Nearshore Built Structures - Impacts on Marine Life
UW Wetland Group
All of the following papers can be downloaded as .pdfs from here. Click on the publication number to go to the site where you can download it.
Publication 9903: Duwamish River Coastal America: Restoration and Reference Sites: Results from 1997 Monitoring Studies
JR CORDELL, LM TEAR, K JENSON, HA HIGGINS ( Univ. of Washington, Wetland Ecosystem Team)
Supported by City of Seattle, US Fish & Wildlife Service, and US Army Corps
May 1999
997 biological surveys at 3 tidal wetland sites in the Duwamish where restoration work had been conducted, in order to conduct systematic biological sampling of long-term reference and restored sites, Study and conclusions focused on:
- invertebrates diversity/density from trees and in mudflats
- juvenile salmon diets;
- bird population numbers, behavior; - vegetation transplantation success; - locations w.r.t. grain size, elevation, accretion rates, salinity gradients, natural successsional trajectories - overall understanding of restored wetland habitats. Restoration Interventions: - removal of rip rap, overwater structures to allow natural biotic colonization; - construction of 'sediment bench' at 0.0-meters elevation for juvenile salmon; - replacement of a drainage pipe with estuarine channel to restore flow; and - riparian buffer plantings w/ native vegetation. Baseline studies in 1993-94 of reference and restoration sites; post-restoration sampling in 1995-96 ConclusioCoastal America: Restoration and Reference Sites: Results from 1997 Monitoring Studiesn: After 5 years of observations, conclude to early to project if any ecological equilibrium to be reached.
Publication 0106: Shoreline and Dock Modifications in Lake Washington
JD TOFT ( Univ. of Washington, Wetland Ecosystem Team)
Prepared for King County Dept of Natural Resources
(2001) 23 pp
Goal : Study estimated to what extent the historical shoreline of Lake Washington has been modified by docks and retaining structures, in order to determine impacts of modifications on endangered populations of chinook salmon, the juveniles use the littoral zone in Lake Washington for rearing and migration to the ocean.
Study utilized aerial photographs from the years 1962, 1974, 1990, and 1999, and conducted field surveys to quantify the historical rate of dock increase, as well as classify current shoreline structures and habitat types.
Conclusion: In general it is unclear how salmon react to shoreline modifications and further information is needed to manage shoreline development in ways that provide vital habitat for the recovery of endangered salmonid populations and their migration phases.70% of the total shoreline retained by either riprap or bulkhead, this in essence truncates the shallow-water zone, removing the gradual natural slope. The retained shorelines and over-water structures create habitat that are avoided by juvenile chinook salmon at night and juvenile chinook salmon prefer shallow water with a gradual slope and small to fine substrate. Information on other fish species in the lake is needed as evidence suggests that piscivores such as non-indigenous smallmouth bass prefer habitat surrounding dock piers.
Publication 302: Inventory and Mapping of City of Seattle Shorelines along Lake Washington, the Ship Canal, and Shilshole Bay
J TOFT, C SIMENSTAD, C YOUNG, L STAMATIOU (UW Wetland Ecosystems Team)
April 2003, 34 pp
For SPU and Army Corps
Goal: The main objective of this study was to inventory and map the above water shoreline habitats and docks along Seattle shorelines throughout Lake Washington, the Ship Canal, and Shilshole Bay in light of the use by juvenile endangered chinook salmon use the littoral zone for rearing and migration to the ocean. Thus there is a need to understand influence of shoreline modifications. Shoreline measurements included current field surveys and GIS aerial photography analyses on: (1) dock characteristics, (2) shoreline modifications, and (3) general shoreline habitats.
Results: There were 914 recreational docks and 519 marina docks along the surveyed shoreline, with 181 overwater structures and 42 overwater platforms. These areas shaded 17.3% of the shoreline’s edge. 74.71% of the shoreline was retained by rip-rap or bulkhead, while an unretained 25.29% of the shoreline was beach, naturally vegetated, or landscaped.
