All African hunting reserves impose bag limits, or quotas, but quotas are supposed to be based on the size of an animal population. Lions, however, are hard to count. Using long-term data on lion behavior, mortality, reproduction and other characteristics gathered by University of Minnesota lion researcher Craig Packer, a team led by graduate student Karyl Whitman created a computer model to predict the effects of different hunting regimes on lion populations over a period of 50 years.
"This is one of very few studies on how hunting changes [lion] behavior and how we can manage hunting to improve its sustainability," said Whitman. "We've put forward two simple rules: You can sustainably shoot male lions without limits as long as they're 5 or older, and you can age lions before shooting them." As cubs, lions have noses that are soft pink to gray at the tips. After a lion reaches age 3, the nose starts to blacken in splotches. If a lion's nose tip is more than 50 percent black, the lion is probably at least 5 years old, the researchers said.
Lion hunting is a controversial activity, and pressures on guides to deliver lions, regardless of their quality as trophies, can be enormous. Clients may pay as much as $100,000 for a hunting safari, and for that amount of money they expect to take home a lion, Whitman said. Given such expectations, a guide could easily be tempted to allow shooting of sub-trophy animals to satisfy the customers. But if hunting were strictly limited to lions at least 5 years old and hunters had realistic expectations, both lion populations and hunting could continue indefinitely.
"I think something needs to be done," said Whitman. "The industry needs to better monitor itself, either at the national level or by the Convention on International Trade in Endangered Species of Wild Fauna and Flora.
"Also, many clients are told they'll definitely get a lion. If the clients were better educated about the chances of getting a good-quality trophy, they would probably be more willing to forego shooting a poorer quality--that is, young--animal, knowing this will improve the sustainability of lion hunting for the long term."
In the study, the researchers created theoretical populations of lions and subjected them to hunting of males at minimum ages between 3 and 6 and with quotas ranging from zero to 20 per year. Individual males were removed (shot) according to the age minimum, but without regard to whether they belonged to a pride or were nomadic. The data showed that after a few years of adjustment to hunting, the number of females stabilized no matter what the yearly quota, as long as only males 5 or older were taken. Female populations stabilized at a slightly higher number if only males 6 or older were taken.
"By maximizing the population, hunters maximize their harvest," said Packer, who is a co-author of the paper. "Another thing that would help is to have a mechanism to assess age after death, and then prohibit exportation of underage males." Such a mechanism does exist; the condition of a lion's teeth is a very good indicator of its age, said Whitman.
"If there's a well-regulated hunting industry, it's one of the best ways to preserve wildlife in Africa," said Packer. "The income helps sustain wildlife conservation. Without hunting, there would be less tolerance for lions [by local human residents]. We're trying to defuse some of the disagreement between hunters and conservationists."
Other authors of the paper were Anthony Starfield, University of Minnesota professor of ecology, evolution and behavior, and Henley Quadling, a computer specialist now working in Texas (D4D Technologies). The study was funded by the National Science Foundation, the Wildlife Conservation Society, the Big Game Special Projects Foundation, the John D. and Catherine T. MacArthur Foundation, the Dayton-Wilkie Foundation, the Global Wildlife Trust and the University of Minnesota Graduate School.
Embargoed by Nature until noon CST (1 p.m. EST, 6 p.m. London time) Sunday, Feb. 22. For a copy of the paper, contact Craig Packer.