Intensive Management in Alaska
Overview of Relationships Between Bears, Wolves, and Moose in Alaska
Relationships between large predators and their prey in Alaska are complex, and no one model fits all situations. It is possible to generalize about some situations, particularly in Interior Alaska. This information on the biology of moose, bears, and wolves, represents highlights from 25 years of research and management programs conducted by universities and state, provincial and federal governments in Alaska and Canada. In 1997, the National Academy of Sciences published a summary and review of predator/prey interactions in Alaska (National Research Council, 1997). More research has been conducted since that review. The published references listed below can be found in most university or large municipal libraries.
In the boreal forest of northern Canada and Interior Alaska, where bears (either black bears, grizzly bears, or both) and wolves are lightly harvested and are major predators on moose, moose densities typically remain well below levels that their habitat can support. Under these circumstances, moose density fluctuates between about 0.1 and 1.0 moose/mi2 over large areas; most commonly densities are 0.4 to 0.6 moose/mi2. Biologists refer to this situation as the Low Density Dynamic Equilibrium or LDDE because moose density fluctuates yet remains low. This occurs primarily because, together, bears and wolves are efficient predators on moose calves, and kill most of the calves born each year. The highest densities reached in these systems (about 1 moose/mi2) tend to occur in very large burns where habitat is excellent and moose apparently are more successful at avoiding predators.
Although the LDDE prevails in much of remote interior Alaska, differences occur between areas. In most areas, bears are the major predator on moose calves. An exception occurs in Game Management Unit 20A where wolf control has been shown to be effective at maintaining high numbers of moose and high long-term harvests of moose. In Unit 20A, initial reductions in wolves increased moose population density, wolves also quickly increased after wolf control because, ultimately, the number of wolves in an area depends mostly on the number of prey animals in the area. Number of moose harvested also remained high after wolves increased. An abundance of trappers in Unit 20A has kept wolves from increasing to the point where they could cause declines in the moose population. A similar situation likely occurs in portions of Units 20B and 20D South.
Grizzly bears have been shown to be particularly effective predators of moose calves from birth to about 2 months of age and often kill adult moose in the spring. In this regard, one grizzly bear is equivalent to many black bears. Not all bears are equal, however, and some bears seem to become specialists at killing both adult and calf moose.
Black bears have been found to be the most important predator of moose calves in some areas of Alaska where grizzly bears are uncommon. In these areas, black bears killed about 40% of all moose calves that were born. Most predation was by adult males.
Biologists expect that significant reductions in bear numbers (either black or grizzly or both) will also lead to higher numbers of moose for harvest. For example, in areas of Canada and the northern states where moose coexist only with wolves, moose are often found at high densities that fluctuate with weather and habitat (e.g. Isle Royale).
Numbers of grizzly bears have probably increased in Interior Alaska since the 1950s. We base this on incidental observations by older hunters, local residents, cabin owners, and Native elders, who all indicate that grizzly bear numbers have increased. This is corroborated to some degree by modern studies. For example, grizzly bears were recently found to be significant predators of moose calves on the Yukon Flats and are commonly seen by local residents, whereas 20-30 years ago, observations of grizzly bears were rare.
In the Anchorage and Fairbanks areas, where wolves and bears are not common, moose are abundant.
Grizzly bear populations appear to be much more resilient to harvest than previously believed. During the last 10 years, the Alaska Board of Game has made a deliberate effort to reduce numbers of grizzly bears in a few important hunting areas (e.g. Game Management Unit 13-the Nelchina Basin) by increasing the bag limit and extending hunting seasons. So far, these new regulations have had no noticeable affect on grizzly bear populations even though hunters have taken an increased number of bears.
Wolves have been found to be very adaptable and they recover from low numbers within a few years. Despite relatively heavy hunting and trapping over the last century in Alaska, wolves occur on nearly all of their traditional habitat throughout mainland Alaska. Historically, wolf numbers were greatly depressed. Specifically, wolves were rare in Interior Alaska between about 1910 and 1925, and during the 1950s. During 1910-1925 wolves may have succumbed to diseases brought in by sled dogs or to widespread poisoning. During the 1950s, federal predator control agents reduced wolves by poisoning and aerial shooting. Wolves have been abundant and have occurred in all of their historic ranges in Alaska since state management began in about 1960 (except for the Anchorage and Fairbanks areas, and the western Seward Peninsula).
Wolves are social animals that live in large family groups. Usually, only a single female per pack successfully raises pups, but depending upon the relationship of adult males and females in a wolf pack, multiple litters may occur in a single pack in a single year. Most pups born into a pack stay in the pack for at least one year, but virtually all have dispersed away from their natal pack by the age of 3. Large packs of 20 or more wolves may occur in areas where food is abundant and pup survival is high. Wolf populations in North America commonly sustain annual harvests or natural mortality rates of 20-40% without experiencing a year-to year decline in numbers. High reproductive rates, high mortality rates and long distance dispersal behavior results in extensive gene flow within wolf populations and between wolf packs.
In Alaska and other areas, if wolves are not hunted or trapped, most mortality is from intraspecific aggression (fighting with other wolves). In trapped wolf populations, natural mortality rates are often lower than in untrapped populations.
In coastal areas of Alaska, where fox rabies is endemic, wolves are periodically reduced to low levels by rabies.
Practical Aspects of managing moose in areas where the LDDE exists
Usually, without predator control, hunters can take about 5% of a low-density moose population each year — almost all of the harvest must be bulls or the population will decline.
LDDE does not present a biological problem — moose are not likely to become threatened, endangered or extinct due to predation.
The fact that the LDDE prevails in large areas does not usually present a management problem either. Interior Alaska is sparsely populated and access to moose populations is often poor. This means that hunting pressure is relatively light in many areas anyway.
The LDDE can cause a management problem around villages, or in areas that have become important hunting areas for Alaskans near the road system. In these areas, people need or want to harvest more moose than the system can support. In Alaska, moose are valuable to people as a source of food and income (i.e. guiding and transporting hunters), particularly in rural areas. This is why people often express the desire for predator control.
In some areas, where there is a demand to increase moose harvests, it might be possible to harvest more moose by reducing bear predation. Although this idea is reasonable, it is a relatively new idea, has not been adequately tested in Alaska, and programs of this nature need to be viewed as experiments.
- Ballard, W.B., J.S. Whitman, and D.J. Reed. 1991. Population dynamics of moose in southcentral Alaska. Wildlife Monographs 114:1-49.
- Boertje R.D., P. Valkenburg, and M.E. McNay. 1996. Increases in moose, caribou, and wolves following wolf control in Alaska. Journal of Wildlife Management 60(3):474-489.
- Gasaway, W.C., R.O. Stephenson, J.L. Davis, P.E.K. Shepherd, and O.E. Burris. 1983. Interrelationships of wolves, prey, and man in interior Alaska. Wildlife Monographs 84:1-50.
- Gasaway, W.C., R.D. Boertje, D.V. Grangaard, D.G. Kellyhouse, R.O. Stephenson, and D.G. Larsen. 1992. The role of predation in limiting moose at low densities in Alaska and Yukon and implications for conservation. Wildlife Monographs 120:1-59.
- Mech, L.D., L.G. Adams, T.J. Meier, J.W. Burch, and B.W. Dale. 1998. The wolves of Denali. University of Minnesota Press, Minneapolis and London. National Research Council. 1997. Wolves, bears, and their prey in Alaska. National Academy Press, Washington.
- Franzman, A.W., and C.C. Schwartz, Editors. 1997. Ecology and management of the North American moose. Smithsonian Institution Press, Washington and London.