radio-collared as part of a long-term study at Denali and that died in or near the park during 1986-2002, and blood samples from moose, sheep and caribou studies in the same area. Spawned out chums were also collected from the Toklat Springs area, a spawning area just north of the park’s boundary. The researchers then looked at 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, the researchers found. Wolves whose home ranges were in areas with salmon present but which also exhibited a low density of 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. One result of a salmon diet is that wolf numbers were substantially higher where salmon were plentiful than would be expected for the ungulate abundance alone, Mr. Adams said.

“Ungulate densities were 78 percent lower in the northwest flats compared with the remainder of the study area, but wolf densities were reduced by only about 17 percent,” he said. Given the estimated wolf diets and the relative abundance of wolves and their ungulate prey, estimated predation rates on ungulates in the northwestern flats of Denali were about three times higher than those in the remainder of the study area, indicative of influences abundant salmon can have on wolf-ungulate relationships.

In addition to helping explain low moose and caribou densities in northwestern Denali, the study also has implications for wildlife managers in much of Alaska.

“Current understanding and management of wolf-ungulate systems is based on the assumption that effects of other food sources are minimal,” Mr. Adams said. That assumption may not be true where ungulate numbers are low and significant numbers of salmon are within the range of wolves.

“Spawning salmon provide a previously unrecognized and dynamic connection between inland wolves, ungulates and distant marine ecosystems,” he added.