Book excerpt: "Aerial block surveys were conducted during 20 to 25 June 2001 to document the number and distribution of Dall's sheep (Ovis dalli) in the Richardson Mountains, Northwest Territories (NWT) and Yukon Territory (YT). We counted and classified 1,057 sheep including 734 nursery sheep, 92 lambs, 231 rams (43 half curl, 55 three-quarter curl and 133 full curl). The annual rate for the non-lamb portion of the population was 8% during 1997 to 2001; this was the first decline documented for this sheep population since surveys began in 1984. The number of full curl rams decreased by 38% (from 373 in 1991 to 231 in 2001). There were 12.5 lambs per 100 nursery sheep; this ratio was significantly lower than those observed during surveys conducted in 1984 to 1997. Little recruitment can be expected in 2002 indicating that further declines in the population can be expected. The majority of lambs, nursery sheep, and rams were found in the NWT; the majority of rams were found in the Rat block. Overall 66% of the sheep observed were found in the NWT"--Page ii.