File Report 136

Wood bison (Bison bison athabascae) that inhabit the boreal forests of Northern Canada were nearly eliminated during the late 1800s. Only bison populations in the area between the Great Slave Lake and the Peace-Athabasca Delta persisted. Historically, wood bison range included the Southwestern portion of the Northwest Territories. As part of a program to establish a minimum of three free-ranging populations of wood bison in their historical range, the Nahanni wood bison population in southwestern Northwest Territories was established in 1980. Twenty-eight wood bison from Elk Island National Park (EINP) were released into the Nahanni Butte area. Supplemental releases in 1989 and 1998 of 12 and 61 individuals respectively, have bolstered the population. Since the initial reintroduction in 1980 research and monitoring of the population has been inconsistent and sporadic. This lack of population monitoring has been a concern of local residents of Nahanni Butte and Fort Liard. In 2002, a more formal research and monitoring program of the Nahanni wood bison population was initiated. Annual sex and age classification surveys from 2002-2006 show large yearly differences in indices of calf production (20-57 calves per 100 adult females) but overwinter calf survival has been ≥50% regardless of calf production during the previous year and has increased with every year of the survey. An aerial census of the population in March 2004 estimated 399 bison (CV = 0.32). Biological sampling has found no evidence of brucellosis (Brucella abortus), tuberculosis (Mycobacterium bovis), or the causative agent of Johne’s disease (Mycobacterium avium subspecies avium), nor has anthrax been detected on the range of the population. It is suspected that the range does not provide suitable conditions for spore persistence. Bison are susceptible to collisions with motor vehicles on the Liard Highway (Hwy 77) during September-October when more animals use the road as a travel corridor. In some years at spring break up animals are swept away and drowned. Bison use both sides of the Liard River Valley making swimming across the river an important component of the ecology of this wood bison population. Although sedges, grasses, and willow (Salix spp generally predominate the diet of Nahanni wood bison, there is a relatively high Equisetum component to the diet.

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