Ecological Studies of Wolves on Isle Royale - Annual Report 1992-1993

Peterson, Rolf

On Isle Royale during 1992-1993, moose continued to increase and the wolf population remained almost unchanged. Only 13 wolves were present early in 1993, including two pups in one pack. As only one wolf died in the past year, reproduction was sufficient to maintain wolf numbers. The single reproducing pack increased to seven members, whereas the other two packs remained at two wolves each. Only one lone wolf survived the recent winter. Between the 1992 and 1993 counts, one lone wolf died of unknown causes, and after the 1993 count another lone wolf was killed by the two-member West Pack II. Three females, one in each pack, were in breeding condition and courted by males in 1993. Only one of these pairs has successfully raised young since 1988, however, and population growth is limited by poor reproduction. In the past five years wolf exposure to canine parvovirus appears to have diminished; there is no evidence that disease is contributing to low reproductive success on Isle Royale. Wolf food supply is now expanding rapidly, as large cohorts of moose born in the early 1980's reach a vulnerable age. Reduced genetic variability and a high degree of relatedness among the wolves suggest that inbreeding depression has led to an unusually low reproductive rate. New outbreaks of disease and total loss of females are now the greatest immediate risks facing the wolf population. The moose population continued to grow in the past year and is now at its highest level in almost 60 years. Coincident with a late spring in 1992 was notable mortality from malnutrition, primarily among old adults and calves born in 1991. Continued expansion of the moose population appears likely.