Event Title

Survival and behavior of steelhead smolts migrating past the Hood Canal Bridge

Presentation Abstract

The Hood Canal Bridge (HCB) spans the northern outlet of Hood Canal in Puget Sound, extends 15 feet underwater, and forms a barrier for steelhead migrating from Hood Canal to the Pacific Ocean. Acoustic telemetry studies performed from 2006-2010 indicated substantial mortality and migration delays associated with the HCB, but fine-scale resolution of fish movement and behavior was needed to resolve the specific mechanisms around migration impediment. Individually coded acoustic telemetry transmitters implanted in juvenile steelhead were used in conjunction with an extensive array of receivers (Vemco VPS system) surrounding the HCB to obtain close approximations of the path each steelhead took as they encountered the bridge structure. Preliminary results of behavioral analysis indicate that steelhead smolts are utilizing the small openings under the east and west elevated segments of the HCB, as well as diving beneath the submerged pontoons to migrate out of Hood Canal. Analysis of stationary tags (prolonged transmission at a single location) suggest that 33% (44/134) of the tags detected at the HCB remain within 1 kilometer of the HCB as probable mortalities, while only 1 tag was detected stationary at the other 4 receiver arrays deployed. Instantaneous mortality rates within the 7 kilometer segment containing the HCB were 6.8% and 8.6% per kilometer for the two steelhead populations tagged, compared with 0.7% and 0.5% per km for the migration segment from river mouth to the HCB. This study confirms the considerable impact of the HCB on steelhead smolt survival, and provides detailed information on what factors dictate successful or unsuccessful migration past the HCB.

Session Title

Big Objects Need Big Solutions: Addressing the Environmental Effects of Major Infrastructure Around the Salish Sea

Conference Track

SSE1: Habitat Restoration and Protection

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE1-390

Start Date

6-4-2018 1:30 PM

End Date

6-4-2018 1:45 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 6th, 1:30 PM Apr 6th, 1:45 PM

Survival and behavior of steelhead smolts migrating past the Hood Canal Bridge

The Hood Canal Bridge (HCB) spans the northern outlet of Hood Canal in Puget Sound, extends 15 feet underwater, and forms a barrier for steelhead migrating from Hood Canal to the Pacific Ocean. Acoustic telemetry studies performed from 2006-2010 indicated substantial mortality and migration delays associated with the HCB, but fine-scale resolution of fish movement and behavior was needed to resolve the specific mechanisms around migration impediment. Individually coded acoustic telemetry transmitters implanted in juvenile steelhead were used in conjunction with an extensive array of receivers (Vemco VPS system) surrounding the HCB to obtain close approximations of the path each steelhead took as they encountered the bridge structure. Preliminary results of behavioral analysis indicate that steelhead smolts are utilizing the small openings under the east and west elevated segments of the HCB, as well as diving beneath the submerged pontoons to migrate out of Hood Canal. Analysis of stationary tags (prolonged transmission at a single location) suggest that 33% (44/134) of the tags detected at the HCB remain within 1 kilometer of the HCB as probable mortalities, while only 1 tag was detected stationary at the other 4 receiver arrays deployed. Instantaneous mortality rates within the 7 kilometer segment containing the HCB were 6.8% and 8.6% per kilometer for the two steelhead populations tagged, compared with 0.7% and 0.5% per km for the migration segment from river mouth to the HCB. This study confirms the considerable impact of the HCB on steelhead smolt survival, and provides detailed information on what factors dictate successful or unsuccessful migration past the HCB.