River Delta Use By Salmon

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• Watershed Characterization Mapper
• The Encyclopedia of Puget Sound
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See also River Delta Restoration Effects On Salmon

Salmon pass through River Deltas twice. Once as adults on thier way to freshwater spawning grounds, and again as juveniles leaving natal rivers to complete their saltwater life history. Juvenile rearing is considered very important for populations. River Delta Restoration has become a critical target for Salmon Recovery. Observation of salmon use before, during and after river delta restoration has resulted in a large body of knowledge. Work in the Skagit Delta by NOAA and SRSC has produced the longest and most detailed data sets. Significant effort in the Snohomish Delta is complementary. Additional intensive data sets are available in the Nooksack Delta, Stillaguamish Delta and Nisqually Delta. Intensive work in the Duwamish Delta provides a contrasting analysis of a severely degraded system. Work has focused on Chinook Salmon due to their listing under the Endangered Species Act and dependence of River Deltas for rearing. A chain of inference suggests that sufficient delta rearing habitat quantity and quality affects populations productivity, and thus abundance.

Juvenile Outmigration Timing and Duration

• All pacific salmon use river deltas during transition from freshwater fry to saltwater smolts.
• Each species uses nearshore habitat differently, with Chinook and chum having the most extensive use (Fresh 2006; Simenstad et al 1982).
• Within Chinook, there is substantial variation in fish arrive in the delta, and how long they stay (Beamer et al 2005). Although these differences likely exist within chum populations, they have not been well described.
• Fish reared in hatcheries likely differ in how they use the delta and nearshore (Fresh 1997), and since we have only recently been able to discriminate between hatchery and wild fish in our studies, it is unclear how our current understanding may be biased by the prevalence of hatchery fish in many systems.
• Chinook fry and parr enter deltas from December through September, with the largest migrations typically from May to July, as parr, although this varies by population. Some of the small fry leave the delta very quickly and appear to preferentially use barrier lagoons and barrier estuaries in the nearshore (Beamer et al 2005). Some early arrivals may stay as long as 120 days in the delta (Simenstad et al 1982; Beamer et al 2005).
• Larger fish that arrive later (Healy 1980; Healy 1982), don't stay as long as those that arrive early as fry. Juveniles may increasingly use larger channels orleave delta altogether as shallow water temperatures increase in summer.
• Chum fry enter the delta shortly after emergence from eggs beginning with Summer run fish emergence in December (Salo 1991), Chum migrants appear to distribute broadly both in natal estuaries, as well as in a range of estuarine habitats in the nearshore (see Fresh 2006).

River Delta Opportunity and Capacity

• Current research considers habitat patches in the context of their landscape, such that configuration and composition of habitats and their relationship to rivers and currents are likely to affect realized habitat services (Fresh 2006). Simenstad and Cordell 2000 describe two attributes:
  1. Opportunity - the the degree to which a given habitat can be accessed by juvenile fish, and
  2. Capacity - the ability of the habitat to provide services like forage and refuge, once accessed.
• Fresh 2006 provides a range of attributes anticipated to affect opportunity and capacity. Juvenile salmon feed throughout their migration on a wide range of prey based both on availability and preference. Juvenile salmon prey appear to be largely dependant on detrital food webs supported by delta vegetation.
• Our understanding of delta use by juvenile salmon is strongest for Chinook, and based on extensive sampling in the Skagit Delta. Beamer et al 2005 both identified the use of small dendritic channels accross the entire delta landscape, while also providing evidence that tidal channel networks closest to main migratory routes have a higher density of juvenile Chinook salmon. Since small tidal channels dewater between tides, low tide refuge may also be important to habitat utilization.
• Fresh 2006 provides a broad assessment of how different human actions which alter the landscape are likely to in turn affect the opportunity or capacity for salmon to find habitat services.

Distributaries and Connectivity

• How does the bifurcation of flow in distributary network affect the density of fish, and thus the use of habitat by outmigrating populations.

Tidal Channel Networks

• How do attributes of tidal channel networks affect fish opportunity and capacity

Fish Observation Methods

• There are four different methods in common use for estimating fish density:
  1. Beach Seine
  2. Fyke Net
  3. Screw Trap
  4. Minnow Traps
• There are a wide range of issues to consider in Fish Sampling Design both at the scale of the site and techniques used, as well as how sampling is used to describe variation of salmon use over the delta, over time, and between years.

