“Killer whales are apex predators, the dominant animals in these waters," explains Christine West, a naturalist aboard the National Geographic Sea Lion. This means their health reflects that of the entire habitat, as pollutants at every trophic level will travel up the food web and into these organisms. By the time these impacts are visible, however, it may be too late for a simple, one-size-fits-all solution. (Mike Harris/Lindblad Expeditions)
Polar bears are one of the many wildlife residents of ANWR (Alan D. Wilson/Wikimedia Commons).