Several recent studies using computer models indicate that climate change will affect salmon in several ways:
* Rising seas could reduce habitat size for young salmon, which may spend several weeks in the estuary preparing for the change from fresh water to saltwater.
* Lower summer stream flows could mean that juvenile salmon, especially coho, will have less habitat and food during the one to two years they spend in the river.
* Increased incidents of flooding will wash away more salmon eggs from streambeds.
* Warmer stream temperatures can cause the fish what amounts to heat exhaustion.
* Higher stream temperatures reduce the amount of dissolved oxygen, making it difficult for salmon to breathe.
* Warmer oceans, such as in an El Niño year, bring other species, such as squid, north where they compete with adult salmon for food.
* Warmer seas prevent the upwelling of the nutrient-rich cold water, reducing the amount of plankton and bait fish, which are an important part of the food web that salmon need.
Scientists studying both salmon and climate change qualify their research by saying the environment is a complex system, which has led them to make a number of assumptions in their computer models.
Although those models can help predict possible impacts of climate change, researchers caution that they cannot account for all variables. For instance, a model looking at sea level rise can indicate where dry farmland might become salt marsh. But it cannot predict the impact of decades of fertilizer and pesticide on the animals and plants that might live in the newly created marsh.
“There’s a lot of uncertainty,” said Greg Hood, a senior restoration ecologist at the Skagit River System Cooperative.
In 2005, Hood published a study using a computer model to look at the possible impacts of sea level rise on salmon habitat on Fir Island in the Skagit River delta. His model predicted that an 18-inch rise in sea level — slightly above the middle of the range of the scenarios predicted by a team of Nobel-prize-winning scientists for 2090 — would lead to a 12 percent loss of salmon habitat. A 32-inch rise would result in a 22 percent loss of habitat, he said.
Hood said he assumed that the remaining marsh habitat would allow salmon to thrive and assumed a 12 percent and 22 percent decline of juvenile chinook — 211,000 and 530,000 fish respectively.
He and two other researchers are working on a more complicated model of the effects that sea levels will have on fish habitat in the delta. That model, which will take another 21⁄2 years to complete, may help make choices about where habitat should be restored.