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An Analysis of the Feasibility of

Using Fertility Control to Manage

New Jersey Black Bear Populations
black bear
The 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:

1) 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.

Research Project Summary

Full Report

Peer Review

Nine 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.

For more information regarding this study please contact Gary Buchanan or Bruce Ruppel.

Related Links

NJDEP Division of Fish and Wildlife

Division of Science and Research
Dr. Gary A. Buchanan, Director

Phone: (609) 984-6070
Fax: (609) 292-7340