This story was originally published by Reveal and is reproduced here as part of the Climate Desk collaboration.

Day after day, Keith Davis stood at the rail of the cargo ship, watching a fleet of rusty long-liners off-load tuna, marlin, and other fish.

His work as an observer for the Inter-American Tropical Tuna Commission was critical. On that ship off the west coast of South America, he was a vital watchman in the struggle to protect the world’s oceans from overfishing.