FY 2017 Hood Canal Bridge Impact Assessment

This project continued to provide resources for the Port Gamble Tribe to participate in the Hood Canal bridge impact assessment. Project contributions supported: 1) conducting data analysis of past acoustic data in conjunction NOAA to determine best placement and timing of an acoustic arrays to track fish movement; 2) placement and operation of acoustic arrays; 3) conducting additional acoustic surveys, surface and subsurface video and camera imagery and visual observations of predation activity during peak outmigration time periods; 4) video & eDNA surveys around the bridge to investigate a secondary hypothesis that the underside of the bridge and anchor cables are creating a significant artificial reef habitat that may be creating a localized ecosystem that attracts predators by creating habitat for other small fish and whether or not juvenile salmonids are being attracted as well to high densities of feed and therefore delaying their transition past the bridge enough to elevate their exposure to predation at the site.

This project is a multiple year monitoring effort intended to build a time series for data analysis purposes.

This project will support the Port Gamble S’Klallam Tribe’s (PGST) Hood Canal Bridge Impact Assessment. The Hood Canal Bridge is an important regional transportation asset. It carries traffic across the northern outlet of Hood Canal, drastically shortening the trip between the Olympic and Kitsap peninsulas and in turn supporting tourism and other economic activities. As a 1.5-mile long floating bridge, its pontoons span much of the width of Hood Canal and extend ~12 feet underwater. Because of its location, all Hood Canal salmon and steelhead must pass the Hood Canal Bridge on their migration to and from the Pacific Ocean. Recent studies indicate the bridge is a barrier to fish passage. Slower migration times and higher mortality rates suggest the bridge is impeding migration and increasing predation. Recent research also shows that the bridge may disrupt water circulation. Fjords depend upon strong surface flows to be replenished with healthy, oxygenated water. The bridge could therefore be contributing to low dissolved oxygen levels and fish kills, and exacerbate effects of ocean acidification—which is more prevalent in Hood Canal than anywhere else in Puget Sound—and climate change. We will work in partnership with NOAA, Long Live the Kings, Hood Canal Coordinating Council, WDFW, Battelle’s Pacific Northwest Laboratories and others.
Our assessment effort will address to the first primary question of the larger assessment effort:
I. How is the bridge acting as a functional barrier to juvenile steelhead and salmon migration and leading to increased mortality?
We must determine where mortality is greatest along the bridge, who the predators are, and functionally how the bridge leads to increased predation. Causal agents may include the pontoons as a functional barrier, or changes to water circulation and other water properties, that may slow migration, heighten fish densities, and thusly increase susceptibility to predation. Light, shade and noise impacts from the bridge may also affect fish and/or predator behavior. Finally, structural voids in the bridge may change water properties and aggregate plankton, attracting planktivorous salmon and steelhead and increasing their susceptibility to predation.
The second goal and question being addressed by the larger group is:
II. How does the bridge impact the entire Hood Canal ecosystem?
Because species throughout Hood Canal respond to changes in water quality, and also because they interact with one another, any effects of the bridge on ecosystem processes or vulnerable species may ripple throughout the food web in unknown ways. We must determine the strength of bridge impact on circulation and water quality, including dissolved oxygen, temperature, acidity, and nutrient dynamics. This information will then be used to characterize the extent of impact the bridge is having on the Hood Canal ecosystem and isolate functionally how the bridge is driving ecosystem impacts. Species of critical concern based on their ecological, commercial, and recreational/tourism importance include shellfish, crab, shrimp, forage fish, rockfish, salmon, steelhead, and killer whales.
We will be focused on the first question and considering acoustic, video, eDNA and visual observations to help get more clarity on what may be happening at the bridge with predation or other possible impacts. This work will help guide follow up research and monitoring for the assessment effort.