Furbearer Management Principles
Furbearing mammals, like all other species of animals, are dependent on having adequate food, water, shelter, and living space if they are to survive. These basic life needs are commonly referred to as habitat. Any given amount of habitat will only support a certain number of animals. The number of animals that the habitat can support on a year-round basis is called carrying capacity.
The carrying capacity depends on the quantity, quality, and arrangement of habitat factors, as well as on the amount of crowding that the animal will tolerate. The ability of the habitat to support animals varies with the seasons and reaches a low in late winter in Minnesota. At that time, lack of adequate food, shelter, or other resources can become a limiting factor, which sets the upper limit on the number of animals that can survive. For example, a marsh may have enough of everything to support 1,000 muskrats in the summer and fall, but in the winter, there may be only enough food or deep enough water for 200. That means that the year-round capacity is 200 and that the remaining 800 will die or possibly disperse (move out). However, even most of the dispersers will ultimately die.
Carrying capacity can be compared to the volume of a bucket. When the bucket (habitat) has been filled, adding more to it simply wastes what is added. That is why most stocking programs fail. As the seasons progress and food and shelter become more limiting, the population is forced into a smaller and smaller habitat “bucket.” Since this smaller bucket cannot support as many animals, the excess must die, one way or another, or attempt to move and find unfilled “buckets.” The only way to bring about a long-term increase in the population is to increase the size of the bucket (improve the quantity or quality of habitat).
Because the chances of survival in the wild are uncertain, nature has provided most species of animals with the ability to produce far more young than are needed to maintain the population. This is nature’s way of assuring that enough animals survive to replenish the breeding population and disperse into available habitats. A portion of this excess, called the harvestable surplus, is the amount that can be taken by people, without reducing the breeding population. his is possible because the trapping or hunting mortality (deaths) replaces or compensates for some of the natural mortality that would otherwise occur.
This harvestable surplus can be compared to the interest from a savings account. The “interest” (harvestable surplus) can be used each year without reducing the “principal” (breeding population). By adjusting the number of animals removed (for example, by seasons or limits) the population can be allowed to increase, decrease, or remain stable. Use of the surplus provides recreation, income, products, food, and employment, without depleting the population. The population remains to provide ecological, aesthetic, and recreational values, and to produce the next year’s surplus.
Sometimes the best management plan requires that a population be held below its carrying capacity, for example, to prevent excessive wildlife damage. Also, management attempts to maintain levels above the carrying capacity of the habitat are invitations to environmental problems, disease, and resource waste. Wildlife cannot be stockpiled.
Some species of furbearers can be safely harvested at a higher rate than others. It is nearly impossible to over-trap a prolific furbearer like the muskrat, which breeds at a young age and has multiple, large litters annually. Muskrat populations typically experience a 70 to 90 percent turnover, whether they are harvested or not. Normally, up to 70 percent of the muskrats present in the fall can be harvested without a detrimental population effect. Practically speaking, except in small areas of restricted habitat, this 70 percent level is difficult to achieve, and over-trapping very seldom occurs. On the other hand, for an animal like the fisher which does not reproduce until two years of age and which has only one small litter per year, a harvest rate of about 20 percent might be the maximum that could be safely allowed. Wildlife managers must take into account not only the biology and population dynamics of the species but also the amount of harvest pressure and how vulnerable the species is to being caught. Fur prices, trapping, and hunting license sales, accessibility of the habitat, and effectiveness of the harvest methods must all be considered when managing some furbearer species.
Furbearer Management in Minnesota
The Department of Natural Resources manages Minnesota’s furbearer resources for the benefit of the citizens of the state. The Department recognizes that furbearers have a variety of ecological, recreational, economic, and aesthetic values and that those values can be positive or negative. Also, since values are determined by people, not nature, the same animal can have a wide range of values depending on the time, the place, and who is being affected by it.
The goal of management is to maintain a productive harmony between people and furbearer resources for present and future generations of Minnesotans. This goal is accomplished by maintaining habitats and controlling harvest so that harvestable surpluses can be utilized, consistent with habitat disease, wildlife damage, and the desires and tolerances of people.
