FY 2019 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) Visual 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 were 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.

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 a comparative assessment of fish, predator, zooplankton densities in pools and eddies vs away from them. Preliminary data suggest pools and eddies near the center of the bridge may have a very unique impact to fish. Water pools in between pontoons where the bridge center drawspan retracts to allow large vessels to pass. Fish, including juvenile chum, have been observed aggregating in these pools presumably to feed on zooplankton, and seals have also been observed foraging on the fish that are in these pools (pers. comm. Hans Daubenberger, Port Gamble S’Klallam Tribe). A preliminary assessment will be performed that compares aggregations of biota in the water passing through structural voids in the bridge (and the surrounding bridge infrastructure) to areas without voids and to the large openings on the east and west sides of the Hood Canal Bridge where water more freely passes. Underwater video observations and plankton tows will be used to characterize sea life including affiliated fish and zooplankton assemblages. DIDSON and/or Blueview acoustic imaging equipment will be installed underwater to collect data about the biota in and around the pools. These observations will be performed at multiple points along the tidal cycle to ensure each area is appropriately characterized. In addition, a surface video observation station will be set up to determine whether seabirds and marine mammals are subsequently attracted to areas with structural voids. Those regions will then be compared to the fish distribution and densities data obtained from hydroacoustic sampling, predator composition and distribution data and zooplankton data will be used to determine whether what is occurring in the pools is in fact unique.
This work with be coordinated with the Hood Canal Steelhead project which is a collaborative effort between National Marine Fisheries Service (NMFS), Washington Department of Fish and Wildlife, Skokomish Tribe, the Port Gamble S’Klallam Tribe, the Point No Point Treaty Council (representing the Jamestown S’Klallam Tribe and Port Gamble S’Klallam Tribe), Long Live the Kings, and the Hood Canal Salmon Enhancem