Increases in moose, caribou, and wolves following wolf control in Alaska

Short-term studies in our study area and southeast Yukon have previously documented substantial increases in moose (Alces alces) and caribou (Rangifer tarandus) following wolf (Canis lupus) control. To provide long-term information, we present a 20-year history beginning autumn 1975 when precontrol wolf density was 14 wolves/1,000 km(2). Private harvest and agency control kept the late-winter wolf density 55-80% ((x) over bar = 69%) below the precontrol density during each of the next 7 years. Wolf numbers subsequently recovered in less than or equal to 4 years in most of the study area and increased further to between 15 and 16 wolves/1,000 km(2) during a period of deep snowfall winters. The post-hunt moose population increased rapidly from 183 to 481 moose/1,000 km(2) during the 7 years of wolf control (finite rate of increase, lambda(r) = 1.15) and increased more slowly during the subsequent 12 years (lambda(r) = 1.05) reaching a density of 1,020 moose/1,000 km(2) by 1994. The Delta caribou herd increased rapidly during wolf control (lambda(r) = 1.16), more slowly during the subsequent 7 years (lambda(r) = 1.06), then declined for 4 years (lambda(r) = 0.78) from a peak density of 890 cariboul 1,000 km(2). This decline coincided with declines in 2 adjacent, low-density herds (240-370 caribou/1,000 km(2)). These caribou declines probably resulted from the synergistic effects of adverse weather and associated increases in wolf numbers. Reduced caribou natality and calf weights were associated with adverse weather. Wolf control was reauthorized to halt the Delta herd's decline in 1993. Similar subarctic, noncoastal systems without effective wolf control have supported densities of 45-417 moose/1,000 km(2) ((x) over bar = 148, n = 20), 100-500 caribou/1,000 km(2), and 2-18 wolves/1,000 km(2) ((x) over bar = 9, n = 15) in recent decades. In our 20-year history, 7 initial winters of wolf control and 14 initial years of favorable weather apparently resulted in 19 years of growth in moose, 14 years of growth in caribou populations, and a high average autumn wolf density after control ended (12 wolves/1,000 km(2)). Benefits to humans included enjoyment of more wolves, moose, and caribou and harvests of several thousand additional moose and caribou than predicted if wolf control had not occurred. We conclude from historical data that controlling wolf populations, in combination with favorable weather, can enhance long-term abundance of wolves and their primary prey, and benefits to humans can be substantial.