With the number of salmon in the North Pacific having doubled in the past 50 years, scientists are increasingly concerned there may not be enough food to support them, and changing ocean conditions could make it even worse.
On the surface, the mounting scientific evidence would seem to contradict conventional wisdom that salmon are a disappearing species. But as with everything salmon, it's more complicated.
While more than $13 billion has been spent since 1978 to try to restore endangered wild salmon populations in the Pacific Northwest, salmon hatcheries in the U.S., Russia, Japan and Canada have expanded rapidly.
In 1970, 500 million hatchery-raised salmon were released. In 2008, more than 5 billion hatchery fish headed out to sea. As with wild salmon, only a small percentage of the hatchery fish actually survive to spawn.
Once in the ocean, the hatchery fish are competing for the same food as the wild salmon. While the North Pacific and the Bering Sea may be vast, salmon often congregate in the same feeding grounds.
"Many hatcheries were built on the premise that the ocean had an unlimited capacity to support all salmon," said Gregory Ruggerone, a fisheries scientist who works for Natural Resources Consultants in Seattle.