Coastal Restoration to Benefit Salmon and Other Fishes in Puget Sound
Research to link shoreline type (armored, restored, natural) with the abundance of salmon and other fishes across multiple spatial scales.
Development has fundamentally changed coastal and estuarine habitats around the world. Major efforts are underway to restore shoreline processes, structures, and functions. In Washington’s Puget Sound, state and local agencies have prioritized removing hard armor-like seawalls. However, we do not know the effectiveness of these restoration programs for subtidal habitats and the fishes that use them.
Study of local restoration impacts
In 2018-2019, we surveyed six restoration sites in Puget Sound monthly from April through September. We compared the abundance of four regionally- and ecologically-important fish species--Chinook salmon, chum salmon, Pacific herring, and surf smelt-- along restored shorelines and adjacent ‘natural’ still-armored shorelines. Surveys revealed a limited association of shoreline restoration with this group of nearshore fishes in the 2-6 years since armor removal.
Overall, we saw no evidence that small-scale shoreline restoration promotes fish use of subtidal habitats. We found that Chum salmon were more abundant at sites with eelgrass than those with no eelgrass. However, neither salmon species showed clear and consistent associations with armored, restored, or natural shoreline types.
Herring were more abundant overall at natural shorelines, whereas surf smelt showed differences in abundance between natural, restored, and armored shorelines that were inconsistent across sites.
Site-related variability significantly influenced abundance for all four species, revealing the influence of underlying regional fish distribution patterns. Our findings suggest that protecting intact shorelines and promoting eelgrass restoration are priorities for providing quality habitat for forage fish and chum salmon.
Understanding the landscape context
We did not detect a clear signal indicating benefits of shoreline restoration at local scales for forage fish, and salmon abundance was not related to shoreline condition at all. These results suggest that shoreline restoration impacts detected in beach and intertidal habitats in other studies (e.g., Dethier et al. 2016) may not propagate into adjacent deeper-water zones, or that subtidal fishes do not aggregate in response to shoreline conditions as we have classified them. One possible explanation is that shoreline armor or restoration impacts may be insignificant relevant to other dynamics in these habitats. The effects of local habitat structure may get lost in the noise of the surrounding landscape matrix. Another possibility is that the effects of shoreline structure may be cumulative over broader spatial scales not accounted for in this first analysis.
To further understand the relative influence of local-habitat versus landscape-scale factors on nearshore fishes, with UW collaborators funded by Washington Sea Grant, we will conduct surveys of restored, armored and natural shorelines again in 2021-2022 at 15-20 additional study sites. We will evaluate how associations between fish assemblages and nearshore habitat vary across spatial scales. We will synthesize our new survey data with existing information from the Puget Sound Beach Strategies database— a highly-resolved dataset on shoreline characteristics and a valuable tool for analyzing the potential effectiveness of shoreline restoration actions — and regional environmental data.
Tessa Francis, Puget Sound Institute, UW Tacoma
Francis et al., in prep.
Dethier et al 2020 Edgewater Beach Restoration Monitoring Report
Dethier et al. (2016) Multiscale impacts of armoring on Salish Sea shorelines: evidence for cumulative and threshold effects. Estuarine, Coastal, and Shelf Science 175: 106-117. https://doi.org/10.1016/j.ecss.2016.03.033