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Sustainable Society:  A society that balances the environment, other life forms, and human interactions over an indefinite time period.

Wolf Management in the 21st Century:
From Public Input to Sterilization

L. David Mech, Steven H. Fritts, & Michael E. Nelson*
 

Abstract
Introduction
   Fig. 1. Trend in numbers of wolves trapped by a federal government
   livestock depredation-control program in Minnesota
Alternate Methods Of Alleviating Wolf Damages
   Translocation
   Compensation for losses to wolves
   Zoning
   Public backlash
    Public education
    Direct wolf control
    The possible role of vasectomy
        Table 1. Pack sizes of vasectomized wolves in the Superior National Forest, Minnesota after vasectomies.
Conclusions
Literature Cited

Abstract:
Human-population increase and land development portend increasing conflict with large predators. Concurrently, changes and diversification of human attitudes are bringing increased disagreement about wildlife management. Animal-rights advocacy resulting from urbanization of human populations conflicts with traditional wildlife management. These forces focus more on wolves than on other wildlife because of strong public and media interest in wolves. Thus wolf management in the future will come under even greater public scrutiny, involve more public input, and may have greater restrictions imposed on it. This will lead to increased complexity in wolf management including more zoning, more experimentation with lethal and non-lethal capture techniques and alternate methods of alleviating damage to pets, livestock, and large ungulate herds, and greater public and private subsidy of wolf damage. One form of non-lethal control of wolf populations that may hold some promise is direct sterilization of males to reduce the biotic potential of the wolf population. Experimental vasectomy of five wild male wolves from four packs in Minnesota indicates that sterile males will continue to hold mates and territories, which would be necessary if sterilization is to be a viable technique for assisting with population control. If sterile males held territories but failed to produce pups, such territories might contain only about a third the number of wolves as fertile pack territories. Because wolves are long-lived in unexploited populations and their territories are large, direct sterilization of relatively few animals each year might significantly reduce populations.

Introduction

As the twentieth century draws to a close, the gray wolf Canis lupus is more widely distributed in Europe and in the contiguous 48 United States than it has been for more than three decades (Promberger and Schroder 1993, Mech et al. 1994). The species has made a comeback in Italy, Spain, Portugal, and Poland, is increasing in Finland, Norway and Sweden, and has begun to colonize France and Germany. In the U.S., the wolf has recolonized northern Wisconsin, Michigan, and Montana and is attempting to recolonize North and South Dakota, Washington, Idaho, and Wyoming. A reintroduction program is planned for central Idaho and Yellowstone National Park (Wyoming), and an Environmental Impact Statement is being prepared for the possibility of reintroducing the Mexican gray wolf to the southwestern U.S. Meanwhile, Minnesota, Canada, Alaska, much of Asia, eastern Europe, and the Mideast still harbor high numbers of wolves (Ginsburg and MacDonald 1990).

At the same time, the human population continues to increase, and land use by humans is intensifying in most areas. The potential for conflict between wolves and humans is increasing, especially in the more accessible regions, where wolves were exterminated three to four decades ago and are now returning. For example, between 1988 and 1993 the number of wolves killed in Minnesota by depredation control personnel increased 127% (Fig. 1). In Spain, annual compensation for damages by wolves now totals one million U.S. dollars (Vila et al. 1993). Because wolves are prolific (Mech 1970) and can disperse distances exceeding 800 km (Fritts 1983, Gese and Mech 1991), conflicts will probably continue to increase, and intensive wolf management will become increasingly necessary.

Fig. 1. Trend in numbers of wolves trapped by a federal government
livestock depredation-control program in Minnesota

Where wolf populations are low and each individual is important to population recovery but some depredations on domestic animals are occurring, translocation of problem animals may be useful. However, based on experiments in Minnesota, wolves must be moved at least 70 km or they will return to their capture area (Fritts et al. 1984). Where wolf populations are large and secure, translocation has little value to the population.

Compensation for livestock losses is another method of dealing with wolf depredations. However, it really is only useful when wolf populations are low and attempts are being made to restore the species to an area. After a large enough population is established, compensation payments only serve to subsidize the wolves. If the compensation program is successful, payments will only increase. At some point the public may object to its funds going to subsidize increasing numbers of wolves. In such cases, private organizations may choose to make the compensation payments as is now being done in the western United States (Fischer et al. 1994). Conceivably, payments by private individuals or organizations may become more important in the future.

As wolf-human conflict intensifies and greater restrictions are placed on wolf control, wolf management will have to become increasingly efficient. This will probably mean tailoring wolf management to the needs of specific areas, and intensification of zoning. Zoning can be useful to wolf management in two ways. First, certain areas can be set aside where wolves can either be allowed to live or prevented from inhabiting. Or in certain zones wolves could be allowed to reach only a certain density before being subject to control. Secondly, areas can be zoned in such a way that at certain times lethal wolf control can be applied to some zones but not to others. Both approaches to zoning have been applied to northern Minnesota wolf range since 1978 (Fritts et al. 1992). Wolves are allowed to inhabit some zones without being subject to control, whereas they are subject to control in other zones. However even in zones where control is allowed, certain criteria must be met before control is initiated. In this way, a legally protected population of wolves numbering from 1,200 to 2,000 (Fuller et al. 1992) has been maintained without much public discontent for about 200,000 USD per year, 75% of which goes toward lethal wolf control, and the rest towards compensation for livestock losses.

On the other hand, if wolf-human conflicts, public payments for compensation, or illegal taking of wolves reach high enough levels, some of the restricted or banned methods of lethal wolf control may be reinstated. Alternatively, techniques such as public hunting, which may also be publicly disapproved of, may seem more acceptable than the use of poison, steel-foot traps, or illegal taking. Three such cycles of protection and persecution have been documented for the wolf in Poland (Okarma 1992).

