Fish: Habitat Opportunity


To determine the impacts of restoration on fish populations–particularly on Chinook salmon–scientists measured the opportunities salmon have to access and use habitat types. Opportunity was measured through the density and timing of salmon usage of the restored and reference habitats, determined through fyke trapping. Research began in 2004 and continued through 2014.

 

Measuring the opportunity for fish to access suitable habitat meant that scientists examined physical attributes of the river delta. These attributes were channel area, channel depth, water temperature, temporal variation in channel availability and landscape connectivity. Fyke trapping also allowed researchers to catch Chinook and chum salmon in each habitat location, which provides information on the number of fish present at different times of the year.

To monitor the physical characteristics, researchers from the Nisqually Indian Tribe and USGS used aerial imagery, physical measurements and inundation modeling. Coupled with the fyke trapping results, scientists were able to track increased opportunities due to broad-scale changes in available habitat on the Nisqually River Delta.

The studies primarily took place at two reference locations (Red Salmon Reference and Animal Slough) as well as at two restoration sites (Phase II, which was restored in 2006, and Madrone Slough, which was a part of the historic 2009 restoration).

Note: in the map below, Animal Slough is referred to as “Nisqually Reference”, Madrone Slough is referred to as “2009 Restored” and Phase II is referred to as “2006 Restored.”

This map shows all sampling locations, including study units, data loggers, channel cross sections, and fyke netting sites across the Nisqually River Delta. Logger locations are marked with a star, and channel cross section locations are color coded by distance from open water. Fyke net locations are marked with a green star.

 

Estuaries are an important habitat type for a variety of plant and animal species: tidal influences spread sediment, nutrients, detritus and aquatic organisms, improving habitat for birds and fish. Estuaries that have been altered by humans often starve the ecosystem of the tidal influence, leading to a loss in tidal channels, sediment starvation, marsh erosion and loss of critical habitat. The Nisqually River supports several salmon populations, including a threatened Chinook stock. Chinook salmon are thought to be the most estuary dependent salmon species, and stand to benefit greatly from the Nisqually Delta Restoration Project.

By examining the increased habitat opportunities for use by Chinook and other salmon, researchers are better able to understand the complex processes that occur after a large-scale restoration project. Indeed, the data shows an enormous increase in major and minor tidal channels across the delta along with increased accessibility. Water quality is also changing as a result of deepening channels, proving more favorable for fish. In fact, salmon catch data shows smolts used the restored channels as soon as one year post-restoration.

Overall, this monitoring effort has shown that estuaries can quickly regain useable salmon habitat, despite long-term alterations to the landscape. The increased opportunities for salmon displayed by the Nisqually Delta Restoration Project demonstrate that large-scale restoration projects can improve Puget Sound estuary habitat, and may play a positive role in salmon recovery.

To learn more about the capacity of the delta to support foraging, click here. To learn more about the realized function–or the response of fish to the area–click here.

Return to Fish

Read more:

  • Ellings, C.S., E. Grossman, M. Davis, S. Hodgson, K. Turner, I. Woo, J. Takekawa, G. Nakai. 2015. Post-Restoration Changes in Salmonid Opportunity [In Revision]. Olympia, Washington.