One of the wildest places on Earth has benefited from anti-poaching measures designed to protect endangered animals from illegal hunting.
The Serengeti national park in Tanzania has had anti-poaching patrols since 1957 but, until now, no one has assessed whether the effort has actually helped to protect endangered wildlife.
Now a study using data collected during the past 50 years has shown that the anti-poaching patrols have been highly effective at boosting the numbers of animals most under threat from illegal poaching.
"Wildlife within protected areas is under increasing threat from the illegal bush meat and "trophy" trades, and many argue that the enforcement within protected areas is not sufficient to protect wildlife," Professor Ray Hilborn, of the University of Washington in Seattle, said. "Some say that the $2m (£1.1m) spent annually on patrols would be better spent on other preventative activities."
The Serengeti covers a vast area of some 5,700 square miles and is home to some of Africa's most important savannah wildlife, including buffalo, elephants and rhinos, all of which have been hunted illegally for their meat, ivory and horns.
In addition to trophy hunting, animals in the Serengeti risk being snared by local villagers for the growing bush meat trade, but estimates vary enormously on how many animals are being hunted or caught by poachers.
One recent report, for instance, suggested that as many as 200,000 animals a year are being poached from the Serengeti but Professor Hilborn said that if this was the case then many species would be in precipitous decline.
"The estimates are just all over the place, not just for the Serengeti but all across Africa," he said.
The study, published in the journal Science, attempted to assess the true scale of poaching by analysing known data on the number of patrols and the number of poachers who have been caught over the past 50 years.
Professor Hilborn, a fisheries experts, decided to study the 50-year history of anti-poaching patrols in the Serengeti using the same method he uses to assess fish populations in the open sea.
It is called the "catch-per-unit-of-effort technique" and it based on a comparison of the number of fish caught in an area with the total number of hours spent fishing in that area, Professor Hilborn said.
The scientists divided the number of poachers arrested by the number of patrols each day to estimate the total amount of poaching that has gone on over the past 50 years.
The number of poaching patrols have varied over the years, collapsing to zero in 1977 for a period of several years when Tanzania suffered economic chaos.
It was widely thought that poaching had increased dramatically after 1977 and the assessment has confirmed the belief.
"We show that a precipitous decline in enforcement in 1977 resulted in a large increase in poaching and decline of many species," Professor Hilborn said.
"Conversely, expanded budgets and anti-poaching patrols since the mid 1980s have significantly reduced poaching and allowed the populations of buffalo, elephants and rhinoceros to rebuild," he said.
"Anti-poaching is effective in protected areas," Professor Hilborn added. Numbers of buffalo, elephants and black rhinos all declined after 1977 but they began to recoverwhen poaching patrols returned after the late 1980s.
The only exception to that recovery was in 1993, when the Serengeti was affected by a severe drought.
"All three data sets support the basic contention that poaching after 1977 was severe and caused major declines in abundance, whereas, since 1993, poaching has been reduced enough to allow populations to rebuild," the scientists said in their study.
The research is the first time anyone has been able to reconstruct the history of poaching going back 50 years, according to Tom Hobbs, a professor of ecology at Colorado State University in Fort Collins.
"The Hilborn team has shown that protection of wildlife by active enforcement of laws and regulations remains an essential tool for conserving biological diversity," Professor Hobbs said.
"This sounds so simple, but it has been controversial," he added.Reuse content