JOHANNESBURG (AP) — South Africa's anti-COVID-19 lockdown is credited with helping to achieve a dramatic drop in rhino killings, but as the country opens up experts warn of a possible resurgence of poaching of one of Earth's most endangered mammals.

Redoubled efforts are critical to protect the country's rhinoceros population, South African officials and wildlife activists say, as World Rhino Day is marked Tuesday.

South Africa's nationwide shutdown to combat the spread of the coronavirus was imposed at the end of March and stopped all international and domestic travel. The country has gradually reopened and will allow a return of international tourists on Oct. 1.

“The lockdown presented an opportunity for us. There was no international or local tourism and the lockdown also prevented poachers from moving around and we were able to ramp up our protective measures,” said Albi Modise, spokesman for the Department of Environment, Forestry and Fisheries.

In the first six months of 2020, the numbers of South African rhinos killed by poachers fell by more than 50% from the previous year, to 166, according to official statistics from the environment department.

“We realize that as the country opens up, we need to up our game to address the possible threat of poaching,” Modise told The Associated Press.

South Africa has about 20,000 rhinos, estimated to be 80% of the world's total population, and the country has been hard hit by poachers killing the animals for the illegal international trade in rhino horns. Other countries with significant rhino populations are Kenya, Namibia and Zimbabwe.

“Although the killings of rhinos have reduced this year, this could be a temporary reprieve,” said Cathy Dean, chief executive of Save the Rhino. “With the economic downturn caused by the coronavirus, and the decline of tourism, many people are desperate and some may turn to poaching. With a resumption of international flights, we may again see seizures of illegal rhino horn, which indicates a resurgent trade.”

South Africa deploys anti-poaching squads throughout its parks to protect rhinos, elephants and other game from poachers.

In the KwaZulu-Natal province, a technologically advanced “smart fence” is being built around the Hluhluwe-iMfolozi park, which alerts park rangers when any intruder tries to sneak into the park.

“The fence has electrics both inside and outside its length and any tampering or cutting of the fence sends us an immediate message, pinpointing the location of the tamper," Nomusa Dube-Ncube, the province's top official for tourism and environmental affairs, said in a statement.

"Two sections of fence have been upgraded to date and we have already seen a shift in rhino poaching activity away from both areas,” said Dube-Ncube, thanking the private organization Wildlife ACT for supporting the fence.

“They have invested resources, technical support and the channeling of donor funding to these key initiatives,” she said. “We are hopeful of the decline in poaching losses.”