I tried to estimate how many grizzly bears there were at the beginning of the 19th century and how many there are today. I wrote about this in my book, Beyond the Stony Mountains: Nature in the American West from Lewis and Clark to Today (available 2012 as an ebook, New York, Croton River Publishers; Originally published in 2004 by Oxford University Press, N.Y. ) Here is material taken directly from that book.
The most dangerous animal Lewis and Clark encountered on their expedition 1804-1806 though the American West was the grizzly bear. For example, on May 11,1805, when the expedition was northeast of what is now the Pine Recreation Area near Fort Peck Dam in eastern Montana, Bratton, one of the members of the expedition, went for a walk along the shore. Soon after, he rushed up to Lewis "so much out of breath that it was several minutes before he could tell what had happened." Bratton had met and shot a grizzly bear, he told Lewis, but the bear didn't fall: instead, it ran after him for about half a mile, and it was still alive.
Lewis took seven men and trailed the bear about a mile by following its blood in the shrubs and willows near the shore. Finding the bear, they killed it with two shots through the skull. Upon cutting it open, they found that Bratton had shot the bear in the lungs, after which the bear had chased him and then moved in another direction, a total of a mile and a half. "These bear being so hard to die reather intimedates us all," Lewis wrote. "The wonderful power of life which these animals possess," the journals continue, "renders them dreadful; their very track in the mud or sand, which we have sometimes found 11 inches long and 7 1/4 wide, exclusive of the talons, is alarming.”
Because grizzlies are so big and dangerous, Lewis and Clark recorded the number of bears (usually one) in each encounter. Reading their accounts, I realized that it was possible to use the journals to estimate the original abundance of these dangerous animals and to learn about their original range. The expedition encountered a total of thirty-seven grizzlies over a distance of approximately one thousand miles, an average of about four grizzlies per one hundred miles traveled. . . . The density of the bears was about four for every one hundred square miles. We assume that on average the men of the expedition could see a half-mile on each side of the river. Using this average along with the assumed presettlement range of the bears, about 530,000 square miles, we estimate that there might have been as many as twenty thousand bears. . . .
Recently, two scientists made use of the method that I first suggested to develop another estimate of early nineteenth-century grizzly abundance from the Lewis and Clark journals. These scientists, Andrea S. Laliberte and William J. Ripple, expanded on the original idea. They reviewed the journals, using both the westbound and the eastbound journey. I avoided the eastbound journey because I assumed that the members of the expedition were hurrying home and not as likely to observe wildlife. However, the comparison is interesting. . .
Although we are legally required to restore the grizzlies, and an estimate of presettlement abundance is the usual method, I was surprised to find that there are few other studies that provide any useful estimate of their abundance. One of these was made by the Craighead brothers, two of America's experts on grizzly bears. Their study was limited to Yellowstone National Park, where they reported an average of 230 grizzlies between 1959 and 1967, an average density of three bears per one hundred square miles, similar to my estimate from the journals.
Strangely, with the sole exception of information gathered in Yellowstone, our present knowledge of the abundance and density of grizzlies is not much better than what someone could have surmised from Lewis and Clark's journals in 1806. If this is what we know about one of the most famous, readily reported, legally threatened, and therefore protected species, whose abundance and whereabouts are of considerable interest to outdoorsmen and government agencies, what could be our knowledge of other species? The answer is, in most cases, much less.
The quotes from the Lewis and Clark expedition are from Moulton, G.E., 1986 The Journals of the Lewis and Clark Expedition, ed. G.E. Moulton. Lincoln, NE: University of Nebraska Press.
The other paper I referred to is: Andrea S. Laliberte and William J. Ripple, "Wildlife Encounters by Lewis & Clark: A Spatial Analysis of Interactions between Native American and Wildlife," BioScience, vol. 53 no.10 (2003): 994-1003.