Maximizing Benefits of Shoreline Armor Removal

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Cramer Fish Sciences is working to develop a study to evaluate the success of shoreline armor removal projects in Puget Sound at increasing juvenile salmon and forage fish abundance and improving habitat conditions. This project will be executed in two phases, Phase I will include dthe study design, site selection, and pilot execution and will be completed in spring 2024. Phase II, if funded, will include the execution of the armor removal study designed in Phase I. The study will provide timely information to guide the design of future shoreline restoration projects and inform future evaluation efforts.

Background

The Puget Sound shoreline has been subject to extensive modification by construction of armor, fill, and other structures to support waterfront infrastructure and prevent flooding and erosion (Johannessen and MacLennan 2007; Simenstad et al. 2011). Given the significant impact of armoring on shoreline processes and both fish and wildlife, widespread efforts are underway to remove and restore previously armored shorelines (Johannessen et al. 2014; PSEMP 2021). Extensive monitoring using traditional field methods (Washington Sea Grant Shoreline Monitoring Toolbox) has shown that these projects have been effective at improving local physical habitat and biotic conditions (Lee et al. 2018; Des Roches et al. 2022). Studies evaluating juvenile salmon and forage fish response have been more limited and are often performed as part of site-specific monitoring , or as part of control or reference-impact or reference-impact studies with a limited number of sites (Toft et al. 2007, 2013; Heerhartz & Toft 2015). While these studies are useful in understanding site-specific processes and overall responses, less is known about how project factors (such as size, age, treatments, and location) drive fish and habitat response for armor removal projects across Puget Sound. Therefore, understanding the impact of armor removal on intertidal fish at restoration sites across the Puget Sound represents a data gap.

To address that data gap, we aimed to develop a study to address if shoreline armor removal projects in Puget Sound improved intertidal habitat for juvenile salmonids and forage fish and the potential explanatory variables, considering project location, implementation, and age. Phase I of this project included three components 1) developing a site selection framework, 2) executing a pilot study, and 3) developing a study plan to be implemented in Phase II.

Goals, and Objectives

• Evaluate the effectiveness of shoreline armor removal at improving local fish use and habitat
• Determine which projects and/or project types have greater direct benefits for fish and fish habitat
• Produce concise and practical guidelines for the prioritization, design, and monitoring of future shoreline armor removal projects to maximize fish benefits
• Generate a quality peer-reviewed manuscript to provide evidence of the potential for beach restoration to provide direct benefits to fish

Key Questions

• Have shoreline armor removal projects in Puget Sound improved habitat for juvenile salmonids?
• Are densities of juvenile salmon higher in treatment (shoreline armoring removal) vs. control areas (armored shoreline)?
• What are the attributes of projects with the largest benefits to fish?
• What is the influence of project size, age, treatments, location, and other factors on project benefits?

Methods

We determined the extensive post-treatment experimental design (EPT) design, comparing paired treatment and control reaches, would be best suited to evaluate the armor removal response at a regional scale and to identify implementation, geographic, and habitat factors correlated with success. By using a paired treatment and control reach, the EPT design corrects for differences among restored (armor removal) sites due to beach type, drift cell, and other factors that can add additional noise or variability, and thus allow those factors to be considered as explanatory variables. Therefore, we can survey of a number of sites across a range of geographic, habitat conditions, and restoration approaches considering each as a potential explanatory variable (Hicks et al. 1991; Simenstad et al. 1991; Roni et al. 2005, 2013). Moreover, given the design is post-treatment, it allows for the inclusion of restoration projects that have already been implemented without pre-project monitoring data and thus allows us to test novel remote sensing approaches at a single site visit. We performed a power analysis to inform sample size, and estimated that between 22 and 32 paired sites would be needed to detect a significant difference in fish densities between reaches. Based on feedback from the TAG we also considered inclusion of reference reaches, which could also be evaluated relative to the treatment reaches using the EPT approach.

Working within this framework, we aimed to identify armor removal sites and paired control reaches to include in the study and methods that would best capture the key fish and habitat metrics that would characterize the impact of shoreline armor removal on intertidal juvenile salmonid and forage fish presence and use relative to control reaches and could potentially be driving or correlated to differences observed in fish use, abundance, and habitat.

Site Selection
We worked to identify and characterize existing restoration sites implemented in Puget Sound by evaluating restoration databases, regional mapping data, and other regional monitoring studies and identified over 100 armor removal sites in Puget Sound. We used restoration planning, monitoring, and supporting spatial data and reports to describe the geographic setting (e.g., LE area, shoretype, position within the drift cell), the pre-project conditions (armor type, elevation of armor on beach), and restoration actions (year of restoration, length of armor removed, additional restoration actions) for each armor removal site, which informed our site criteria and site selection framework. We used aerial imagery, regional data, and previous study extents to identify potential control and reference reaches.

Pilot Study
The Pilot Study focused on testing and refining physical (mapping) and biological monitoring methods to ensure that they can be applied to the entire population of sites. With assistance from our NOAA project partners, we tested fish, traditional field, and remote sensing (LiDAR and SfM) data collection methods at three pilot sites, Boulevard Park, Cornet Bay, and Seahurst Park, in Spring and Summer 2023. We tested both snorkel and beach seining approaches and determined that seining was more effective at capturing fish presence, since visibility limited our ability to detect fish at all three pilot sites. We collected wrack, wood, substrate, and riparian data using traditional field methods (Washington Sea Grant Shoreline Monitoring Toolbox) and by analyzing aerial imagery, and found that both were effective at assessing intertidal habitat. Lastly, we compared drone-collected SfM and LiDAR methods for mapping beach topography and found that SfM would be suitable for the needs of the study.

Study Plan
Utilizing the information gathered in the literature review, inputs from the TAG, and the results of the pilot study, we developed a study plan that utilized a hybrid field-remote sensing approach, that recommends collection of SfM and orthoimagery using a UAV and using traditional field methods for collecting fish, fine-scale habitat composition (e.g., wrack, subsurface substrate), and validation data. We selected key fish, wrack, vegetation, aquatic vegetation, sediment, and beach morphology metrics that will help us holistically assess habitat and fish response to armor removal relative to armored control reaches.

Notes

• This project was funded as part of an ESRP/Learning Program and executed by Cramer Fish Sciences alongside partners from NOAA NWFSC and Seattle Public Utilities.
• The project was contracted in 2022 and a final report will be completed in the spring of 2024.
• Progress reports and associated PRISM contract and documents are available online PRISM Project #20-1940
  

Please contact Jason Hall (jason.hall@fishsciences.net) with any questions regarding this project.

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