Bulkhead Removal Forage Fish Spawning Survey

King Conservation District has implemented a novel bulkhead removal project along the Puget Sound shoreline near Three-Tree Point in Burien, Washington State to improve habitat for forage fish species critical to the Puget Sound ecosystem. The project treatment included the removal of an existing timber bulkhead, followed by the installation of boulders, partially embedded large wood, and the planting of native vegetation. It is anticipated that this form of soft-shore armoring will allow for more natural sediment processes to occur, thereby improving site potential for forage fish spawning. Wild Fish Conservancy designed and implemented a Before-After-Control-Impact assessment of the project, sampling for presence of forage fish spawn, and changes in habitat characteristics such as sediment deposition.

Sampling occurred once a month, from late August, 2019, through late March 2022, at a site with soft shore armorment and a site with a traditional bulkhead. Two transects were laid at each site encompassing the typical range of spawning habitat utilized by both surf smelt and sand lance. The surface sediment was collected along each transect and the samples were processed by sieving the contents to remove larger sediment while retaining egg-sized materials. The remaining mix of finer materials and any potential existing eggs were added to a vortex device which is designed to separate and lift materials lighter than the sediment. The lightweight material was collected and examined under a microscope to identify eggs, their species, and their development stage.

A total of 11 eggs were found during the winter of 2022, all of which were identified as pacific sandlance. All 11 eggs measured under 1mm, ranging from .73mm to .8mm and appeared to be under 24 hours old, lacking an observable coil. Eight of the eggs were found in bulk samples collected at the control site, two on 1/5/2022 and six on 2/26/2022. The remaining five eggs were found at the impact site on 1/5/2022. On both occasions when eggs were found, no spawn was observed on the beach during the survey.

The low quantity and frequency of egg detection leads us to believe that this site is either an outlier spawning ground, or the duration and frequency of sampling was not robust enough to accurately reflect changes resultant from the soft shore armormemt project.