• Common approaches for demonstrating restoration of opportunity within an action is to focus on one or more target salmon species at the juvenile life stage and determine if juvenile salmon use new channels and marsh habitat at densities similar to a reference site (adjusted for channel allometry differences) and as new tidal channel systems develop whether juvenile salmon use increases proportionally. This can be in combination with other measures of juvenile salmon habitat including their macroinvertebrate prey base. Juvenile salmon densities are often used as a good proxy for habitat use by salmon. These are usually compared to reference sites. Diagnostic monitoring by contrast attempts to explain the physical and biological factors that are controlling the change in juvenile salmon density (Rice et al 2001).
• Site conditions may constrain whether a fyke net, beach seine or both are used to sample juvenile salmon. Beyond site and system scale monitoring, there is a desire to link site and system scale changes in juvenile salmon densities with recovery targets for juvenile salmon at various scales. This requires an understanding of landscape variables that affect status and trends of juvenile salmon densities that can be independent of river delta restoration actions. These are numerous and can reduce the inference limits of site and system scale monitoring. Standardizing methods of experimental design and analysis can go a long way in supporting meta-analysis of juvenile salmon density trends and how juvenile density factors into regional population level recovery.

Salmon and River Delta Topics

The following Product pages are categorized with Salmon and River Delta.

Effects of River Delta Restoration on Salmon Populations  •  Fish Sampling Design in River Deltas  •  Tide Gate Effects on Salmonid Passage and Utilization

Efforts and Products in Salmon and River Delta

  Efforts

• Automating Landscape Connectivity for Puget Sound River Deltas and Pocket Estuaries
• Chinook Response to Estuary Restoration
• Effects of Exposed Tidal Flats on Water Temperature in the Snohomish Estuary
• Evaluating Salmon Rearing Limitations in River Deltas
• Juvenile salmon response to landscape connectivity change within two Puget Sound river estuaries
• Predicting Sea Level Rise Impacts on Ag Production
• Puget Sound Large River Delta Tidal Restriction and Wetland Mapping
• Puget Sound Marine Riparian Mapping
• Puget Sound Tidal Restriction and Wetland Mapping
• Skagit Farm, Fish and Flood Initiative
• Snohomish Delta Ecosystem Monitoring and Evaluation
• Snohomish Estuary Restoration Effects on Temperature, Salinity, and Tides
• Tide Gate Effects Analysis

  Products

26 documents in Salmon,River Delta and {{{3}}}

• Beamer 2014 nisqually connectivity effects on salmon density
• Beamer 2016 fisher slough restoration effectiveness
• Beamer et al 2006 deepwater slough effectiveness
• Beamer et al 2007 fish assemblage greater skagit delta
• Beamer et al 2013 fisher slough fish monitoring 2011
• Beamer et al 2013 fisher slough fish monitoring 2012
• Beechie et al 2017 salmon habitat status monitoring
• City of Everett 2001 snohomish estuary wetland salmon overlay
• Cornu et al 2008 large wood placement in tidal wetlands
• David et al 2014 chinook salmon foraging nisqually after restoration
• Fresh 2006 juvenile salmon in nearshore
• Greene & Beamer 2005 skagit delta recovery plan analysis
• Greene & Beamer 2011 skagit intensively monitored watershed report
• Greene et al 2012 effects of tidegates on fish
• Greene et al 2021 chinook salmon estuary density dependance
• Hall et al 2019 DRAFT snohomish monitoring plan
• Hayes et al. 2019 non-natal marine basin use
• Hood 2002 channel geometry effect on invertebrates
• Lyons & Ramsey 2013 tide gate synthesis
• Quinn et al 2013 coho salmon elwha delta pre restoration
• Rossenkotter et al 2007 nearshore salmon recovery gap analysis
• SDHP 2014 skagit hydrodynamic model report
• Simenstad et al 1982 role of estuaries in salmon life history
• Smith et al 2005 tide gate salmon recovery analysis skagit
• Snohomish County 2020 smith and mid-spencer monitoring year 0-1
• TNC 2011 fisher slough monitoring baseline report

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