Wolf-Moose Monitoring Program, 1984, Isle Royale National Park

Peterson, Rolf

In 1983-84 the Isle Royale wolf population remained at about the same level as last year, in spite of considerable turnover and changes in all 3 wolf packs. The moose population appears to have declined slightly to less than 800 animals, although the long-term trend for moose is expected to remain upward (Fig. 1). Our current ideas on wolf-moose dynamics at Isle Royale lead to the prediction that the wolf population should stabilize at the current level while the moose population continues to increase. The wolf population continues to be partitioned into 3 packs, with all packs reproducing in 1983. Overall numbers were maintained as the West Pack II increased and the Harvey Lake Pack and East Pack II both declined. The 1984 population included 10-11 pups, implying 39-43% mortality among animals present in 1983. Territorial overlap and conflicts continued in 1984; the Harvey Lake alpha female was killed by the West Pack during the winter study. After 2 years of impressive growth, Isle Royale moose apparently declined slightly during 1983-84. A reduced cohort of 1983 calves appears to be most reasonable explanation. It remains to be seen if lower recruitment resulted primarily from loss to wolves or if it is only a temporary reflection of the young age structure of the population. Midwinter mortality to wolves continues to be low, with wolves relying largely on old adult moose exhibiting a very high incidence of arthritis. The 1983 calves continued to exhibit the low vulnerability to wolves in winter that has been characteristic of recent cohorts. We expect continued growth of the moose population in spite of a lower rate of increase caused by wolf predation.