Zimbabwean authorities say at least 81 elephants have been killed for their ivory tusks by poachers using cyanide poison in water holes in a vast western national park.

Wildlife department officials said industrial cyanide, used in gold mining, was put in the park’s remote water holes, killing smaller animals drinking there and vultures and other predators feeding on the dead animals.

Nine alleged poachers were arrested after rangers tracked them to a cache of ivory hidden in the park.

Zimbabwe’s state media reported Tuesday that newly-appointed environment minister Saviour Kasukuwere has vowed harsher jail penalties for poachers.