How do you keep bears from procreating? Very carefully. Environmental Protection Commissioner Bradley Campbell approved a multi-approach plan to cut back on human/bear contact. The most controversial portion of the plan is the bear hunt. Officials also advocate the use of bear-proof trash cans as well as more public education about how to react when encountering the animals. But perhaps the most ambitious idea in the plan involves bear contraception, in which doctors inject the animals with chemicals to ward off reproduction. The technology is still in its infancy, but two studies by a team of scientists are underway at an animal park in Jackson, New Jersey. Black bears typically mate in the summertime, but an embryo lives in the female’s uterus until late fall before implanting itself in the uterine wall and beginning its two-month gestation. In the meantime, the would-be mother investigates the nutritional environment: If food has been abundant, she will produce more cubs. Litters can range from one to six. A healthy female black bear can weigh more than 200 pounds (90 kilograms), but she produces newborns that are no bigger than kittens. Dr. Allen Rutberg, a research professor at Tufts University’s Center for Animals and Public Policy in Grafton, Massachusetts, said his team began testing a contraceptive called PZP on six female bears in fall October 2004. The vaccine, made from pig tissue, prevents sperm from attaching to an egg. Since female bears give birth every other year, it will be February before the doctors know whether the vaccine has worked. ``So far there’s been nothing discouraging, but nothing terribly encouraging either,’’ Rutberg said. His work is partly funded by the Humane Society of the United States. Burlington County, New Jersey, veterinarian Dr. Gordon Stull is overseeing the injection of some male bears at the animal park with Neutersol, a chemical that in long-term tests on dogs suppresses sperm production but not testosterone. The researchers think male bears will continue to mate, causing their female partners to ovulate and their bodies to believe, incorrectly, that they are pregnant and females won’t accept other suitors when pregnant. Translating the results of either study into practice is at least a few years off. While opinions among the scientists about next month’s hunt vary, Stull said he was sorry to see it approved. He said that stricter garbage control would better reduce the number of unwanted encounters between bear and human. The physiology of the female bear underscores Stull’s belief that getting humans in bear country to be more conscientious about securing their trash is key to reducing human-bruin contact. ``That’s why it’s so important to control garbage in areas where bears live,’’ he said. ``Not only is it the source of many nuisance complaints, but it increases their level of nutrition to the point where they’re much more prolific.’’