(CNN) One of Africa's largest wildlife preserves says it's been a year since it found an elephant that was killed by poachers.

The last time an elephant in the Niassa Reserve was recorded killed by a poacher was May 17, 2018, according to the Wildlife Conservation Society, which assists Mozambique's government in managing the reserve.

The drastic decline in poached elephants is credited to a new rapid-intervention police force, an increase in surveillance by helicopters and Cessna aircraft and tougher legal action, said Joe Walston, Senior VP of Global Conservation Programs at WCS.

"Any one of those things alone isn't going to be successful, which is why it has taken so long to be able to get us to a point where we've been able to get poaching under control," Walston told CNN.

The Niassa Reserve is in a remote region of northern Mozambique, where thousands of animals have been killed in recent years.

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