those for an untreated population. With high immigration, periodic sterilization reduced pup production, but not territory recolonization and,
therefore, resulted in only moderate reductions in population size relative
to the untreated population. While periodic wolf removal produced the
same population size trends as sterilization, more than twice as many wolves
had to be removed than sterilized.
While sterilizing free-ranging wolves for population control has never
been attempted, the simulation results of Haight and Mech (1997) suggested that for small, disjunct wolf populations, such as those that inhabit
much of Wisconsin, Michigan, and central Minnesota, vasectomy may be a
practical, cost-effective method of controlling wolf numbers. The method
would require handling fewer wolves than would lethal trapping, although
sterilizing captured wolves would require more highly trained workers.
Whether vasectomy would be effective or practical in larger populations
is unknown. The simulation results of Haight and Mech (1997) suggested
that, when turnover in breeding tenure is high, vasectomy is less effective.
However, lethal methods would also be less effective in such populations.
Thus, experimentally comparing sterilization and lethal control appears to
be worth trying even in larger populations.
2.3.6 Wolf Removal Strategies for Animal
Damage Control
Wolf management planners in Minnesota, Wisconsin, and Michigan must
develop strategies that balance competing demands for wolf protection and
animal damage control. As wolf populations in these states increased in the
1990s, wolf range expanded into areas with farms and livestock, and wolf
depredations on livestock and domestic animals increased. For example,
from 1979 to 1988, an average of 26 Minnesota farms were affected, and 32
wolves were destroyed annually; from 1989 to 1998, an average of 66 farms
were affected, and 126 wolves were destroyed each year (Mech 1998).
As a result, many farmers and rural residents expressed concern about
expanded wolf range and increased animal damage, calling for population controls or sport harvest seasons. At the same time, wolf protection
advocates argued that depredation control should continue as a government program but without a general harvest or limitations on wolf range
and population expansion.
Given these conflicting demands for wolf management in agricultural
regions, we used the wolf population model to evaluate and compare the
performance of three types of wolf removal strategies that were considered
by state management agencies as candidates to balance those demands.
The removal strategies included reactive management, in which wolves
were removed from territories following recent depredation; preemptive
management, in which wolves were removed from territories in which
depredation had occurred in 1 or more of the previous 5 years; and
2. Modeling for Endangered-Species Recovery
37
therefore, resulted in only moderate reductions in population size relative
to the untreated population. While periodic wolf removal produced the
same population size trends as sterilization, more than twice as many wolves
had to be removed than sterilized.
While sterilizing free-ranging wolves for population control has never
been attempted, the simulation results of Haight and Mech (1997) suggested that for small, disjunct wolf populations, such as those that inhabit
much of Wisconsin, Michigan, and central Minnesota, vasectomy may be a
practical, cost-effective method of controlling wolf numbers. The method
would require handling fewer wolves than would lethal trapping, although
sterilizing captured wolves would require more highly trained workers.
Whether vasectomy would be effective or practical in larger populations
is unknown. The simulation results of Haight and Mech (1997) suggested
that, when turnover in breeding tenure is high, vasectomy is less effective.
However, lethal methods would also be less effective in such populations.
Thus, experimentally comparing sterilization and lethal control appears to
be worth trying even in larger populations.
2.3.6 Wolf Removal Strategies for Animal
Damage Control
Wolf management planners in Minnesota, Wisconsin, and Michigan must
develop strategies that balance competing demands for wolf protection and
animal damage control. As wolf populations in these states increased in the
1990s, wolf range expanded into areas with farms and livestock, and wolf
depredations on livestock and domestic animals increased. For example,
from 1979 to 1988, an average of 26 Minnesota farms were affected, and 32
wolves were destroyed annually; from 1989 to 1998, an average of 66 farms
were affected, and 126 wolves were destroyed each year (Mech 1998).
As a result, many farmers and rural residents expressed concern about
expanded wolf range and increased animal damage, calling for population controls or sport harvest seasons. At the same time, wolf protection
advocates argued that depredation control should continue as a government program but without a general harvest or limitations on wolf range
and population expansion.
Given these conflicting demands for wolf management in agricultural
regions, we used the wolf population model to evaluate and compare the
performance of three types of wolf removal strategies that were considered
by state management agencies as candidates to balance those demands.
The removal strategies included reactive management, in which wolves
were removed from territories following recent depredation; preemptive
management, in which wolves were removed from territories in which
depredation had occurred in 1 or more of the previous 5 years; and
2. Modeling for Endangered-Species Recovery
37