The majority of the shoreline was partially exposed to wave energy, had a moderate or low gradient terrestrial slope, an upland cover of garden/lawn or impervious surface, and shoreline substrata of sand or mixed coarse substrates. Submerged aquatic vegetation (SAV) was present along 59.1% of the shoreline.
Future research should attempt to assess the impacts that such shoreline modifications have on the surrounding biological community. This is a challenging avenue for scientific studies, but one that is necessary in order to quantify possible affects of altered shorelines. Managing urbanized waterways and shoreline developments may be an important component for enhancing the recovery of endangered salmonid populations.
Publication 0310: Inventory and Mapping of City of Seattle Docks Along Lake Washington, the Ship Canal, and Shilshole Bay
J TOFT, C SIMENSTAD, K DODD, T MILLER (UWWetland Ecosystem Team )
Prepared for the City of Seattle’s Department of Design Construction and Land Use
October 2003, 15 pp
Objective: The main objective of this study was to outline and map the above-water docks and piers along City of Seattle shorelines throughout Lake Washington, the Ship Canal, and Shilshole Bay. Juvenile endangered chinook salmon from Lake Sammamish and Lake Washington watersheds use the littoral zone for rearing and migration to Puget Sound and the ocean. Understanding the degree of shading along the shoreline edge is an important information need in planning salmon recovery, as the function of the littoral zone may be influenced by shoreline modifications such as overwater structures.
Method : We conducted field surveys locating and classifying dock types and amount of shading, which were merged with Geographic Information System (GIS) aerial orthophotography analysis. We documented a total of 1,551 acres of shading by docks along the surveyed shoreline. The majority of the shade was caused by boat marinas (42.6%), followed by industrial marinas (17.45%), houseboat marinas (14.98%), recreational docks (11.21%), overwater structures (9.12%), and overwater platforms (4.65%). Most of the dock area was composed of non-floating structures (77.03%), as compared to floating docks (22.97%).
Future research should attempt to assess the impacts that different dock types and amount of shoreline shading have on the surrounding biological community. This will be a challenging but necessary step in order to quantify possible effects of shoreline modifications. Managing shoreline developments in the urbanized landscape may be an important component for enhancing the recovery of endangered salmonid populations.
Publication 301: Analysis of Methods for Sampling Juvenile Salmonids along City of Seattle Marine Shorelines
J TOFT, C SIMENSTEAD, J CORDELL, C YOUNG, L STAMATIOU ( Univ. of Washington, Wetland Ecosystem Team) Prepared for Seattle Public Utilities)
2003, 36 pp Summary: Four sampling techniques were pilot-tested in order to determine effectiveness in sampling juvenile salmonids at various habitat types along Seattle marine shorelines: (1) enclosure nets, (2) underwater videography, (3) snorkel surveys, and (4) above water observations. Success of each technique varied under different habitats and conditions.
Publication 0401: Fish Distribution, Abundance, and Behavior at Nearshore Habitats along City of Seattle Marine Shorelines, with an Emphasis on Juvenile Salmonids
J TOFT, C SIMENSTAD, J CORDELL, L STAMATIOU (UW Wetland Ecosystems Team) Prepared for Seattle Public Utilites
March 2004 Rationale: Shoreline modifications have altered many of the natural habitats in nearshore areas of Puget Sound. Prevalent shoreline modifications include various methods of retaining and armoring (e.g., bulkheads, rip-rap), overwater structures, and filling of intertidal area for industrial, urban and residential development. The effects of retaining structures on ecological processes are poorly known, especially in regards to processes influencing the quality of juvenile salmonid (Oncorhynchus spp.) habitats.
Goal: The main goal of our study was to quantify the abundance and behavior of juvenile salmonids and other fishes along various modified and undeveloped habitat types of Seattle’s marine shorelines.
