Two caribou mortality events in Northwest Alaska: possible causes and management implications

During fall and winter 1994—1995 and winter 1999—2000, caribou (Rangifer tarandus granti) from the Western Arctic Herd experienced high, localized mortality in northwest Alaska near Cape Thompson. Substantial numbers of caribou wintered in this area during 1986—1987, 2001—2002, and 2002—2003 without suffering high mortality. During the 1994—1995 event, 2000 to 3000 caribou died out of roughly 10 000 that wintered in this area. About 4000 caribou perished out of approximately 20 000 that wintered here during 1999—2000. During both mortality events, gross characteristics and tissue analyses indicated caribou in this area were malnourished. Weather near Cape Thompson during winter 1994—1995 was colder, windier, and had more snow than other years when caribou wintered in this area; in contrast, conditions during 1999—2000 were not unusually severe. Additionally, Cape Thompson experienced 2—5 occurrences of severe conditions during winter 1994—1995 while 1999—2000 experienced only 1 such occurrence at most. Several indicators suggested severe storms killed some caribou before starvation was fatal. Cape Thompson consistently experienced higher wind, lower ambient air temperature, and shallower snow cover than other portions of winter range used by this herd. Unlike years when caribou wintered in this area without experiencing high mortality, caribou were in relatively poor body condition during the autumn that preceded each die-off. Although these mortality events were inconsequential to size of this caribou herd, they raised local residents' concerns that contaminants had poisoned caribou and possibly jeopardized human health. Muskoxen (Ovibos moschatus) in this area were not affected by weather or snow conditions during either caribou mortality event