Photo courtesy of City of Seattle
New shoreline strategies piloted in Puget Sound could help young fish in urbanized estuaries elsewhere.
When Seattle rebuilt its seawall in 2017, they hoped to make the hardened shoreline
a little less daunting for the young salmon that hug it closely on their journey to the ocean. Project managers took a three-pronged approach. First, they added texture and complexity into the new concrete seawall to encourage invertebrates, food for the young fish, to settle in nooks and crannies and on horizontal “shelves” built into the wall. Mussels, ecosystem engineers, have settled on the shelves and attracted many other organisms. Next, they installed a habitat “mattress” in the seafloor in front of the wall. This horizontal structure of mesh-covered rocks lifts the seafloor, calms waves, and encourages the growth of kelp and invertebrates for the salmon. “It brings up the bottom into productive light and adds complexity for smaller epibenthic invertebrates,” says Jeff Cordell, Principal Research Scientist with the University of Washington. Onshore, they built glass blocks into the sidewalk that overhangs the water, to allow more light to reach beneath the water’s surface. The salmon, which do not like crossing shadow lines, now feed beneath the piers and move from sunlit spot to sunlit spot, says Cordell. “It’s a methodology that’s transferable to any area where small fish use nearshore habitat for nurseries,” Cordell says. In the Bay Area, regulators are now asking applicants who want to build docks or similar structures to include light penetrating surfaces in their designs. “We are looking for projects to incorporate light-transmitting surfaces in overwater structures, for fish and growth of submerged aquatic vegetation like eelgrass,” says Gary Stern, San Francisco Bay Branch Supervisor, NOAA Fisheries, West Coast Region.