A new out of Simon Fraser University is casting light on juvenile salmon populations.
The study found that some species of salmon are migrating from streams and rivers earlier than ever, desynchronizing from their only food source.
It is the largest-ever study of out-migrating wild juvenile salmon, from Oregon to Alaska, with data spanning back to 1951.
Scientists expected to find signs of earlier migration due to climate change, and they did.
“On average, we did see that climate signal we were expecting to see but what was really surprising was the amount of variability that we saw,” said Sam Wilson, a postdoctoral researcher in the Salmon Watersheds Lab at SFU and lead author on the review. “So within a species some populations were getting earlier as we expected but some were actually getting later.”
The scientists may have been hoping for a clear sign from the salmon on what the future is bringing, but they didn’t get it.
“We saw a remarkable variation across the range and no matter what variable we threw at it we just couldn’t predict it so that’s really important because climate change is happening but we can’t predict it very well,” said Jonathan Moore, Professor, Biological Science and Resource and Environmental Management.
The reason this all matters is because the food they eat, like plankton for smaller juvenile salmon is also growing at a different time.
“The food is shifting and the salmon aren’t tracking that food source and that could lead to problems in the future and like I said we do know from other studies that juvenile salmon when they miss that window of opportunity fewer adults come back,” added Wilson.
The SFU study published in the Journal Nature, Ecology and Evolution doesn’t point to this as a single factor hurting wild salmon, just one of many.
“I think it’s not a single smoking gun,” added Moore. “I think it’s a death by a thousand cuts and climate change is hurting salmon in many places.”
An ongoing study of returning wild salmon will give scientists a better idea of how climate change is affecting overall numbers.