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Climate change and salmon in the Oregon Coast Range

Fractal dimension (sinuosity) measures available salmonid habitat in estuaries.

Sea level rise will inundate estuaries changing the
amount and location of critical estuarine habitats for
salmon. Changes in stream flow and water temperature
will impact stream habitat.

Research Description:

The effect of global climate change may be experienced differently by salmon in different habitats throughout the stream network. Based on projected changes in estuarine habitat types and locations that may occur due to sea level rise, as predicted by the IPCC (International Panel on Climate Change), we hypothesize that sea-level rise will submerge existing complex habitats, which may or may not be able to rebuild themselves upstream due to topography and human development. Higher in the stream system, fish populations may be affected by changes in precipitation timing that alter flow regimes and make existing spawning and rearing habitats inhospitable.

Key Findings:

Diagram of a watershed from estuary to headwaters, showing the habitat areas used by four species of salmonids.

Figure 1. Estuary habitat use.

Species Matters

Some salmonid species may be more heavily affected by climate change due to their distribution. Chinook and coho salmon will be heavily affected throughout their distribution while steelhead and cutthroat may experience changes that more directly affect the freshwater portion of a river system.

Figure 1. Anadromous salmonids have diverse life histories that include emergence and rearing in freshwater before migration to the ocean with adults returning to natal streams to spawn. There is great variety within populations of salmon in the amount of time juveniles spend rearing in freshwater or the estuary. Such diversity breeds resilience in the population as a whole. Potential effects of climate change on estuarine and freshwater habitats may affect salmonid species differently depending on how individual species use the stream network.

Cartoon of a river-dominated estuary.

Figure 2. A. River-Dominated Estuary.

Topography Matters: River-dominated Estuaries

We hypothesize that steep river-dominated estuarine systems will have a less pronounced change in habitats due to sea level rise than low gradient ocean-dominated estuary systems. We further hypothesize that in steep, river-dominated estuarine systems the head of tide (upstream extent of tidal influence) will move upstream, but little estuarine habitat will move or be created.

Figure 2. We predict that in river-dominated estuaries, changes in mean sea level may have minimal effects on salmonid habitats.

Cartoon of an ocean-dominated estuary.

Figure 3. An Ocean-Dominated Estuary.

Topography Matters: Ocean-dominated Estuaries

In flat, ocean-influenced systems, we hypothesize that sea-level rise will submerge existing complex habitats in low salt marsh and brackish marsh areas. Head of tide likely will move upstream, and we predict estuarine habitats will be flooded near the river mouth, moving upstream if there is space available for them to do so.

Figure 3. We predict that ocean-dominated estuaries may experience significant changes in the diversity and availability of nursery habitats for juvenile salmonids

Salmon Life History and Hydrology

We are exploring linkages between adult coho salmon run timing and freshwater stream hydrology. In this process, we seek to understand the connection and potential predictability of changes in the timing and intensity of stream hydrology on available spawning habitat.

Fractal dimension (sinuosity) measures available salmonid habitat in estuaries.

Figure 4. Fractal Dimension.

First Results: Estuarine Margin Sinuosity Changes

A change in the fractal dimension (sinuosity) of estuarine margins occurs with increasing mean sea level. Depending on the estuary, sinuosity increases or decreases. Increases in sinuosity imply increased complexity at the edges of estuaries and potentially greater habitat complexity. A decrease in complexity of estuarine margin implies a reduction in the quality and quantity of available nursery habitat for juvenile salmonids.

Figure 4. The sinuosity of the estuarine margin may give insights into the amount of available edge habitat for juvenile rearing. The fractal dimension of the margin summarizes the sinuosity with smaller numbers corresponding to low sinuosity and larger numbers corresponding to higher sinuosity.