Juvenile salmon response to landscape connectivity change within two Puget Sound river estuaries
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The Skagit River System Cooperative and partners will monitor Salmon density in the Skagit Delta and Stillaguamish Delta to test how the configuration of distributary channels affects outmigration of juvenile salmonids. This effort observes change in response to restoration in the Stillaguamish and natural avulsion in the North Fork Skagit estuary. This supports River Delta Restoration planning by allowing prediction of relative value of restoration based on landscape position. It contributes to our understanding of River Delta Restoration and Salmon Populations. This effort is supported by the ESRP learning program.
Whole Project Scope[edit]
Landscape connectivity is commonly thought of as the extent to which a landscape facilitates the movements of organisms and/or geneflow (Rudnick et al 2012). The ability of landscapes to facilitate biotic movement is dependent on landscape structure and scale, natural processes occurring across the landscape, and the behavior of biota on the landscape. As such, landscape connectivity within natural ecosystems has declined due to ecosystem fragmentation and habitat loss, which has contributed to declines in species and their population status. This is especially true for large river estuaries within Puget Sound where much more estuary habitat has been lost than remains, and the losses have contributed to declines in natural origin Chinook salmon populations. Habitat loss within Puget Sound large river estuaries is typified by reductions in total tidal footprint (estuarine wetlands and channels), but also selective reduction of distributary channels within estuaries. Both types of habitat loss change landscape structure within an estuary, but the changes to the distributary channel network within an estuary can have a larger effect on landscape connectivity, because the distributary channel network is critical to the whole estuary’s movement pattern of water, sediment, fish, and other materials.
While biotic applications of landscape connectivity are well developed for fresh water, tropical coral and terrestrial systems, the discipline is not well developed in estuarine systems nor for application to salmon recovery (Flitcroft et al. 2019), although concepts underpinning the importance of landscape structure and scale within PNW estuaries were postulated by Simenstad et al. (2000). Principles of landscape connectivity were applied in some watershed chapters of the Puget Sound Chinook Recovery Plan and resulted in proposed projects aimed at recovery of ESA Listed Chinook salmon populations (see Table 1), which heightens the importance of fully including landscape connectivity into the evaluation of restoration benefits for Puget Sound salmon that ESRP supports. Specifically, this proposal will measure juvenile Chinook salmon response to landscape connectivity change in the Skagit and Stillaguamish estuaries. The Skagit Delta opportunity is a natural experiment where a newly formed avulsion channel provides a natural experiment that can be analyzed with existing long-term monitoring fish data across the entire north Skagit delta. The Stillaguamish delta provides an opportunity to evaluate the application of landscape connectivity concepts across local and regional scales. Two Stillaguamish delta projects intend to improve local connectivity, including North Leque Island that will establish a cross island connector channel and Port Susan Bay Phase 1 that will establish additional dike breaches in a 35-acre area. Port Susan Bay Phase 2 and the Thurmond Property restoration projects intend to build a number of delta distributaries that could convey freshwater and salmon to the northern portions of Port Susan Bay to alter regional connectivity.
The proposed work will improve our understanding of the importance of landscape connectivity to juvenile salmon habitat use in a general sense, and it will answer specific questions relevant to habitat restoration planning. In an already fish-accessible site, does increasing the number of dike breaches (e.g., from one to five for North Leque, or from two to five for Port Susan Bay Phase 1) increase fish use of the site, or does improving distributary network connectivity significantly increase the number of fish that might use available habitats across broader scales (e.g., North Fork Skagit River delta or Port Susan Bay)? Can we develop predictive landscape connectivity models that estimate increased fish usage, so that cost/benefit and restoration value can be determined?
