The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)

Well before Corey Arnold ever thought about photography, he fished. As a child, he dressed as a fisherman for four consecutive Halloweens, and once brought a dead 3-foot Mako shark to school for show-and-tell. He knew he wanted to be a professional fisherman, even if he didn’t understand what that actually meant.

Global wildlife populations will decline by 67% by 2020 unless urgent action is taken to reduce human impact on species and ecosystems, warns the biennial Living Planet Index report from WWF (World Wide Fund for Nature) and ZSL (Zoological Society of London). From elephants to eels, here are some of the wildlife populations most affected by human activity. Here: The maned wolf is among the large mammals in the Brazilian Cerrado that are threatened by the increasing conversion of grasslands into farmland for grazing and growing crops. (Photo by Ben Cranke/Nature Picture Library/Alamy Stock Photo)

A woman reacts as anti-government protesters place a dead body on a stretcher after violence erupted in the Independence Square in Kiev, in this February 20, 2014 file photo. (Photo by Vasily Fedosenko/Reuters)

A participant rests while people take part in the Mermaid Parade at Coney Island, in Brooklyn, New York, June 20, 2015. The annual parade, founded in 1983, seeks to bring mythology to life for residents, create confidence in the district and to allow artistic self-expression in public, according to the parade's website. (Photo by Eduardo Munoz/Reuters)

Children play football in front of an abandoned train compartment next to a railway track in Dhaka, in this May 29, 2014 file photo. (Photo by Andrew Biraj/Reuters)

China's Shang Chunsong prepares to compete in the uneven bars event of the women's individual all-around final artistic gymnastics competition at the Namdong Gymnasium Club during the 17th Asian Games in Incheon, in this September 23, 2014 file photo. (Photo by Kim Hong-Ji/Reuters)

Jiejin Qiu, who is six months pregnant with her first baby, poses underwater during a photo shoot at a local wedding photo studio in Shanghai, in this September 5, 2014 file photo. (Photo by Carlos Barria/Reuters)