Method: We utilized enclosure nets and snorkel surveys to sample fishes during high tides directly along shore at five main habitat types: cobble beach, sand beach, rip-rap that only extends into the upper intertidal, deep rip-rap that extends into the subtidal, and overwater structures.
Results:
- Minimal differences were found in fish densities between cobble beaches, sand beaches, and rip-rap that only extended into the upper intertidal. Densities were significantly different only for bottom-dwelling fishes, generally higher abundances of juvenile flatfish (Pleuronectidae) at sand beaches, crabs (Cancer and Pugettia spp.) at cobble beaches, and sculpins (Cottidae) at rip-rap. This suggests that substrate type and slope may be the most important factors influencing fish densities when shoreline modifications only extend to the upper intertidal.
- Effects on nearshore fish assemblages were more evident when shoreline modifications extended from the supratidal into shallow subtidal waters. Deep rip-rap and overwater structures truncate the shallow water zone, creating deep water immediately adjacent to the shoreline. We typically found higher densities of total fish and juvenile salmonids along these extensively modified shorelines. This implies that juvenile salmonids occupying deep rip-rap and overwater structure modified habitats are forced to inhabit deeper water and also school more.
- Our observations showed that juvenile salmonids avoid swimming beneath overwater structures, whereas surfperches (Embiotocidae), crabs, and sculpins were observed beneath or adjacent to pilings. Deep rip-rap sites were characterized by significantly higher densities of surfperches and gunnels (Pholidae), fishes that are more often found in structurally complex habitats with interstitial spaces.
- Behavior data shows that most juvenile salmonids were either schooling or swimming away, and occupying the middle to surface of the water column. Juvenile salmonid categories with Chinook and coho were located more at the surface of the water column at deep rip-rap sites, perhaps due to the underlying rip-rap structure and associated fishes which can hide in the interstitial spaces. At other habitat types they were more distributed between the middle and the surface of the water column.
- Chum were only observed in the middle of the water column at overwater structures, perhaps due to the greater water depths allowing more elevation to inhabit. At other habitat types, chum were always located at the surface. Examination of prey consumed by juvenile Chinook in the enclosure nets indicated that input from either marine benthic/epibenthic or terrestrial riparian resources were the two major contributors to their diets. Riparian insects in Chinook guts were lowest at sites with retaining structures at either the intertidal or supratidal zone, suggesting limited availability of terrestrial insect prey resources along such modified shorelines.
- Terrestrial riparian resources are more important for Chinook as compared to other salmon species, as coho and chum had minimal amounts of insects in their diets, with especially chum feeding more on marine planktonic/neritic prey sources.
Overall: Overall, our results indicate that shoreline modifications have the most dramatic effect on nearshore fish densities and behaviors when the alterations extend from the supratidal through the subtidal zone. Densities of juvenile salmonids were most significantly different between shallow gradient shorelines and steep gradient shorelines with extensive modification through or over much of the intertidal zone. While we are confident in our estimates of fish density, interpreting the results in relation to salmon habitat is more ambiguous. Since our surveys were designed to sample directly along the shoreline, it is a question whether our results indicate active selection by fish to various habitat types, or whether the fish are merely responding to indirect effects of shoreline modifications such as changes in water depth and slope. Due to the nature of shoreline modifications that truncate the shallow water zone, fish that may typically be spread-out over a broad intertidal/shallow subtidal area may by compressed against the shoreline.
As it is not feasible to sample along the same depth and distance from shore profiles at all of the various habitat types, it is possible that fish usage patterns would be more similar if all fish could be sampled across a stable array of space (e.g., 5-m water depth and 50-m from shore). We interpret the observed differences in fish responses to more often depend on consequences of shoreline modifications, such as changes in water depth, slope, substrate, and shoreline vegetation. Future research should continue to examine the effects of shoreline modifications on ecological communities in regard to bank type, tidal height, and salinity regimes.
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