UNDERSTANDING HABITAT

An introduction to in-water, seawall habitat

Elliott Bay Seawall:  An important salmon migration corridor

Tens of thousands of salmon migrate along the Elliott Bay Seawall and then up the Green/Duwamish River and its tributaries every year to spawn.  After beginning their lives in freshwater rivers, juvenile salmon then swim down the Green/Duwamish River to enter Elliott Bay in the spring and summer – along the Elliott Bay Seawall. Because the Elliott Bay Seawall Project area is such an important link in the salmon migratory route, improving salmon habitat within Elliott Bay is pivotal to the success of regional salmon recovery.

Historically, the eastern shoreline of Elliott Bay looked much like other unaltered shorelines across Puget Sound—a bluff-backed beach with intertidal marshes and mudflats.  The mudflats and gently sloping beaches of Elliott Bay were home to a bounty of birds, fish, and marine invertebrates. 

When the seawall was built, the nearshore was cleared to make room for piers, roads, and buildings. With the lack of typical nearshore habitat, salmon migrating along the waterfront can become confused and vulnerable to predators.  Current challenges that juvenile salmon encounter along the seawall include: 

• Large piers, which cast shadows on the water, limiting the ability of aquatic vegetation to grow and making it difficult for juvenile salmon to navigate along the seawall.
• Vertical hard surfaces make it difficult for marine invertebrates, an important food source for salmon, to colonize the seawall.
• The seawall currently lacks an intertidal zone.  In intertidal zones, land is above water at low tide and below water at high tide.  Intertidal zones provide outstanding sources of food and shelter for juvenile salmon.
• The seawall lacks bluffs with riparian vegetation, a typically important source of habitat structure, refuge, and food for salmon.

Despite these challenging aspects, today’s seawall still provides a home to many species of aquatic life. 

• The naturally lighted areas between piers along the central waterfront are home to many types of aquatic vegetation, such as sea lettuce, and marine invertebrates like barnacles, mussels, and sponges. 
• Biologists have identified eight species of salmon, and many other species of fish, that use seawall habitats.

Light areas between piers have rich habitat	Dark areas (under piers) support little habitat

Researching how to improve habitat

As part of the seawall replacement program, the City of Seattle is committed to restoring a functional salmon migration corridor along Seattle’s waterfront.  The Elliott Bay Seawall Project has been researching how best aquatic habitat can be restored.

Since 2008, four major studies have been conducted along Seattle’s waterfront:

• Habitat monitoring at Olympic Sculpture Park – Researchers are monitoring how marine life is responding to habitat restoration along the park’s shoreline.

• Exploring habitat-friendly surfaces – Researchers are monitoring test panels with new possible surfaces for the seawall to understand which surfaces are best for marine life.

• Habitat mapping – Through underwater video and SCUBA dives, biologists are mapping what plants and animals can currently be found along the seawall.

• Examining juvenile salmon migration patterns – To understand how habitat restoration along the new seawall could help juvenile salmon migration, researchers are studying current migration patterns to learn how juveniles migrate and how limited habitat along the seawall currently affects their migration patterns.

Habitat restoration along Seattle’s seawall

To make life better for juvenile salmonids and other marine creatures, the City is designing a shallow, lighted migratory corridor along the seawall to enhance habitat for juvenile salmon and other marine life.  The City is planning to restore habitat by: