Disease

Three major bacterial diseases affect wild bison: brucellosis, bovine tuberculosis, and anthrax.  Brucellosis and tuberculosis were introduced to Wood Buffalo National Park with the transplant of plains bison from Wainwright, Alberta in 1925-28.  Both diseases are prevalent in bison in the park and in the Slave River Lowlands.  Brucellosis causes abortions, still births, lower pregnancy rates, and can cause crippling arthritis in infected joints. The infection is transmitted primarily through contact with contaminated fluids or tissues associated with abortions or birth.  Males may acquire brucellosis through sexual contact with infected females.  Bovine tuberculosis is a chronic, infectious disease that usually progresses slowly in bison.  Over the years it weakens the bison and may eventually result in death. These two diseases increase the vulnerability of bison to wolf predation.

Anthrax is the other serious disease affecting bison in the NWT. During the first documented outbreak of anthrax, in the summer of 1962, 281 bison died near Hook Lake, in the eastern Slave River Lowlands.  Outbreaks soon became widespread, extending during the course of the next few years to as far south as bison herds in the Sweet Grass area. In 1965, an anthrax vaccination program was initiated.  Vaccinations were carried out in late winter or spring, before the time when anthrax usually occurred.  The vaccination program was hard on the bison.  Constant human activity and herding by helicopters and other vehicles caused extreme harassment.  Many bison died from exhaustion and panic.  The program continued intermittently from 1965 to 1977 resulting in close to 20,000 vaccinations.  The effectiveness of the vaccination program was poorly documented.

An outbreak of anthrax in the isolated Mackenzie herd in 1993, 30 years after bison were introduced to the Fort Providence area, leads to the question, "Where does anthrax come from?".  Anthrax is found in the soil as a dormant, highly resistant endospore. It survives best in basic or alkaline, calcium-rich soils, such as those found in the most productive bison ranges in the Northwest Territories. The spores can remain viable and infectious for decades if not hundreds of years.  When water levels recede after a period of flooding, the spores that have been washed out of the soil become concentrated in pockets. Herbivores like moose or bison become infected by ingesting or inhaling the spores.

Infected animals become sick and die within four days and few recover. Anthrax spores are formed again when carcasses are opened by scavengers and anthrax organisms are exposed to the air. Scavengers like the raven are not affected by anthrax and can transport spores over long distances. Since the disease can be lethal in humans if untreated, anthrax outbreaks are treated very seriously.  Bison herds are closely monitored during anthrax season (June to August) and contaminated carcasses are incinerated as soon as possible.

For more information on disease that affect wood bison in the NWT, go here

Accidents

Drowning is a frequent cause of death in bison.  Although they are normally excellent swimmers, entire herds of bison have drowned in flooded rivers.  In 1958, spring floods in the Sweet Grass area in Wood Buffalo National Park, caused the death of about 500 bison.  In 1959, more than 1,000 animals died during autumn flooding.  In both 1961 and 1974, several thousand bison drowned in the same area. In May 1989, 177 bison died in the Mackenzie bison range when they broke through rotten spring ice. Catastrophes do not affect long term trends in large bison populations, but they can cause the extinction of small local populations.

Hunting

Between 1968 and 1977, resident sport hunters took an average of 123 bison per year during regulated seasons in the Slave River Lowlands.  At the same time, hunting by General Hunting Licence (GHL) holders had no season or quota limit.  Between 1973 and 1976, the bison population declined and sport hunting was closed in 1977, but GHL hunting has remained unregulated.  

Regulated hunting for male bison was allowed for the Mackenzie bison herd beginning in 1988. The quota is divided between Fort Providence, Rae-Edzo, and an open draw for eligible hunters from the NWT.  Fort Providence provides outfitting and guiding services for a limited number of non-resident bison hunters.

A quota was first implemented for the Liard River herd in 1998. The quota was set at 2 animals, 1 each for the communities of Fort Liard and Nahanni Butte, however, no tags were utilized until the 2002/03 season.

Hunting is not permitted in Wood Buffalo National Park.