Japanese Zoo Kills 57 Monkeys by Lethal Injection After Discovery of Invasive Alien Genes

The Takagoyama Nature Zoo in Chiba prefecture, Japan, has culled 57 snow monkeys under their care after discovering that these animals are carrying genes of "invasive alien species."

A city official said Tuesday that the animals were killed via lethal injection. The execution lasted over a month and ended in early February, Phys Org reports.

Previous DNA testing revealed that the 57 monkeys were a crossbreed between two primates: the rhesus macaque (Macaca mulatta) and the Japanese macaque (Macaca fuscata). The former is widely distributed in Asia and is currently banned in Japan while the latter is an endemic species that lives in Japan's northern, snowy mountains -- thus, its local name "snow monkey."

Crossbreed species, such as the snow-rhesus macaque crossbreed, is illegal in Japan after a revision of the country's environmental law in 2013. Execution of the said animal is permitted by law.

An official from the Chiba Prefectural Government told Japan Times that killing of invasive species is done to "protect the indigenous environment." The revised environmental law aims to protect endemic animals from crossbreeding to keep the balance between native and foreign species.

Even though killing monkeys may seem cruel, Junkichi Mima, spokesman for WWF Japan, said it's vital as these animals "get mixed in with indigenous animals and threaten the natural environment and ecosystem.”

Zoos can apply for an exemption to keep crossbreeds, given that they are not classified as invasive species. In the case of Chiba prefecture, however, local government has started to prevent the growing number of rhesus macaque monkeys since 2005.

To appease the souls of the 57 killed monkeys, the Takagoyama Nature Zoo officials held a memorial service at a local Buddhist temple.