In order to responsibly manage furbearers, the Department monitors furbearer populations and harvests, sets regulations, maintains habitats, and enforces laws related to furbearers.
Seasons – Seasons are based first of all on their population impacts. No season, which would be detrimental to the survival of a species in the state, is permitted. Once that biological requirement is met, further decisions are based primarily on the concerns of people who use, value, or are affected by the resource. Recreational opportunity, fur primness, damage problems, landowner concerns, non-harvest values, disease problems, and all other factors enter into these decisions, and opportunities for public input are provided.
Surveys – Harvest and fur price surveys are conducted for all species of furbearers in Minnesota. In addition, relative changes in population densities are monitored by scent-post surveys for land carnivores and by aerial surveys for beaver. For species, which are highly sensitive, exact figures are determined through pelt registration. For those species, carcasses are also collected from trappers, and information on sex ratios, ages, and productivity is used to “model” their populations with the aid of a computer. A number of special surveys are also conducted each year to evaluate particular areas of concern.
Habitat – Although furbearers are often not the highest priority in many habitat management programs, the fact remains that fur-bearing animals are primary beneficiaries of many of these practices. This is particularly true of wetland areas, which are prime habitats for muskrats, mink, beavers, raccoons, foxes, and other furbearers. In fact, furbearers often do so well in these areas that conflicts develop with management for other species such as waterfowl. Forest management practices also influence furbearer populations, with some species favoring early successional stages and others favoring later stages.
Enforcement – Minnesota Conservation Officers enforce the laws relating to furbearers in all 87 counties of the state. Of course, they have many more duties in addition to the furbearer regulations, but they are always interested in and concerned about situations where violations are occurring. It is important, however, for trappers to police their own ranks and to help enforcement officers by reporting violators. People who take furbearers illegally are stealing from the honest citizens of the state.
Conservation and Trapline Management – Furbearer regulations are established for the entire state, or for large regions of the state, depending on the species. Conditions vary within such large areas, and it is up to the trapper to practice conservation on his own trapline and to attempt to take only a portion of the surplus. This sounds simple but is actually quite complicated because in many areas a number of trappers and hunters are competing for the same resource in the same area. Fortunately, trapping and hunting tend to be self-limiting for many species. The time and effort required to take these animals exceeds the benefit long before they are reduced to critically low levels. For other species which are not so resilient, regulations have to be correspondingly more restrictive.
In areas where trappers have exclusive or near-exclusive trapping privileges, individual trapline management is much more feasible. In these areas, the trapper can manage not only the harvest but in many cases the habitat as well. By doing so he can be assured of having a relatively high-sustained harvest year after year.
Minnesota's Furbearer Resource
Minnesota is blessed with a rich and diverse furbearer resource. Because of Minnesota’s geographic position, the state has furbearer representative of both northern and southern climates, and of prairies (and agricultural areas) and forests.
Minnesota’s furbearer resource has a variety of positive values to trappers, hunters, landowners, campers, photographers, and other outdoor users. Over the years, the economic value of the fur resource to Minnesota trappers and hunters has been from $3 million to $20 million annually. The other values are more difficult to measure. There is no doubt that the presence of beaver, otter, wolves, and other animals adds immeasurably to the aesthetic value of outdoor experiences for many people.
Furbearers also sometimes have negative values such as predation on livestock by foxes or coyotes; destruction of sweet corn by raccoons; and flooding of roads, fields, or forests by beaver. Although the positive values of furbearing mammals far exceed their more detrimental aspects, the damage that they cause costs hundreds of thousands of dollars annually in Minnesota. Trapping is the single most effective, safe, and important tool for resolving these situations. Because the people who most benefit economically from furbearers – trappers and hunters – are not often the ones bearing the burden of the costs – livestock producers and farmers – it is in the best interest of trappers and hunters to provide assistance with wildlife damage problems whenever possible.
In addition to the values that people place on furbearers, all wildlife species have a function in nature. The ecological influences of these animals vary, and whether their influence is “beneficial” or “detrimental” depends solely on the perspectives of people, and not all people agree. Nearly everyone does agree, however, that all species of native wildlife do have a place in the Minnesota wildlife community. We all have a responsibility to wisely manage those species so that they can be perpetuated.