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Analysis of the Feasibility of
Using Fertility Control to Manage
New Jersey Black Bear Populations
Division of Fish and Wildlife (DFW) is responsible for managing black
bears and developing comprehensive management strategies for the control
of the state’s growing black bear population. DFW requested an assessment
of the current status of, and feasibility of using fertility control agents
as a method of population control. The Division of Science, Research and
Technology (DSRT) provided technical support to DFW and funded this project
to conduct this independent literature review.
The New Jersey black
bear (Ursus americanus) population has been growing rapidly in both
distribution and abundance in recent years (Carr and Burguess 2005).
Although fewer than 100 bears, restricted to the northern most part,
are thought to have been present in the state in the 1950s, by 2001,
the population was estimated at 1,777 in northern New Jersey and the
range had expanded to occupy roughly the western two-thirds of the state.
This is believed to be a consequence of protection afforded by game-animal
status, which was conferred on bears in 1953, and of the maturation
of young forests in the state, leading to improved habitat and food
supply (e.g., hard mast). Natural food is supplemented by food of human
origin, such as garbage and agricultural crops. The expanding bear population
has led to an increasing number of conflicts with humans in New Jersey.
The New Jersey Department of Environmental Protection, Division of Fish
and Wildlife, has regulatory authority for managing the state’s
bear population. Hunting, which can both control numbers and result
in aversive conditioning of bears (Geist 2005), has become controversial.
Better management of garbage, bird feeders, and other bear attractants
could help to reduce human-bear conflicts. However, conflicts are bound
to increase if the bear population continues to expand. In 2004, United
States state wildlife agencies reported a perceived 45 % increase in
expenditures to control bear-related damage, a 22 % increase in personnel-hours
to resolve bear-related complaints, and a 19 % increase in the overall
number of complaints over the previous 5 years (International Association
of Fish and Wildlife Agencies 2004).
The size of a wildlife
population is governed by just 4 basic factors: 1) fertility, 2) mortality,
3) emigration, and 4) immigration. Emigration and immigration are difficult
to control and have little potential as tools to affect bear populations
in a particular area, although the removal and long-distance displacement
of individual problem bears is a common practice in many jurisdictions.
Mortality and fertility can potentially be manipulated to affect the
size of particular populations. In the past, the size of game animal
populations, has been managed largely by adjusting the harvest, and
a large body of information about this approach has developed over the
years. On the other hand, over the past 25 years, managing wildlife
populations by controlling fertility has been a focus of considerable
interest (Fagerstone 2002). Despite this interest, however, fertility
control (FC) has been applied in few situations, so little practical
experience exists – none of it involving bears.
The following conclusions
were reported by the Principal Investigator based on the literature
review and assessment of the Feasibility of Fertility Control of the
Black Bear Population:
Immunocontraception, using a pZP (porcine zona pellucida) vaccine administered
to females, has the best potential to control reproduction in individual
female bears, while minimally affecting normal social dynamics. Neutersol®
is very likely to be effective in sterilizing male bears, although treated
males will be relegated to subordinate social status because of the
effects of the treatment on hormone levels. (Males could, however, be
vasectomized without affecting social structure and dynamics.)
2) Because one male can inseminate many females and because males tend
to disperse more widely than do females, fertility control applied to
females, is the most effective strategy for managing population size
of wildlife species, including black bears.
3) Of the options presently being considered for bear fertility control,
only Neutersol® and vasectomy have regulatory approval. Although
pZP vaccines, which contracept females with minimal effects on treated
animals, are best suited for wildlife population control, none has regulatory
approval. Whether the FDA would permit field trials of pZP vaccines
on black bears is unknown.
4) If all or most dominant male bears in a population are effectively
removed from their social positions by sterilization with Neutersol®,
it is likely that the consequential social disruption would allow an
influx of young males, which would do much of the breeding.
5) Managing black bear populations using fertility control will be much
more technically difficult and costly than in other wildlife species,
such as deer and wild horses, where this approach has been successfully
applied. This is a consequence of the difficulty of capture, lower density,
and the variable and wide-ranging nature of bear movements.
6) Fertility control is very unlikely to be a feasible means of managing
black bear populations in New Jersey.
professionals with extensive experience with large mammals and/or bears
were identified and contacted to peer review the final report. Comments
were received from five reviewers. Four of the five peer reviewers agreed
with the report conclusions. One peer reviewer thought additional numerical
analysis should be performed once management objectives were clearly defined.
more information regarding this study please contact Gary
Buchanan or Bruce Ruppel.
Division of Fish and Wildlife