In the Upper Cook Inlet, Chinook salmon runs have decreased in size for the past five years. The science isn’t in stone, but a leading theory of why this is occurring has been associated with Pacific Decadal Oscillation, or PDO. PDO is the recurring pattern of warmer and cooler surface waters in the Pacific ocean and is thought by scientists to play a key role in the survival of Alaska salmon by impacting the prey that Alaska salmon feed on. Depending on where the PDO cycle is occurring, it can determine the abundance of prey populations, which, in turn, determines the abundance of the salmon population.
“While the PDO is a naturally occurring event, some folks think that climate change may be exacerbating the strength of the PDO. So, to the extent that Chinook salmon runs are impacted by the PDO or other oceanographic temperature anomalies, it is possible that climate change might affect our salmon runs in 2016. But, it is a very difficult thing to quantify,” Patrick Shields, Upper Cook Inlet area salmon and herring management biologist for the Alaska Department of Fish and Game said.
Bill Holt, a boat captain of a salmon gill net boat in Cook Inlet, has been fishing for over 40 years. Over the last few years Holt has noticed changes in the patterns of his usually fishing routine.
“It seems to me that the climate is changing. The last three winters have been very mild here. We’ve been having these issues the last couple years with real warm water temperatures. So, it’s gotta be affecting the fish somewhat,” Holt said. “It may not be affecting them so much if they grow in the rivers, but the returning fish seem to be returning in different patterns than what they usually do. Strange entry patterns for fish make it it hard to catch fish. I’ve only been fishing for forty years, so maybe the fish patterns were different before that too. It sounds like a long time, but it’s really not a lot, biologically.”
Other concerns for future salmon, with regards to climate change include, ocean acidification. Salmon rely on organisms like pelagic sea snails, or pteropods, for food. Pteropods could be affected greatly by ocean acidification which would affect the population of Alaska’s salmon, especially in the Cook Inlet area.
” Pteropods are highly sensitive to changes in the pH of the marine environment in which they live. Pteropods are such an important food source to many salmon that if their abundance is impacted due to our oceans becoming more acidic, then our salmon runs in the future could be negatively impacted,” Shields said.
Freshwater temperature change could also carry a negative impact for Alaska’s salmon. Salmon are intolerant to warm water, and if rivers where salmon spawn warm, the salmon won’t be able to handle the temperature change and spawn. Water temperatures beyond 20 degrees celsius can become lethal for salmon.
“Last year in the Columbia River, thousands and thousands of salmon perished due to lethal water temperatures. We have noted this in some of our local watersheds. If climate change is to result in a period of years or decades with increased air temperatures, it is possible that some of our streams that salmon now spawn and rear in will become environments that salmon will not be able to tolerate,” Shields said. “Thus, climate change, as it relates to water temperature, can definitely play a role in future salmon runs.”
The changes may seem slow, but in geologic time, the changes are happening rapidly, leaving little time for adaptation. Salmon, an important resource for all of us in Alaska, are slowly, but surely facing the impacts of climate change through water temperatures.