One of the first studies that we did with grizzly bears was to ask how important were salmon historically to grizzly bears in Washington, Oregon, and Idaho when there were still millions of salmon spawning in Northwest rivers. This is an important question when we think about restoring grizzly bear populations in central Idaho and the North Cascades of Washington where salmon populations currently are quite depleted. There are many historical accounts of bears eating salmon in these areas, but how could we actually quantify the amount or importance of salmon that bears actually ate a hundred years ago? Fortunately, we have been able to use the captive bears to develop techniques that we can use to answer those questions. Surprisingly, the techniques that we’ve developed require only a few hairs or a chip of bone from bears killed long ago in which the pelt or skull was preserved in a museum, such as the Smithsonian. By actually quantifying the unique atoms of nitrogen and carbon that come from salmon as compared to all of the other foods that bears eat, we now know that salmon provided an average of 58% of the nourishment for grizzly bears in the 3 northwest states, and for some bears as much 90% of their nourishment came from salmon.
In more recent studies, we’ve compared those values to bear diets in places like Kodiak, Alaska where salmon runs may be near historical levels. For Kodiak bears, salmon provides 48% of the annual nourishment for adult females and 68% for adult males, so very similar to the average for bears that once lived in Washington, Oregon, and Idaho. This insight is a good indication of how much Northwest aquatic and terrestrial ecosystems have changed in the past 150 years and what has been lost. Fortunately, there are many populations of grizzlies that subsist almost entirely on plant-based foods, such as berries, forbs, grasses, and roots. Thus, while there is still enough food in Northwest wildernesses to support healthy grizzly bear populations, the density and productivity of the populations will be only a fraction of what would occur if there were still healthy, wild salmon runs in the rivers of Washington, Oregon, and Idaho.
While we’ve always thought of salmon as a wonderful bear food based on Alaskan experiences, salmon in the rivers south of the Canadian border also carry a disease that affects dogs, coyotes, and bears. That disease is known as salmon poisoning disease. The salmon aren’t really poisonous, but they carry a parasite that hatches when consumed by a bear or dog. The parasite implants into the lining of the bear’s digestive tract, and releases a bacteria into the bear’s circulation. In dogs if left untreated, the bacteria kills 90% of those unlucky enough to have eaten any portion of an infected salmon. Fortunately, bears are not affected by that form of the bacteria, but they are susceptible to a new species of that bacteria that occurs widely in Asia and was first reported in Washington in the early 1970s. While the new bacteria makes bears sick for a few days to weeks, it does not appear to kill them. Thus, if Northwest fisheries managers are able to recover salmon populations, relocated grizzly bears in Washington and Idaho will be able to make use of them.