Ongoing research into why so many Pacific salmon are returning in smaller size is focused on an assortment of variables brought on by climate change, with rising temperatures being a big concern.
“The problem appears to be that the hot years are becoming more common,” says Bill Templin, chief fisheries scientist for salmon with the Alaska Department of Fish and Game in Anchorage. “If temperatures rise, they need more food. Their metabolism goes up and down with the temperatures.”
“On average, all five species of Pacific salmon appear to be getting smaller,” he added. Whether they are returning younger or simply smaller for other reasons is still an unknown.
One concern is that as the salmon decrease in size, they become more vulnerable to predation.
There are many variables to consider. Sockeye, coho and Chinook salmon stay mostly in fresh water, even up to three years before going to the ocean. Changes in size by age might be related to what happens in the fresh water, as it impacts food availability, water temperatures and the duration of winter, he said.
While researchers are seeing salmon move north in the ocean, they still want to come home to their natal streams to spawn. When and if temperatures stop rising, Pacific salmon could return to their former size, depending in part on how long it took to stop those temperatures from rising.
“If things were to turn around right now, we could (maybe) go back to larger fish, but that would just be a guess,” Templin said.