Presentation Abstract

Use of tidal marsh surfaces by juvenile salmon in Pacific Northwest estuaries has generally been ignored by ecologists, engineers and planners involved in salmon habitat restoration. In contrast, fish use of marsh plains has been documented in many other parts of the world. Are Pacific Northwest marshes an exception to the pattern of fish use that is so common elsewhere? For three consecutive years, fish were sampled bi-monthly in tidal channels and on tidal marsh plains of the Skagit Delta to answer this question. Juvenile Chinook and chum salmon, as well as sticklebacks were the most consistently caught and abundant fish in channels and on the marsh surface, but eight other fish species were also found on the marsh surface. While fish densities were much higher in tidal channels than on marsh surfaces, marsh surface area was much greater than channel area, so sticklebacks and juvenile chum were potentially 50% more numerous on the marsh surface than in channels. However, due to their high channel densities, juvenile Chinook were nevertheless more abundant in tidal channels than on the marsh surface; those on the marsh surface amounted to 40% of those in tidal channels. The ratio of marsh surface to channel fish density peaks late in the season for all three fish species, which may be a response to increased prey production over the marsh plain. The substantial use of the marsh surface by juvenile salmon that we observed suggests estuarine habitat restoration for salmon recovery should not neglect the direct value of vegetated marsh plains to juvenile salmon. Tidal marsh habitat for juvenile salmon is more than just tidal channels. Partial habitat restoration that only restores tidal flow to channels and not to adjacent marshes, e.g., using self-regulating tide gates (SRTs), has a direct impact on juvenile salmon habitat use.

Session Title

Salmon and their Habitats

Keywords

Salmon, Tidal marsh, Juvenile salmon

Conference Track

SSE11: Species and Food Webs

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE11-15

Start Date

6-4-2018 9:00 AM

End Date

6-4-2018 9:15 AM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 6th, 9:00 AM Apr 6th, 9:15 AM

Juvenile salmon density on marsh surfaces versus within tidal channels

Use of tidal marsh surfaces by juvenile salmon in Pacific Northwest estuaries has generally been ignored by ecologists, engineers and planners involved in salmon habitat restoration. In contrast, fish use of marsh plains has been documented in many other parts of the world. Are Pacific Northwest marshes an exception to the pattern of fish use that is so common elsewhere? For three consecutive years, fish were sampled bi-monthly in tidal channels and on tidal marsh plains of the Skagit Delta to answer this question. Juvenile Chinook and chum salmon, as well as sticklebacks were the most consistently caught and abundant fish in channels and on the marsh surface, but eight other fish species were also found on the marsh surface. While fish densities were much higher in tidal channels than on marsh surfaces, marsh surface area was much greater than channel area, so sticklebacks and juvenile chum were potentially 50% more numerous on the marsh surface than in channels. However, due to their high channel densities, juvenile Chinook were nevertheless more abundant in tidal channels than on the marsh surface; those on the marsh surface amounted to 40% of those in tidal channels. The ratio of marsh surface to channel fish density peaks late in the season for all three fish species, which may be a response to increased prey production over the marsh plain. The substantial use of the marsh surface by juvenile salmon that we observed suggests estuarine habitat restoration for salmon recovery should not neglect the direct value of vegetated marsh plains to juvenile salmon. Tidal marsh habitat for juvenile salmon is more than just tidal channels. Partial habitat restoration that only restores tidal flow to channels and not to adjacent marshes, e.g., using self-regulating tide gates (SRTs), has a direct impact on juvenile salmon habitat use.