Table 1. Restoration projects identified in Chinook recovery plans having linkages to landscape connectivity in the Skagit and Stillaguamish estuaries. TBD are projects with implementation dates to be determined.
|
Project Name |
Project Lead |
Chinook Populations |
Year of Implementation |
|
McGlinn Island Causeway |
SRSC |
Skagit |
TBD |
|
Fir Island Cross Connector |
SRSC/WDFW |
Skagit |
TBD |
|
N Leque Island breach |
WDFW |
Skagit and Stillaguamish |
2022* |
|
Port Susan Bay Phase 1 |
TNC |
Stillaguamish and Skagit |
2023* |
|
Port Susan Bay Phase 2 |
TNC |
Stillaguamish and Skagit |
2024 |
|
Thurmond Property |
Stillaguamish Tribe |
Stillaguamish and Skagit |
2024 or 2025 |
|
Zis a ba 2 |
Stillaguamish Tribe |
Stillaguamish and Skagit |
TBD |
- Project is fully funded
Agreement Scope[edit]
The overarching hypothesis motivating this study is that landscape connectivity, i.e., distributary network geometry, affects juvenile salmon distributions in estuarine landscapes. However, there are several corollaries that will more specifically be investigated for their application to tidal marsh restoration design and planning. The first is that landscape connectivity can be quantitatively related to juvenile salmon distributions, so that a useful predictive model can be generated. Second, the predictive model can apply to any reasonable configuration of delta distributary channels, so that the model is general rather than specific to a particular distributary network. Finally, changes in landscape connectivity will change juvenile salmon distributions; intentional changes in landscape connectivity, i.e., those resulting from a restoration design, can have predictable benefits to juvenile salmon usage of estuarine habitat. Previous works (Beamer and Wolf 2016, Beamer et al. 2020) have found evidence for all but the last corollary. This proposal builds on the antecedent work with the aims of buttressing support for the hypothesis, specifically addressing the second and last corollaries, and extending their relevance to practical application to habitat restoration.
We propose testing these hypotheses in the North Fork Skagit River natural avulsion (Figure 2), North Leque Island cross island connection channel, and Port Susan Bay Phase 1 channel breaching; in addition, we will set up baseline data for evaluating the change in landscape connectivity and fish densities from the extensive distributary development of Port Susan Bay Phase 2 and the Thurmond Property projects expected to be build soon after this work. The North Fork Skagit Delta (NF) is the location of a new distributary avulsion, which provides a natural experiment where connectivity to a large part of the delta has been severely diminished over the past decade but increased in a smaller part of the delta. This site allows us to evaluate the effects of both increasing and decreasing landscape connectivity on fish densities in different parts of the delta. The North Leque Island site is more than a restoration project; it is a local-scale manipulation of landscape connectivity that tests the effect on fish density of increasing the number of dike breaches from one to five, where several of the new dike breaches will connect to a major distributary (West Pass) and significantly increase the site’s landscape connectivity. The site is already accessible to fish and can be made even more accessible, i.e., support a greater density of juvenile salmon, if additional dike breaches are created. This is a fundamental question with important implications for restoration design. The Port Susan Bay Phase 1 restoration of 35 acres is similar to the North Leque Island site in that dike breaches will increase from two to five. However, increased site connectivity will occur only in the northern half of the site, while connectivity will not change for the southern half of the site. Thus, the site provides a treatment area (the north half), a control area (the south half), and a reference condition (the adjacent natural marshes), making it an ideal experimental site.
Fish sampling[edit]
No new fish sampling will be required for the North Fork Skagit Delta site. That site will be analyzed using existing IMW data that has been collected over the past 25 years (Greene et al. 2016). The expectation is that juvenile salmon densities at sampling sites upstream of the North Fork avulsion will not have changed; however, sites downstream where landscape connectivity has declined will have experienced declining trends in juvenile salmon densities; and sites downstream where connectivity has increased will have experienced increasing density trends. Multiple years of IMW data will be needed to control for interannual variability in out-migration to measure the general effect of landscape connectivity on salmon density.