Because the Minnesota wolf population has saturated most of the wilderness and continues to increase, more wolves are currently inhabiting agricultural lands. Thus depredation control costs and compensation costs continue to rise. For example, when wolf numbers increased from about 1,600 in 1988 (Fuller et al. 1992) to probably 2,000 in 1994, the number of depredation complaints, the amount of compensation paid, and number of wolves trapped for depredation control increased disproportionately (Fig. 1). Presumably in Minnesota, Spain, Italy, and elsewhere, the public eventually will object to the cost of subsidizing wolves and demand wolf population reduction in certain areas.

One of the most effective approaches to wolf management is to educate the public about wolf biology and management. Misconceptions about wolves, both negative and positive, tend to cause people to hold extreme views about wolf protection. Generally, agricultural cultures in current or recent wolf range tend to view wolves far more negatively than urbanites, who tend to deify the animal and object to wolf control. Promoting accurate, objective information about the wolf will be a constant need in the 21st century just as it is at present. If successful, however, it will greatly facilitate ecologically sound wolf management.

Wolf control or reduction can be done by the government or the public or some combination. If the control involves the public, it could be by sport hunting or trapping with various regulations such as seasons, zones, methods of capture, limits, etc. All these methods have been used in the past either on wolves or other species and they will have relevance in the future depending on various circumstances.

Another possibility of controlling wolf populations, at least in certain areas, could be through the use of vasectomy to reduce a population's reproductive potential. Because most wolf packs contain a single breeding pair (Mech 1970, Harrington et al. 1982) and breeding pairs hold territories (Rothman and Mech 1979), sterilizing members of each of several pairs could result in an attenuated wolf population. The only practical method of sterilizing wild wolves at present is by live-trapping the males and vasectomizing them.

The question remains, however, as to whether sterilized pairs lacking pups would continue to hold territories. Intact pairs, of course, hold territories long enough to produce pups (Rothman and Mech 1979, Fritts and Mech 1981). However, some wolf pairs that do not produce pups sometimes break up and leave their territory (Mech 1987, Mech and Seal 1987). If vasectomized pairs did so, then sterilization would have little lasting effect, for other lone wolves would soon fill the vacant territories (Rothman and Mech 1979, Fritts and Mech 1981).

To determine whether vasectomized wolf pairs would continue to hold territories, we conducted an experiment in the Superior National Forest of northeastern Minnesota from 1987 through 1994. During summers 1987 and 1988, five adult male wolves, weighing 32-38 kg and with testis lengths 3.0-3.9 cm were live-trapped from four packs, transported to a veterinary lab, and surgically vasectomized. Veterinarians removed large portions of the vas deferens of each. The animals were then radio-collared, released in their territories, and followed by aerial radio-tracking approximately weekly and their presence in packs, pairs and territories was observed. We observed post-vasectomy pack sizes of the four packs for 1,3, 4, and 7 years respectively (Table 1).
 

Table 1. Pack sizes of vasectomized wolves
in the Superior National Forest, Minnesota after vasectomies.¹

1. Wolves 35, 77, and 79 were vasectomized in summer 1987; 119 and 129, in summer 1988.
2. Killed by other wolves in July 1988; the only observation of this pack after the 1988 whelping season was of 4 adult wolves in July.
3. Members of the same pack; one possible observation of pups was made with this pack on 2 November 1988.
4. Dispersed 18 km, paired with female and held new territory until killed.

The effectiveness of the vasectomies in sterilizing males cannot be fully documented because there were other pack members present which could have been breeding males. However, the sterilization technique used is standard for dogs, and the veterinarians who performed the vasectomies were practiced at the technique. Only one possible observation of pups was made, and that observation was questionable. In all years, the pack size either remained the same or decreased after the males were vasectomized (Table 1).

All of the vasectomized wolves for all the years observed remained in territories until they died or their transmitters expired. One wolf spent two years in one pack territory after being vasectomized, then dispersed about 18 km and bonded with a female; the pair held its new territory for 2 years until the male was killed. Another vasectomized wolf remained in his territory for 7 years after being vasectomized (Table 1). The evidence obtained in this study demonstrates that vasectomized wolves do not necessarily lose pair-bonds or territories; one wolf even formed a new pair bond.

The greatest disadvantage of the vasectomy technique is that individual wolves must be captured and handled. However, chemical vasectomy involving the non-surgical injection of sclerosing agents directly into the epididymides (Freeman and Coffey 1973, Pineda and Hepler 1981), which the authors learned about after this study, could be applied by wildlife biologists in the field. This technique would make vasectomy far more practical.

Thus it may be possible to vasectomize wolves around local livestock herds sustaining chronic losses from wolves and reduce the local wolf population by as much as 2/3 given that wolves usually produce an average of 4-6 pups per litter (Mech 1970). This should also reduce depredations considerably because a litter of pups would quadruple a wolf pair's need for food. Situations may also arise in which it would be preferable to vasectomize members of non-depredating pairs rather than remove them and risk their territories being filled by others who might.

Furthermore, as a general wolf-population-control measure, vasectomizing a certain percentage of a population would tend to reduce its biotic potential and its size for periods of several years. If each year, a certain percentage of the wolf population was sterilized, population growth and recolonization of new areas could be curtailed while a reservoir wolf population was maintained. Field studies and wolf-population modeling would give reasonable insights into the approximate percentage of each population that might need vasectomizing so that a given wolf population might be adjusted to a desired level.

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