Seven species of salmonids,
including the sockeye, Coho, and Chinook salmon species, swim U.S. Pacific coast waters. But these fish are no longer found in much of their historic habitat, and today's populations may be only 10 percent of peak numbers.
Young salmon hatch in inland fresh water, descend to the sea to feed for some two to five years, and then undertake an migration that, in the best cases, eventually returns them to their birth waters to spawn.
Many salmon runs, which can cover thousands of miles, have been disrupted by dams or other human developments, and a once thriving fishing industry has been decimated.
Now global warming is complicating the picture, according to the December 2009 Endangered Species coalition report.
Some western rivers have now passed the 72 degree Fahrenheit (22 Celsius) threshold beyond which salmon can't long survive. The ocean is changing too, and climate-induced shifts, like more acidic waters, may stress salmon during their saltwater years.
Photograph by David McLain, National Geographic Stock