In N. Leque Island and Port Susan Bay Phase 1, we do not have the advantage of a long-term monitoring program as the Skagit IMW. We do have fish monitoring in adjacent areas of N. Leque Island since 2016 including zis a ba, Leque Island south of Hwy 532 and reference areas including Davis Slough, West Pass and South Pass (Beamer et al. 2019, Henrichs et al. 2020, LeMoine et al. 2022). The monitoring frame was then expanded in 2021 and 2022 (LeMoine et al. 2022) to include landscape connectivity considerations and again in 2022 to include sampling the N. Leque Island site directly before restoration. Monitoring in 2021 and 2022 is funded in a partnership with The Nature Conservancy and Washington State Department of Fish and Wildlife. Funding for fish monitoring will be extended to 2023 under the similar agreements with TNC and WDFW. ESRP funds will be applied to 2024 fish monitoring in order to determine fish response to restoration projects that target connectivity. Overall, we will have four years of fish sampling across Port Susan Bay with some more historical monitoring that will provide additional observations. Barring future funding to evaluate a true before and after comparison, we could follow the Skagit IMW design (Greene et al. 2015). The portions of Port Susan Bay north of the Stillaguamish River mouth are receiving all of the restoration treatment and change in landscape connectivity, conversely the portions of Port Susan Bay south of the Stillaguamish River mouth will have zero restoration treatment. Comparisons in juvenile Chinook densities over landscape connectivity measures could be made between these portions of Port Susan Bay. Hypotheses could be formed around understanding of dispersal across the landscape regarding the influence of landscape connectivity on site specific densities (see Baguette et al. 2013).
Table 2. Data that are available for each area under consideration for this scope of work.
|
Focal Area of Study |
Years of Data |
Funding |
|
NF Skagit Delta |
1995-Present |
IMW and BIA |
|
N Leque Island |
2016, 2018-2019, 2021-2022 |
WDFW |
|
Port Susan Bay Phase 1 |
2021-2022 |
TNC |
|
Port Susan Bay Phase 2* |
2021-2022 |
TNC |
|
Thurmond Property* |
2021-2022 |
TNC |
|
Thurmond Property* |
2021-2022 |
TNC |
- will not be evaluated as part of this project
Sampling methods will follow established procedures from long-standing IMW monitoring (Greene et al. 2015). Briefly, fish will be sampled twice per month from tidal channel outlets using fyke traps or by use of beach seines within the tidal channel networks. Juvenile Chinook salmon catch are adjusted by trap recovery efficiency (RE) estimates derived from multiple mark-recapture experiments using a known number of marked fish released upstream of the trap at high tide. Fin clips will be retained for a subset of Chinook salmon to determine natal origin as Leque Island and Port Susan Bay are known to be occupied by multiple Chinook stocks (Small et al. 2021). The adjusted Chinook catch is divided by the top width channel area of the blind channel network upstream of the trap to calculate a juvenile Chinook density for each fyke trap set. Top width channel area is surveyed in the field with RTK-GPS. Fish are sampled according to a BACI design (Underwood 1994) for the manipulative restoration experiments, where control and treatment sites are sampled for one or more years before and after restoration occurs.
For each sampled tidal channel in each study site, landscape connectivity indices will be calculated as in previous work (Beamer and Wolf 2011, Beamer et al. 2020). Briefly, planform distributary channel geometry will be measured from aerial photographs in a GIS, including migratory pathway lengths, and distributary bifurcation widths and order; this data will be used to create a landscape connectivity index reflecting length and complexity of juvenile salmon migratory pathways through the delta distributary networks. For N. Leque Island, given the scale of the project we will assess landscape connectivity starting from west pass. For Port Susan Bay, we will assess landscape connectivity from the Stillaguamish River and focus on Stillaguamish Chinook.
Data and analyses conducted as part of this ESRP learning project will be used to inform PSEMP project “Using bioenergetics and landscape connectivity to plan effective tidal delta restoration projects for Chinook salmon under a changing climate”. Knowledge of landscape connectivity influence on juvenile Chinook salmon densities will be applied to evaluate restoration design alternatives for Port Susan Bay Phase 2 and possibly the Thurmond property adjacent, however design considerations of this project may be finalized before results are produced.
Project Leads and Project Partners[edit]
- Greg Hood - Skagit River System Cooperative
- Michael LeMoine - Skagit River System Cooperative
Project Information[edit]
PRISM Snapshot: *[1]
Project Documents[edit]
- Reports - Landscape Connectivity Project Documents
