From Galbraith’s, Hudson's Bay Company as an Imperial Factor, page 95 and, Fort Vancouver, Fur trade Returns MS, in provincial Archives of British Columbia, Victoria, B. C.
The old Snake party remarkably successful in meeting its main objective -- the reduction of the Snake Country to a fur desert. The story is told by the declining returns. From the "nearly 5000" beaver pelts brought in by Ross in 1824, the numbers grew smaller almost every year until an apparent equilibrium was reached: 3577 in 1826; 4000 in 1829; 1295 in 1830; 737 (large beaver only) in 1831; end 788 large beaver in 1832. After the end of the regular Snake brigades the returns for the Snake Country were even more revealing: 350 large beaver in 1834; 220 large beaver in 1835; and 800 large beaver in 1836. For 1844 the returns were 722 large beaver and 272 small; for 1845 they amounted to 978 large beaver and 588 small, and for 1846 they were 897 large beaver and 544 small.