A Pacific Northwest icon, Puget Sound is the second-largest estuary in the United States. Its unique geology, climate, and nutrient-rich waters produce and sustain biologically productive coastal habitats. USGS is conducting research in the region as part of the Coastal Habitats in Puget Sound program, an interdisciplinary collaboration to coordinate, integrate, and link USGS studies with the Puget Sound Nearshore Ecosystem Restoration Project goals and objectives. Natural resource managers look to the USGS as a critical science resource needed to solve problems in this important ecosystem.
The degree to which eelgrass on river deltas provides critical habitat for estuarine fishes, especially out‐migrating juvenile salmon, is an important scientific and management issue that bears on efforts to conserve and restore both eelgrass and fish. In a journal article published in Marine and Coastal Fisheries, we report on spatiotemporal variation in abundance and body size of juvenile Chinook Salmon and three forage fish species in relation to eelgrass on a large river delta in Puget Sound and consider how diking and river channelization potentially influenced eelgrass use by these fish. Fish–eelgrass associations were unique for each species. Puget Sound Chinook Salmon are currently listed as threatened under the U.S. Endangered Species Act. The river delta selected has abundant populations of all forage fish species.
In the Puget Sound region, seagrasses, such as Eelgrass, form complex habitats that support other aquatic organisms by providing attachment substrate, food, refuge from predation, and nursery areas. Eelgrass can form extensive meadows on Puget Sound river deltas. The extent to which these meadows provide critical rearing habitat for local estuarine fishes, especially out‐migrating juvenile salmon, is not well understood. Delta eelgrass also has been impacted by diking and river channelization with unknown consequences for fish. Current issues facing eelgrass include:
Coastal Habitats in Puget Sound (CHIPS)
CHIPS current studies have three themes:
The primary focus within these themes is on developing information on the physical, chemical, and biological processes—as well as human dimensions—associated with the restoration or rehabilitation of the nearshore environment. Puget Sound partners and citizens will receive USGS results through databases, geospatial models and analyses, technical reports, and formal publications.
The study was conducted in the Skagit River delta in Puget Sound during April–September, when juvenile salmon were out‐migrating, juvenile forage fish were resident in the area and growing and eelgrass standing crop was at its seasonal maximum. Eelgrass growing on the outer margins of large river deltas may be particularly important to salmon because it forms extensive meadows in this setting and is the first eelgrass encountered by out‐migrating juveniles. Eelgrass also has been found to continue to support high abundances of juvenile Chinook Salmon in July and August, after they had mostly vacated other nearshore habitats.
Analyses were focused on four fish species occurring most frequently in the catch:
Map showing Skagit Bay study area.
The Skagit River is the largest river entering Puget Sound, accounting for 35% of the freshwater and 40% of the sediment entering the sound. This river retains important salmon populations including Chinook Salmon runs that are relatively healthy compared with other Puget Sound populations. The Skagit River delta has been extensively diked and the river channelized to develop farmland and protect it from flooding and saltwater intrusion, and a jetty was constructed to maintain a navigation channel.
Five null hypotheses were developed concerning abundance and body size of Chinook Salmon, Pacific Herring, Surf Smelt, and Shiner Perch in relation to eelgrass and water column properties. Specific information about each hypothesis is available in the journal of Marine and Coastal Fisheries.
Hypothesis 1: Abundance of each species does not differ between eelgrass and unvegetated habitat. This test used data from paired eelgrass and unvegetated habitat from 2009–2010 and zones 2–4.
Hypothesis 2: Abundance of each species in eelgrass does not differ among zones 1–4. This test used data from all sampling years (2008–2010).
This visualization functions as a representation for both scenarios proposed by hypotheses 1 and 2. The interactive capabilities of the visualization allow for specific selections to be made to represent each hypothesis.
Abundance of each species is not related to water column depth, water temperature, or salinity.
Body size (length) of each species does not differ between eelgrass and unvegetated habitat.
Body size (length) of each species in eelgrass does not differ among the four zones.
Results suggest that conservation and restoration of delta eelgrass would benefit all four species and help to identify the settings in which these actions would be most beneficial.
Chinook Salmon were more abundant in eelgrass than in unvegetated habitat in June–July and were relatively more abundant in eelgrass compared with unvegetated habitat in regions with intact eelgrass than offshore from a channelized distributary outlet.
Abundances of Pacific Herring and Shiner Perch were consistently severalfold higher in eelgrass than in unvegetated habitat. Surf Smelt were more abundant in eelgrass than in unvegetated habitat at some locations, but never less abundant in eelgrass.
Juvenile Chinook Salmon and Forage Fish Use of Eelgrass Habitats in a Diked and Channelized Puget Sound River Delta
Read the Journal ArticleData collected in 2008-2010 to evaluate juvenile salmon and forage fish use of eelgrass on the Skagit River Delta, Washington State, USA
Download the Data